What is Biology? Biology is the branch of science that deals with the study of living things. In Greek, Bios means life while Logos means knowledge. Branches of biology There are two main branches: 1. Botany: Study of plants 2. Zoology: Study of animals br br The others include: br br 1. Ecology: Study of living things in their surroundings. 2. Genetics: The study of inheritance and variation. 3. Entomology : Study of insects 4. Parasitology: Study of parasites 5. Taxonomy: Study of classification of organisms 6. Microbiology: Study of microscopic organisms 7. Anatomy: S tudy of structure of cells 8. Cytology: Study of cells 9. Biochemistry: Study of chemical changes inside living br br organisms br br Name at least six other smaller branches of biology 6 marks . Importance of Biology br br 1. Solving environmental problems e.g. Food shortage, poor br br health services, pollution, misuse of environmental resources etc. br br 2. Choice of careers e.g. Medicine, Agriculture, public health, Veterinary, Animal husbandry, Horticulture, Dentistry etc. 3. Acquiring scientific skills e.g. observing, identifying, recording, br br classification, measuring, analyzing, evaluating etc. br br 4. International co-operation e.g. Development of HIV AIDS vaccine, fight against severe Acute respiratory Syndrome SARS , fight to save ozone layer from depletion, management of resources through international depletion. Others br br Help on study of other subjects Learn what living things are made up of and their bodies br br work br br Acquire knowledge about plant and animal diseases and br br their treatment. br br Know the effects of our bodies on drug and substance abuse br br and can kill. br br Learn about HIV AIDS diseases and other viral diseases e.g. its treatmentbalanced diets, proper hygiene, spreading, sexual behavior, cultural practices etc. br br List five professional occupations that require the study of biology. 5 marks Characteristics of living things; br br 1. Nutrition: Process by which living things acquire and utilize nutrients: plants photosynthesize; animals feed on already manufactured foods. br br 2. Respiration: energy-producing process occurring in all the cells br br of living things. br br 3. Gaseous Exchange: where living things take in air oxygen and br br give out air carbon iv oxide across respiratory surfaces. br br 4. Excretion: Process by which waste or harmful materials resulting br br from chemical reactions within cells of living things are eliminated. Excess of such materials poison living things. br br 5. Growth and Development: Growth is the irreversible increase in size and Mass.Essential for body function . Development Irreversible change in complexity of the structure of living things. 6. Reproduction: Process by which living things give rise to new br br individuals of the same kind. br br 7. Irritability: Is the ability of living things to perceive changes in br br their surroundings and respond to them appropriately. E.g. reaction to changes in temperature, humidity, light, pressure and to the presence of certain chemicals. br br 8. Movement: Change in position by either a part or the whole br br living thing. Locomotion Progressive change in position by the br br 2 whole living thing. In animals, movement include; swimming, walking, running, flying. In plants, closing of leaves, folding of leaves, closing of flowers, growing of shoots towards light etc. br br Question br br 1. List four uses of energy obtained from the process of br br respiration. 4 marks . br br 2. List six characteristics of living things 6 marks . br br Collection of specimens Apparatus used br br 1. Sweep net: for catching flying insects. 2. Fish net: For trapping small fish and other small water br br animals. br br 3. Pooter: For sucking small animals from rock surfaces and br br tree barks. br br 4. Bait trap: For attracting and trapping small animals e.g. br br rats. br br 5. Pit fall trap: For catching crawling animals. 6. Pair of forceps: picking up small crawling animals e.g. br br stinging insects. br br 7. Specimen bottles: keeping collected specimen. Larger br br specimens require large bottles. br br 8. The magnifying lens: Instrument used to enlarge objects. br br Lenses are found in microscope and the hand lens magnifier . Its frame is marked e.g. x8 or x10indicating how much larger will be the image compared to object. Precautions during Collection and Observation of specimens Collect only the number of specimen you need. Do not harm the specimens during the capture or collection br br exercise. br br Handle dangerous or injurious specimens with care e.g. stinging plants or insects i.e. use forceps or hand gloves. The teacher will immobilize highly mobile animals. diethyl br br ether, formalin, chloroform br br Do not destroy the natural habitat of the specimens. br br Practical activity 2 br br 3 Practical activity 3 Comparison between plants and animals br br Plants 1. Green in colour have Animals 1. Lack chlorophyll thus br br chlorophyll 2. Their cells have feed on readymade food. 2. Cells lack cellulose cell br br cellulose cell walls. 3. Respond slowly to changes in the environment. 4. Lack specialized excretory organs. 5. Do not move about. br br walls. br br 3. Respond quickly. br br 4. Have complex excretory organs. 5. Move about in search of food and water. 6.Growth occurs in all body parts9intercalary growth . br br 6. Growth occurs in shoot and root tips. apical growth br br Revision questions CLASSIFICATION I br br INTRODUCTION Living things are also known as living organisms. Organisms forms of life have distinguishing characteristics and therefore are grouped. The Magnifying lens -Is used for enlarging small objects. Diagram Procedure of its use br br Place the object on the bench. Move the hand lens from the object to the eye. An enlarged image is seen. br br Drawing magnification Length of the drawing/ drawing Length Length of the object/Actual Length br br 4 External features of plants and animals External features of plants br br i Rhizoids as in moss plant. ii Fronds in ferns. iii Roots, stems, leave, flowers, seeds, fruits, and cones in higher br br plants. br br External features of animals i Tentacles in hydra ii Feathers in birds iii Shells in snails iv Wings in birds v Fur and hair in mammals vi Scales and fins in fish vii Proglotids in tapeworms viii Mammary glands in mammals ix Locomotory Structures e.g. limbs in insects x Body pigmentation Practical activity 1 To collect and observe animal specimens To collect and observe plant specimens br br What is classification? -I s an area of biology that deals with the grouping of living organisms according to their structure. Organisms with similar structures are put under one group referred to as a taxontaxa plural . The groupings also consider evolutionary relationships phylogeny since all living organisms had a common origin at one time. TaxonomyScience of classification. TaxonomistBiologist who studies taxonomy. Need for classification. Reasons 1. To identify living organisms into their correct groups for br br reference and study br br 2. To bring together living organisms with similar characteristics but br br separate those with different features. br br 3. To arrange information of living organisms in an orderly manner. br br This avoids chaos and confusion. br br 4. To understand the evolutionary relationship between different br br organisms Taxonomic Units Are groups taxa into which organisms are placed as a matter of convenience. Groups are based on observable characteristics common in the group. In a classification scheme taxonomic units or groups, a hierarchy of groups are recognized starting with the first largest and highest group; the Kingdom to the smallest and lowest unit; the species . There are 7 major taxonomic units. The Kingdom There are five Kingdoms of living organisms, namely: br br 1. Kingdom Monera : bacteria 2. Kingdom protoctista : algae, protozoa, amoeba, paramecium 3. Kingdom Fungi : Moulds, Yeast, Mushrooms 4. Kingdom Plantae : Moss plants, ferns, maize, garden pea, pine, br br meru oak, bean etc. br br 5. Kingdom Animalia : hydra, tapeworms, bees, human beings etc. br br 6 A kingdom is divided into Phyla in animals or divisions in plants and sorts out organisms based on body plan and form. Plan is the adaptation to a special way of life. The Class is further divided into small groups; Orders using structural features. Orders are divided into families using structural features, then Families into Genera singular genus based on recent common ancestral features that are less adaptive. Genus is divided into species i.e. kind of plant, or animal. Down the hierarchy, the number of organisms in each group decreases but their similarities increases. The Species group members naturally interbreed to produce fertile off springs. Minor differences are exhibited in the species groups e.g. on colour of the skin in human beings and varieties of plants. The groups of the species are termed to as varieties, races or strains. Classification of A human being and a maize plant Human being maize Taxonomic unit kingdom Phylum or division class order family genus species br br bean br br Animalia Chordata plantae Angiospermaphyta Angiospermae br br plantae br br Mammalia monocotyledonae Dicotyledonae Primates Hominidae homo sapiens Graminales Graminaceae zea mays Rosales Leguminosae Phaseolus Vulgaris br br Scientific name Homo sapiens Zea mays phaseolus vulgaris Scientific Naming Of Living Organisms P resent naming was developed by carolus Linnaeus 18th c, where organisms were given 2 names in Latin language. Living organisms have their scientific names and common names i.e. local or vernacular names. br br 7 Scientific naming uses the double naming system Binomial system . In binomial system, an organism is given both the genus and species name. Binomial nomenclature Double naming system -Is the assigning of scientific names to living organisms governed by a definite set of rules recognized internationally. Principles of binomial nomenclature br br a The first, genus name, should begin with a capital letter and the br br second name, species, should begin or written in small letters e.g. Lion---- Panthera leo Leopard ----- Panthera pardus Domestic dog ----- Canis farmiliaris Human being--- Homo sapiens Maize plant--- Zea mays br br Lion and Leopard are closely related ---Same genus but distantly relateddifferent species. br br b The scientific names must be printed in italics in textbooks and br br where hand written to be underlined e.g. Panthera leo. br br c The specific name species is frequently written with the name of br br the scientist who first adequately described and named the organism e.g. Phaseolus vulgaris i.e. Vulgaris is the scientist who described and named the bean plant. d Biologists should give a Latinized name for a newly described br br animal or plant species where Latin name is missing e.g. Meladogyne kikuyuensis Is a scientific name of a nematode from kikuyu. Aloe kilifiensis --- A member of Aloeceae family from Kilifi discovery. Garinsoga parviflora waweruensis --- a member of Macdonald eye family discovered by Waweru. br br Study Question 1 Complete the table below Lion Taxon br br Domestic dog Garden pea Napier grass br br kingdom br br 8 CLASSIFICATION 1 br br Review of the magnification lens Calculating Magnification External characteristics of plants and animals br br Diversity of Living Organisms br br Organisms with similar characteristics are placed under one group br br called taxon taxa . br br The science of classification is known as taxonomy . Biologists who study taxonomy are called taxonomists . br br Need For Classification br br 1. Help in identifying living organisms into their correct groups for br br reference. br br 2. It brings together organisms with similar characteristics and br br separates those with different features. br br 3. Help to organize information about living organisms in an orderly br br manner avoiding any confusion. br br 4. Help to understand the evolutionary relationship between br br different living organisms. br br Historical Background of Classification br br Long time ago classification was artificial where living things br br were classified as either plants or animals. br br Plants were classified as herbs, shrubs and trees. Animals were further divided into carnivores, herbivores and br br omnivores. Today modern classification uses evolutionary relationships br br between living organisms. Taxonomic Units of Classification br br This refers to the groups into which living organisms are placed br br in classification. br br These units start from the first largest and highest group kingdom to the smallest and lowest unit species . br br There are seven taxonomic units as shown below. Kindom Phylum division Class Order Family Genus Species br br 1. Kingdom br br Carolus Linnaeus 1707-1778 initially introduced the two kingdom system of classification. However many new life forms have been discovered which are neither animals nor plants. This has led to a more accepted classification system that adopts five kingdoms. These are; i. Monera .eg bacteria ii. Protoctista e.g algae and protozoa iii. Fungi e.g. mushrooms, moulds and yeast. iv. Plantae e.g. maize, ferns and all types of trees. v. Animalia e.g. man, cow tapeworm, flies etc. Kingdom is further divided into several phyla in animals or divisions in plants. br br 2. Phylum phyla or Division in plants. br br It is the second largest and further divided into classes. br br 3. Class br br Each class is divided into several orders . br br 4. Order Orders are divided into smaller groups called families . br br 5. Family br br Family is divided into several Genera. br br 6. Genus br br Here members are closely related. It is further divided into the species. br br 7. Species br br This is the smallest unit of classification. Species is defined as a group of organisms whose members naturally interbreed to produce fertile offsprings . Members of a given species have small differences such as skin colour, height etc. Classification of Man and Maize plant. Table 2.1 KLB Bk 1 Scientific Naming of Living Organisms. br br Today organisms are given two names in Latin language. This br br was developed by Carolus Linnaeus. br br Latin language was used because it was widely spoken during his br br time. br br In scientific naming, an organism is given the genus and the br br species name . br br This double naming system is known as Binomia l system two br br name System Binomial Nomenclature. This is the double naming system of organisms where organisms are assigned two names i.e. the generic name and the specific name. In binomial nomenclature the following rules are observed. br br i. Generic name is written first followed by the specific name. First letter in the generic name is in capital and the rest are in small letters. Specific name is written in small letters. br br ii. The two names are underlined separately when handwritten or br br italicised when printed. br br iii. Newly discovered species must be given Latinized names. iv. Specific name is frequently written with the name of the scientist br br who first adequately described and named the organism. br br 11 Revision Questions br br CELL PHYSIOLOGY br br This is the study of the functions of cell structures. br br Membrane Structure and Properties br br A membrane is a surface structure which encloses the cell and br br organelles. Membranes regulate the flow of materials into out of the cell or organelle. br br Examples of membranes: cell membrane, tonoplast membrane surrounding the vacuole , nuclear membrane, mitochondrial membrane, chloroplast membrane etc. br br The Cell Membrane br br It has three layers, two protein layers and a phos-pholipid layer br br sandwiched in between the two. br br Diagram Properties of Cell Membrane br br 1. Semi-permeability. It has small pores allowing for the passage of molecules of small size into and out of the cell. Cell Wall however allows all materials to pass through it hence it is referred to as being Permeable . br br 2. Sensitivity to Changes in Temperature and pH Extreme br br temperature and pH affects the cell membrane since it has some protein layers. Such changes alter the structure of the membrane affecting its normal functioning. br br 3. Possession of Electric Charges it has both the negative and br br positive charges helping the cell to detect changes in the environment. These charges also affect the manner in which substances move in and out of the cell br br Physiological Processes br br The ability of the cell to control the movement of substances in and out of the cell is achieved through physiological processes such as Diffusion, Osmosis and Active Transport . br br 12 Diffusion br br This is a process by which particles move from a region of high br br concentration to a region of low concentration . br br Practical Activity 1 To demonstrate diffusion using potassium permanganate VII The difference in concentration of particles between the region of high concentration and the region of low concentration is known as the diffusion gradient. br br Role of Diffusion in Living Organisms br br 1. Absorption of Materials Mineral salts in the soil enter the root by diffusion since their concentration in the soil is greater than in the root hair cells. Digested food glucose and amino acids diffuse across the wall of the ileum into the blood for transport to rest of the body. br br 2. Gaseous Exchange in Plants and Animals In both plants and animals, respiratory gases oxygen and Carbon IV oxide are exchanged through simple diffusion depending on their concentration gradient. br br 3. Excretion of Nitrogenous Wastes 4. Transport of Manufactured Food form Leaves to other Plant br br Parts. br br 5. br br Factors Affecting Diffusion a Diffusion Gradient A greater diffusion gradient between two points increases the rate br br of diffusion. br br b Surface Area to Volume Ratio The higher the ratio the greater the rate of diffusion and the lower br br the ratio the lower the rate. br br This means that small organisms expose a large surface area to c Thickness of Membranes and Tissues The thicker the membrane the lower the rate of diffusion because the distance covered by the diffusing molecules is greater. The thinner the membrane, the faster the rate. br br Size of the Molecules Small and light molecules diffuse faster than large and heavy br br molecules. d Temperature Increase in temperature increases the energy content in molecules br br causing them to move faster. br br Osmosis br br This is the process where solvent molecules water move from a lowly concentrated solution dilute to a highly concentrated solution across a semi-permeable membrane . br br Diagram fig 4.6 The highly concentrated solution is known as Hypertonic br br Solution . br br The lowly concentrated solution is called Hypotonic solution . Solution of the same concentration are said to be Isotonic . Osmosis is a special type of diffusion because it involves the br br movement of solvent water molecules from their region of high concentration to region of low concentration across a semi permeable membrane. Practical activity 2 Practical activity 3 Osmotic Pressure br br This is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semi permeable membrane. This is the pressure needed to nullify osmosis. br br Osmotic pressure is measured using the osmometer. br br Osmotic Potential br br This is the measure of the pressure a solution would develop to withdraw water molecules from pure water when separated by a semi permeable membrane. Water Relations in Animals br br Cell membrane of the animal cell is semi permeable just like the br br dialysis/visking tubing. br br Cytoplasm contains dissolved sugars and salts in solution form. If an animal cell e.g. a red blood cell is placed in distilled water br br hypotonic solution , water flows in by osmosis. br br The cell would swell up and eventually burst because the cell membrane is weak. The bursting of the red blood cell when placed in hypotonic solution is called Haemolysis . br br If a similar red blood cell is placed in a hypertonic solution, water br br is drawn out of the cell by osmosis. The cell will shrink by a process called Crenation . br br Body fluids surrounding the cells must therefore have same br br concentration as to that which is found inside the cell. br br Diagrams Water Relations in Plants br br When a plant cell is placed in a hypotonic solution it gains water br br by osmosis and distends outwards. br br As the cell gains more water, its vacuole enlarges and exerts an br br outward pressure called turgor pressure. As more water is drawn in, the cell becomes firm and rigid and is said to be turgid . The cell wall in plant cell is rigid and prevents the cell from bursting unlike the case in animal cells. br br The cell wall develops a resistant pressure that pushes towards the inside. This pressure is equal and opposite the turgor pressure and is called wall pressure. br br Diagrams br br When a plant cell is placed in hypertonic solution, water br br molecules move out of the cell into the solution by osmosis. The cell shrinks and becomes flaccid . br br If the cell continues to lose more water, plasma membrane pulls br br away from the cell wall towards the center. The process through which plant cells lose water, shrink and br br become flaccid is called plasmolysis. br br Plasmolysis can be reversed by placing a flaccid cell in distilled br br water and this process is called deplasmolysis. br br Study Question 5 Practical Activity 4 Wilting br br When plants lose water through evaporation and transpiration, cells lose turgidity , shrink and the plant droops . This is called wilting. br br If water supply from the soil is inadequate, plants do not recover br br hence permanent wilting. br br Study Question 6 Role of Osmosis in Organisms br br 1. Absorption of water from the soil br br Root hair cells of plants absorb water from the soil by osmosis. br br 2. Support br br Cells of herbaceous plants, which are less woody, absorb br br water, become turgid hence support. br br 3. Opening and closing of the stomata br br During the day, guard cells synthesize glucose, draw in water, br br become turgid hence open the stomata. br br During the night, they lose turgidity since there is no br br photosynthesis. As a result, they shrink thus closing the stomata. br br 4. Feeding in insectivorous plants br br These plants are able to change their turgor pressure on the leaves which close trapping insects which are digested to provide the plant with nitrogen. Factors Affecting Osmosis br br i. Concentration of Solutions and Concentration Gradient. The br br greater the concentration gradient between two points, the faster the rate of osmosis. br br ii. Optimum Temperature as long as it does not destroy the br br semi-permeability of the membrane. br br Active Transport br br This is the process that moves substances across cell br br membranes against a concentration gradient. br br This process requires energy to move these substances across br br cell membranes and involves carriers. br br Substances such as amino acids, sugar and many ions are taken br br in by living organisms through active transport. br br Role of Active Transport br br i. Re-absorption of sugars and useful substances by the kidney ii. Absorption of some mineral salts by plant roots iii. Absorption of digested food from the alimentary canal into br br the blood stream br br iv. Accumulation of substances in the body to offset osmotic br br imbalance in arid and saline environment br br v. Excretion of waste products from body cells br br Factors Affecting Active Transport. br br i. Oxygen concentration. ii. Change in pH. iii. Glucose concentration. iv. Temperature. v. Enzyme inhibitors. NB/ Any factor affecting energy production affect the rate of active transport. Revision Questions. Cell Specialization, Tissues, Organs and Organ Systems br br 1. Cell specialization This is where cells are modified to perform specific functions. br br Such cells are said to be specialized. Examples include the sperm cell which has tail for swimming and the root hair cell which is extended creating large surface area for water absorption. br br br br 2. Tissues. These are cells of a particular type that are grouped together to br br perform the same function. br br Animal tissues include; br br - Epithelial tissue which is a thin continuous layer of cells for br br lining and protection of internal and external surfaces. br br - Skeletal it is a bundle of elongated cells with fibres that can br br contract. Its contraction and relaxation brings about movement. br br - Blood tissue this is a fluid containing red blood cells, white blood cells and platelets. It transports many substances and protects the body against infections. br br 18 br br - Connective tissue made up of strong fibres that connect br br other tissues and organs holding them together. br br Plant tissues include: br br - Epidermal tissue of a plant this is a single layer of cells br br protecting the inner tissues of the plant. br br - Palisade tissue this is a group of cells rich in chloroplasts containing chlorophyll. They absorb light energy during photosynthesis. br br - Parenchyma tissue it is made thin walled irregularly shaped br br cells. They store water and food. br br - Vascular bundle consists of the xylem and phloem. Xylem conducts water and mineral salts while phloem conducts food substances. br br 19 3. Organs br br Many tissues become specialized and grouped together to br br perform a functional unit called the organ . br br Examples of organs in plants include; roots, leaves, flowers br br and stem. br br In animals they include heart, lungs, kidney, brain, stomach br br and the liver. 4. Organ systems. br br This is made of several organs whose functions are coordinated br br and synchronized to realize an effective action is called an organ system . Examples include; digestive, circulatory, excretory, respiratory, reproductive and nervous system . br br Revision Questions MICROSCOPE Microscope Parts Function Parts of the Microscope br br 1. Eyepiece br br Contains a magnifying lens that focuses the image from the objective into your eye. br br br br 2. Course Adjust br br For focusing under low magnification br br 3. Fine Adjust br br For focusing under high magnification or low br br 4. Low Power Objective For large specimens or overview br br 20 5. High Power Objective For detailed viewing or small specimens br br 6. Specimen on glass slide br br What you want to look at br br 7. Stage br br Supports specimen in correct location to lens br br 8. Condenser Focuses the light on specimen br br 9. Diaphragm iris or disc br br Regulates amount of light and contrast br br 10. Light Source br br Illuminates the specimen for viewing Handling and Care of the Microscope The following rule should be observed: br br 1. Use both hand when carrying the microscope. One hand should br br hold the base and the other holds the limb. br br 2. Never place the microscope too close to the edge of the bench. 3. Do not touch the mirror and the lenses with the fingers. 4. Clean dirty lenses using soft tissue. 5. Clean other parts using a soft cloth. 6. Do not wet any part of the microscope. br br 7. Make sure the low power clicks into position in line with the eye br br piece before and after use. br br 8. Always store the microscope in a safe place free from dust and br br moisture. br br Using the Microscope br br 1. Place microscope on the bench with the stage facing away from br br you. br br 2. Turn the low power objective lens until it clicks into position. 3. Ensure the diaphragm is fully open. 4. Look through the eyepiece with one eye. Adjust the mirror to br br ensure maximum light can pass through. br br 5. Place the slide containing the specimen on the stage and clip it into position. Make sure the slide is at the centre of the field of view. br br 6. Again look through the eyepiece while adjusting the mirror to br br ensure maximum light reach the specimen. br br 7. Use the coarse adjustment knob to bring the low power objective lens to the lowest point. While viewing through the eyepiece, turn the coarse adjustment knob gently until the specimen comes into focus. br br 8. Use the fine adjustment knob to bring the image into sharp focus. 9. Make a drawing of what you see. 10. br br For higher magnification, turn the medium power into position and adjust the focus using the coarse knob. Use the fine adjustment knob for sharper focus. 11. For even large magnifications, turn the high power objective br br lens into position. In this case use only the fine adjustment knob to bring details into sharper focus. br br Magnification Magnification of the object viewed under the microscope is br br calculated by; Magnification Eye Piece Lens Magnification X Objective Lens Magnification. If the eyepiece lens has the magnification of x5 and the low power objective lens has a magnification of x10, the total magnification is 5x10 50. br br Study Question 1 Fill the table below. Eye piece lens maginification X5 X10 X10 br br Objective lens magnification X4 X5 br br Total magnification br br X100 X600 br br X40 X100 X10 Practical Activity 1 Cell Structures as Seen Under the Light Microscope The following cell organelles can be seen under the light br br microscope. - Cell wall. - Cell membrane - Cytoplasm - Nucleus - Vacuole. - Chloroplasts. br br Diagrams- plant and animal cells br br The Electron Microscope. It is more powerful than the light microscope. It can magnify up to 500,000 times and has high resolving power. The high resolving power of the electron microscope enables it to br br separate objects which lie close to one another. br br Electron microscope uses a beam of electrons instead of light to br br illuminate the object. br br Study Question 2 Practical Activity 2 Diagrams Plant and Animal Cells The Cell Organelles br br i Cell membrane Plasma Membrane . It has three layers i.e. one layer of phospho-lipid layer br br sandwiched between two protein layers. br br It is flexible with pores and ahs the following main functions. br br a Encloses all the cell contents. b It allows selective movement of substances into and out of the br br cell since it is semi-permeable. br br Diagram ii Cytoplasm It is s fluid medium in which chemical reactions take place. It has some movement called cytoplasmic streaming. It contains organelles, starch, glycogen, fat droplets and other br br dissolved substances. br br iii Nucleus It has double membrane called the nuclear membrane. The membrane has pores allowing passage of materials into and br br out of the cell. br br Nucleus has a fluid called nucleoplasm in which the nucleolus br br and chromatin are suspended. br br Nucleolus manufactures ribosomes while chromatin contains the br br hereditary material. br br iv Mitochondria Mitochondrion They are sausage shaped and are the respiratory sites . Mitochondrion has two membranes. Inner membrane is greatly folded into cristae to increase the surface area for respiration. Some endoplasmic reticulums have granules called Ribosomes on their surfaces hence referred to as rough endoplasmic reticulum. br br Others do not contain ribosomes hence the name smooth br br endoplasmic reticulum . br br Rough endoplasmic reticulum transport proteins while the br br smooth endoplasmic reticulum transports lipids. br br Diagrams vi Ribosomes They are spherical in shape and form the site for protein br br synthesis . vii Lysosomes They contain lytic enzymes which break down large molecules, br br destroy worn out organelles or even the entire cell. br br viii Golgi Bodies Golgi apparatus Their function is to package and transport glyco-proteins. They are also associated with secretion of synthesized proteins br br and carbohydrates . br br Diagram ix Centrioles They are rod shaped structures that are used in cell division and in br br the formation of cilia and flagella . br br Plant cells lack the Centrioles. x Chloroplasts They are egg shaped and contain two membranes. Chloroplast has chlorophyll which traps light energy to be used during photosynthesis. br br xi Vacuoles This are sacs filled with a fluid called cell sap. Animal cells contain small vacuoles while plant cells have large br br vacuoles. br br Sap vacuoles store sugars and salts. Food vacuole store and digest food while contractile vacuoles br br excrete unwanted materials from the cell. br br xii Cell wall br br 25 It is a rigid outer cover of the plant cells made of cellulose . It gives the plant cell a definite shape while providing br br mechanical support and protection . br br Cell wall also allows water, gases and other materials to pass br br through it. br br Study Question 3 NUTRITION IN PLANTS AND ANIMALS br br Nutrition br br This is the process by which organisms obtain and Assimilate br br nutrients. br br There are two modes of nutrition; Autotrophism and br br Heterotrophism. br br Autotrophism br br This is where living organism manufacture its own complex food substances from simple substances such as carbon iv oxide, water, light or chemical energy. br br Where sunlight is used as a source of energy, the process is br br referred to as photosynthesis . br br Photo means light while synthesis means to make. Some none green plants make their own food using energy obtained from certain chemicals through a process called chemosynthesis. br br Organisms that make their own food are referred to as br br autotrophs . Heterotrophism This is where organisms take in complex food materials such as carbohydrates, proteins and fats obtained from bodies of plants and animals. br br Organisms that feed on already manufactured foods are called br br Heterotrophs . br br Autotrophism External Structure of a Leaf A leaf is a flattened organ which is attached to the stem or a branch of a plant. Diagrams Parts of a leaf Lamina: This is the flat surface. It is green in colour and contain the photosynthetic tissue. Midrib: This is a thick structure running through the middle of the leaf Veins: They arise from the midrib to forming an extensive network of veins. Leaf Apex: This is the tip of the leaf and usually it is pointed. Petiole: It attaches the leaf to the stem or branch. br br In some monocotyledonous plants the leaves are attached to the stem by the leaf sheath. br br Practical Activity 1: To examine the External Features of a Dicotyledonous and Monocotyledonous leaf Study Question 1 Internal Structure of a Leaf br br Internal structure of the leaf is composed of the following parts. i. Cuticle. It is a thin waterproof and transparent layer that coats the upper br br and lower surfaces of the leaf. br br It reduces excess water loss and protects the inner tissue of the br br plant against mechanical injury. br br It also prevents entry of disease causing micro organisms. Since it is transparent, it allows penetration of light for br br It is a one cell thick tissue on both the upper and lower leaf br br surfaces. br br It secretes the cuticle and also protects the inner tissues from br br mechanical damage and prevents entry of pathogens. br br Epidermal cells have no chloroplast except the guard cells . Guard cells are special bean shaped cells. They have chloroplast and are able to carry out photosynthesis hence controlling the opening and closing of the stomata. br br Air moves into and out of the leaf through the stomata. iii. This is layer of cells located beneath the upper epidermis. It is made of cylindrical shaped cells closely packed together. They have numerous chloroplasts containing chlorophyll. br br Palisade layer. br br Their position and arrangement enables them to receive br br maximum light. br br iv. This is below the palisade layer. The cells are irregularly shaped and loosely packed creating large air spaces in between them. The air spaces allow gases to diffuse in between the cells. They contain fewer chloroplasts as compared to the palisade cells. br br Spongy Mesophyll Layer. br br v. Each vein is a vascular bundle consisting of xylem and phloem. Xylem conducts water and mineral salts from the roots to the br br Leaf Veins. br br leaves while the phloem translocates manufactured food from the leaves to the rest of the plant. br br br br 28 Study Question 2 Adaptations of Leaves to Photosynthesis. br br 1. Broad and flat lamina to increase surface area of Carbon IV br br oxide and sunlight absorption. br br 2. Thin transparent cuticle and upper epidermis; to allow easier br br penetration of light to photosynthetic cells; br br 3. Thin; for faster diffusion of gases; 4. Palisade cells placed next to the upper surface; to trap maximum br br light for photosynthesis; br br 5. Palisade cells with numerous chloroplasts; to trap maximum br br amount of light for photosynthesis; br br 6. Large/ intercellular air spaces in the spongy mesophyll layer; for br br storage of Carbon IV oxide for easier gaseous exchange; br br 7. Waxy water proof cuticle; to reduce water loss sand reflect excess br br light; br br 8. Leaf mosaic/ non-overlapping leaves; for maximum exposure to br br light; br br 9. Guard cells, modified cells to open and close stomata; to control amount of water loss from the leaf and allows gaseous exchange; 10. br br Leaves have leaf veins; xylem to conduct water to photosynthetic cells, Phloem to translocate products of photosynthesis to other parts of plant; br br The Chloroplast br br They are disc shaped organelles found in the cytoplasm of plant br br cells. br br Each chloroplast has a double membrane; the inner and outer br br membrane. br br Chloroplasts are made of layers of membranes called lamellae br br contained in a fluid matrix called stroma . br br Several lamellae come together to form the granum grana . Granum contains chlorophyll molecules and other photosynthetic br br pigments . The stroma contains enzymes that speed up the rate of br br photosynthesis. br br br br Practical Activity 2: To Observe Distribution of Stomata Study Question 3. The Process of Photosynthesis br br The raw materials for photosynthesis are; water and carbon IV oxide. The process however requires the presence of sunlight energy and chlorophyll pigment. br br The products of photosynthesis are glucose and oxygen. The br br process can be summarized using an equation as shown below. br br 6H2O 6CO2 ---------- C6H12O6 6O2 Water Carbon IV oxide Glucose Oxygen. The above chemical equation translates as: Six molecules of water plus six molecules of carbon IV Oxide produce one molecule of sugar plus six molecules of oxygen br br The process of photosynthesis is however more complex than br br shown in the above equation and can be divided into two stage; the light and dark stages. br br Light stage Light Dependent Stage - Occurs in the grana containing chlorophyll which traps / absorbs sun light energy . - and oxygen gas. - br br This Energy is used to split water molecules into hydrogen ion br br This process is called photolysis of water and is shown below. br br LIGHT ENERGY br br 2H2O br br 4H 30 br br O2 CHLOROPHYLL Water Hydrogen atom Oxygen br br - Hydrogen atoms produced here enter into the dark stage. - Oxygen gas removed through stomata or is used for respiration within the plant ; - br br Some Light energy is used in Adenosine Triphosphate ATP formation; ATP an energy rich compound. br br - ATP is later used in the dark stage. Dark stage. Light Independent Stage - glucose/simple carbohydrate. - br br Carbon IV oxide combines with hydrogen atoms to form br br This is called Carbon IV Oxide fixation. Carbon IV oxide Carbohydrate CO2 - present or not. - ATP Energy from light stage is used to provide the required energy in this reaction ; - br br Hydrogen Atom Simple br br 4H C6H12O6 br br This stage takes place in the stroma and proceeds whether light is br br Simple sugars formed are used for respiration to provide energy or are converted to storable forms e.g lipids, proteins, starch, cellulose, etc. Study Question 4 Practical Activity 3: To Investigate the Presence of Starch in a br br Leaf. br br Study Question 5 Factors Affecting the Rate of Photosynthesis br br i. Light Intensity. Increase in light intensity increase the rate of photosynthesis up to br br a certain level where it slows down and finally levels off. br br Very bright sunshine may damage the plant tissues due to high br br amount of ultra violet light. br br Light quality or light wavelength also affects the rate of br br photosynthesis. Light intensity br br ii. Increase in Carbon IV oxide concentration increases the rate of photosynthesis linearly up to a certain level after which it slows down and levels off. br br Carbon IV oxide concentration Carbon IV oxide concentration Temperature br br iii. Photosynthesis is an enzyme controlled process, therefore br br increase in temperature increase the rate of photosynthesis up to the optimum temperature. br br Increase in temperature beyond the optimum decreases the rate br br sharply as the enzymes become denatured. br br br br iv. Water Plants need water for photosynthesis. Hydrogen atoms required in the dark stage during Carbon IV oxide fixation are derived from water during photolysis. br br Study Question 6 Practical Activity 4: To Investigate Factors Necessary for Photosynthesis. a Light br br Study Question 7 br br b Carbon IV oxide. br br Study Question 8 c Chlorophyll. Study Question 9 Study Question 10 Practical Activity 5: To Investigate the Gas Produced During Photosynthesis. Study Question 11 br br 33 Chemical Compounds Which Constitute Living Organisms Cells, tissues and organs are made of chemicals which are br br referred to as chemicals of life . br br The study of chemical compounds found in living organisms and br br reactions in which they take part is called Biochemistry . Chemicals of life include carbohydrates, lipids and proteins. a Carbohydrates They are compounds of carbon, hydrogen and oxygen in the ratio br br of 1:2:1 respectively. br br Carbohydrates have a general formula of CH2O n where n represents the number of carbon atoms in a molecule of carbohydrate. br br Carbohydrates are divided into three groups; Monosaccharides, br br Disaccharides and Polysaccharides. br br i Monosaccharides They are the simplest carbohydrates and have a general chemical br br formula of CH2O n where n 6. br br Their chemical formular is therefore C6H12O6 . They include; br br glucose, fructose, galactose etc. br br Properties of Monosaccharides br br i They are soluble in water to form sweet tasting solutions. ii They are crystalissable. iii They have the reducing property where they reduce copper sulphate in Benedicts solution to red copper I oxide. Functions br br i They are oxidized to release energy during respiration. ii When condensed together, they form polysaccharides such as br br starch, cellulose or glycogen. br br ii Disaccharides They are formed by linking two Monosaccharide molecules br br through the process of condensation where a molecule of water is liberated. Monosaccharide Monosaccharide br br Disaccharide Water. C6H12O6 C6H12O6 C6H22O11 br br H2O Examples Glucose Water. Glucose Water Glucose Galactose Lactose br br Water. br br The type of disaccharide formed depends on the monosaccharide br br units that condense together. br br Properties of Disaccharides i Soluble in water to form sweet tasting solutions ii They are non reducing sugars . Some such as the maltose can reduce copper sulphate in Benedicts solution when heated together and are therefore referred to as complex reducing sugars . br br iii They are readily broken into their constituent br br monosaccharide molecules in a process known as Hydrolysis in the presence of water. br br Hydrolysis br br Disaccharide br br Water Monosaccharide Monosaccharide br br C6H22O11 br br H2O C6H12O6 C6H12O6 Water br br Hydrolysis br br Sucrose Hydrolysis br br Glucose Fructose br br Lactose br br Water Glucose Galactose br br Maltose Water br br Glucose Glucose. br br 35 Naturally disaccharides are hydrolyzed by enzymes. In the laboratory, hydrolysis is achieved by boiling them in dilute Hydrochloric acid. br br Functions They are hydrolyzed by enzymes into monosaccharides which br br are then oxidized to produce energy. br br iii Polysaccharides. They are made of many monosaccharide br br molecules hence are long and more complex. br br They have a general formula of C6H10O5 n; where the value of n br br is a very large number . Examples of polysaccharides br br i It is present as stored food in plant tissues e.g. maize, wheat, br br Starch br br potatoes, rice etc. br br ii Cellulose This is the component of the cell wall in plants. Cellulose gives br br the plant cells their definite shape. br br iii Glycogen This is the form in which carbohydrates are stored in animal br br tissues. Excess glucose is converted into glycogen for storage in the liver. br br Properties of Polysaccharides br br i All are insoluble in water. ii Do not have a sweet taste hence are referred to as non-sugars. Study Question 12 Practical Activity 6: To Carry out Food Tests for Carbohydrates Starch i ii Reducing sugars iii Non Reducing Sugars br br b Lipids These are the fats and oils. Fats are found in animals while oils br br are found in plants. br br Oils are liquid while the fats are solid at room temperature. br br They contain carbon, hydrogen and oxygen just like the br br carbohydrates. However they contain fewer number of oxygen atoms than in carbohydrates. br br Lipids are made up of three fatty acid molecules and one br br molecule of Glycerol. br br The nature of a lipid formed, depends on the fatty acids it br br contains. Glycerol remains the same in all lipids. br br Diagram br br Complex lipids are formed through condensation of many lipid br br molecules just like in carbohydrates. br br Examples of complex lipids include; phospholipids, waxes, br br steroids and cholesterol. br br Presence of lipids in a food sample is detected using the grease br br spot test or emulsion test . br br Properties of Lipids br br 1. When fats are heated they change into liquid while oils solidify br br under low temperature. br br 2. Both fats and oils are insoluble in water. They however dissolve br br in organic solvents such as alcohol to form emulsions and suspensions. br br 3. Lipids are inert hence can be stored in the tissues of organisms. br br Functions of Lipids br br i They give almost twice as much energy as the Monosaccharides. ii Source of metabolic water When oxidized, lipids release more water than Monosaccharides. br br Source of energy Such water is referred to as metabolic water . br br iii Structural compounds Lipids are constituents of plasma membrane and protoplasm. iv Heat insulation Fats are deposited under the skin of animals forming the adipose br br tissue which acts as a heat insulator. br br Mammals in the temperate regions have thick adipose tissue to br br greatly reduced heat loss. Thick adipose tissue in aquatic animals helps them to be buoyant br br in water. v Protection Fat is deposited around the major organs such as kidney, heart etc br br where they act as shock absorber. br br Wax in plant cuticles reduces excessive water loss. br br Study Question 13 Practical Activity 7: testing for the Presence of Lipids i The Grease Spot ii The Emulsion Test br br c Proteins Like carbohydrates and lipids, proteins are compounds of carbon, br br hydrogen and oxygen. br br In addition they contain nitrogen and sometimes phosphorous br br and sulphur . br br Some proteins such as haemoglobin contain other elements such br br as iron. br br Proteins are made up of small units called amino acids. There are br br about 20 different types of amino acids. br br All amino acids contain the amino group -NH2 which consists br br of hydrogen and nitrogen. br br Two amino acids combine to form a dipeptide molecule through br br the process of condensation. br br The bond between two amino acids is called peptide Bond . Many amino acids join together to form a long protein chain called polypeptide chain . br br The type and sequence of amino acids contained in such a chain br br determine the uniqueness of the protein being formed. br br Properties of Proteins br br i. They dissolve in water to form colloidal suspensions not true br br solutions where particles remain suspended in water. br br They are denatured by temperatures above 40 0C. Heat alters the structure of the protein molecule. Chemicals such as detergents, acids, bases and organic solvents also denature proteins. br br ii. br br 38 iii. br br They are amphoteric whereby they have both acidic and basic properties. This property enables them to combine with non-protein compounds to form conjugated proteins such as mucus, and haemoglobin. In mucus the non protein compound is a carbohydrate while in haemoglobin, iron is a non protein. br br Functions of Proteins br br i. Structural Functions br br Proteins make the framework of living systems e.g. plasma membrane, connective tissues, muscle fibres, hair, nails, hooves, skeletal materials etc. br br ii. Metabolic Regulators br br These are divided into two a Enzymes Enzymes are organic catalysts which speed up the rate of metabolic reactions such as respiration, photosynthesis, digestion etc. b Hormones They are chemical messengers which regulate many body br br processes such as growth, reproduction, amount of sugars, salts and water in the blood etc. br br iii. Source of Energy br br Under extreme starvation, proteins are broken down to release br br energy. br br Study question 14 Practical Activity 8 To Test for Proteins Enzymes They are organic catalysts which are protein in nature. They speed up or slow down the rate of chemical reactions in the body without themselves being used up. br br They are divided into two; a Extracellular Enzymes Extracellular enzymes are produced within the cells but are used outside the cells which produce them e.g. the digestive enzymes. br br 39 Naming of the Enzyme br br There are two methods on naming enzymes; br br i Trivial Naming br br Enzymes are given names of persons who discovered them. The names end in -in such as pepsin, trypsin ptyalin etc. br br ii Use of suffix ase br br This is the modern method of naming. The suffix ase is added br br to the substrate type of food or the reaction the enzyme catalyzes. Example 1 Substrate Carbohydrate Starch e.g. amylose Amyl ase Sucr ase Sucrose Malt ase Maltose Prote ase Protein Lipid Lip ase Example 2 Reaction Enzyme Hydrolysis Hydrolase Oxidation Oxidase Reduction Reductase br br Enzyme Carbohydr ase br br Properties of Enzymes br br 1. They are protein in nature hence are affected by changes in br br temperature and pH. br br 2. They are substrate specific. 3. They are efficient in small amounts as they are not affected by the br br reactions they catalyze. They can be used again and again. Factors Affecting the Rate of Enzyme Controlled Reactions br br i. Temperature br br Enzymes are sensitive to changes in temperature and pH since br br they are protein in nature. br br Enzymes work best within a narrow range of temperature br br called the optimum temperature. br br Above the optimum temperature, reaction decreases sharply as br br the enzymes are denatured. br br Most enzymes have optimum temperature between 35-40oC. Very low temperature inactivates the enzymes hence decrease br br rate of reaction. br br Diagrams br br ii. pH br br Most enzymes have a pH of close to 7. Some however work best in acidic pH e.g. pepsin while others br br work best in alkaline conditions. br br As pH changes from the optimum, enzyme activity decreases. Extreme acidity or alkalinity denatures most enzymes. br br Diagrams iii. Specificity br br Enzymes are specific in nature where a particular enzyme acts br br on a particular specific substrate. br br For example, sucrose works on sucrose and not any other br br substrate. br br iv. br br Substrate Concentration and Enzyme Concentration. When substrate concentration increases, the rate of enzyme reaction also increases upto a certain level. br br Further increase does not increase the rate of reaction as all the br br active sites of an enzyme are occupied. br br When enzyme molecules are increased, the rate of reaction br br increases proportionally. br br Diagrams br br v. Enzyme Co-factors and Co-enzymes Co-factors are non protein substances which activates enzymes. They are required in small quantities and they include metallic ions such as those of iron, magnesium, zinc, copper etc. Some are vitamins. br br Co-enzymes are non protein molecules that work in association with particular enzymes. Most co-enzymes are derived from vitamins. br br vi. Enzyme Inhibitors br br Inhibitors compete with the normal substrate for the active sites and they take up the active site of the enzyme permanently. br br There are two types of inhibitors; a Competitive Inhibitors br br These are chemicals closely related to normal substrate and they compete for active sites with the normal substrate. They slow down the rate of reaction. b Non Competitive Inhibitors br br They do not compete with the substrate. They combine br br permanently with enzyme molecules thus blocking the active sites. They include poisons such as cyanides, mercury and silver- arsenic compounds. Importance of Enzymes Enzymes speed up the rate of cellular reactions and also control them. This way, they help prevent violent reactions in the cells. br br Study Question 15 Practical Activity 9 Study Question 16 Study Question 17 Practical Activity 10 FORM TWO BIOLOGY NOTES br br EXCRETION AND HOMEOSTASIS Excretion -Process by which living organisms separate and eliminate waste products formed during metabolic processes from the body. They include; carbon IV oxide, excess water and mineral salts, nitrogenous wastes etc. accumulation of these substances may become toxic to cells. br br Homeostasis -This is the maintenance of internal environment of cells under constant conditions E.g. temperature, osmotic pressure, blood sugar and chemical constituents. br br Egestion . - This is the removal of undigested and indigestible br br materials from the alimentary Canal of animals. br br Secretion . - This is the release of certain useful substances br br produced by cells e.g. hormones, Enzymes, sebum, saliva and mucus. Excretion in Plants br br Plants do not have complex organs for excretion because; br br i. There is very little accumulation of toxic wastes such as br br nitrogenous wastes. br br ii. Some waste products are re-used in the same plant such as Co2, br br oxygen and water. br br iii. Some of these gases are removed by simple diffusion through the br br stomata and lenticels. br br iv. Some plants store wastes in their tissues in non-toxic forms such as nicotine, caffeine, tannins, resins, quinine, morphine etc. br br Economic Importance of Plant Excretory Products br br i. Tannins They are deposited in dead tissues of wood and br br barks of trees e.g. in acacia and wattle tree. Tannin is used to treat leather. br br ii. Caffeine it is stored in coffee berries and tea leaves. It is used br br as a stimulant. br br iii. Quinine it is stored in the leaves of aloe and bark of cinchona br br tree. It is used in the treatment of malaria. br br 43 iv. Cocaine it is obtained from the leaves of coca plant and is br br used as an anesthetic. br br v. Cannabis found in the leaves and flowers of Cannabis sativa br br bhang . It is used to manufacture some drugs. br br vi. Nicotine found in leaves of tobacco plant and is used in the manufacture of insecticides and narcotic drugs. It also manufactures cigarettes. br br vii. Rubber it is made from latex of rubber plant. It is used in br br shoe industry and manufacture of chewing gum. br br viii. Colchicines it is used in plant breeding and treating of cancer. ix. Pappain - it is obtained from raw paw paw and it is used as a br br meat tenderizer. br br x. Khat/miraa its chewed and acts as a mild stimulant. br br Excretion and Homeostasis in Unicellular Organisms br br Most simple organisms such as the protozoa amoeba and br br paramecium live in aquatic environment. br br They depend mainly on diffusion as the means of excretion. Their bodies have a large surface area to volume ratio providing a large surface area for gaseous exchange and excretion to take place by simple diffusion. br br Waste products diffuse from the cytoplasm where they are highly concentrated across the cell membrane into the surrounding water where their concentration is low. br br The organisms also use the contractile vacuole to achieve br br excretion. br br Amoeba and paramecium live in an aquatic environment that is br br hypotonic to their body fluids. Water therefore tends to move into their cytoplasm by osmosis. br br The excess water and dissolved chemicals accumulate in the br br contractile vacuole which releases them to the surrounding water. br br Diagram Excretion in Mammals br br Mammals have an elaborate excretory system since their bodies br br are complex. The main excretory organs in mammals include; lungs, skin, br br kidneys and the liver. br br A Structure and Function of the Mammalian Skin br br Skin is the largest body organ covering the whole body surface. It has the following functions. i. Protection of the underlying tissues from entry of micro- br br organisms, physical damage and ultra violet rays from the sun. br br ii. Regulation of body temperature. iii. Excretion of salts, excess water and traces of urea. iv. Reception of stimuli such as heat, cold, pain, touch and br br pressure. br br v. Synthesis of vitamin D. vi. Storage of fats. br br Diagram br br The skin is made up of two layers; a Epidermis upper and outer layer b The dermis inner layer a Epidermis upper and outer layer It is made up of three other layers; br br i. Cornfield layer. ii. Granular layer. iii. Malphigian layer. i. Cornifield layer br br The Cornifield layer of the epidermis consist of dead cells which form a tough outer coat; that protects the skin against mechanical damage, bacterial infection and water loss; ii. Granular layer br br Its the middle layer of the epidermis and is made up of living br br cells that give rise to the Cornifield layer. br br iii. Malphigian layer br br Malphigian layer consists of actively dividing cells that contain br br fine granules of melanin; that prevents the skin against ultraviolet light rays from the sun; melanin gives the skin its colour. br br b The Dermis inner layer It is thicker than the epidermis and consists of the following br br structures; br br 1 Sebaceous glands produce an oily secretion sebum which give br br hair its water repelling property; that keeps the epidermis supple and prevents it from dying Sebum also prevents bacterial attack due to its antiseptic property; br br 2 Has blood vessels; that dilate and contract; br br In hot conditions, they dilate; increasing blood flow near the skin surface enhancing blood flow near the skin surface; minimizing heat loss; Blood vessels supply nutrients and oxygen to skin tissues and also remove waste products and carbon IV oxide. br br 3 Has Hair follicle ;hairs stand during cold weather thus trapping a layer of air which prevents heat loss; In hot weather they lie close to the skin surface; to enhance heat loss to the atmosphere. 4 Have many sensory neurons which detects environmental br br changes; increasing sensitivity of the skins. br br 5 Has subcutaneous layer ; contains fat which acts as a heat- br br insulating layer and a fuel storage. br br 6 Lymphatic vessels ; they drain excess tissue fluid. 7 Sweat glands ; are involved in temperature regulation through loss of excess heat by the evaporating water. Sweat also excretes excess water, mineral salts, urea and lactic acid. B The Lungs br br They are involved with the removal of carbon VI oxide which is br br released by cells during their metabolism. br br Carbon IV oxide would be toxic if it was left to accumulate in the br br tissues. br br C Structure and Function of the Kidney Diagram fig. 4.3; generalized urinary system of a mammal page 88 KLB br br Mammals have a pair of kidneys which are bean shaped and dark br br red in colour. br br 46 The kidneys are surrounded by a layer of fat which cushions them br br against mechanical injury. br br Above each kidney are the adrenal glands which secrete br br hormones. br br Renal artery supplies blood to the kidneys and the renal vein br br removes the blood. br br Ureter transports urine from the kidney to the bladder which br br temporarily stores the urine. br br The mammalian kidney has three distinct regions; cortex, medulla br br and pelvis. br br Diagram fig. 4.4 a and 4.4 b page 89 KLB Cortex br br It is the outermost region and is dark red in colour. br br Medulla br br It is red in colour and extends to form conical structures called br br pyramids. br br Pyramids open up into the pelvis. br br Pelvis br br Its white in colour and narrows down to form the Ureter. The human kidney contains urinary tubules called the nephrons. br br Nephron br br It is the basic functional unit of the kidney. Each nephron is made br br up two main parts; Renal tubule Glomerulus. br br Diagram fig. 4.6. The structure of the kidney nephron X br br br br B br br A br br D C C br br The renal tubule has 5 main parts. br br 1. Bowmans capsule 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting tubule 1. Bowmans capsule br br It is a thin walled and cup shaped structure which contains the br br glomeruli. br br Glomerulus is a fine network of blood capillaries enclosed by br br the Bowmans capsule. br br It is made the afferent and efferent arterioles. Blood entering the kidney via the renal artery is rich in br br nitrogenous wastes such as urea. br br Also it has dissolved food substances, plasma proteins, mineral br br ions, hormones and oxygen. br br Afferent arteriole entering the Glomerulus is wider than the br br efferent arteriole leaving it. br br This creates extremely high pressure in the Glomerulus br br coupled with the fact that renal artery branches directly from the aorta where blood is at high pressure. br br Diagram: structure of the nephron 48 Due to the high pressure in the glomeruli, the liquid part of the br br blood and dissolved substances of low molecular sizes including urea, glucose, salts and amino acids are forced out of the Glomerulus into the cavity of the Bowmans capsule. The large sized molecules in the plasma such as proteins and br br blood cells are not filtered out. br br This is because the capillary walls of the Glomerulus and bow br br mans capsule have very small pores. br br This process is known as ultra-filtration and the filtrate formed br br is called glomerular filtrate. br br The filtrate then enters the proximal convoluted tubule. br br Diagram of ultra-filtration at the Glomerulus br br 2. Proximal convoluted tubule br br As the filtrate flows along the renal tubules, most of the filtered br br substances in the glomerular filtrate useful to the body are selectively reabsorbed back into the blood. br br The following substances are actively reabsorbed using energy in the proximal convoluted tubule; All glucose, Amino acids and Mineral salts. br br The proximal convoluted tubule is adapted in the following ways for efficient re-absorption of these substances. br br i Presence of mitochondria in the cells lining to provide with br br energy required br br ii Cells of the tubule have micro-cilli infoldings which br br increase surface area for re-absorption. br br iii Tubule is long and coiled to increase the surface area. iv Coiling of the tubule reduces the speed of flow of filtrate br br giving more time for efficient re-absorption. br br v Tubule is well supplied with blood capillaries. br br 3. Loop of Henle br br This is where particularly sodium chloride is actively br br reabsorbed into the blood. br br Loop of Henle has counter current flow between the flow of br br filtrate and the flow of blood i.e. the filtrate and blood flow in opposite directions. br br 49 The hormone Aldosterone secreted by the adrenal glands br br regulate the absorption of sodium salts. br br Low content of sodium salts in the blood stimulates adrenal br br glands to secret more Aldosterone hormone and therefore more salts are reabsorbed from the filtrate. br br 4. Distal convoluted tubule br br When the filtrate reaches here, some water is reabsorbed into br br the blood by osmosis. br br This is made possible by the following; br br - Active intake of sodium salt into the blood at the loop of br br Henle increases the osmotic potential of the blood. br br - The antidiuretic hormone ADH secreted by the pituitary gland. ADH increases the permeability of the tubule and blood capillaries to water br br When there is excess water in the body there is less production of ADH and less water is reabsorbed hence production of large amounts of dilute urine. br br If the body has lost a lot of water such as through sweating, this raises the osmotic pressure of blood. Pituitary gland releases more ADH which increases permeability of the kidney tubules to water. More water is reabsorbed hence production of little but concentrated urine. br br The distal convoluted tubule has large surface area, it is has a wall that is one cell thick and is surrounded by may blood capillaries. 5. Collecting tubule br br The filtrate in the collecting tubule becomes the urine and br br moves to the collecting duct. br br Urine flows into the pelvis via the pyramids and is finally br br emptied into the urinary bladder through the ureter. About 1-2 litres of urine are formed in a day. br br About 250ml of urine in the urinary bladder initiates the urge br br to urinate. The sphincter muscles relax and urine pass. br br Urine Composition br br Substance br br 50 Composition. 95 2 0.03 0.1 1.4 0.04 0 0 Water Urea Uric acid Creatine Salts Ammonia Proteins Glucose The quantity and concentration of the urine in animals is affected br br by i Physiological adaptations. ii Habitat of an organism e.g. terrestrial, desert or aquatic. iii Structural adaptations of the animals e.g. a desert rat has long kidney tubules to increase water reabsorption. br br Study Questions. . Comparison Between Aquatic and Desert Animals Desert Animals. Fresh Water Animals i Have many glomeruli to Few glomeruli to reduce ultrafiltration. increase ultrafiltration. ii Short loop oh Henle to reduce Long kidney tubules to increase water reabsorption. Produce small quantity of concentrated urine. br br water reabsorption. iii Produce large quantity of br br dilute urine. Comparison of Composition of urine with that of Glomerular Filtrate and Blood Plasma. br br Substance Composition of; br br Plasma Glomerular urine br br Filtrate. 0.03 0.005 0.001 0.1 Urea Uric acid Ammonia Glucose 0.03 0.005 0.001 0.1 2.0 0.03 0.004 0 br br 51 Amino acids 0.05 Mineral salts 0.70 8.00 Blood proteins.Functions of the kidney include:i Excretion. ii Osmoregulation. iii iv Ionic balance. Regulation of PH br br Kidney Diseases br br i Nephritis This is the inflammation of the glomerulus of the kidney. It is caused by bacteria or infections such as small pox and measles. Symptoms Headaches and vomiting Treatment Use of antibiotics ii Use of just adequate amounts of salts and proteins in diets br br Fever Passing coloured urine Presence of proteins in urine br br Kidney stones br br Causes Lack of vitamins such as vitamin A and inadequate intake of br br water br br Chemical salts in urine that crystallize to form hard stones. Symptoms br br Increased frequency in passing out urine Pain and soreness in the upper backside Difficulty in passing out urine Fever br br Control Treatment br br Seeking medical assistance br br Taking a balanced diet with adequate amount of water and br br vitamins br br Dialysis or artificial washing out of the wastes Use of laser beam to disintegrate the stones Kidney transplant br br iii Kidney failure br br This is the failure of the kidney to perform as a result of a br br drop in blood pressure due to heart failure, haemorrhage or shock. br br If failure is due to other causes, the condition can be br br corrected by; - Kidney dialysis - Kidney transplant iv Albiminuria Proteins in Urine . This is also called Proteinuria Capillaries of the glomerulus lose their ability to be selective and start allowing blood proteins to pass through into the kidney tubules. These proteins are released in urine. br br D The Liver and its Structure br br This is the second largest excretory organ after the skin. It receives blood from two blood vessels; the hepatic portal vein from the alimentary canal and hepatic artery from the aorta . br br br br Homeostatic Functions of the Liver br br 53 Regulation of blood sugar level Excess glucose is converted to glycogen ;and stored in the liver br br under the influence of the hormone insulin secreted by the pancreas. Another hormone called glucagon; stimulates the conversion of glycogen to glucose; when there is shortage of glucose in the body; Glucagon is also secreted by the pancreas br br 1. Deamination br br The liver breaks down excess amino acids; The amino group is br br removed as ammonia which is toxic; br br Ammonia is changed into urea which is less toxic in the br br ornithine cycle . br br Ornithine Cycle br br 2NH3 CO2 H20 Ammonia Water Toxic br br CO NH2 2 Enzyme arginase br br Carbon iv Urea br br Oxide less toxic The remaining carbon skeleton oxidized to carbon IV oxide br br and water; this process leads to release of energy. The carbon skeleton may be converted to glucose to be used during respiration; 2. Detoxification br br Toxic substances are made harmless in the liver e.g. Ammonia from the process of deamination is converted in the br br liver into urea; which is less toxic. br br Bacterial toxins are converted to less toxic substances by liver br br cells; br br Hydrogen peroxide produced by respiring cells is broken down br br into water and oxygen which are harmless by the enzyme catalase found in the liver. br br Enzyme br br Catalase Hydrogen Peroxide Water br br Oxygen br br 54 H2O2 br br 3. Regulation of plasma proteins br br The liver produces most of the proteins found in blood; br br fibrinogen and prothrombin which play a role in blood clotting. Albumin and globulins are also produced by the liver. Globulins act as antibodies;. Albumin contributes to the maintenance of osmotic pressure in the body; Non essential amino acids are synthesized by the liver; br br 4. Storage of vitamins A, B,D,E and K and mineral salts br br The liver store vitamins A, B, D, E and K. Iron released from the breakdownof erythrocytes is stored in the liver cells; in the form of a compound called ferritin. The liver therefore is a good source of these vitamins and iron; br br 5. Heat production Thermoregulation br br The various metabolic activities of the liver lead to release of heat energy; This energy is distributed by the blood to other parts of the body hence contributing to maintenance of constant body temperature; br br 6. Inactivation of hormones and drugs br br After performing their functions, hormones and drugs are br br chemically modified to inactive compounds; The by-products are eliminated through the kidneys and faeces and via bile; 7. Storage of blood br br The large size and high capacity for contraction and expansion of its veins enables the liver to hold a large volume of blood; It therefore regulates the volume of blood in the general circulation depending on the bodys requirements ; br br 8. Regulation of cholesterol and fat metabolism br br When carbohydrates are in short supply in the body, fats in br br different parts of the body are mobilized and taken to the liver; The fats are oxidized to carbon IV oxide and water with the production of energy or modified and sent to tissues for oxidation; br br 9. Manufacture of red blood cells in foetus. br br Liver Diseases and Disorders br br 55 1. Liver Cirrhosis br br This is the hardening of the liver tissues due to death of br br liver cells. br br This is caused by ingestion of toxic chemicals such as br br alcohol. br br Bacteria, viruses and parasites such as liver flukes can br br also cause the disease. br br Control br br Avoid excess alcohol. Avoid fatty diets. Low salt intake br br 2. Hepatitis br br This is a viral disease causing inflammation of the liver. It is transmitted through contaminated food, milk and br br water. br br There are two types of hepatitis; Hepatitis A and B . br br 3. Jaundice br br This is characterized by the yellowing of the skin due to br br the failure of the liver to excrete bile. br br Homeostasis br br This is the maintenance of internal environment of cells under constant Conditions E.g. temperature, osmotic pressure, blood sugar and chemical constituents. br br Principles of Homeostasis br br Various body systems such as circulatory, excretory, br br endocrine hormonal and nervous work in a coordinated way to bring about homeostasis. br br These systems work on a feedback mechanisms. There are two types of feedback mechanisms . br br a Negative Feedback Mechanism br br When a factor in the body such as temperature or blood sugar br br level falls below normal or rises above the normal, it is detected and corrected via the negative feedback mechanism. br br Such an action is through: br br 56 Temperature Osmoregulation water and salt balance Ionic content regulation Blood sugar regulation br br a Temperature Regulation. Thermoregulation Hypothalamus of the brain is the thermoregulatory center. It also br br controls other homeostatic processes such as Osmoregulation, and blood sugar level. Skin and Thermoregulation The skin is adapted in the following ways to effect thermoregulation; br br 1. It has Hair shaft; br br Connected to erector pili muscles ; In low Temperature Erector pili muscle contract raising hair br br shaft erect ; br br Hair traps air which insulates the body/poor conductor of heat.; In high temperature, the Erector pili muscle relax and extends ; Hair shaft lies on the skin ; Little or no air is trapped ; Skin loses heat through convection /conduction /radiation ; br br 1. Blood vessels br br In High temperature they vasodilate ; More blood flows near skin surface ; Heat is lost through conduction /convection/ radiation ; In Low temperature they Vasoconstrict ; Little blood flows near the skin ; Less heat or ho heat lost through conduction/convection/ radiation ; br br Diagrams 3 Sweat gland br br In High temperature , Sweating occurs and evaporates and br br Carries latent heat of vaporization; cooling the body ; br br 4 Has subcutaneous layer ; contains fat which acts as a heat- br br insulating layer. Organisms in cold areas have thick subcutaneous layer for heat insulation. br br 58 Homoiotherms and Poikilotherms Homoiotherms Endotherms br br They are the animals whose body temperature is maintained at a constant body temperature despite the wide fluctuations in the temperature of the external environment e.g. birds and mammals. br br Poikilotherms Ectotherms br br These are organisms with variable body temperature according to the temperature of the local atmosphere e.g. in organisms such as reptiles, amphibians, insects, and fish. br br Methods of Regulating Body Temperature in Animals . br br i Metabolic activities of the Body, such as shivering to raise br br body temperature. Insulatory mechanisms such as dilation or constriction of blood vessels, hair movement etc. br br ii br br iii Behavioral activities such as clustering together, burrowing, br br basking, hibernation, aestivation, putting on warm clothes etc. br br iv Presence of adaptive features such as hair/fur, subcutaneous br br tissue etc. br br Hibernation is where animals go into deep sleep for long period of time due to cold. Aestivation is where animals go into deep sleep due to dry and harsh conditions. Differences Between Homoiotherms and Poikilotherms. br br Poikilotherms i They are sluggish under Homoiotherms i They remain active even br br cold conditions. br br under cold conditions. ii Only the small animals hibernate because they have large surface area to volume ratio hence lose a lot of heat. iii They do not aestivate because they can maintain constant body br br ii They hibernate to avoid death by freezing under very cold conditions. br br iii They aestivate under very hot conditions. br br 59 iv They are easy prey to predators due to their hibernation and aestivation. v Require less food v Require more food br br because they get heat from the environment to warm their bodies. br br because they use it to generate heat for maintaining the temperature constant. br br b Osmoregulation Water and Salt Balance . br br The osmotic pressure of the body fluids must be kept at a br br constant so as to have a favourable environment for the normal functioning of cells. This is determined by the relative amounts of water and solutes salts in the body fluids. br br If the osmotic pressure of these fluids falls below that of the br br cells, the cells take in water by osmosis, swell and may burst. If the osmotic pressure of thee fluids was higher than that of br br the cells, the cells would lose water and shrink. br br The hypothalamus and the Pituitary gland are involved in br br Osmoregulation in the following ways; br br i When the osmotic pressure of the blood rises due to br br dehydration, the hypothalamus is stimulated and sends an impulse to the pituitary gland which secretes the Antidiuretic Hormone ADH or Vasopressin into the blood. ADH increases permeability of the kidney tubules to water. More water is reabsorbed, osmotic pressure of the blood falls hence production of little but concentrated urine. ii When osmotic pressure of the blood falls due to excess water in the body there is less production of ADH and less water is reabsorbed hence production of large amounts of dilute urine. br br Diabetes Insipidus br br This is a condition whereby large quantities of dilute urine are produced when the pituitary gland fails to produce ADH or produces it in inadequate amounts. This condition is also known as Diuresis. br br c Regulation of Ionic Content br br Important ions must be regulated within narrow ranges for br br efficient functioning of the cells. br br Ions are involved in processes such as respiration, protein br br synthesis, muscle contraction etc. br br The level of sodium ions is regulated by a hormone called br br Aldosterone produced by the adrenal glands. br br When the level of sodium ions is low in the blood, more Aldosterone is released which stimulates reabsorption of sodium ions into the blood. br br If sodium ions concentration in the blood rises above the br br optimum level, adrenal glands produce less Aldosterone into the blood and less amounts of sodium ions are reabsorbed. br br d Regulation of Blood Sugar Level . br br All sugars such as galactose, lactose and fructose are converted br br to glucose. br br Glucose is broken down to release energy and excess is br br converted into glycogen and stored in the liver or converted into fats as stored as adipose tissue. br br Some glucose flows in general circulation of blood and is br br maintained within a narrow range of 90-100mg per 100cm3 of blood. The pancreas produces two hormones Insulin and Glucagon br br that are responsible for blood sugar regulation. br br When there is excess sugar in the blood, insulin is produced br br and regulates the blood sugar level by the following; br br i Converts excess glucose into glycogen for storage. ii iii Converts glucose into fats. iv Increases breakdown of glucose to release energy. br br Inhibits conversion of glycogen to glucose. br br When the level of the blood sugar falls, glucagon is secreted br br and corrects the situation by the following; br br i Increases the breakdown of glycogen into glucose. br br 61 ii iii Inhibits the conversion of glucose into energy. NB/. The hormone adrenaline produced by the adrenal glands also has homeostatic effect on glucose. It is released during emergencies to avail glucose for fight or flight. Diabetes Mellitus Sugar Disease br br Increases the conversion of fats and proteins into glucose. br br This is due to a deficiency in insulin secretion from the br br pancreas. br br This leads to very high levels of sugar in the blood that cannot br br be utilised by cells hence eliminated by kidney in urine. br br Symptoms br br Presence of glucose in urine Loss of body weight due to breakdown of fats and proteins Chronic starvation Thirst sensation. br br Control br br Insulin injection into the blood stream Avoid foods rich in sugars. Avoid excessive intake of alcohol. br br Question br br Explain why insulin is not administered orally through the br br mouth Corrective mechanism, the liver; i br br Converts excess glucose into glycogen for storage. Inhibits conversion of glycogen to glucose. Converts glucose into fats. Increases breakdown of glucose to release energy. ii iii iv br br Fall br br Normal glucose level 90mg/100ml blood Rise br br Corrective mechanism, the liver; i br br Increases the breakdown of glycogen into glucose. Increases the conversion of fats and proteins into glucose. Inhibits the conversion of glucose into energy. br br ii br br iii Revision questions Gaseous Exchange br br This is the process by which respiratory gases oxygen and carbon IV oxide are passed across the respiratory surface. br br Gases are exchanged depending on their concentration gradient. In simple organisms such as amoeba, diffusion is enough to bring br br about gaseous exchange. br br CO2 diffuses out into the surrounding water while oxygen br br diffuses from the water across the plasma membrane into the amoeba. Importance of Gaseous Exchange br br 1. Promote oxygen intake for respiration. 2. Facilitate carbon IV oxide removal from the body as a metabolic br br waste product. br br Gaseous Exchange in Plants br br During the day, green plants take in carbon IV for photosynthesis. Oxygen is given out as a byproduct of photosynthesis and is br br released into the atmosphere. br br Examples of respiratory Surfaces in Plants br br Stomata in leaves Roots e.g. pneumatophores Lenticels in woody stems br br Structure and Function of the Stomata br br They are tiny openings on the leaf surfaces. They are made up of br br two guard cells. br br Guard cells are the only epidermal cells containing chloroplasts. br br They regulate the opening and closing of the stomata. br br Adaptations of Guard Cells br br i They are bean shaped/sausage shaped. ii Contain chloroplast hence can photosynthesize. iii Inner walls are thicker while outer wall is thin to facilitate br br the opening and closing of stomata. br br Diagram Mechanism of Opening and Closing of Stomata br br There are three theories that try to explain how the stomata open and close. br br i Photosynthetic theory ii Starch Sugar inter-conversion Theory. effect of changes in br br pH of guard cells br br iii i Photosynthetic theory br br Potassium Ion Theory. br br During the day, guard cells photosynthesize forming glucose. This glucose increases the osmotic pressure in the guard cells. Guard cells draw in water from the neighbouring epidermal cells br br and become turgid. br br 64 The stoma opens. During the night, there is no photosynthesis due to absence of br br light. br br Glucose is converted into starch lowering the osmotic pressure in br br the guard cells. br br Guard cells lose water and become flaccid closing the stomata. br br ii Starch Sugar inter-conversion Theory. effect of changes br br in pH of guard cells br br This is under the influence of pH in the guard cells. During the day CO2 is used up during photosynthesis raising the br br pH in the guard cells. br br In this high pH, enzymes convert more starch into glucose. Osmotic pressure of the guard cells increases and water enters into them, making them turgid hence opening the stomata. During the night, there is no photosynthesis. The level of CO2 br br increases lowering the pH. br br Enzymes become inactivated and starch is not converted into br br glucose. br br Osmotic pressure of guard cells falls making them to lose water br br by osmosis. br br Guard cells become flaccid and stoma closes. Mechanism of Gaseous Exchange in Plants Oxygen diffuses from the atmosphere where it is more concentrated into the plant. br br CO2 diffuses out as a metabolic waste product along a br br concentration gradient into the atmosphere. a Gaseous Exchange through the Stomata Stomata are modified in number of ways depending on the habitat br br of the plant. br br Xerophytes: These are plants adapted to life in dry areas. br br They have less number of stomata that are small in size. Stomata may be sunken, hairy and in some they open during the br br night and close during the day. br br Hydrophytes: These are the aquatic plants water Plants br br 65 They have many stomata that are large in size and mainly found br br on the upper leaf surface. br br Hydrophytes have the aerenchyma tissue with large air spaces to br br store air for gaseous exchange. br br Diagrams Mesophytes : They are plants growing in areas with adequate amounts of water. br br They have a fairly large number of stomata found on both leaf br br surfaces. br br b Gaseous Exchange through the Lenticels They are openings found on woody stems and they are made of br br loosely packed cells. br br They allow gaseous exchange between the inside of the plant and br br the outside by diffusion. br br Actual gaseous exchange occurs on some moist cells under the br br lenticels. br br Diagram c Gaseous Exchange through the Roots Plants like the mangroves growing in muddy salty waters have br br specialized aerial breathing roots called pneumatophores. br br Pneumatophores rise above the salty water to facilitate gaseous br br exchange. 1. Cell Membrane. Water 2. Gill Filaments Water 3. Tracheoles Air 4. Alveoli/Lungs Air br br 5. Skin br br Water Air Air 6. Buccal Cavity The respiratory surface is the basic unit of any breathing system br br upon which actual gaseous exchange occurs by diffusion. Respiratory surfaces have the following main characteristics. i Must have a large surface area. ii Must be moist to allow gases to diffuse in solution form. iii Have a dense network of blood capillaries for efficient br br gaseous exchange. br br iv Have a thin membrane to reduce the diffusion distance . br br Gaseous Exchange in Insects Insects have their gaseous exchange system made of many air tubes forming the tracheal system. br br Tracheal system is made up of spiracles and Tracheoles. Spiracles are external openings found on both sides of the br br abdomen and thorax. br br Spiracles have valves to control their opening and closing. They also have hairs to prevent excessive water loss from the body tissue. br br Spiracles open into tubes called trachea. Trachea is reinforced br br with spiral bands of chitin to keep them open. br br Trachea subdivides into finer air tubes called Tracheoles. br br Tracheoles are in direct contact with body tissues and organs and they supply individual cells with oxygen. Diagram Mechanism of Gaseous Exchange in the Tracheal System of an Insect br br Air is drawn into and out of the tracheal system by muscular br br movement of the abdominal wall. br br When spiracle valves are open, air is drawn into the tracheal br br system. The valves close and air is forced along the system by muscle movement. br br Oxygen diffuses into the tissue fluid and into the cells. CO2 diffuses out of the cells and into the tissue fluid then into the br br tracheal system. Gaseous Exchange in Fish The breathing system of the fish consists of the following; br br o Mouth buccal cavity. o Gills. o Opercular cavity. o Operculum. br br Gills are made of a long curved bone called the gill bar. Gill filaments arise from one side of the gill bar. They are many and suspend freely in water providing a large surface area for gaseous exchange. br br Gill rakers arise from the other side of the gill bar. They are teeth like and they prevent solids present in water from damaging the delicate gill filaments. br br Blood vessels enter the gill bar and branch into the gill filaments br br as blood capillaries. br br Operculum is found on either side of the body near the head and br br it also protects the delicate gills. br br Diagram Floor of the mouth cavity is lowered increasing the volume of the br br mouth cavity but lowering the pressure. br br Water flows into the mouth cavity and the operculum closes. Operculum on either side bulge outwards without opening. This br br increases volume in the gill cavity but the pressure drops. br br Water containing dissolved oxygen flows from the mouth cavity br br to the gill chamber over the gills. br br The mouth closes and the floor of the mouth cavity is raised. The remaining water in the mouth is forced to flow towards the br br gill chamber. br br Oxygen diffuses from the water into the blood through the thin walls of the gill filaments. It combines with haemoglobin for transportation to all body parts. br br CO2 diffuses from the blood into the flowing water. To ensure maximum gaseous exchange, the water flowing over the gills and the blood in the gills flows in opposite directions. This is called counter current flow system and it ensures that at all the points, concentration of oxygen is always higher in the water than in the blood. br br Diagram If the water and blood were flowing in the same direction, br br gaseous exchange will not be that effective. br br Where the oxygen is 50 in water, there is no concentration gradient because blood also has 50 oxygen concentration. br br Diagram Mechanism of Gaseous Exchange in Amphibians br br Amphibians live on both land and water and therefore exhibit the br br following methods of gaseous exchange. br br 1. Gaseous exchange through the lining of the buccal cavity 2. Gaseous exchange through the lungs 3. Gaseous exchange through the skin a Gaseous exchange through the mouth buccal cavity br br Air is taken in or expelled from the mouth cavity by raising and br br lowering of the floor mouth. br br Lining of the mouth cavity is moist to dissolves oxygen. There is a rich supply of blood capillaries under the lining of the mouth cavity. Oxygen diffuses into the blood and is carried by haemoglobin to all parts of the body. br br Carbon IV oxide from the tissues is brought by the blood to the br br mouth cavity where diffuses out. br br Gaseous exchange through the lungs The frog has two lungs which are connected to the buccal cavity. T he inner lining of the lungs is moist, thin and is richly supplied br br with blood capillaries. br br During inspiration, the floor of the mouth cavity is lowered and nostrils are open. Air rushes through the open nostrils into the mouth cavity. br br Nostrils close and the floor of the mouth cavity is raised. This br br reduces the volume and increase the pressure in the mouth cavity forcing air into the lungs. br br Carbon IV oxide from the tissues diffuse into the lung while the br br oxygen from the lungs diffuses into the tissues. b Gaseous exchange through the skin Frogs have a thinner and moist skin than the toads. There is large network of blood capillaries below the skin to carry br br the respiratory gases. br br Oxygen from the air and water diffuse through the skin into the br br blood stream. br br Carbon IV oxide diffuses out of the blood capillaries through the br br moist skin into the surrounding water and air. Mechanism of Gaseous Exchange in Mammals br br The following structures are involved in gaseous exchange in br br mammals; br br - Nose Nostrils - Larynx br br 70 - Trachea - Chest cavity ribs and intercostals muscles - Diaphragm . br br a Nose It has two openings called nostrils which let in air into the air br br passages. br br As air moves in the passages, it is warmed and moistened The lining of the nasal cavity has also the sense organs for smell. b Larynx It is located on top of the trachea It is called the voice box. It controls the pitch of the voice. c Trachea It is a tube made of rings of cartilage which prevents it from br br collapsing during breathing. br br Inside it is lined with ciliated epithelium. Cilia beat in waves and move mucus and foreign particles away from the lungs towards the pharynx. br br As the trachea enters the lungs, it divides into two branches called br br Bronchi Bronchus . br br d Lungs They are found in the chest cavity and they are enclosed by a br br double membrane called the pleural membrane. br br The space between the membranes is called the pleural cavity. Pleural cavity is filled with pleural fluid which reduces friction making the lungs to move freely in the chest cavity during breathing. Diagrams In the lungs each bronchus divides into small tubes called The mechanism of breathing br br Breathing is achieved by changes in the volume and air pressure br br of the thoracic cavity. br br Thoracic cavity is enclosed by ribs. Ribs are covered by intercostals muscles. The diaphragm is a muscular sheet of tissue below the chest br br cavity. It curves upwards in the form of a dome shape. br br Breathing mechanism involves two processes. a Inspiration Inhalation i.e. breathing in. b Expiration Exhalation i.e. breathing out. br br Inspiration Inhalation i.e. breathing br br This occurs when the volume of thoracic cavity increases and the br br pressure decreases. br br External intercostals muscles contract while the internal br br intercostals muscles relax. br br Ribs are pulled upwards and outwards. Diaphragm flattens increasing the volume of the thoracic cavity br br while decreasing the pressure inside it. br br Air rushes into the lungs through the nose and trachea inflating br br the lungs. Diagrams page 62 Expiration Exhalation i.e. breathing out br br Volume of thoracic cavity decreases while pressure increases. br br This is brought about by the following; External intercostals muscles relax while internal ones contract. Ribs move downwards and inwards. Diaphragm relaxes and regains its original dome shape. Volume of the thoracic cavity decrease and pressure increases. Air is forced out of the lungs through the air passages to the br br atmosphere. The wall of the alveolus is covered b a film of moisture which br br dissolves oxygen in the inhaled air. br br Oxygen diffuses through the epithelium of the alveolus, the br br capillary wall and through the cell membrane of the red blood cells. br br In the red blood cells it combines with haemoglobin. Carbon iv oxide is more concentrated in the blood capillaries br br than in the alveoli. br br It therefore diffuses from the capillaries into the alveoli. Water vapour also passes out of the blood by the same process. br br Diagram page 64 KLB br br br br M br br N br br Z Percentage composition of gases in inhaled and exhaled air Gas in inhaled air. in exhaled air Oxygen 20 0.03 Carbon iv oxide Nitrogen and other gases 79.97 16.9 4.0 79.97 br br Regulation of Breathing This is controlled by a part of the brain called Medulla oblongata . br br 73 Factors affecting the rate of breathing in humans br br 1. Exercise br br Breathing rate increases during vigorous activity. br br 2. Age br br Younger people have a faster breathing because their bodies have more energy demand. 3. Emotions br br Things like anxiety, fear and fright increases the breathing rate. br br 4. Temperature br br Relatively high temperatures increase the rate of breathing. However, very high temperatures reduce the breathing rate. br br 5. Health br br If there is fever high body temperature , the breathing rate increases. Some respiratory diseases however, make breathing difficult. Lung Volumes br br i br br Lung capacity This is the total amount of air the lungs can hold when completely filled. The lungs of an adult have a capacity of about 5,500cm3 br br ii Tidal volume br br This is the amount of air taken in and out of the lungs during normal breathing. Tidal volume is about 500cm3 br br iii Inspiratory reserve volume br br This is an additional volume attained after having a forced inhalation in addition to the tidal volume. It is about 2000cm3 Inspiratory capacity This is the tidal volume Inspiratory reserve volume. br br iv br br v Expiratory reserve volume br br This is air removed after a forced exhalation. It can be up to 1,300cm3 vi Vital capacity br br This is the deepest possible exhalation. This air can only be forcibly pushed out of the lungs. br br vii Residual volume Diseases of the Respiratory System br br i Asthma br br It is caused by: br br Allergens such as pollen grains, certain foods and drugs Infections of the lungs by bacteria and viruses br br Symptoms br br Difficulty in breathing Wheezing sound when breathing Treatment and Control br br Avoiding the causative agents Injection of drugs and oral application of pills Spraying directly into the bronchial tubes with a muscle br br relaxant ii Bronchitis br br There are two types; Acute and Chronic br br Symptoms br br Production of thick greenish or yellowish sputum Difficulty in breathing Difficulty in walking and sleeping br br Treatment br br Seeking early medical assistance iii Whooping cough It is caused by a bacterium called Bordetella pertussis. Symptoms Prolonged coughing and vomiting Conjuctival haemorrhage bleeding Convulsions and coma Severe pneumonia in the bronchioles Ulcers and heart complications br br 75 Emaciation due to repeated vomiting Treatment br br Use of antibiotics Use of a balanced diet on patients br br Control br br Children immunization at early age br br iv Pneumonia It is caused by a bacterial called Streptococcus pneumoniae Symptoms br br Coughing Fever Chest pains Deposits of fluids in the lungs br br Treatment br br Use of antibiotics such as penicillin and sulphonamides br br Control br br Avoid overcrowding. Good ventilation in living houses br br v Pulmonary Tuberculosis It is caused by a bacterium called Mycobacterium tuberculosis . Symptoms br br Weight loss Coughing with blood stained sputum. Fever Treatment br br Use of antibiotics such as streptomycin br br Control br br Pasteurization of milk Immunization using BCG Bacille Calmette Guerin Use of radiography X-Ray br br vi Lung cancer Cancer is uncontrolled cell growth in the body causing tumours. Some general causes br br Smoking br br 76 Inhalation of cancer causing substances such as asbestos Exposure to radiations such as X-rays, radioactive substances br br such as uranium and substances that alter the genetic composition of the cell such as mustard gas br br Treatment and control Surgery to remove the tumour Radiotherapy Chemotherapy Use of some drugs Not smoking Revision Questions RESPIRATION br br Process by which food substances are chemically broken down in living cells to release energy, carbon iv oxide, water or alcohol. br br Respiration takes place mainly in the mitochondria. It has two br br membranes, inner and outer. br br Inner membrane is folded into projections called cristae. Cristae provide a large surface area for respiratory enzymes. Respiratory enzymes are bound to the cristae. br br Diagram Practical Activity 1 To investigate the gas given off when food is burnt . Types of Respiration br br Aerobic Respiration Anaerobic Respiration. br br Aerobic Respiration br br Process by which food substances such as glucose are broken down in the presence of oxygen to release energy, water and carbon IV oxide. br br The energy is stored in the form of a chemical substance called br br Adenosine Triphosphate ATP . br br This energy is released in small quantities since a lot of heat br br energy would burn the body cells. Respiratory br br Enzymes 77 C6H12O6 6O2 6CO2 Energy ATP Respiration takes place in two phases with each phase consisting br br 6H2O br br of series of reactions. First Phase Glycolysis This takes place in the cell cytoplasm . Oxygen is not required in br br this stage. br br Glucose is broken down into a 3 carbon compound called Pyruvic br br acid through a process called glycolysis. br br In glycolysis one molecule of glucose gives 2 molecules of ATP . In absence of oxygen Pyruvic acid is broken down into lactic acid br br in animals and into alcohol ethanol in plants. br br lactic acid br br pyruvic acid br br glycolysis enzyme controlled reactions in cytoplasm glucose enzyme controlledd in animals br br carbon iv oxide glycolysis br br pyruvic acid glucose ethanol enzymecontrolled in plants br br Second phase Krebs Cycle This takes place in the matrix of the mitochondria and involves a br br series of enzyme controlled reactions that require oxygen . br br Pyruvic acid formed in the first phase is oxidized by oxygen in a br br series of enzymatic reactions Krebs cycle into energy, water and carbon IV oxide. br br In this phase one molecule of glucose gives 38 molecules of ATP . br br 78 The following conditions are required in this phase; i. Cells must be provided with glucose/food. ii. Oxygen must be present. iii. Respiratory enzymes must be present to catalyse the reaction. iv. Temperature must be favourable for efficient functioning of br br enzymes. br br v. End products of the reaction energy, water and carbon iv oxide must be constantly removed from the mitochondrion. br br Practical Activity 2 To investigate heat production in germinating seeds . Anaerobic Respiration in Plants and Animals br br This is the process by which food substances are broken down in br br the absence of oxygen to release energy. br br The glucose is not completely broken down hence less energy is br br given out. br br In plants glucose is broken down into energy, carbon iv oxide br br and ethanol alcohol . br br Glucose oxide C6H12O6 CO2 Anaerobic respiration in plants is also referred to as fermentation . br br Ethanol Energy. Carbon iv br br 2C2H5OH ATP In animals glucose is broken down into energy and lactic acid Glucose C6H12O6 Oxygen Debt br br Lactic acid Energy. br br 2C3H6O3 ATP br br This is oxygen required to get rid of the lactic acid that br br accumulates in the body tissues when the oxygen supply is less than required. br br Accumulation of lactic acid causes fatigue and muscle crumps. Oxygen debt is paid back by breathing more quickly and more br br deeply in order to increase oxygen supply such as during recovery period after a race when a person pants. br br When paying back the oxygen debt, lactic acid is oxidized to br br energy, water and carbon iv oxide or it is taken to the liver and converted into glycogen. br br Application of Anaerobic Respiration i. Baking industry ii. Beer brewing and distillery industry. iii. Dairy industry in the production of yoghurt and cheese. iv. Production of vinegar citric acid, oxalic acid, butyric acid and br br some drugs. br br v. Production of power alcohol which is used as a substitute for br br petrol. vi. Silage making. vii. Biogas production. viii. Making compost manure br br Practical Activity 3 To investigate gas produced during fermentation. Comparison between Aerobic and Anaerobic Respiration Aerobic Respiration i. Oxygen is required ii. High amount of energy is released as one molecule of glucose yields 38 ATP molecules 2880 KJ br br Anaerobic Respiration. Oxygen not required Low amount of energy is released as one molecule of glucose yields 2 ATP molecules 210 KJ There is incomplete breakdown iii. There is complete br br 80 breakdown of the substrate into carbon iv oxide and water. br br of substrate hence lactic acid or alcohols are produced. br br iv. End products are energy, water and carbon iv oxide br br End products are energy, alcohol in plants and lactic acid in animals. Water molecules are not produced. Over short period of time, energy is released faster. br br v. Water molecules are br br produced. br br vi. Over a short period of time, energy is not released faster br br vii. Occurs in the cytoplasm br br Occurs only in the cell cytoplasm. and in the mitochondrion. Respiratory Substrates br br These are energy rich foods which when oxidized release energy. br br They include; i. Carbohydrates br br They are the main source of energy mainly in the form of simple br br sugars such as glucose, fructose and galactose. br br They produce about 17KJ 2898/mole per gram when completely br br oxidized. br br ii. Fats br br They produce more energy than carbohydrates or proteins. One gram of fats yields about 38 KJ of energy when completely oxidized. br br They are however not the main substrate because they are not br br very soluble in water hence not easily transported to the sites of respiration. It also requires more oxygen to oxidize one gram of fats than one gram of glucose. br br iii. Proteins br br They are not normally used in respiration unless in cases of br br extreme starvation. br br One gram of proteins yields 22KJ of energy when completely br br oxidized. br br 81 Assignment br br Where do plants and animals get the following from; br br - Carbohydrates. - Fats - Proteins br br Respiratory Quotient RQ and its Significance br br RQ is the ratio showing the relationship between the amounts of carbon iv oxide used against the amount of oxygen used in respiration. br br RQ varies with the type of substrate being oxidized. For example carbohydrates have a RQ of 1.0 when fully oxidized, fats have 0.7 and proteins have 0.9. br br RQ RQ can therefore be used to indicate the type of substrate being oxidized and also whether aerobic respiration or anaerobic respiration is taking place. br br RQ is also affected by factors such as age, health of the organism br br and the temperature. br br Factors Affecting the Rate of Respiration i. Oxygen concentration. When the amount of oxygen increases, the respiration rate also increases. Decrease in oxygen concentration will lead to decreased respiration rate. br br ii. Substrate concentration. Increase in sugar concentration increases br br respiration and vice versa. br br iii. Hormones. Presence of some hormones such as adrenaline and br br thyroxine in the body increases the rate of respiration. br br iv. Surface area to volume ratio Body size . If the SA/volume ratio is high, the organism would lose more heat energy. As more heat is lost to the surrounding more is required to replace the lost energy hence more respiration. br br v. Age. Young people require more energy because their cells are actively dividing hence respiration rate is higher in them than in older people. vi. Occupation. People engaged in heavier tasks have higher rate of br br respiration. br br vii. Sex. Generally males have faster respiration rate than females br br due to presence of more muscles in their bodies. br br viii. Basal metabolic rate. This is the energy required to maintain normal body functions such breathing, heartbeat, blood circulation etc while at rest. br br Revision Questions FORM THREE BIOLOGY NOTES br br ECOLOGY br br Introduction Ecology is the study of the interrelationships of organisms to each other and to their environment biotic and Abiotic factors . Autecology ; study of single species within a community and how it relates with both the biotic and Abiotic factors. Synecology. This is the study of many different species of organisms interacting among themselves within an ecosystem. Ecology helps to address the following issues. br br Sustainable food production Pollution control Natural resources conservation Pest and disease control Population control Eco-tourism Prediction of adverse weather conditions br br Concepts of ecology br br Biosphere/ecosphere. This is the part of the earth and br br atmosphere inhabited by living organisms. br br Habitat. This is a specific locality with a particular set of br br conditions where an organism lives. Habitats can be terrestrial or aquatic. br br 83 Ecological niche. This is the position occupied by an organism in a habitat. It includes the physical space where an organism is found and its role in the habitat. br br Population. This refers to all members of a given species in br br particular habitat. br br Community. This refers to all organisms belonging to different species interacting in the same habitat. Many populations make up a community. br br Ecosystem. This is a natural unit made of biotic and Abiotic br br factors whose interactions lead to a self sustaining system. E.g. a tropical rain forest, a small pond etc. br br Biomass. This is the total dry weight of living organisms at a br br particular Trophic feeding level or per unit area. br br Carrying capacity. This is the maximum number of organisms br br an area can comfortably support without depletion of the available resources. E.g. the maximum number of cows a pasture land can comfortably hold without overgrazing. br br Study Question 1 br br Factors in an Ecosystem br br They are divided into two: br br 1. Abiotic factors or the non living factors 2. Biotic or the living factors Abiotic Factors br br Light. This is required by plants and photosynthetic bacteria to manufacture food. The sun is the source of light energy. Light intensity and quality wavelength affects the rate of photosynthesis, flowering and germination in plants, while in animals it affects migration, hibernation and reproduction. Light intensity is measured using a Photographic Light meter while a Seechi disc measures light penetration in water. br br Atmospheric pressure. Variation in atmospheric pressure affects br br the availability of oxygen and carbon IV dioxide in the atmosphere. These two gases in turn affect the distribution of living organisms. Low atmospheric pressure increases the rate of transpiration. Barometer is used to measure it. br br Humidity. This is the amount of water vapour in the atmosphere. It affects the rate of water loss from plants and animals surfaces through transpiration and sweating respectively. The higher the humidity the lower the rate of loss and vice versa. It is measured using the hygrometer. br br Salinity. This refers to the salt concentration of the water. This br br divides the aquatic environment into marine, estuarine and fresh water . Only organisms with adaptable osmoregulatory features can comfortably occupy such habitats. In estuaries, there are fluctuations of salt concentrations at different times. When the sea tide is low, the salt concentrations are low due to the greater diluting effect of the fresh water being discharged. High tide raises the salt level. Estuarine organisms must therefore be adapted to cope with such wide salt variations. br br Wind. This is moving air. It increases the rate of water loss from organisms affecting their distribution. It also influences rain formation. It helps in formation of sand dunes in deserts which become habitats for the growth of deserts plants. Its an agent of seed and fruit dispersal Temperature. This affects the distribution of organisms in any br br habitat. Very low temperature may inactivate enzymes while very high temperatures denature them. Temperature varies due to seasons, altitude, and latitude and diurnally in hot deserts. br br pH hydrogen ion concentration. This is the measure of acidity or alkalinity of water in aquatic habitats or soil solution. This influences the distribution of plants and animals in soil and aquatic habitats. Different organisms have different pH requirements. pH is determined using the pH meter. br br Study Question 2 Practical Activity 1 Study Question 3 Biotic Inter-Relationships Competition br br 85 Living organisms compete for resources such as nutrients, space, light and mates. There are two types of competition. br br i. Inter-specific competition. This is the competition between individuals of different species for the same resources. For example. An experiment6 was carried out on two closely related species of paramecia- Paramecium caudatum and Paramecium aurelia. It was observed that when each species is grown separately in controlled cultures with constant food supply, they show normal population growth. When they are grown together in the same culture, thre is competition and Paramecium caudatum is eliminated. See graphs. However, closely related species can live together without competition. For example, when Paramecium caudatum and Paramecium bursoria are grown in the same culture, there is no competition because each species occupies a different part of the culture. Similarly, browsers and grazers can occupy same habitat without competition because they feed at different levels of the same plants. For example, the zebras eat the softer shoots, followed by the 86 wild beasts, and the gazelles which eat the fibrous left over of the same grass. Study Question 4 ii. Intra-specific competition. This is the competition between br br members of the same species for the same resources. br br When there is competition the best adapted organisms survive while the less adapted ones may die or be forced to migrate. br br Predation br br This is the relationship where one organism kills another for food and feed on it either as a whole or a part of it. The predator is the one which kills while the prey is the one being killed for food. Predators have various adaptations to enable them to be efficient in capturing the prey. These include; br br Sharp eyesight as in eagles, kites and hawk Fast flight, Modified beaks Strong jaws with carnassials teeth as in leopards and lions. Large claws on strong forelimbs. Colour camouflage such as the spotted pattern of the leopard br br blends well with the background colour of the bushes and trees. br br Moving against the wind while stalking the prey. Preys also have structural and behavioural adaptations. These include: Swift movement e.g. the antelope and gazelle Camouflage e.g. in gazelles and stripes of the zebra. Large eyes on the sides of the head to giving them a wide field of NB/. When the number of the prey increases that of the predators also increases. An increase in the number of predators leads to a decrease in the population of the prey. This decrease in prey population leads to a fall in predator population which in turn gives space for the increase in the population of the prey. This is the basis of biological control. See the graph below. . br br n o i t a u p o p r o t a d e r p d n a y e r P br br Prey l br br Predator Time br br Parasitism This is the relationship where an organism parasite obtains nutrients from another live organism host without killing it. The parasite obtains food and shelter from the host causing some harmful effects. Parasites may weaken the host and also transmit diseases which may kill their host thus reducing their number an d distribution. There are two types of parasites; br br Ecto-parasites Endo-parasites Study Question 5 Symbiosis br br This is an association between two of different species in which both benefit. For example the association of colon bacteria with humans and other animals, especially plant-eating animals, the ox-pecker bird and the ox etc. The Rhizobium bacteria help the leguminous plants to fix nitrogen while the bacteria obtain shelter and carbohydrates from the plants. Diagram br br Saprophytism br br This is where organisms obtain nutrients from dead organisms causing decomposition hence releasing nutrients into the ecosystem. Saprophytes include the bacteria and fungi. The Nitrogen Cycle This refers to the cycling of nitrogen and its compounds in the natural environment. Although nitrogen is abundant in the atmosphere as nitrogen gas, it cannot be utilised by plants. It has to be converted into a form that can be absorbed by plants through a process called nitrogen fixation. br br Nitrogen fixation is done in two ways; Biological fixation . This can occur in two forms br br 1. Nitrogen fixation by symbiotic bacteria such as br br Rhizobium spp . They are found in the root nodules of legumes. They convert nitrogen gas into ammonia which is then converted into nitrates for plant utilisation. br br 2. Nitrogen fixation by free living bacteria e.g. Clostridium, Azotobacter, and some algae such as Anabaena, chlorella and Nostoc. br br Non-Biological nitrogen fixation . This is done by lightning. br br During thunderstorms, lightning energy combines atmospheric nitrogen gas with oxygen to form nitrous and nitric acid. These are then converted into nitrates. br br Plants absorb nitrates and convert them into plant proteins. br br Animals feed on these plants and obtain the proteins. They are then digested into amino acids and become assimilated into animal proteins. When living organisms die, saprophytic bacteria and fungi break br br down the proteins in their bodies into ammonia. Nitrifying bacteria convert this ammonia into nitrates thorough a process called nitrification. Nitrosomonas and Nitrococcus convert ammonia into nitrites and Nitrobacter convert nitrites into Nitrates. br br Some soil micro organisms such as Pseudomonas denitrificans Thiobacillus denitrificans utilise the oxygen in the nitrates reducing it to nitrites, ammonia and eventually into nitrogen gas. This is called de-nitrification. br br This reduces the amount of nitrogen available to plants but it frees the nitrogen so that it becomes available for the cycle to continue. br br Diagram br br 89 Practical activity 2 Study question 6 br br Energy Flow in an Ecosystem br br The sun is the natural source of energy. This energy is transferred to the following feeding levels; Producers Primary consumers Secondary consumers Tertiary consumers Quaternary consumers These feeding levels are called Trophic levels Decomposers They break down organic materials into simple substances which are made available for re-use by other organisms. Decomposers are mainly fungi and bacteria. Food Chains This is the representation of energy flow from a producer to other organisms linearly. Green plants are eaten by herbivores which are eaten by carnivores. Producers Primary consumers Secondary consumers Tertiary consumers Quaternary consumers Some energy is lost as it is moved from one trophic level to the next. This is through respiration, defecation, excretion and in form of heat. Fig. 2.7 Examples When the decomposers are included in a food chain, they are placed at the end. Study Question 7 Food Webs These are several interconnected food chains. Simple food chains br br rarely exist since in any ecosystem, many populations interact. Ecological Pyramids These give a simplified representation of feeding relationships and br br energy flow in an ecosystem. They are of three types. br br Pyramid of numbers Pyramid of biomass Pyramid of energy br br Pyramid of Numbers br br There is a progress decrease in the number of organisms as one move from the producers all the way to the quaternary consumers. Producers have the greatest number followed in a decreasing order by primary, secondary, tertiary and quaternary consumers. Construction of Pyramid of Numbers br br i. Use data provided or collected. ii. From the data, identify and draw the most suitable food chain. iii. iv. Choose a suitable scale for the data. v. Using the chosen scale draw a horizontal rectangular bar to br br Indicate the numbers at each trophic level in the food chain. br br represent the number of the producers as the base of the pyramid. vi. Progressively draw horizontal bars of the other trophic levels in br br their ascending order. br br Ensure that the width of the bars is uniform. br br Study Question 9 Interpretation of Pyramid of Numbers Generally the body size of organisms increases at each trophic level from the base to the apex of the pyramid as their number decreases. br br At each trophic level much energy is lost through respiration, excretion, sweating, defecation etc. therefore less energy is transmitted to the succeeding trophic level. Fewer organisms can therefore be supported. br br Inverted pyramid of numbers also exist. For example where one mango tree supports several monkeys each being fed on by several fleas. Pyramid of Biomass Biomass of an organism is its constant dry weight. In an ecosystem, the producers have the highest biomass followed in decreasing order by primary, secondary, tertiary and quaternary consumers. br br Mango tree br br 20 Consumer br br Primary Consumer br br Producer Study Question 11 Population Populations change in size, structure and organisation. Characteristics of a population. br br Density. This is the number of individuals per unit area. E.g. 50 br br gazelles per Km2. br br Dispersion. This is the distribution or spread of organisms in a br br habitat. br br Population growth. This refers to the rate of increase in br br numbers. br br Population Estimation Methods Usually a representative sample is used to estimate the population of organism in a big habitat. A sample is a small number of individuals taken from the habitat that is a representative of the whole population. The following methods are used when sampling. br br Quadrat method. Line transect. Belt transect. Capture-recapture method. br br Adaptations of plants to various Habitats An adaptation is a change to suit environment: the development of physical, physiological or behavioural characteristics that allow organisms to survive and reproduce in their habitats. There are four main groups of plants namely; br br Xerophytes. Mesophytes. Hydrophytes. Halophytes. Xerophytes These are plants adapted to survive in the dry habitats. These habitats have the following characteristics. i. Unpredictable and poorly distributed rainfall between 250- br br 350mm per year. br br ii. Very high day temperatures and very low night temperatures br br hence high diurnal temperature range. br br 93 iii. They are very windy. iv. Low humidity. Adaptations of Xerophytes i. Shedding of leaves during the dry season to reduce the surface br br exposed to transpiration. br br ii. Reduced leaves in size such as in pine or modified into spines as in cactus. This reduces the surface area over which transpiration occurs. br br iii. Leaves have a thick waxy cuticle to reduce the rate of br br transpiration. br br iv. Some store water in large parenchyma cells contained in br br succulent stems and leaves. br br v. Some have reversed stomatal rhythm. vi. Sunken stomata vii. Folded leaves reduced the surface area. viii. Reduced number of stomata br br ix. Some have deep roots to absorb water from deep in the soil. br br Others have superficial roots growing horizontally close to the surface to absorb water after a light br br Mesophytes These are plants growing in well watered areas. Such habitats have the following general characteristics. br br Adequate rainfall; 950-1800mm that is well distributed br br throughout the year. Relatively high humidity Thick clouds Moderate to high temperatures Shallow water table Less windy Adaptations of Mesophytes They show various adaptations depending on where they grow. Some of these adaptations are for reduction of water loss, others for increased water, loss and some are also adapted to light conditions. Forest Ecosystem i. Vegetation grows fast to compete for light. br br 94 ii. Trees grow very tall to compete for light. iii. Some develop buttress roots or prop roots for extra support such br br as the Ficus natalensis. br br iv. Climbers such as lianas support themselves on stems of tall trees br br to reach light. br br v. Epiphytes support themselves on the branches of tall trees. vi. Others are adapted to carry out photosynthesis under low light intensity by having many chloroplasts that are sensitive to low light intensity. br br vii. They show leaf mosaic pattern to minimise overlapping enhancing trapping of light for photosynthesis. br br Those in areas with a lot of water have broad leaves, thin cuticle and many stomata on both surfaces to encourage high rate of transpiration. br br Those in dry areas have waxy and shiny cuticle to reflect light. Others are deep rooted to obtain water from deep in the soil. Hydrophytes These are plants growing in fresh water either partially or wholly. Such habitats have the following general characteristics. br br Low concentration of dissolved gases such as oxygen Presence of waves and currents Inadequate light in water Adaptations of hydrophytes i. Broad leaves with maximum number of stomata on upper leaf br br surface providing a large surface are for transpiration. br br ii. They have a large air filled tissue called aerenchyma tissue. The air reduces the density hence creating buoyancy to the plants and also aids in gaseous exchange. br br iii. Submerged ones have dissected leaves to offer large surface area br br for light absorption required during photosynthesis. br br iv. They have chloroplasts sensitive to low light intensity. v. They have poorly developed leaves and lack the root hairs to br br reduce water absorption br br vi. Flowers are raised above the water to allow for pollination. br br 95 Diagrams Halophytes These are plants which are able to tolerate very salty conditions in soil and marine water. Such habitats have the following general characteristics. br br High concentration of mineral salts Low concentration of dissolved gases Low light intensity in marine water Presence of waves and currents in marine water br br Adaptations of Halophytes i. They root cells which concentrate a lot of salts to enable them to br br absorb water by osmosis. br br ii. Some have salt glands that secrete excess salts. iii. Many have water storage tissues. iv. Some like the mangroves have breathing roots called br br pneumatophores. These rise above the water surface to obtain oxygen from the atmosphere. br br v. Mangroves growing on mud flats have buttress roots for support. vi. Submerged halophytes are adapted to photosynthesise under low br br light intensity. br br vii. Their fruits are adapted for dispersal by having aerenchymatous br br tissue for air storage to make them buoyant. CLASSIFICATION II Classification, in biology is the identification, naming, and grouping of organisms into a formal system based on similarities such as internal and external anatomy, physiological functions, genetic makeup, or evolutionary history. Study Question 1 General Principles of Classification Organisms that have similar and common features are grouped together while those that have different features are grouped separately. Taxonomy is the study of grouping of organisms according to their relationship. There are seven major taxonomic units taxa . br br 96 Kingdom Phylum phyla or Division in plants Class Order Family Genus Species br br As you move from the kingdom to the species the differences decrease as the similarities increases. Species is a group of organisms that can freely interbreed to give rise to viable/fertile offsprings. Sometime members of different species may interbreed to give an offspring which is sterile . E.g. a donkey and a horse can interbreed to give rise to a mule which is infertile. Binomial Nomenclature This is the double naming system of organisms where organisms are assigned two names i.e. the generic name and the specific name. Examples In binomial nomenclature the following rules are observed. v. Generic name is written first followed by the specific name. vi. First letter in the generic name is in capital and the rest are in br br small letters. br br vii. Specific name is written in small letters. viii. The two names are underlined separately when handwritten or br br italicised when printed. br br Study Question 2 The Five Kingdoms of Classification Carolus Linnaeus initially introduced the two kingdom system of classification. However many new life forms have been discovered which are neither animals nor plants. This has led to a more accepted classification system that adopts five kingdoms. These are; Animalia. br br Fig. 1.2 1. Kingdom Monera The kingdom is made up of mainly the bacteria e.g. nitrobacter, azotobacter. Vibrio cholerae etc. General characteristics i. They are unicellular and microscopic. Some are single cells while br br others are in colonies. They have different body shapes. br br Fig. 1.4 br br ii. Most are heterotrophic, feeding either saprophytically or br br parasitically. Some are autotrophic. br br iii. They are prokaryotic i.e. their nuclear material is not enclosed by br br a nuclear membrane. br br iv. They have few organelles which are not membrane bound. They br br dont have mitochondria. br br v. They have a cell wall though not made of cellulose. vi. They reproduce asexually mainly through binary fission. vii. Most of them respire an-aerobically but some respire aerobically. viii. Most of them move by use of flagella. br br Diagrams Study question 3 2. Kingdom Protoctista Examples include paramecium, amoeba, plasmodium, chlamydomonas, euglena, spirogyra, and trypanosome. General characteristics i. They are eukaryotic whereby their nuclei is bound by a nuclear membrane. br br ii. Some are heterotrophic while others are autotrophic. iii. They have may organelles including mitochondria all of which br br are membrane bound. They have different body forms; some are unicellular or colonial while others are multicellular. br br iv. br br v. Reproduction is mainly asexual by fission, fragmentation or sporulation. Some reproduce sexually by conjugation. vi. They are mobile and move by means of cilia, flagella or br br pseudopodia. br br vii. Some may have specialised structures that perform specific br br functions such as contractile vacuole for osmoregulation. br br Diagrams br br Practical Activities 1 and 2 br br 3. Kingdom Fungi Examples Saprophytic ones include mushrooms, toadstools, bread moulds, penicilia, yeast etc. Parasitic ones cause plant diseases such as wheat rust, potato and tomato blight and animal diseases such as athletes foot and ringworm. br br Practical Activities 3 General characteristics i. They are eukaryotic. ii. Most have cell walls made of chitin but a few have cellulose cell br br walls. br br iii. They store food particles in their cytoplasm in the form of br br glycogen or oil droplets but not starch. br br iv. The basic unit is the hyphae . Hyphae are thin filaments and many br br of them make up structures called mycelium . br br v. Fungi have neither the chloroplasts nor the chlorophyll. They feed on already manufactured food. Hyphae act as the roots and are sent into the food material to obtain nutrients. In saprophytic fungi the hyphae are referred to as rhizoids and in parasitic ones as haustoria . br br vi. They reproduce sexually fusion of nuclei in hyphal branches br br and asexually spores and budding . 4. Kingdom Plantae Study question 5 General Characteristics i. They are eukaryotic and multicellular. ii. iii. They reproduce both sexually and asexually. iv. Their cells have cellulose cell walls v. They have photosynthetic pigment hence are autotrophic. vi. Majority have a transport system vii. They show alternation of generation. br br In most their body is differentiated into leaves, stem and roots. A. Division Bryophyta These are the mosses and the liverworts. General Characteristics i. The lack the vascular system ii. Contain chlorophyll and are therefore photosynthetic. iii. They have rhizoids for anchorage and water and mineral salts br br absorption. br br iv. They show alternation of generations. v. Fertilisation depends of availability of water. Male gametes are br br produced by the antheridia and female gametes by the archegonia. br br vi. They grow on damp substratum such as walls, rocks and marshes. vii. They are thalloid as in liverworts or differentiated into simple br br leaf like and stem like structures as in mosses. br br Diagrams . General Characteristics i. They have leaves, stems and roots but no flowers. ii. They are photosynthetic. iii. They have a clearly defined vascular system made of xylem and br br phloem. br br iv. They have compound leaves with leaflets called pinna. v. On the lower side of mature leaves are the spores bearing br br structures sporangia which occur in groups called sori sorus- singular . see diagram. br br vi. They show alternation of generations where the sporophyte fern plant is the dominant one while the gametophyte is a heart shaped structure called Prothallus . See diagram. br br vii. They have sexual reproduction which is dependent of water. br br Study Question 6 br br Practical Activity 4 br br Study Question 7 br br Practical Activity 5 C. Division Spermatophyta This comprises of all the seed bearing plants. General Characteristics i. They contain chloroplasts hence are photosynthetic. ii. The plant body is differentiated into roots, stems, leaves and seed br br bearing structures. br br iii. Vascular system is highly developed with xylem tissue consisting br br of both xylem vessels and tracheids. iv. Sexual reproduction is well defined. v. Seeds are produced after fertilisation. vi. They show alternation of generation. The division Spermatophyta is made up of two main subdivisions i.e. br br Gymnospermaphyta Angiospermaphyta br br Gymnospermaphyta General Characteristics br br 101 They bear male and female cones. After fertilisation seeds are borne on the female cones and they br br are naked i.e. they are not enclosed in a fruit wall. br br They show xerophytic characteristics such as needle like leaves, br br rolled leaves, thick waxy cuticle and sunken stomata. br br Phloem doesnt contain companion cells and xylem mainly br br consists of tracheids. This subdivision has three main classes. br br Coniferales Cycadales Ginkgoales i Class Coniferales br br These include all the common gymnosperms. They are found in areas of little water. They have small needle-shaped leaves with waxy cuticle. They have cones and most of them are ever green. Male cones are in form of clusters at the base of the terminal br br bud . br br Female cones are on lateral buds of young shoots and they br br contain naked seeds. br br Diagrams. ii Class Cycadales br br They resemble the palm trees by appearance. They have long compound leaves which are clustered at the apex br br of a thick short un-branched stem. br br They bear cones at the apex of the trunk. br br iii Class Ginkgoales br br Members here are very rare. They include the Ginkgo biloba of China. They are deciduous with fan like leaves. br br Angiospermaphyta General characteristics br br Are usually bisexual and flower bearing. br br 102 Seeds are enclosed in an ovary which develops into a fruit. Xylem has tracheids and vessels while the phloem has companion br br cells. br br They have double fertilisation. br br This subdivision is divided into two classes. br br Monocotyledonae. examples Dicotyledonae . examples Class Monocotyledonae Class Dicotyledonae. br br They have seeds with one Have two cotyledons. br br cotyledon. br br They have narrow-long leaves Broad leaves with reticulate br br with parallel venation. Most of their leaves have a modified petiole to form a leaf sheath. br br venation. br br Leaves have distinct petioles. br br Their stems have scattered br br Vascular bundles are arranged to form a concentric ring. vascular bundle. br br Pith is usually absent. Vascular cambium is usually absent hence no secondary growth. Pith is present. Vascular cambium is present hence there is secondary growth. br br They have a fibrous root They have a tap root system br br system br br Floral parts are in threes or in Floral parts are in fours, fives br br multiples of three. br br or their multiples. In roots, the xylem is br br In the root vascular bundles are arranged in a ring with phloem and xylem alternating. br br centrally placed and star shaped with the phloem alternating with the arms of the xylem. Practical activity 6 ix. Kingdom Animalia Study Question 9 General characteristics i. Most show locomotion but a few are sessile ii. Most reproduce sexually and a few asexually iii. They are eukaryotic and multicellular iv. All are heterotrophic v. Their cells have no cell walls Kingdom Animalia has nine phyla but only two will be discussed i.e. Arthropoda and chordata. Phylum Arthropoda Practical Activity 7 General Characteristics i. They are segmented. ii. They are bilaterally symmetrical. iii. They have open circulatory system where blood flows in open br br cavities called haemocoel. br br iv. Head is well developed with eyes, sensory structures and a fairly br br developed brain. br br v. Gaseous exchange is through the tracheal system which opens br br through the spiracles to the outside. Some aquatic ones use gills. br br vi. Reproduction is mostly sexual with internal fertilization. They br br have different sexes. br br vii. They have jointed appendages hence the name arthropoda. viii. They have a body covered with exoskeleton made of chitin. This provides a surface for muscle attachment. It is shed periodically to allow growth through a process called moulting . ix. Most have their body divided into head, thorax and abdomen. In some, the head and the thorax are fused to form Cephalothorax . The thorax and the abdomen are all segmented. The phylum arthropoda is divided into five classes. br br Crustacea Chilopoda Diplopoda br br 104 Arachnida. Insecta. br br Different members of the phylum are placed to their respective classes based on; br br Number of limbs Presence and number of antennae Number of body parts. br br 1. Class Crustacea Examples. Daphnia, crayfish. Crab and prawn. General Characteristics i. Head and thorax are fused to form cephalothorax. ii. They have two pairs of antennae. iii. They have between five and twenty pairs of limbs modified for different functions e.g. locomotion defence and feeding. br br iv. They have a pair of compound eyes. v. Gaseous exchange is through the gills. vi. They have three pairs of mouth parts made of one pair of mandibles lower and two pairs of maxillae upper . 2. Class Chilopoda These are the centipedes. Diagram General Characteristics i. Body is divided into two parts, the head and the trunk. ii. The body is dorsa-ventrally flattened. iii. Body is made up of 15 or more segments. iv. Head has a pair of simple eyes. v. Each segment has a pair of walking legs. vi. Head has a pair of antennae. vii. Have poison claws n the head and are therefore carnivorous. viii. Have a tracheal system for gaseous exchange. br br ix. Have separate sexes. br br 105 General Characteristics i. They have cylindrical body. ii. Have three body parts, head, and thorax and body trunk. iii. They have two clumps of many simple eyes. iv. They have no poison claws and are therefore herbivorous. v. Heads has a pair of short antennae and mandibles. vi. Each body segment has a pair of spiracles for breathing. vii. Body has between 9-100 segments. viii. Each segment has two pairs of walking legs except the first br br thoracic segment. br br 4. Class Arachnida These include the scorpions, spiders, ticks and mites. Diagrams General Characteristics i. Body has two parts, cephalothorax and abdomen. ii. Cephalothorax has two chelicerae which produce poison to br br paralyse the prey. br br iii. Cephalothorax has four pairs of walking legs each having seven br br joints. br br iv. At the end of each leg are two toothed claws. v. Cephalothorax has eight simple eyes. vi. Most have lung books for gaseous exchange, some use gill books br br or tracheal system. br br vii. They have no antennae but have a pair of pedipalps which are br br sensitive to touch. br br 5. Class Insecta They include grasshoppers, bees, houseflies, butterflies, termites, beetles etc. Insects form half the population of animals on earth. They occupy all habitats i.e. air, water, and land. Their food is varied such as plant tissues, animal fluids, dead animals and excretions of animals making them to be found almost everywhere on earth. General Characteristics i. Body is divided into three parts, head, thorax and abdomen. ii. Thorax is made up of three segments with three pairs of legs. br br Some have one or two pairs of wings on the thorax. br br iii. Head has one pair of antennae. iv. They undergo complete or incomplete metamorphosis. v. Excretion is through the malpighian tubules which remove uric br br acid. br br vi. Gaseous exchange is through the tracheal system but they breathe br br through the spiracles. br br vii. The head a pair of compound eyes and several simple eyes. viii. Abdomen is made up of 11 or fewer segments. The terminal br br segments are modified for reproduction. br br ix. Mouth parts consist of the mandibles, maxillae and labium. The Phylum Chordata Chordate, common name for animals of the phylum Chordata, which includes vertebrates as well as some invertebrates that possess, at least for some time in their lives, a stiff rod called a notochord lying above the gut. About 43,700 living species are known, making the chordates the third largest animal phylum. In animals such as the Amphioxus the notochord persists but in others it is replaced at later stages of development by the vertebral column. br br 107 Members in this phylum inhabit both aquatic marine and fresh water and terrestrial burrowers and arboreal environments. General Characteristics i. Members have a notochord at some stage of their development. ii. They are bilaterally symmetrical. iii. Heart is ventrally placed. Blood flows from the heart through the br br arteries and gets back to the heart through the veins. br br iv. They have a post anal tail although it is greatly reduced in some. v. They have an endoskeleton. vi. They have a closed circulatory system. vii. They have visceral clefts where in fish they become the gills in br br higher chordates they are only present in the embryo. br br viii. They have a tubular dorsal nerve cord. It develops anteriorly into br br brain and posteriorly as the spinal cord. Spinal cord is enclosed by the vertebral column. br br ix. They have segmented muscle blocks called myotomes on either br br side of the body. br br The main classes of the phylum chordata are; br br Pisces Amphibia Reptilia. Aves. Mammalia Pisces Diagram These are the fishes. They include those with a skeleton made of cartilage e.g. shark and those with a bony skeleton such as the tilapia, Nile perch, lung fish, dog fish, and cat fish etc. General Characteristics i. The move by fins ii. Bodies are covered with scales iii. Have gills for gaseous exchange in water. iv. They dont have a middle or inner ear. v. They have streamlined bodies. br br 108 vi. They have a lateral line for sensitivity. vii. Their heart has two main chambers i.e. the auricle and the br br ventricle. br br viii. They are poikilothermic/ectothermic. br br ix. Eyes are covered by a nictating membrane. br br Amphibia br br They include the toads, newts, salamanders and frogs. The toad is the most advanced amphibian. Its skin is less moist and therefore uses the lungs more for gaseous exchange. They therefore stay mostly on land and only return to the ponds during reproduction. Diagrams General Characteristics i. They have a double circulatory system. ii. They have a three chambered heart with two atria and one br br ventricle. br br iii. Fertilisation is external and they breed in water. iv. Gaseous exchange is through the skin, lungs and gills. v. They have two eyes and an eardrum behind the eyes. vi. They are ectothermic. vii. They have 4 well developed limbs. The hind limbs are more br br muscular than the forelimbs. br br Reptilia Examples include tortoise, turtles, snakes, crocodiles, lizards and chameleons. General Characteristics i. They are ectothermic. ii. They have a well developed lung for gaseous exchange. iii. They have double circulatory system with the heart having three br br chambers i.e. two atria and a partially divided ventricle. Crocodiles however have a four chambered heart. br br iv. The body is covered with a dry scaly skin reducing desiccation. v. Some have four limbs while others dont have any limbs such as br br the snakes. vi. Fertilisation is internal. They lay eggs with a leathery shell to avoid desiccation. Some species of chameleons give birth to young ones. br br Aves br br Examples include doves, chicken, hawks, eagles and turkeys. They are terrestrial and arboreal while some have been adapted for aquatic life. General Characteristics i. Bodies are covered with feathers for in insulation. ii. They have beaks. iii. They internal auditory canal/ meatus iv. Fertilisation is internal and they lay hard calcareous eggs. v. They have lungs for gaseous exchange. vi. They have air sacs which store air in them reducing their body br br density for flight. vii. They are endothermic. viii. They have hollow bones. br br ix. They have scales on their hind limbs. x. They have double circulatory system with a four chambered br br heart. br br xi. The sternum is enlarged to form keel for attachment of flight br br muscles. Mammalia Study Question 11 br br Some are arboreal such as the tree squirrels, and some monkeys. Some are terrestrial either on the surface of the earth or in tunnels. br br Some are aquatic such as the dolphins and whales. br br General Characteristics i. They have double circulatory system ii. They have mammary glands hence the name Mammalia. iii. Their body is usually covered with fur or hair. iv. They have two eternal ears pinna v. They have sweat glands. vi. They have lungs for gaseous exchange. br br 110 vii. They have four limbs. viii. They have a diaphragm which separates the body cavity into br br thoracic and abdominal cavities.. br br ix. The brain is highly developed. x. They have seven cervical vertebrae at their neck. xi. They are endothermic. xii. They have heterodont type of dentition where the teeth are br br differentiated into four types, incisors, canines, pre-molars and molars. The number varies in relation to feeding habits. br br Although most mammals give birth to live young ones, some br br are egg laying such as the duck billed platypus. After hatching, the young ones are fed on milk. br br Practical Activity 9 Practical Activity 10. The Dichotomous Key The word dichotomous means separating into two. I.e. Separation of different or contradictory things: a separation into two divisions that differ widely from or contradict each other. As you move down the key you progress from general characteristics to more specific characteristics. The last single choice reveals the identity of the unknown organism. Rules Used in Constructing a Dichotomous Key i. Use morphological features as far as possible. ii. Start with the major characteristics and proceed to lesser br br variations that separate the organisms into smaller groups. E.g. in leaves start with type of leaf i.e. simple or compound. br br iii. Select a single characteristic at a time and identify it by a number br br such as. br br Type of leaf Type of venation br br iv. Use identical forms of words for the two contrasting statements br br e.g. br br 1. br br a leaf simple. b Leaf compound br br 111 2. br br a Leaf net veined. b Leaf parallel veined. br br v. The statements should always be written in positive form. Where br br a negative statement cannot be avoided, the first statement must be in the positive form e.g. br br a Animal with wings b Animal without wings vi. Avoid overlapping statements or generalisations such as br br Short plants Tall plants br br Be very specific in your description such as br br Plant I metre tall and above. Plant 15cm to 60cm tall. br br Some common Features Used For Identification. br br In animals br br i. Locomotory structures legs, wings and fins ii. Antennae, presence and number iii. Presence and type of eyes iv. Number of body parts v. Body segmentation vi. Type of skeleton present vii. Feeding structures viii. Presence of hair, fur, scales or feathers on the body In plants br br Part of plant Leaf br br Some characteristics. br br Phylotaxy Leaf type Leaf venation Margin Lamina Colour Inflorescence Flower shape br br Flower Number of floral Type of stem woody, herbaceous or fleshy Shape rectangular or cylindrical Texture of the stem smooth or spiny/thorny Root system taproot or fibrous Storage roots. Summary of the Five Kingdoms. Practical Activities. Revision Questions. br br REPRODUCTION IN PLANTS AND ANIMALS br br This is the process by which mature individuals produce br br offsprings. br br There are two types of reproduction. br br 1 Sexual reproduction which involves male and female br br gametes br br Diagram 2 Asexual reproduction where no gametes are involved. Diagram br br Importance of Reproduction br br 1 Procreation br br This ensures that a species does not become extinct. br br 2 Quality improvement br br Reproduction allows for mixing of genetic materials bringing about variations. These variations are important tools in the refinement of quality of offsprings. br br 113 Cell Division br br Life in all living things start as a single cell as a spore or as a br br zygote. br br The cells have to divide further to give rise to make cells. Cell division starts with division of the nucleus chromosome br br and then the cytoplasm. br br Chromosomes br br These are microscopic thread like structure within cells that carries the molecule deoxyribonucleic acid DNA the hereditary material that influences the development and characteristics of each organism. br br Each chromosome is made up of two parallel strands called br br chromatids. br br Chromatids are joined together at one point by the centromere . br br Diagram br br Each cell has a fixed number of chromosomes e.g. each human br br body cell has 46 chromosomes. br br Chromosomes occur in pairs in the nucleus. A member of each br br pair is called homologous chromosomes. br br Homologous chromosomes are similar in appearance, size, and br br shape but their genetic constitution may be different. Genes are found along the length of the chromosomes. Genes are very tiny and made up of a chemical substance called br br DNA De oxy Ribonucleic Acid DNA determines the characteristics of the offspring. There are two types of cell division i Mitosis ii Meiosis br br Mitosis br br In this type of cell division, each cell divides into two daughter br br cells each having the same number of chromosomes as the parent cell. br br Mitosis occurs in series of stages i.e. br br i Interphase br br 114 ii Prophase iii Metaphase. iv Anaphase v Telophase . 1 Interphase During this stage the following activities take place within the cell in preparation of the division. br br Synthesis of new cell organelles such as ribosomes, centrioles, br br mitochondria and Golgi apparatus. br br Multiplication of genetic material so that each daughter cell will br br have same number of chromosomes as the parent cell. br br Build up of enough energy stores in form of ATP Adenosine br br Triphosphate during respiration. This energy is important to see the cell through the process of division. br br At this stage the chromosomes are not clearly visible. br br Diagrams br br 2 Prophase The following events take place in this stage. br br Centrioles separate and move to opposite poles of the cells. Spindle fibres begin to form Nuclear membrane begins to break down and nucleolus br br disappears. br br Chromosomes thicken and shorten and they can be stained easily br br hence become visible. Diagram br br 3 Metaphase br br Nuclear membrane disappears and chromosomes are free in the cytoplasm. br br Spindle fibres lengthen and attach to the centrioles at both poles. Chromosomes align themselves at the equator and are attached to br br the spindle fibres by their centromere. br br Diagram br br 3 Anaphase Chromatids separate at the centromere and migrate to opposite poles. This is brought about by the shortening of the spindle fibres. br br Spindle fibres begin to disappear. In animal cells, cell membrane begins to constrict towards the end br br of anaphase. br br Diagram br br 4 Telophase br br Chromatids collect together at the two opposite poles of the br br spindle. br br Nuclear membrane forms around each set of chromatids and are br br now referred to as chromosomes. br br Cytoplasm divides into two hence the formation of two daughter br br cells. br br Chromosomes become less distinct. br br In animal cells, division of cytoplasm is by constriction of cell membrane. In plant cells, a cell plate forms within the cytoplasm and grows to separate the cell into two. Diagrams Significance of Mitosis br br i br br Forms basis for asexual reproduction e.g. budding and spore formation. br br ii Causes cell growth when the cells formed increase in br br number and size. br br iii Ensures genetic constitution of the offspring is the same br br as the parents. br br iv Replaces damaged and dead cells in the body. Meiosis br br This involves two divisions of the parental cell resulting into four br br daughter cells. br br First meiotic cell division involves the separation of the br br homologous chromosomes. It is referred to as Reduction division because the numbers of chromosomes are reduced by half. In the second stage, the sister chromatids are separated and it is br br referred to as Equatorial division br br Each daughter cell has half the number of chromosomes haploid br br n as the parent cell. br br This takes place in the reproductive organs of animals testis and br br ovary and plants anthers and ovary . br br Meiosis is divided into same series of stages as in mitosis. The phases are given names as in mitosis but each is followed by br br I or II. br br First Meiotic Division Interphase I The cell prepares for division by the following. br br Replication of chromosomes. Synthesis of new cell organelles. Build up of energy. br br Prophase I br br Nucleolus disappears. Centrioles move to opposite poles. Chromosomes shorten and thicken becoming more visible. Homologous chromosomes lie side by side in the process of br br synapsis forming pairs called bivalents. br br Homologous chromosomes may become coiled around each other br br with their chromatids remaining in contact at points called chiasmata. br br NB/. During chiasma formation homologous chromosomes may exchange genetic material during crossing over. These genetic exchanges are important because they bring about variations in offsprings. Metaphase.I Nuclear membrane disappears. Homologous chromosomes as a bivalent move to the equator of br br the cell. br br Spindle fibres are fully formed and get attached to the br br chromosomes at the centromere. br br 117 Homologous chromosomes orientate towards different poles. Diagram Anaphase I Homologous chromosomes separate and migrate to the opposite br br poles with their centromeres leading. This is brought about by the shortening of the spindle fibres. br br Diagram Telophase I br br Cell divides across the middle when the chromosomes reach the br br poles. br br At the end of meiosis I homologous chromosomes are separated. br br Diagram Second Meiotic Division . In this stage the sister chromatids are separated from each other. Interphase II br br Cells go into a short interphase. br br Prophase II br br Chromosomes become shorter and thicker. New spindle fibres are formed. br br Metaphase.II br br Chromosomes align at the equator of the cell. Spindle fibres attach to their centromeres. Chromosomes orientate themselves towards the opposite poles. br br Anaphase II br br Sister chromatids separate from each other. Spindle fibres shorten pulling them to the opposite poles. br br Telophase II br br Spindle fibres disappears Nucleolus reappears and nuclear membrane forms around each set of chromatids. br br Chromatids uncoil and become threadlike. Cytoplasm divides. Four cells are formed tetrad . Each cell has haploid n number of chromosomes. br br 118 Significance of Meiosis br br 1. Gamete formation sperms and ova forming basis for sexual br br reproduction br br 2. Provides opportunities for genetic variations during crossing over br br Similarities between mitosis and meiosis 1. Both take place in plants and animals. 2. Both involve division multiplication of cells. br br Differences between meiosis and mitosis Mitosis. Meiosis No association of homologous chromosomes br br 1. Homologous br br chromosomes associate with each other. br br 2. Takes place in 2 nuclear br br Takes place in one nuclear division. 2 daughter cells are produced each diploid 2n Occurs in somatic body cells leading to growth. br br divisions. br br 3. 4 daughter cells are br br produced each haploid n br br 4. Occurs in reproductive br br organs leading to gamete formation. br br 5. Chiasma formation takes place leading to crossing over hence variation No chiasma formation therefore no crossing over hence no variation. Asexual Reproduction br br This is the production of offsprings from a single organism br br without fusion of gametes. br br This type of reproduction involves mitosis. br br Types of Asexual Reproduction br br 1. Binary fission in amoeba, plasmodium and bacteria 2. Sporulation in rhizopus 3. Budding in yeasts 1. Binary fission in amoeba When there is enough food and favourable temperature and pH, a br br mature amoeba divides into two. During binary division, in amoeba, internal reorganization of molecules necessary for structural construction takes place. br br Nucleus first divides mitotically Karyogamy into two followed br br by the division of the cytoplasm Cytogamy br br Diagrams br br 2. Sporulation in Rhizopus This is the formation of spores in substrates like the bread to form br br bread moulds br br A spore is a microscopic reproductive unit which contains a br br nucleus and a small amount of cytoplasm. br br Spores are produced by bacteria, most fungi, mosses and ferns. Rhizopus has a vegetative body called the mycelium. Mycelium is made up of many branched threads called hyphae . Horizontal hyphae are called stolons . Vertically growing ones are called sporangiophore . Tips of sporangiophore swell up to form the sporangia br br sporangium . br br Sporangia are the spore bearing structures. When fully mature, sporangium wall burst releasing the spores. If spores land on a suitable medium, they germinate and develop into other rhizopus. br br Rhizopus uses structures called rhizoids for anchorage and to br br obtain nutrients from the substrate. br br Diagrams Budding in Yeast Under favourable conditions such as plenty of sugar, moisture, oxygen and optimum temperature, the yeast cell reproduces asexually by budding. br br A projection of bud forms on the parent cell. Nucleus divides into two. One nuclei moves into the new bud. Bud grows in size and forms new cell organelles. Later the bud br br separates off. br br Diagrams Sexual Reproduction in Plants br br In flowering plants the flower is the reproductive organ. br br Structure and Function of a Flower br br A flower is made up of a flower stalk pedicel and a receptacle. Attached to the receptacle are four groups of floral structures i.e. i Calyx sepals ii Corolla/petals iii iv Androecium male parts Gynoecium female parts i Calyx sepals Made up of the sepals which are usually green. If sepals are fused they form gamosepalous calyx. If they are free, they form polysepalous calyx. Calyx protects the inner parts of the flower especially during bud br br development. br br Some flowers have sepal like structures below the calyx called br br the epicalyx . ii Corolla/petals Its made up of the petals which are brightly coloured, large and br br conspicuous especially in insect pollinated flowers. br br If fused gamopetalous. If free polypetalous iii Androecium male parts Made up of one or more stamens Satmen is made up of the filament and anthers. Another has four pollen sacs containing pollen grains. Pollen grains contain the male gametes. br br Diagrams br br iv It may contain one or more carpels A carpel consists of the ovary, the style and the stigma. Ovary contains the ovules. br br Gynoecium female parts br br 121 Ovaries are described as epigynous, hypogynous or perigynous br br depending on the place they occur in the flower. br br i Epigynous inferior ovary Ovary is located within the receptacle. All other floral parts occur above it such as in the apple flowers. Diagram ii Hypogynous superior ovary Ovary is above the receptacle and other floral parts such as in br br hibiscus. Diagram iii The receptacle surrounds the carpel. All other floral parts arise around the ovary such as in roses. Diagram The gynoecia can also be grouped into different types dependi.ng on the number of carpels present i.e. monocarpous or syncarpous. Monocarpous Gynoecium It has only one carpel e.g. in beans. Diagram Polycarpous Gynoecium It has two or more carpels. It is divided into two. br br Perigynous ovary br br a Apocarpous gynoecium br br The carpels are free e.g in roses and bryophyllum. Diagrams br br b Syncarpous gynoecium br br The carpels are fused together such as in hibiscus. br br Diagrams Terms Used in Describing a Flower br br i Complete flower has all the four floral parts; calyx, corolla, br br androecium and gynoecium. br br ii Incomplete flower has one or two floral parts missing. iii Unisexual flower a flower with only one of the reproductive parts either male or female flower. br br iv Staminate flower male flower. v Pistillate flower female flower. br br 122 vi Monoecious plant bears both male and female parts of the br br flower. br br vii Dioecious plants - the plant is either male or female e.g. in br br paw paw. br br viii Hermaphrodite or bisexual flower has both the male and br br female parts. br br ix Regular or actinomorphic flower a flower that can be br br divided into tow similar halves by any vertical section passing through the center i.e. radial symmetry such as in morning glory. br br x Irregular or zygomorphic flower can be divided into two similar halves on one particular plane only i.e. bilateral symmetry e.g. in clotalaria. br br xi Pedicillate flower- flower with a stalk. xii Solitary flower are flowers occurring singly. xiii Inflorescence flowers that grow in clusters. xiv Essential parts of the flower are the androecium and br br gynoecium. br br xv Non essential floral parts are the calyx and corolla. br br Pollination This is the transfer of pollen grains from the anther to the stigma. Types of Pollination i br br Self pollination . Transfer of pollen grains from the anther to the stigma of the same flower. br br ii Cross Pollination transfer of pollen grains from the anther of one flower to the stigma of another flower but of the same species. Agents of Pollination br br Insect Wind br br Adaptations of Insect Pollinated Flowers Entomophilous br br i br br Flowers are large, conspicuous with brightly coloured petals and inflorescence to attract insects. br br ii Flowers are scented and produce nectar to attract insects. iii Pollen grains are relatively large, heavy, rough or sticky so as br br to stick on to the body of the sticks. br br iv They have small and firmly attached anthers to a firm filament. v Stigmas are small, sticky and contained within the flower. This ensures that pollen grains from the body of an insect stick onto it. br br vi Flowers have a tubular or funnel shaped corolla, landing br br platforms and honey guides. br br Adaptations of Wind Pollinated Flowers Anemophilous e.g. maize and other grasses br br i br br Small flowers with inconspicuous petals, bracts or inflorescence. br br ii Flower structure is simple and flowers have no particular br br shape. br br iii Stigmas are long, feathery and hang outside the flower to trap br br pollen grains. br br iv Pollen grains are small, smooth and light to be easily carried by br br the wind. br br v Flowers are not scented and lack nectar. vi Anthers are large and loosely attached to a flexible filament to br br be easily released when the wind blows. br br Diagram of a grass flower br br Stigma br br br br Anther Filament br br Features and Mechanisms Hindering Self Pollination and Self Fertilization br br i Heterostyly condition whre the stigma na d style have different arrangements e.g. coconut flowers have shorter br br 124 stamens than pistils hence pollen grains from the anthers cannot reach the stigma. br br Diagram ii Self sterility or incompatibility condition where pollen grains br br of a flower fail to germinate if they land on the stigma of the same flower. br br iii Protogyny and Protandry condition where either male parts br br of a flower mature before the female ones. Protandry stamen mature before the stigma e.g.in sunflower. Protogyny stigma matures before the anthers mature e.g. in maize. br br iv Dioecious plants and presence of features that promote cross pollination such as brightly coloured petals which attract insects hence cross pollination. br br Fertilization in Flowering Plants Fertilization in plants is the fusion of the male and female nuclei in the embryo sac. br br Male gamete is contained in the pollen grain produced in the br br anther. Diagram br br Female gamete egg cell is found in ovules contained in the embryo sac. br br br br 125 Process of Fertilization br br br br Style br br Integuments Ovary wall br br Antipodal cells br br Embryo sac Polar nuclei br br Egg cell br br Synegids br br funicle Micropyle br br Pedicel br br - Pollen grains land stick to the stigma and germinates to form br br pollen tube, which grows through the tissue of the style towards the ovary br br - The generative nucleus undergoes mitosis, forming 2 male br br nuclei br br - The pollen tube gets into the embryo sac through the micropyle; pollen tube nucleus disintegrates, creating a passage for the male nuclei. br br - The egg cell fuses with one of the two male nuclei to form a br br diploid zygote. The zygote undergoes mitosis to form an embryo - The two polar nuclei fuse with the second male nucleus to form br br a triploid nucleus. br br - The triploid nucleus forms the endosperm. The two con current fertilization incidents are collectively referred to as double fertilization br br Seed and Fruit Development br br - Some changes occur to the ovary, ovule and the entire flower br br after fertilization. br br - Calyx dries and falls off or may persist. - Petals and stamens wither and fall off. br br 126 Development of the Seed br br - Zygote undergoes mitotic division to become the embryo br br plumule and radicle and one or two cotyledons. br br - Primary endosperm nucleus develops into the endosperm. - Ovule forms the seeds. - Ovary develops into a fruit. - Integuments become the seed coat testa . - Testa has got a scar hilum which is the attachment point to the br br placenta. br br - A seed a tiny opening called the micropyle which allows water br br into the seed during germination. br br - Water is withdrawn from the seed from about 80 to 15 by br br mass making the seed dry and hard. br br Development of Fruits br br - A fruit is a fully grown fertilized ovary containing fully br br developed seeds. br br - This is brought about by the hormones gibberellins and occurs br br after fertilization. br br - As the ovules develop into seeds, the rest of the ovary develops br br into the fruit wall or the pericarp. br br - Pericarp has two scars indicating the points of attachment to the br br style and to the receptacle. br br - Pericarp has three layers; epicarp/exocarp outer most , br br - In some fruits such as pineapples and bananas fruit formation br br takes place without fertilization. This is called parthenocarpy . br br - False fruits are formed when other parts of the flower such as br br the receptacle enlarge and enclose the ovary e.g. in pineapples, apple, straw berry and cashew nut. br br Classification of Fruits br br berry e.g tomato orange br br succulent fruits br br drupe e.g mango and coconut br br schizocarp e.g castor br br fruits br br legume e.g. beans dehiscent br br capsule e.g. poppy br br dry fruits br br nuts e.g. macadamia br br caryopsis e.g maize indehiscent br br cypsela e.g black jack br br Succulent fruits They are divided into berry and drupe. br br 128 Berry has a succulent pericarp divided into epicarp, mesocarp and endocarp e.g. orange, tomato, passion fruit, melon, paw paw etc. Diagram Drupe they have a thin epicarp, fleshy or fibrous mesocarp and a very hard endocarp enclosing the seeds. In mango the fleshy edible part is the mesocarp while in coconut the mesocarp is a fibrous cover just before the hard endocarp. Diagram Dry Fruits br br - They are divided into dehiscent and indehiscent. br br Dry Dehiscent fruit They dehisce to release their seeds. They are divided into; br br 1. Legume e.g beans Diagram br br 3. Schizocarp e.g. castor. br br Diagram br br Dry indehiscent fruits br br - These do not dehisce. - They include; 1. Caryopsis - pericarp and seed coat are fused together to form a br br thin covering round the seed e.g. maize. br br Diagram 2. Cypsela - its a one seeded e.g. the blackjack. br br Diagram br br 3. Nut the pericarp becomes hard and woody and it is separate br br from the seed coat e.g. macadamia. Diagram br br Placentation br br - This is the arrangement of the ovules in an ovary. They include; br br 129 1. Marginal Placentation . - Ovules are attached to the placenta in a row e.g. peas in a pod. Diagram 2. Basal placentation - Placenta is formed at the base of the ovary. Ovules are attached br br to it sunflower and sweet pepper. br br Diagram 3. Axile Placentation - The edges of the carpels fuse together to form a central placenta br br in the axile. br br - Ovules are arranged on the placenta. - The ovary is divided into a number of loculi by the walls of the br br carpel e.g. in orange br br Diagram 4. Parietal Placentation - Edges of the carpels fuse together and dividing walls disappear br br leaving a loculus. br br - Placentas from each carpel appear as a ridge on the ovary wall br br and have numerous ovules on them e.g. in paw paw. br br Diagram 5. Free central placentation - Edges of carpels fuse together and the dividing walls disappear br br leaving one loculus. br br - Placenta appears at the center and have numerous ovules on it e.g. in primrose br br Diagram br br Adaptations of Fruits to Various Agents of Dispersal a Water dispersal br br - Such seeds and fruits enclose air in them to lower their br br density for buoyancy; br br - They are fibrous/ spongy to lower the density for br br buoyancy; br br - Have impermeable seed coat or epicarp to prevent water from entering during flotation so as to avoid rotting; br br - The seeds can remain viable while in water and only br br germinate while on a suitable medium; br br b Wind dispersal br br - They are light; and small; to be easily carried by wind br br currents due to lower density; br br - Have developed extension Parachute like structures and Wing like structures which create a larger surface area; so as to be kept afloat in wind currents e.g. sonchus and jacaranda br br - In some a Perforated capsule is usually loosely attached to a long stalk which is swayed away by wind scattering seeds; br br c Animal dispersal br br - Brightly colored to attract animals - Fleshy to attract animals; e.g. mangoes, passion fruits, br br oranges, tomatoes etc. br br - aromatic /scented to attract animals; - The seed coats are hard and resistant to digestive enzymes; the seeds are therefore dropped away in feaces/droppings e.g. passion fruit and tomatoes. br br - Some have hook like structures to attach on animals fur br br e.g. blackjack br br d Self dispersal br br - They have weak lines sutures on the fruit wall pod , along which they burst open to release seeds, which get scattered away from the parent plant e.g. in legumes such as peas and beans. SEXUAL REPRODUCTION IN ANIMALS br br This involves gamete fusion. The male produces the male gamete sperms and the female br br produces the female gamete ovum/ova . br br The gametes are produced in special organs called gonads i.e. the br br testes and ovaries. The sperm fuses with the ovum to form a zygote through a br br process called fertilisation the gametes are haploid and the zygote is diploid. br br Fertilisation may be internal or external. br br External Fertilisation in Amphibians br br The female lays eggs and the male sheds sperms on them to br br fertilise them . This is only possible in water. br br Many eggs are released to increase the chances of survival since br br bacteria and other organisms can eat fertilised eggs. br br Eggs are also in long strands of slippery jelly like substance, br br which offer the eggs protection. br br This substance separates the eggs from each other allowing for br br good aeration. br br It also attaches the eggs to water plants and makes them buoyant. br br Internal Fertilisation br br This occurs in reptiles, birds and mammals where fertilisation br br occurs within the body of the female. br br Sperms are introduced into the females body. Few eggs are produced because there are high chances of br br fertilisation and the gametes/zygote receive further protection. br br In most mammals, some chameleons and some snakes the br br fertilised eggs develop into young ones within the body of the female. They give birth to young ones. Study Question 8 Reproduction in Mammals br br Mammals have internal fertilization where eggs are laid or br br develop within the females body in the uterus. br br The egg laying mammals monotremes they are said to be br br oviparous such as the platypus. br br Platypus The duck-billed platypus, Ornithorhynchus anatinus, found only in eastern Australia, belongs to an unusual group of egg-laying mammals called monotremes. It lives in streams, rivers, and occasionally lakes. The duck-billed platypus feeds on bottom- dwelling aquatic insect larvae, which it finds by probing the streambed with its pliable, sensitive bill. In marsupials such as the kangaroo the zygote does not develop fully within the uterus but completes development in the pouch. br br Mother Kangaroo and Baby br br Kangaroos are a type of mammal called a marsupial. Baby marsupials are unable to survive on their own when they are born, so they must live in a pouch on their mothers belly. A newborn kangaroo, called a joey, stays in its mothers pouch for about six months, where it feeds on her milk. br br The ability to give birth to young ones as in placental mammals is br br called viviparity. br br Mammals have mammary glands, which produce milk on which the young ones are fed. Parental care is highly developed in mammals. br br 133 Reproduction in Human beings Structure and Function of The male Reproductive System br br br br Male Reproductive System br br The organs of the male reproductive system enable a man to have sexual intercourse and to fertilize female sex cells eggs with sperm. The gonads, called testicles, produce sperm. Sperm pass through a long duct called the vas deferens to the seminal vesicles, a pair of sacs that lies behind the bladder. These sacs produce seminal fluid, which mixes with sperm to produce semen. Semen leaves the seminal vesicles and travels through the prostate gland, which produces additional secretions that are added to semen. During male orgasm the penis ejaculates semen. br br Testes are found outside the abdominal cavity in the scrotal sac. This position provides a cooler environment for sperm production since sperms develop best at lower temperature than that of the body. br br Testis is made up of highly coiled tubes called seminiferous tubules whose inner lining has actively dividing cells which give rise to sperms. br br Between the seminiferous tubules are interstitial cells, which br br produce the male hormones androgens . br br 134 br br Internal View of Male Reproductive System br br The reproductive anatomy of the male human is largely external. Beginning at puberty, sperm are produced within seminiferous tubules of the testicles, a pair of glands that reside in a pouch called the scrotum. The external location of the scrotum keeps the temperature of sperm slightly below body temperature, which is necessary for their healthy development and survival. From each testicle, sperm migrate to a long, coiled tube known as the epididymis, where they are stored for one to three weeks until they mature. Also located outside the body is the penis, the erectile organ responsible for the excretion of urine and the transfer of sperm to the vagina of the female. Just before ejaculation during sexual arousal, mature sperm travel from the epididymis, a coiled tube behind each testicle, through a long duct called the vas deferens. Sperm leave the body in semen, a fluid produced by the seminal vesicles. br br Seminiferous tubules unite to form the epididymis, which is br br about 6m long and highly coiled. It stores the sperms. br br Its connected to the sperm duct/vas deferens. Sperm duct br br connects the epididymis to the urethra, which is the ejaculatory duct. br br Seminal vesicles provide an alkaline fluid, which contains br br nutrients for the sperms. br br 135 Prostate gland secretes an alkaline substance to neutralise the br br vaginal fluids. It also activates the sperms. br br Cowpers glands secrete an alkaline fluid that neutralizes the br br acidity along the urethra. br br All these fluids combine with the spermatozoa to form the br br semen. br br Since the urethra serves both passage of urine and semen it is br br said to be urino-genital in function. br br The penis is erectile and made of spongy tissue, muscle and br br blood vessels. br br Once erect, the penis is able to penetrate the vagina in order to br br deposit sperms into the females reproductive tract. br br Study question 9 and Practical. Structure and Function of The Female Reproductive System . Diagram br br The internal sex organs of the female consist of the vagina, br br uterus, fallopian tubes or oviducts , and ovaries. br br The vagina is a flexible tube-shaped organ that is the passageway between the uterus and the opening in the vulva. Because during birth the baby travels from the uterus through the vagina, the vagina is also known as the birth canal. br br The woman's menstrual flow comes out of the uterus and through br br the vagina. br br When a man and a woman engage in vaginal intercourse, the br br penis is inserted into the vagina. br br The cervix is located at the bottom of the uterus and includes the opening between the vagina and the uterus. It secretes a plug of mucus, which prevents entry of pathogens into the uterus during pregnancy. br br The uterus is a muscular organ that has an inner lining br br endometrium richly supplied with blood vessels and glands. During pregnancy, the uterus holds and nourishes the developing foetus. br br Although the uterus is normally about the size of a fist, during pregnancy it is capable of stretching to accommodate a fully developed foetus, which is typically about 50 cm about 20 in long and weighs about 3.5 kg about 7.5 lbs . br br The uterine muscles also produce the strong contractions of br br labour. br br At the top of the uterus are the pair of fallopian tubes oviduct br br that lead to the ovaries. br br The two ovaries produce eggs, or ova the female sex cells that can become fertilized , and female sex hormones, primarily oestrogen and progesterone. br br The fallopian tubes have finger like projections at the ends near the ovaries that sweep the egg into the fallopian tube after it is released from the ovaries. br br Movement of ovum is also aided by the smooth muscles of the br br oviduct. br br If sperm are present in the fallopian tube, fertilization br br conception may occur and the fertilized egg will be swept into the uterus by cilia hair like projections inside the fallopian tube . Practical br br The Human Sperm br br Are formed in the seminiferous tubules of testes by meiosis. Final products of meiosis enter the sertoli cells where they are br br nourished and undergo maturation. br br Mature sperms leave for epididymis where they are stored. A mature sperm has an ovoid head, short neck, middle piece and br br a tail. br br Diagram br br Head has a large nucleus carrying the genetic material, which is br br haploid n . At the tip of the head there is the acrosome containing lytic br br enzymes. These enzymes digest the wall of ova. br br The short neck contains centrioles. Middle piece has a large number of mitochondria, which provide with the energy required for propulsion of the sperm to reach the ova. br br The tail propels the sperm forward by its side-to-side lashing br br action. br br Formation of The Ova br br In females egg formation begins in the ovary of the foetus before br br birth unlike in males where production of sperms starts at puberty. br br At birth there are about 70,000 potential egg cells in the ovaries br br of a baby girl. br br A layer of ovary cells called primary follicles , which provide br br them with nourishment, encloses them. br br Only about 500 of them develop into ova during puberty. During puberty the primary follicles grow to become Graafian follicle . At ovulation, the Graafian follicle bursts open to release a mature br br ovum surrounded by a layer of cells. br br Diagram br br A mature ovum is spherical in shape with a diameter of about 0.2 br br mm. br br It has a large haploid nucleus surrounded by a nuclear membrane. Nucleus is within the cytoplasm enclosed by the plasma membrane . Vitelline membrane surrounds the plasma membrane. Fertilisation br br Process where the nucleus of a male gamete fuses with the br br nucleus of a female gamete to form a zygote. br br This takes place in the upper part of he oviduct after copulation. Sperms are drawn up by suction through the cervix into the uterus. They swim up to the oviduct using their tails. br br Very many sperms are released but only one is required to br br fertilise the ovum. br br The ovum releases chemical substances, which are neutralised by br br those released by the acrosome. br br When the ovum comes into contact with the egg the acrosome br br bursts releasing lytic enzymes, which dissolve the egg membranes. br br The acrosome turns inside out forming a filament, which is used br br to penetrate the eggs. br br Diagrams br br The Vitelline membrane undergoes a change, which stops any br br other sperm from entering the ovum. br br Once inside the cytoplasm the head bursts to release the male nucleus, which then fuses with the female nucleus to form a diploid zygote. br br After ovulation the ovum can remain viable for 8-24 hours before br br it dies. br br The sperm can remain viable for 2-3 days in the female br br reproductive tract. After fertilisation, the zygote undergoes various mitotic divisions as it moves down the oviduct. Its movement is aided by cilia in the oviduct and by the contractions of the smooth muscles lining the oviduct. br br By the time it reaches the uterus it has formed a hollow structure br br of cells called blastocyst. br br Movement of the zygote from the oviduct to the time it is br br implanted takes about 7 days. br br Diagrams br br Sometime the zygote may fail to move down to the uterus and gets implanted into the walls of the oviduct. This condition is referred to as ectopic pregnancy . br br Formation of Placenta br br During implantation the blastocyst differentiates into three layers, br br chorion, amnion and allantois. br br Diagram br br Chorion is the outermost and it has finger like projections called chorionic villi . These villi grow into the endometrium. During the early stages of embryo development, villi form the sites for material exchange between the embryo and maternal blood vessels. br br Amnion surrounds the embryo forming an amniotic cavity. br br Amniotic cavity contains the amniotic fluid, which suspends the foetus providing it with support. It also acts as a shock absorber hence protecting it against mechanical injury. br br The chorionic villi, allantois and the endometrium form the br br placenta. br br The embryo is attached to the placenta by a tube called the br br umbilical cord . br br When the placenta is fully formed, the embryo becomes the br br foetus at about three months of pregnancy. br br 140 The Role of The Placenta br br This is a temporary organ found only in placental mammals. It is the only organ in animals composed of cells derived from two different organisms; the foetus and the mother. br br It facilitates the transfer of nutrients and metabolic waste products between the mother and the foetus. It selectively allows some materials to pass through and not others. br br Refer to the table below br br Drugs, alcohol and some chemicals from cigarette smoke pass br br through the placenta. Pregnant mothers should therefore not take alcohol or smoke excessively. br br There is no direct connection between the foetal blood system and br br that of the mother. br br If the two systems were directly connected, the delicate blood vessels of the foetus would burst due the higher pressure in the maternal circulatory system. br br Exchange of materials occurs across the sinus in the uterine wall and the capillary system of foetus across intercellular space by diffusion. br br Diagram br br Study question 13 br br During pregnancy, placenta takes over the role of producing br br hormones oestrogen and progesterone. br br Major functions of oestrogen and progesterone during pregnancy Oestrogen i. Growth of mammary Progesterone. i. Growth of mammary br br glands Inhibits FSH release. Inhibits prolactin release. br br glands. Inhibits FSH release Inhibits prolactin release. Inhibits contraction of ii. iii. iv. Prevent infection in ii. iii. iv. uterus Increase size of the uterine muscle cells. Increase ATP and creatine phosphate formation. Increases sensitivity of myometrium to oxytocin. br br myometrium. br br v. br br vi. br br What is allowed to pass through the placenta From the mother to the foetus. br br What is not allowed to pass through the placenta i. All blood cells. ii. Plasma proteins. iii. Most bacteria. br br i. Oxygen ii. Vitamins iii. Mineral salts iv. Hormones v. Water vi. Antibodies and antigens. vii. Glucose, amino acids, br br fatty acids and glycerol. br br From the foetus to the mother br br i. Carbon iv oxide. ii. Nitrogenous wastes. br br Gestation Period br br This is the period between conception and birth. This varies in br br different animals. E.g. mice 22 days Rabbits, 30 days Man, 9 months Elephants, 18 month When the human embryo is two weeks old, allantois, br br chorion and amnion have already formed. Embryo then differentiates into tissues and organs. br br By the end of the third month , the heart and blood vessels are fully developed. Spinal cord and the head region, which includes the eyes and the nose, are also well developed. Limbs show early signs of development. br br By the end of 6 months the alveoli and nose are well developed. Foetal movement can as well be felt. br br By the end of the nine months , the foetus head is directly br br above the cervix. br br By now all the organs and systems are fully developed. If birth occurs before completion of 6 months, this is called br br miscarriage and the baby cannot survive. br br If the foetal development is interfered with either br br physically or chemically such that the foetus is released, this is called abortion. br br If birth occurs after 7 months but before term, this is called premature birth . Such babies are raised in incubators and they do survive. br br Pregnant mothers must have a balanced diet. Calcium, br br proteins, phosphates and iron should be abundant in her diet. br br Calcium and phosphorous are needed for bone formation br br while iron is for haemoglobin formation. Pregnant mother should visit antenatal clinic. Birth/Parturition br br Maternal posterior pituitary gland releases hormone oxytocin. Progesterone level goes down. Oxytocin stimulates contraction of the myometrium. br br Oxytocin is released in waves during labour. This provides the force required to expel the foetus from the uterus. br br The cervix dilates, the amnion and chorion rupture br br releasing the amniotic fluid. br br The uterus starts contacting from the top downwards pushing the foetus downwards head first through the widened cervix and the birth canal. br br After birth, the umbilical cord is ligatured/cut to separate the baby from the placenta. Placenta is expelled later after birth. br br Then newborn baby takes in the first breath, lungs expand and become functional. The respiratory role of the placenta is taken over by the lungs. br br Diagrams br br Caesarean delivery br br This is the surgical incision of the abdominal and uterine br br walls for delivery to be achieved. This is done where there are complications ns such that the foetus cannot pass through the birth canal. br br Parental care br br The newborn baby is given food and protection. Placental mammals feed their young ones on milk. Milk is produced by the mammary glands under the influence of lactogenic hormones e.g. prolactin. br br Mothers milk is the best as it contains all the nutrients needed for the growth and development of the body. For the first 3 days, colostrum is produced which contain antibodies, which provide natural defence to the foetus against diseases. br br Milk is deficient of iron. The baby relies on iron stored in br br its liver during gestation. br br Milk let down is an example of a reflex action. The prevailing environment as shown below influences it br br either positively or negatively. br br Milk production in various environments br br Positive Environment Negative Environment br br Sucking at the breast, smell of the baby or crying of the baby trigger milk let down. br br Milk let down may be inhibited or blocked if the breastfeeding mother experiences embarrassment, fatigue or anxiety. br br Hypothalamus relays impulses to pituitary gland which releases hormone oxytocin Oxytocin reaches the breasts and causes alveoli to contract forcing milk into the ducts. br br Ducts conduct milk into the reservoirs behind the areola br br Baby sucks the milk from this reservoir. br br Assignment br br Child labour br br Role of Hormones in Human Reproduction br br Secondary sexual characteristics br br These are physiological, structural and mental changes associated with masculinity and femininity. They are controlled by oestrogen in females and androgens in males. They occur at puberty. br br Secondary sexual characteristics in males br br Hypothalamus stimulates pituitary gland to release br br gonadotrophic hormones i.e. FSH and LH. br br FSH stimulates sperm synthesis. LH is also known as Interstitial Cell Stimulating Hormone br br ICSH and it stimulates interstitial cells to release Androgens mostly Testosterone. It stimulates the onset of secondary sexual characteristics mostly at the age of 14. These include; br br i. Deepening of voice ii. Growth of hair in pubic parts and armpit region iii. Appearance of beards iv. Body becomes masculine v. Testes enlarge and begin to produce sperms br br Secondary sexual characteristics in females br br In females they start at early age 10-12 years. They include, br br i. Development of mammary glands ii. Growth of hair in pubic parts and armpit region iii. Enlargement of the pelvic girdle and widening of the br br hips br br iv. Body becomes feminine. v. Ovaries mature and start releasing eggs under the br br influence of FSH and LH hence ovulation and menses. Unlike in males, the production of gonadotrophic hormones br br is not continuous. It is produced periodically in cycles. br br Menstrual Cycle br br br br Menstruation An average menstrual cycle begins with three to five br br days of menstruation, the shedding of the uterine lining, during which hormone levels are low. br br At the end of menstruation, pituitary gland secrets FSH which has two functions. It stimulates new Graafian follicles to develop in the ovary and stimulates the ovary to secrete the hormone oestrogen. br br Oestrogen brings about repair and healing of the br br endometrium, which is destroyed during menstruation. br br Oestrogen accumulates to levels, which stimulate the release of LH. LH stimulates the maturity of Graafian follicle. The mature Graafian follicle releases the ovum into the fallopian tube. This is called Ovulation and occurs on the 14th day. br br The empty Graafian follicle forms the corpus luteum, an br br endocrine body that secretes progesterone. br br LH stimulates corpus luteum to secrete hormone br br progesterone. This hormone stimulates thickening and increased blood supply to the endometrium preparing the endometrium for implantation. br br If fertilization takes place, the level of progesterone increases and thus inhibits FSH from stimulating the maturation of another Graafian follicle. br br If fertilization does not take place, the corpus luteum dies br br and progesterone hormone levels fall. br br Without hormonal support, the uterine lining br br disintegrates and discharges, beginning a new menstrual period and cycle. br br This cycle lasts for 28 days in human beings. br br 146 Assignment Sanitary Health br br Menopause STI br br Advantages of Asexual reproduction i. Good qualities from the parents are retained since there br br is no variation. br br ii. There is faster maturation. iii. br br Its independent of processes such as pollination, fertilisation and fruit and seed dispersal br br iv. New offsprings are able to obtain nourishment from their parents and are therefore able to survive under unsuitable conditions. br br v. There is no wastage of a large number of offsprings . br br Disadvantages i. Reduction in strength and vigour in offsprings. ii. Undesired qualities are easily inherited. iii. Due to faster maturation there are chances of br br overcrowding and competition. br br iv. Offsprings may not withstand changing environmental br br conditions due to lack of variation. br br Advantages of sexual reproduction i. There is hybrid vigour due to mixing of genetic material. ii. There is high adaptability iii. Variation form basis for evolutionary changes. Disadvantages i. May produce individuals with undesirable qualities. ii. Method is dependent of union of gametes and therefore may not take place if the two organisms are isolated br br Revision Questions BIOLOGY FORM FOUR NOTES br br THE EYE The mammalian eye is spherical; fluid filled and has three layers; br br Outer layer or sclera Middle layer or choroid Inner layer or retina Adaptations of the eye br br Part Properties Functions 1. Sclera Protects delicate inner br br parts of the eye. br br Maintain shape of the br br eye. br br 2. Cornea Allow light into the br br eye. br br Refract light entering br br the eye br br 3. Conjunctiva Thin and Allow light into the br br transparent layer before the cornea. Have cells that have melanin, arteries veins br br eye. br br Protects the cornea. br br 4. Choroid Provide nourishment to br br the eye. br br Pigment prevents reflection of light within the eyeball. Produce the aqueous 5. Ciliary body Have thin rings br br of thickened tissue arising from choroids. br br humour br br br br 6. Ciliary muscle Have circular Muscles alter the br br and radial muscles which are antagonistic. fibrous br br tension of suspensory ligaments. br br 7. Suspensory ligaments. br br Alter the shape of the br br lens. br br 8. Pupil br br Hole at the center of iris. br br Regulates the amount of light entering the eye. br br 9. Iris br br Contain melanin, circular and radial muscles. br br Give the eye its colour. Regulates the amount br br of light entering the eye humor from vitreous humor. br br allow light pass / refract light, br br Hydrostatic pressure maintain shape of eyeball. br br Contains sugars / proteins / salts provide nutrients to eye. br br Rods are sensitive to br br low light intensity and detect black and white and more in nocturnal animals. Have photochemical pigment called rhodopsin. Cones are sensitive to high light intensity, detect colour and present in large numbers in diurnal animals. Have photochemical pigment called iodopsin . br br Its the most sensitive part of the retina. Image is formed here. Optic nerve leaves the br br retina. br br Blood vessels emerge br br here to nourish the eye. br br Transmits nerve br br impulses to the brain for interpretation. Tears moisten the br br cornea and washout foreign particles. Tears have antiseptic br br effect. br br Draw across the eye br br move eyeball within br br socket br br orbi t- protective eye lids -protect the eye br br by closing br br Eye lashes -prevent br br entry of small foreign particles. br br Eye brows -prevent dust sweat from entering eye. Image formation and interpretation br br Light from an object is refracted by cornea, aqueous br br humour, the lens, through the vitreous humour and focused on the yellow spot of the retina. br br Image formed is recorded as real, inverted and small. Photoreceptors are stimulated and generate a nerve impulse which is transmitted by the optic nerve to the cerebrum of the brain for interpretation. br br In the brain the image is interpreted as real, upright and br br normal. br br Images from the right eye are interpreted by the left br br hemisphere of cerebrum while those from the left eye by the right hemisphere. Diagram pages 100 KLB Binocular vision or Stereoscopic Vision br br This is the ability of both eyes to look straight ahead but br br see the same scene from a slightly different angle. br br The eyes' visual fields overlap in the center, and the brain merges these images to create a sense of depth important for judging distance. br br Humans and other mammals have stereoscopic vision. Birds, fish, and snakes have monocular vision in which each eye sees a separate image covering a wide area on each side of the head. br br 3. Damage to one eye is compensated by the other 4. Cancels the effect of blind spot br br Accommodation of The Eye br br This is the refraction of light in order to fall on the fovea centralis yellow spot for clear focus of image regardless of the distance of the object. Accommodation of a close object br br Ciliary muscles contract thereby relaxing the tension on br br suspensory ligaments. br br Curvature of the lens increases. The close objects are greatly refracted by the lens focusing br br them on the retina. br br Diagram Accommodation of a distant object br br Ciliary muscles relax increasing the tension on suspensory br br ligaments. br br The lens is stretched decreasing its curvature i.e. lens br br become thinner. br br Light rays from the object are less refracted and focused on br br the retina. br br Diagram Control of Light Entering the Eye br br 1. Bright Light Circular muscles of iris contract and the radial muscles br br relax. br br Diameter of pupil decrease and less light enters. This protects retina from damage by too much light. Diagram br br 2. Dim Light. Circular muscles relax and radial muscles contract. Diameter of pupil increase and more light enters the eye. This allows in enough light to stimulate photoreceptors on br br the retina. br br Diagram Defects of the Eye 1. Short sightedness Myopia br br This is the ability to view near objects clearly but distant br br objects are blurred. This is due to a long eyeball and image is formed before the br br retina. Correction br br Wearing concave Diverging lens br br Diagram 2. Long sightedness Hypermetropia br br This is the ability to view distant objects clearly but near br br objects are blurred. br br This is due to a short eyeball and image is formed behind br br the retina. br br Correction br br Wearing convex converging lens br br Diagram 3. Astigmatism br br The curvature of the cornea is uneven hence the image is br br formed on different planes. br br Its corrected by wearing cylindrical lens. br br 4. Squintedness br br Eyeballs face different directions due to defective muscles br br which move the eye left and right. br br Corrected surgically 5. Old sight Presbyopia 6. Cataracts 7. Colour blindness Diagram br br Adaptations of the ear to its Functions The ear is divided into: br br 1. Outer ear Pinna. - Pinna is funnel shaped to direct sound waves into br br auditory canal; br br - its large to offer large surface area for collection of br br sound waves; br br Auditory meatus/canal - Tube that directs sound waves to ear drum. - Lined with hairs to trap solid particles. - Lined with wax secreting cells to trap dust. 3. Inner ear. Its fluid filled br br Cochlea - Its responsible for hearing - Its filled with endolymph and perilymph - Highly coiled to occupy a small space ; and increase br br surface area ; for accommodation of many sensory cells br br - Vibrations from oval window are transmitted to br br perilymph which vibrates br br - Sensory cells are stimulated by these vibrations to br br generate nerve impulses which are transmitted to the brain for interpretation. Diagram Semi circular canals - Has semi circular canals which are at right angles to each br br other br br - Each canal has a swelling called ampulla at one end br br containing sensory cells. br br - Contains endolymph Terms used in genetics br br 1. Inheritance ; transmission of characteristics from the br br parents to the offsprings br br 2. Variation; possession of characteristics different from those br br of the parents and other offsprings. br br 3. DNA ; De-oxyribonucleic acid 4. RNA ; Ribonucleic acid 5. Monohybrid inheritance ; inheritance of one characteristic controlled by one pair of hereditary factors e.g. Tallness 6. Dihybrid inheritance ; inheritance of two characteristics at the same time e.g. colour and Texture/shape in the garden pea plant br br 7. Dominance; ability of a trait to only express itself 8. Recessiveness; a trait that only expresses itself when in br br homozygous state. br br 9. Heterozygosity ; presence of two dissimilar members of an br br allele e.g. Rr, Tt etc. br br 10. Homozygosity ; presence of two similar of an allele e.g. br br TT, RR, tt, rr etc. br br 11. Allele ; one pair of genes which occupy corresponding br br loci/positions in homologous chromosomes 12. Phenotype - the physical appearance of an individual br br or organism. Its influenced by the genotype and environment. br br 13. Genotype - the genetic constitution of an organism. Its br br purely genetical. br br 14. br br F1 generation first filial generation - are the offsprings that represent the first generation of organisms or individuals under study. br br 15. F2 generation second filial generation - these are br br offsprings obtained after self crossing the F1 gen. br br 16. Incomplete dominance/ co-dominance - a condition br br where no allele is dominant over the other. The phenotype of the offspring is intermediate between that of the parents. br br 17. Multiple allelism - are characteristics determined by br br more than two variant forms of a single gene e.g. inheritance of the Blood groups in man ABO br br 18. br br Test cross / back cross - its a crossing involving a homozygous recessive to determine the genotype of an organism. br br 19. Mutation- these are spontaneous changes in the br br individuals genetic makeup. br br Concepts of Variation Variation refers to observable differences among living organisms. Types of variation br br 1. Discontinuous variation in this type of variation, there are distinct and definite groups of individuals with no intermediate forms. E.g. br br sex either male or female, blood groups- one can only belong to one of the br br four blood groups A,B,AB,O br br ability to role the tongue Presence of long hair in the nose and on the ear br br pinna. br br Presence of a free or attached ear lobe. All these traits are controlled by one or two major genes. These traits are not influenced by the environment br br 2. Continuous variation this variation has a wide range of differences for the same characteristic from one extreme to the other e.g. Height Skin colour/pigmentation A normal distribution curve of heights This type of variation is brought about by the interaction of both the genetic environmental factors. E.g. a plant with genes for tallness may fail to grow tall due to climate and poor soils. br br Practical Activity 1 br br Tongue rolling Finger prints Height br br Causes of variation br br 1. Gamete formation during gamete formation two br br processes contribute to variation. These are br br Independent assortment - during metaphase I of meiotic division, homologous chromosomes come together in pairs and segregate into daughter cells independently of each other. This independent assortment produces a variety of different gametes. The total number of combinations is given by 2n where n is the haploid number of chromosomes. In man n 23 hence 2n 223 which is equal to 8,388,608. br br Crossing over during the prophase I of meiotic cell division. I.e. when homologous chromosomes break and rejoin at certain points called chiasmata. br br 2. Fertilization during fertilization parental genes ca br br come together in different combinations. Therefore desirable and undesirable qualities of parents can be combined in the offsprings. br br 3. Mutation - these are spontaneous changes in the genetic makeup of an organism. Mutation brings about changes in the living organisms. br br The Chromosome Each chromosome is made up of two parallel strands called chromatids. Each pair of chromatids is connected at a point by the centromere. Chromosomes contain the hereditary material called the genes. All cells including the sperms and ova have chromosomes. Chromosomes are present in the nucleus and are only visible under the microscope during cell division mitosis and meiosis. There is a definite number of chromosomes in each cell for every species of animal or plant. E.g. in man somatic cells body cells have 46 chromosomes while the sex cells/gametes have 23 chromosomes. During fertilization fusion of the sperm- 23 chromosomes and the ova - 23 chromosomes restores the 46 chromosomes to form a diploid zygote. br br Chromosomal numbers in different organisms br br Organism Number of chromosomes br br Somatic cells 2n 56 60 8 br br Gametes - n br br Sheep Ovis auries Cow Bos Taurus Fruit-fly Drosophila melanogaster Maize Zea mays Wheat Triticum vulgare Tobacco Nicotiana tabacum Man Homo sapiens br br 28 30 4 br br 20 14 12 br br 46 23 Practical Activity 2 br br Chromosomal behaviour during mitosis Chromosomal behaviour in meiosis br br GENES AND DNA Genes occupy specific positions on the chromosomes called the gene loci gene locus The gene is a chemical in nature. The genes are in the form of a nucleic acid molecule called De-oxyribonucleic acid DNA . In 1953 two Biologists Francis Crick and James Watson worked out the structure of the DNA. DNA was found to be composed of three different components; br br 1. A five carbon sugar-pentose 2. phosphate molecule 3. nitrogenous base br br There are four types of the nitrogenous base; br br Adenine N Guanine G Thymine- G Cytosine C br br A combination the pentose sugar, a phosphate molecule and a nitrogenous base forms a nucleotide. I.e. br br Phosphate br br Base Pentose sugar DNA structure contains several nucleotides fused together to form long chains called DNA strands. Two parallel strands twist on one another forming a double helix structure. Adenine always combines with Thymine and Cytosine with Guanine. br br Diagram br br Role of DNA br br Stores genetic information in a coded form Enables transfer of genetic information unchanged to br br daughter cells through replication br br Translates the genetic information into the br br characteristics of an organism through protein synthesis br br DNA REPLICATION br br During cell division both daughter cells arising from mitotic division have the same genetic constitution as the parent cell. DNA in the parent cell must therefore duplicate accurately before the cell divides. The process through which a DNA molecule forms an exact Replica is called DNA replication . br br The two strands forming the double helix separates br br like a zipper . Each parallel strand becomes a template that specifies the base sequence of a new complimentary strand. Through the action of replicating enzymes, free nucleotides take up positions along the template strands. br br The specificity of the base pairing ensures that only complimentary bases link together with those on the template strands. I.e. G-C and A-T. br br Covalent bonds are formed between the nucleotides resulting in the formation of a new DNA strand. The template and the new DNA strand the undergo coiling to form a double helix. In this way, two identical DNA molecules are formed from the original single molecule. br br Each of the new DNA molecules gets incorporated into one of the two nuclei formed just prior to the separation of the daughter cells. Diagram br br Role of the DNA in protein synthesis The sequence of bases along the DNA strand acts as the alphabet and determines the sequence of amino acids when they join to form a polypeptide chain. Protein synthesis takes place in ribosomes found in the cytoplasm. Since the DNA molecules are confined in the nucleus, there has to be a way of communicating the DNA information to the ribosomes where actual protein synthesis occurs. The cell therefore has a special molecule called the Ribonucleic acid RNA . Its role is to carry genetic information from the DNA to the site of protein synthesis in the cytoplasm. Its referred to as messenger RNA mRNA . RNA is formed from the DNA strands. During formation of the mRNA a section of the DNA strands acts as the template strand. The double helix of the DNA unzips and free nucleotides align themselves opposite the template. The base sequence of the template strand is copied onto a new strand. In RNA, Thymine is replaced by another base called Uracil U The transfer of DNA sequence on the mRNA strand is referred to as Transcription. triplets known as Codons which code for a particular amino acid of a protein molecule e.g. br br AAA-phenylalanine TTT-lysine CAA- valine CTA- aspartic acid br br Differences between DNA and RNA br br DNA 1. Has De-ox ribose sugar 2. Double stranded 3. Confined in the nucleus br br RNA br br Has ribose sugar Single stranded Found in nucleus and cytoplasm Has organic bases as cytosine, guanine, adenine and uracil br br cytosine, guanine, adenine and thymine. THE FIRST LAW OF HEREDITY MENDELS EXPERIMENTS An Austrian monk known as Mendel is considered to be the father of genetics. He carried out various breeding experiments and observed variations in different characteristics of the garden pea. The characteristics include: br br Height of the stems- tall or dwarf Texture of the seed coat- smooth or wrinkled Colour of the seeds- yellow or green Texture of the ponds Colour of the flowers- white or purple Position of the flower- axial or terminal br br He selected a group of dwarf plants and self pollinated them by dusting mature pollen grains onto the stigmas of the same plant. He collected the resulting seeds and planted them. He noted that these seeds grew into dwarf plants only. He repeated the experiment for several generations and obtained the same results. In another experiment, Mendel selected tall plants and self- pollinated them. He planted the resulting seeds and observed that they grew into a mixture of tall and dwarf plants. He took seeds from the tall offsprings only and repeated the experiment for many generations until he obtained only tall plants. This way he was able to obtain a pure line of tall garden peas and a pure line of dwarf garden peas. He then cross-pollinated pure bred tall garden pea s with the pure bred dwarf variety. He planted the resulting seeds and he observed that all the offsprings were tall plants. br br Diagram He further crossed two of these tall offsprings and planted the resulting seeds. Mendel observed that this second generation consisted of a mixture of tall and dwarf plants. After counting these plants he noted that the ratio of tall to dwarf plants was approximately 3:1 respectively. He observed that this ratio was always obtained when crosses were made between the non-pure breeds of tall plants. br br Diagrams Mendel concluded that the traits of an organism are determined by hereditary factors which occur in pairs. Only one of pair of such factors can be represented in a single gamete. This later became Mendels First Law, The Law of Segregation At this time Mendel had no idea of genes and so he called them factors. He postulated that these factors are found on the chromosomes and are passed from the parents to the offsprings via gametes. br br Reasons behind Mendels success br br 1. He used favourable materials i.e. the garden pea plant br br which is normally self pollinated. This made it easy for him to employ cross pollination at will. br br 2. the pea plant he used had several contrasting traits 3. His study was focused on particular traits while those br br before him had been attempting to determine wholesome heredity of each organism. br br 4. He kept accurate data on all his experiments and fro the analysis of this data he was able to formulate definite hypothesis. Mendel chose the garden pea plant because of the following reasons br br Plant had many contrasting traits e.g. flower colours, br br seed coat texture, length of the stems etc. br br Plant is normally self pollinated but cross pollination br br can be employed t will. Plant matures relatively fast Plant produces many seeds that can be planted to br br produce many offsprings Monohybrid Inheritance This is the inheritance of one trait like height in the garden pea plant that is controlled by a single pair of hereditary factors genes contributed by both parents. Genes occur in pairs on chromosomes and such gene pairs are known as alleles. The genetic constitution of an organism is called the Genotype while the physical appearance is known as the Phenotype. The genotype of an organism is represented using paired letter symbols. Capital letters represents the dominant gene while small letters represent the recessive gene. br br Genetic Cross br br Components of a genetic cross Parental phenotypes The parental genotype the crossing X should be br br shown here. br br The gametes and should be circled. The fusion process or fertilization. The filial generation genotypes br br NB. The conventional symbol for male is and that of female is br br Example 1 During gamete formation in the dwarf plat, each gene in the pair segregates into different gametes. When the female and male fuse during fertilization, the offspring produced contain the same number of genes as in each parent. The inheritance of dwarf ness in the pea plant can be illustrated diagrammatically by the following genetic cross Diagram Example 2 Similarly the pair of genes in the pure breed tall plants will segregate into different gametes during gametogenesis. When self fertilised the resulting seeds will have half the number of genes from each parent i.e. br br Diagram br br Example 3 When the purebred tall plant is crossed with dwarf plants, the resulting seeds grow into tall plants only. These offsprings represent the first generation F1 gen Diagram. In the genetic cross above, the male plant is tall and the female plant is dwarf. If the cross is reversed so that the female is tall and the male a dwarf, this is referred to as a reciprocal cross . The F1 results will be the same for either cross. br br Diagram br br Example 4 When the F1 offsprings are self pollinated, they produce offsprings which that grow into a mixture of tall and dwarf plants. These offsprings are known as the F2 gen. br br Diagram A Punnet Square can also be used to work out genetic crosses e.g. Parental phenotype tall tall Parental genotype Tt X Tt Gametes T t T t When the allelic genes are identical, as in TT and tt, the condition is known as homozygous . An individual with such a condition is known as a homozygote. When the allelic genes are not identical as in Tt, the condition is referred to as heterozygous . An individual with such a genotype is referred to as a heterozygote . An individual with genotype Tt, will be physically tall because the gene T i s dominant over t. The allele t is recessive . A dominant gene expresses itself in both the homozygous TT and heterozygous Tt states while a recessive gene only expresses itself I its homozygous state tt . TT is therefore referred to as homozygous dominant and tt is homozygous recessive. The ratio 3 tall: 1 dwarf, in the F2 gen is characteristic of monohybrid inheritance where one gene is completely dominant over the other. This is referred to as complete dominance. The monohybrid crosses are based on Mendels first law, The law of Segregation which states the characteristics of an organism are determined by internal factors which occurs in pairs. Only one of a pair of such factors can be represented in a single gamete. Diagram - the process of segregation br br Ratios and Probability The 3:1 ratio in monohybrid inheritance can be represented in the form of probability. When a large number of heterozygous garden pea plants are selfed, the probability of getting tall plants is or 75 and that of dwarf will be or 25 . br br Diagram NB. The inheritance of characteristics involves probability. The chance that a particular gamete will fuse with another is a random occurrence, in genetics this done by showing all possible fusions. br br Practical Activity 3 and 4 br br Tossing a coin To demonstrate random fusion of gametes in br br monohybrid inheritance. br br Similar monohybrid inheritance results as those of Mendel have been obtained by using the fruit fly Drosophila melanogaster the insect has many observable characteristics that are contrasting such as, br br Wing length long wing dominant over vestigial wing Eye colour red eyes dominant over white eyes Size of the abdomen broad abdomen dominant over br br narrow abdomen br br Body colour grey body colour dominant over black br br body colour. Assignment br br Using appropriate letters work out the following crosses with respect to the fruit fly br br Cross between a purebred long winged and a vestigial br br winged br br Cross between two long winged heterozygotes Cross between a red eyed heterozygote and a white br br eyed fruit fly. br br The fruit fly is suitable for genetic study because of the following reasons. br br 1. The female lays very many eggs hence increasing the br br sample size for study. 2. Have many observable characteristics that are distinct br br and contrasting. br br 3. It is easily bred in the laboratory with minimum br br requirements. br br 4. It has a short generation time 10-14 days. Therefore many generations can be studied in a short period of time. br br 5. Offsprings can be crossed with their parents at will br br backcrossing br br 6. Flies are safe to handle because they do not transmit br br any known human diseases. br br Study Question 10 br br Practical Activity 5 br br Breeding fruit flies. br br Incomplete Dominance Co-dominance In Mendels experiments with garden pea p plants, the genes determining the various traits were clearly dominant or recessive. However in some species, alleles determining several contrasting traits do not have a clear cut dominant-recessive relationship. This implies that neither of the alleles is completely dominant over the other. Heterozygous individuals are phenotypically different from either of the parents. Mostly the phenotype of the heterozygous offspring is intermediate between that of the parents. This phenomenon is called Incomplete Dominance . Examples of incomplete dominance. br br 1. I nheritance of flower colour in the 4 oclock plant br br Mirabilis Jalapa . If a true breeding plant producing red flowers is crossed with a true breeding plant producing white flowers, all the F1 offsprings will have pink flowers. When the F1 plants are self pollinated, they yield red flowered, pink flowered and white flowered offspring at a ratio of 1:2:1 respectively. Diagrams br br 2. Incomplete dominance in short horn cattle . Mating red and white shorthorn cattle yields Roan light Red calves due to presence of both red and white hairs. A mating between two roan coloured shorthorns yields a mixture of red, roan and white coloured calves at a ratio of 1:2:1 respectively. Diagrams br br Study Question 12 Inheritance of the Blood groups Multiple allelism In all the kinds of inheritance discussed so far, each phenotypic characteristic is determined by 2 variant forms of a single gene located at a specific locus on the homologous chromosome. However some characteristics are determined by more than two variant forms of a single gene. This phenomenon is referred to as multiple allelism and the genes involved are called multiple alleles . E.g. in the ABO blood groups in humans, there are three genes involved and they are responsible for the presence of antigen types on the red blood cells. These are gene A responsible for the presence of antigen A , gene B for antigen B and gene O responsible for absence of antigens on the red blood cells. Genes A and B have equal degree of dominance i.e. are co- dominant . They both express themselves when present together as in the blood group AB. Genes A and B are dominant over gene O. Gene O is recessive and only expresses itself in the homozygous condition. The genotypes for the four blood groups in the ABO system are therefore, Blood group Phenotype A B AB O br br Genotype Antigens br br AA, AO BB,BO AB OO A B A and B O- Zero br br i.e. br br AA or AO-Blood group A BB or BO blood group B AB blood group AB OO blood group O br br A marriage between a man of blood group A and a woman of blood group B will produce children of all the four blood groups if both parents are heterozygous. br br Diagram Marriage between a man of genotype AA blood group A and Woman of genotype BB blood group B results in all the offsprings having blood AB. Diagram. br br Assignment br br Work out the following crosses br br Both parents with blood group O Heterozygous blood group A and blood group O br br Study Question 13 br br Inheritance of the Rhesus factor In man the possession of Rhesus antigens makes one Rh and this is dominant over Rhve. If blood from a Rhesus positive person is transfused into a rhesus negative person, this induces antibodies against the Rhesus factor of the donor. This causes agglutination of red blood cells of the recipient. If a Rh-ve woman is married to a Rhe ve, when she becomes pregnant, the child will be Rh ve. Rhesus antigens cross the placenta into the mothers blood stream. This stimulates the mothers immune system to produce Rhesus antibodies. When these antibodies get into the foetal circulation, an antigen- antibody reaction takes place and the red blood cells of the foetus are destroyed Haemolysed . During the second pregnancy, the amount of Rhesus antibodies are more and cause a lot of damage to the foetuss red blood cells resulting to death. This is called Haemolytic Disease of the Newborn or Erythroblastosis foetalis. Determining Unknown Genotypes This can be done in two ways. 1. Carrying out a Test Cross A test cross is a cross between an individual of unknown genotype with an individual of a recessive genotype. A test cross where an offspring is crossed with one of its parents is called a Back Cross. In garden pea plants the gene that determines red flowers is dominant over that which determines white flowers. A plant with red flowers may either be homozygous RR or heterozygous Rr for this characteristic. To establish its correct genotype it is crossed with a homozygous recessive plant i.e. a white flowered one rr If all their offsprings bear red flowers then this indicates that the red flowered plant is homozygous or its from a pure line. Diagram If the offsprings bear a mixture of red and white flowers in the ratio of 1:1, this indicates that the red flowered plant was heterozygous. Diagram Selfing Unknown genotypes can also be determined by carrying out selfing experiments. For example, a phenotypically tall plant is either homozygous TT or heterozygous Tt for this trait. If selfed and all its offsprings are tall, the parental genotype is TT that is homozygous dominant. br br Diagram But if after selfing both tall and dwarf offsprings are produced in the ratio 3:1 respectively, then the parental genotype is heterozygous Tt . Diagram Sex Determination The sex of an organism is a genetically determined characteristic. Cells of most organisms contain a pair of chromosomes called sex chromosomes in addition to the ordinary chromosomes. In man there are 46 chromosomes 23 pairs of homologous chromosomes in everybody cell . The genes determining whether a child becomes a female or a male are located on the specific pair of sex chromosomes called the X and the Y named after their shapes. The remaining 22 pairs of chromosomes are called Autosomes. Autosomes are responsible for other inheritable traits. A male human being carries the XY chromosome i.e. he is Heterogametic The female carries the XX chromosomes i.e. Homogametic . After meiosis in a male the spermatozoon can either carry the X or Y chromosome while the female ova contain only the X chromosome. The sex of a child is a matter of chance and depends only on whether a spermatozoon that fertilizes the ovum carries X or Y chromosome. There is therefore a 50 chance that fertilization can result in either XY Boy or XX Girl i.e. XY br br X br br Y br br I.e. 2 girls: 2 Boys In terms of probability, the chance that a boy or a girl is produced in a family is . br br NB/ in birds the female is XY heterogametic and the male is XX homogametic . br br In some insects, the female is XX and the male is XO with the Y chromosome absent. br br In the fruit fly Drosophila melanogaster sex determination br br is as exactly as in man, i.e. male XY and Female XX. br br Linkage An organism has a large number of traits controlled by many different genes. Because the number of chromosomes is limited, each gene cannot be located on its own chromosome. Therefore chromosomes must accommodate many genes each controlling particular characteristics. Those genes located on the same chromosome are called linked Genes. All the linked genes constitute a linkage group. Linked gene are inherited together and do not segregate/separate during meiosis. They are therefore transmitted into the same gamete. br br Diagram If genes Q, R and T are linked, then all the three pairs of genes are accommodated on a homologous pair of chromosome. In Drosophila sp , it has been found that the genes for wing length, abdomen size and body colour are located on the same chromosome. Therefore these characteristics are usually inherited together. Sex-linked Genes All the genes located on the sex chromosomes are said to be sex- linked . They are therefore transmitted together with those that determine the sex. In Drosophila melanogaster , the gene, which determine eye colour, is located on the X chromosome. However the corresponding allele on the Y chromosome is absent. This is because most sex-lined genes are carried on the X chromosome whereas the Y chromosome carries very few genes and is almost empty. In humans there are few genes located on the Y chromosome, which control traits that are exclusively found in males. These are, Premature baldness and tufts of hair in the in the inner pinna and in the nose. Diagrams. The characteristics controlled by genes located on the X chromosome include Colour blindness and Haemophilia. These characteristics can arise in either male or females. br br Colour blindness br br This is the inability to distinguish Red and Green colours by some people. This trait is linked to the X chromosome. The gene that determines normal colour vision is dominant over that for colour blindness. A marriage between a colour-blind man and a woman homozygous for normal colour vision results in their daughters being carriers but with normal colour vision. The daughters are said to be carriers because they are heterozygous and colour blindness is suppressed/masked by the dominant gene for colour vision. All the sons are of the two parents are however normal. This is illustrated below. Let N represent the gene for normal colour vision and n represent gene for colour blindness. Since the gene is linked to X chromosome, its alleles are represented as XN and Xn. br br Colour blind male br br Xn Y br br XnY Normal Woman XNXN All the daughters are carriers- XNXn All the sons have normal colour vision-XNY br br If a carrier daughter from the above parents married a normal man, some of their sons will suffer from colour blindness while the daughters will either be carriers or homozygous for normal colour vision as shown below. Carrier female XN Xn XNY XnY Y br br Offsprings are; XNXN vision br br -Daughter with normal colour br br XNXn XNY XnY -Carrier Daughter -Son with normal colour vision -Colour blind son. br br The above examples show that the gene for colour blindness is passed from mother to sons. br br This is because the only X chromosome a man inherits is from the mother. If the X chromosome carries the gene for the trait, then this gene will be expressed since allele on the Y is absent. Therefore there are more male sufferers in a population compared to females. br br Females only suffer when in homozygous condition of the recessive gene. Inheritance of colour blindness through several generations can be clearly illustrated using a pedigree. A pedigree is a record in table form showing the distribution of one or more traits in different generations of related individuals. Fig. 1.24 br br Haemophilia br br This is another sex-linked trait where the blood of the sufferer takes abnormally long time to clot. There is prolonged breeding in the event of a cut hence the term Bleeders Disease . A recessive gene on the X chromosome causes haemophilia. br br If a normal man is married to a carrier woman for br br haemophilia, there is a probability of that if their child is a boy will be a haemophiliac and if a daughter, she will be a carrier. None of the daughters of the couple will be haemophiliacs. Let H represent the gene for normal blood clotting and h to represent gene for haemophilia i.e. br br Carrier woman XH Xh XHY XhY Y br br -XHXH -Normal daughter br br Their offsprings will be; XHXh -Carrier daughter XHY XhY -Normal son -Haemophiliac son. br br Study question 14 Apart from carrying the sex-linked traits, the X chromosome in the females and the Y in males bring about the development of both the primary and secondary sexual characteristics. At puberty, secondary sexual characteristics in females include breast enlargement, widening of the hips, and growth of pubic hair and onset of menstrual cycle. The X chromosome controls these. In males, they include growth of pubic hair and beard, deepening of the voice, widening of the shoulders etc. br br Effects of Crossing Over on Linked Genes br br Some of the linked genes separate and are transmitted on different chromosomes. This happens during crossing over prophase I of meiosis when sections of chromatids of a bivalent intertwine and may break off. Some of these sections get rejoined to different chromatids thus separating genes that were previously linked. The fusion of such gametes containing chromatids whose genes have changed places produces new combinations recombinants . Crossing over results in chromosomal mutations, which in turn cause variations. Diagrams Mutations Mutation is brought about by spontaneous changes in the individuals genetic makeup. Mutations are normally due to recessive genes most of which are transmitted in the usual Mendelian fashion. Therefore they are quite rare. Individuals with mutations are referred to as mutants . Mutation can be induced by certain factors. Such factors are called Mutagens. They include, br br Exposure to Gamma rays Ultra violet light br br Colchicine Mustard gas br br NB: Mutations occurring in gametes are more important than those in somatic cells. Mutational changes are the basis of discontinuous variation in population. br br Types of Mutations 1. Chromosomal mutation 2. Gene mutation br br Chromosomal Mutations This involves the change in the structure or the number of chromosomes. During crossing over in meiosis homologous chromosomes intertwine at points called chiasmata. These points are later broken creating various opportunities for changes on the chromatids. There are five types of chromosome mutations chromosome aberrations . Deletion Duplication Inversion Translocation Non-disjunction br br Deletion This occurs when some sections of chromatids break off and fail to recombine. They are therefore completely lost and the genetic material they contain is said to be deleted out. Most deletions are lethal since the offspring may lose genes responsible for the synthesis of some vital protein molecules. Diagrams br br Duplication In this case a section of chromatids replicates and adds an extra length to itself. Duplication can produce serious effects depending on the chromosome sections involved. Diagrams Inversion In this case a chromatid breaks at two points. When rejoining, the middle piece rotates and joins in an inverted position. This reverses the gene sequence along the chromatid. This might bring together genes whose combined effects are advantageous or dis-advantageous. Diagrams Translocation This occurs when a section of one chromatid breaks off and becomes attached to another chromatid but of a non-homologous pair. Translocation therefore involves the movement of genes from one non-homologous chromosome to another. Diagrams br br Non-disjunction This leads to addition or loss of one or more whole chromosomes. If it occurs at anaphase of the first meiotic division, two homologous chromosomes fail to segregate and they move into the same gamete cell. If it happens at anaphase of the second meiotic division, sister chromatids fail to segregate. This results in half the gametes containing two of the same chromosome while the others have none. br br Diagrams br br Non-Disjunction causes the following br br 1. Downss Syndrome : this is where there is an extra somatic br br chromosome number 21. such individuals have; br br Slit eye appearance Reduced resistance to infections Mentally deficient Thick tongue Cardiac malfunctions Short body with thick fingers NB/ these conditions are common among children born of br br mothers above 40 years old. 2. Klinefelters Syndrome: in this case individuals have an br br extra sex chromosome. Such individuals have a total of 47 chromosomes in their cells i.e. XXY male and XXX female . This occurs as a result of non-disjunction during spermatogenesis or oogenesis. The symptoms of Klinefelters syndrome are br br Infertility in males due to lack of sperm production Under developed testes Reduced facial hair in males Very tall with signs of obesity Diagrams br br 3. Turners syndrome: This is where an individual lacks one sex chromosome hence there are 45 chromosomes XO or YO . br br 4. Polyploidy: sometimes during meiosis chromosomes might undergo non-disjunction. This results in half the number of gametes having two of each type of chromosome i.e. diploid the rest having none. If the resulting diploid gamete fuses with a normal haploid gamete a triploid zygote is formed. If two diploid gametes fuse, a tetraploid individual is obtained. This is what is called polyploidy. br br Polyploidy is rare in animals but common in plants where br br its considered to be advantageous. Polyploidy increases yields, early maturity and resistance to pests and diseases. It can be artificially induced using a chemical called colchicine , which prevents spindle formation during mitosis leading to a cell with double the number of chromosomes 4n . br br Gene Mutation br br This involves a change in the structure of a gene. Gene mutations are also referred to as point mutations. A gene mutation arises as a result of a change in the chemical nature of the gene. The change may involve some alterations in the DNA molecule. A change in the DNA molecule is passed onto the m-RNA. This alters the sequence of amino acids during protein synthesis. This may result in unintended protein molecules being synthesised, which may be lethal. Types of gene mutations; br br Insertion Substitution Inversion Deletion Insertion This is the addition of an extra base onto the existing DNA strand. br br Diagram By this insertion no polypeptide chain is formed as it were intended. br br Deletion This is the removal of a gene portion. If the base Thymine is deleted from its position as indicated below, the base sequence becomes altered at this point. Diagrams br br Substitution This is the replacement of a portion of the gene with a new portion. If Adenine is substituted by Guanine on a DNA strand, the base sequence is altered at this particular portion. Diagrams br br Inversion If a portion of the DNA strand is rotated through 1800 that portion is said to be inverted as shown below. This alters the base sequence at this point. Diagrams Study Questions Disorders Due to Gene Mutations Such disorders include albinism, sickle cell anaemia, haemophilia, colour blindness and chondrodystrophic dwarfism. br br 1. Albinism This a condition where the synthesis of skin pigment called melanin fails. The victim has a light skin, white hair and pink eyes. Such a person is referred to as an Albino. Melanin is derived from two amino acids Phenylalanine and Tyrosine. Melanin is synthesised through a series of reactions controlled by a specific gene. br br Gene A is responsible for presence of melanin and a is responsible for its absence. Gene aa in homozygous state blocks in one or two places in the synthesis of melanin hence no melanin is formed. This occurs as a result of one enzyme Tyronase failing to be formed in the presence of the recessive gene. br br A person with genotype AA has normal skin pigmentation. One with genotype Aa is a carrier and has normal skin pigmentation. In a family an albino can be born under three conditions only. If both parents are albinos If one of the parents is an albino and the other a carrier If both parents are carriers br br Assignment br br Work out crosses in each case. What is the probability of getting an albino child in br br each case? 2. Sickle Cell Anaemia This is a gene mutation as a result of substitution. Normal haemoglobin Hb A consists of two polypeptide chains. In the sickle cell condition, one amino acid called glutamic acid is substituted by another amino acid called valine in each of the two-polypeptide chains of the haemoglobin molecule. The resulting haemoglobin is known as Haemoglobin S Hb S and is different from the Hb A in several ways. Comparison between Hb A and Hb S br br Normal haemoglobin Hb A 1. A position in each polypeptide chain is occupied by glutamic acid 2. Does not easily crystallise in low oxygen concentration 3. The haemoglobin is efficient in oxygen loading and transportation Red blood cells are sickle 4. The red blood cells are shaped crescent shape biconcave in shape Sickle cell anaemia is therefore the condition where the victim is homozygous for the defective gene that directs the synthesis of haemoglobin S. Most of the victims red blood cells are sickle shaped and the person frequently experiences oxygen shortage to the body tissues. Such a person cannot carry out strenuous physical exercises. Many sickle cell victims die young due to insufficient oxygen br br Defective Haemoglobin Hb S The same position is occupied by valine in each polypeptide chain Easily crystallises in low oxygen concentration br br Not efficient in oxygen loading and transportation br br supply to body tissues. br br In the heterozygous condition, less than half the number of the red blood cells is sickle shaped. The rest are normal and efficient in oxygen transport. This is referred to as sickle cell trait . An individual with the sickle cell trait experiences a mild case of anaemia but leads a normal life. Inheritance of Sickle Cell Anaemia br br If a man with sickle cell trait marries a normal woman, the probability that any of the offspring will carry the sickle cell trait is . br br If both parents are carriers the probability of getting an br br offspring with sickle cell anaemia is . 3. Haemophilia : This condition where the blood takes br br abnormally long time to clot. A haemophilic gene that prevents the production of the clotting factors causes the condition. br br 4. Colour blindness: There are different forms of colour br br blindness. The most common one is the red-green colour blindness. In this case an individual is unable to distinguish between red and green colours. br br NB. Most disadvantageous genes are recessive. Very few are br br dominant e.g. the gene for chondrodystrophic dwarfism br br Study Question 16 br br Effect of Environment on Heredity The genotype and the environment influence the development of an individual. In animals genetically identical individuals reared under different environments will appear different than those reared under very different conditions. Consider identical twins. Practical Applications of Genetics o Plants and animal breeding o Blood transfusion o Genetic counselling o Genetic engineering br br 1. Plants and Animal Breeding br br Man chooses those plants and animals with the desirable qualities. This is referred to as artificial selection. Inbreeding or crossbreeding does this . Inbreeding however increases the chances of undesirable genes whereas crossbreeding increases heterozygosity with the offsprings having better performance than both parents. This is referred to as hybrid vigour e.g. a cross between Boran and Hereford. Polyploidy has also been used in planting. The original wheat had a diploid number of 14 chromosomes but the commercial wheat has either 28 or 42 tetraploid-4n or hexaploid-6n . Examples of characteristics, which have been selected in agriculture. br br 1. Resistance to diseases e.g. cassava resistant to cassava br br mosaic, coffee variety resistant to CBD. br br 2. Early maturity in animals and plants. 3. Adaptations to various conditions e.g. rainfall, temperature br br etc. br br 4. Ease of harvesting e.g. in coffee and bananas where dwarf 2 Blood Transfusion br br Before blood is given to a recipient, blood typing is first done. This is done to ensure compatibility between the donor and the recipient. Blood typing also can be used to solve disputed parentage. However the most recent technique in establishing parentage is the DNA matching. br br 3 Genetic Counselling This is the provision of information and advice on genetically inherited disorders to individuals. The individual is given such advice to enable him or her make the best choice. br br Examples of disorders for which genetic counselling may be done include br br Sickle cell anaemia Haemophilia Albinism Erythroblastosis foetalis Colour blindness Klinefelters syndrome br br In order to confirm the disorder the doctors can do the following Physical examination e.g. Lack of breasts in Turners br br syndrome. br br Laboratory tests e.g. blood tests to confirm sickle cell br br anaemia br br Amniocentesis for chromosomal abnormalities in br br foetus br br Family history may be used to determine possible br br inheritance of the disorder e.g. haemophilia. Genetic screening of the defective gene in the br br population a Identify the nerve cell. br br 1mark br br b i Give a reason for your answer in a above br br 1mark ii Show by use of an arrow the direction of flow of br br the nerve impulses. 1mark 2. Below is a diagram showing parts of a synapse observe and other the questions that follow. br br a Name the parts labeled: A, B. br br 2mks br br b What is the role of part labeled C . br br 1mk br br 3. below. br br A student set up an experiment as shown in the diagram br br br br Light br br Box with black paint br br Seedlings br br The set up was left for 4 days. a What was the aim of the experiment. br br 1mk br br b i State the expected results after 4 days. 1mk ii Account for the results you have stated in b i above. br br 4mks br br c In another experiment, a student placed a seedling horizontally on moist cotton wool. Later the shoot grew upwards while the Radicle grew downwards. Explain why the radicle showed a downward curvature. br br 2mks br br 180 a Name the parts labelled. A, B br br 2mks br br b State three adaptations that enable the neurone to br br carry out its functions efficiently. 3mks br br c State two features that would distinguish sensory br br neurone from the above neurone. 2mks 6. The diagram below shows the structure of its human ear. br br C D G J H br br a State the functions of the ear. 2mks b Give the names of the structure labelled C,G and F. br br 3mks br br c i What is the function of the structure labeled H? br br 1mk br br ii Name the structure in the ear that detects sound waves. br br 1mk br br d In which structure of the ear is the velocity of the sound waves fastest? 1mk br br 7. The diagram below represents a nerve cell. Study it and answer the questions that follow. b Name the parts labelled N, P, Q and R. br br 4mks br br c State the functions of the parts labelled N and Q. br br 2mks br br 8. Use the diagram below to answer the questions that follow br br br br a i Name the eye defect represented above br br 1 mk br br ii What is the cause of this defect br br 1 mk br br iii How can the defect you have named a i be corrected? 1 mk br br 9 The diagram below shows three different types of neurones br br along a reflex arc br br a Identify the neuron labelled 1 ,2 and 3 br br 3 mks br br b Using arrows show the direction of impulse transmission on the diagram c Name the part of the spinal cord where the cell bodies of neurone 2 and 3 are located 1mk d Describe the transmission impulse across the part labelled P br br 1 mk br br 3 mks br br 10 A response exhibited by a certain plant tendril is illustrated below br br i Name the type of response br br 1mk br br ii Explain how the response named in i above br br occurs. 3mks br br iii What is the importance of tactic responses to br br microscopic plants? 1mk br br 11 Describe how the mammalian ear is adapted to perform its functions. 20mks br br 182 12. a Describe how the structure of the eye is adapted to its function. b rectified. br br 16mks br br Identify two defects of the eye and how they can be br br 4mks br br 13 Differentiate between nervous and endocrine br br communication in animals 3mks br br 14. The diagram below represents a section through the br br mammalian ear. Study it and answer the questions that follow. br br br br a Name the structures labeled H and J br br 2mks br br b State how the structures labeled H, M and N are adapted to their functions c State what would happen if the structure labeled K was completely damage 1mk d Name the fluid contained in structure N br br 3mks br br 1mk br br e Apart from hearing, state the other role performed by the human ear 1mk br br 15 The following experiment was set up in a chamber made from two connected Petri dishes. Housefly maggots were introduced at the centre of the chamber, so the maggots could move to either Petri dish A or B as shown below. br br a Name the type of response being investigated in the set up. 1mk br br b State the survival value of the response named in a above. 1mk br br 183 c Give the role of calcium chloride in the experiment above. 1mk br br 16 a What is accommodation? 1mk br br b Describe the sequence of events that occur in the eye br br for one to be able to see clearly br br i a distant object br br 4mks br br ii if one moved from a dim lit room to bright light. 3mks MARKING SCHEME STIMULUS AND RESPONSE REVISION QUESTIONS 1 a Motor neuron/Motor nerve cell; br br b i cell body is terminally situated/located at the end of the axon; br br ii Arrow should point away from the cell body br br 2. a A-Synaptic cleft B- Mitochondria br br b Contains the transmitter substance/ Acetylcholine. br br 3. seedling / plants; br br a Show the effect of unilateral light on growth of br br 1mk br br b source light; br br i Curvature of the tip of the shoot toward the br br Auxins / IAA/ Growth harmones; produced by the apical bud; move away from light / move to the dark side; causing faster elongation; hence curvature; br br ii br br c br br In the roots / radicle higher concentration of auxins / IAA inhibits growth; hence the upper side with less auxins grows faster than the lower side; hence curvature downwards br br 2mks br br 4. Phototropisms; for maximum photosynthesis; Allows for leaf mosaic; Chemotropism; -Growth curvature in response to contact/ hard surface; br br -enables plant shoots to grow and get light br br -Make plants with weak stems to get support on large br br plants /trees; this makes then to br br reach and get light for maximum photosynthesis; br br Geotropism; -Growth curvature in response to gravity; enables plant roots to grow deep into the soil to Maximum support/ anchorage; br br Hydrotropism; - Growth curvature in response to moisture / water; br br - Enable plant roots to grow and find water in br br the soil; water is then used as a raw material During photolysis stage; Chemotropism; -Growth curvature in response to chemical concentration gradient; br br - Enables pollen tubes to grow down the style and into the ovary for fertilization to occur in plants flowers; br br Thermo tropism; -Growth curvature in response to temperature changes; br br -Enables some plants to grow to where they can acquire optimum temperature for effective plant processes; e.g. Sunflower orientates towards the directions of the sun. br br 5 a A- B-Cell body br br Dendrites br br b br br - Has long axon to conduct impulses from CNs to effectors / muscles / glands; - Axon enclosed with myelin sheath with nodes of ranvies to enhance speed of impulse conduction. br br - Has dendrites which receive impulses from br br adjacent neurones. br br c S.N - Cell body has no dendrites -Cell body has dendrites - Cell body at a point along nerve fibre; -Cell body located at the top of nerve fiber; 6 a br br - Hearing / detection of sound; Body balance / posture; br br 2marks. b br br i C- Ear canal / External auditory meetas; ii G- Semi Circular canals; iii F- Auditory nerve; br br 3marks br br c i Equalise air pressure between middle ear br br and outer ear / prevent damage of ear drum; br br 1mark ii Cochlea/ E; br br 1mark d 1mark a 7. i br br Sensory neurons / afferent neurone ii Cell body located off the axon br br b N- Axon br br P- Cell body Q- Myelin Sheath Schwann cell R- c N- Transmission of impulse br br Q- Insulation / speed up impulse transmission. br br 8 a Long sightedness / Hypermetropia ; br br 1 mk br br b Short eye ball; br br Weak lens any one ;1 mks br br c Wearing of convex lens / conveying lenses; 1 mk br br rj if a i is wrong br br 9 a 1- Sensory neurone / Afferent neurone br br 2- Relay neurone 3- Motor neurone/ efferent neurone br br / intermediate neurone br br 3 mks br br b 3 from 2 and 1 : c Grey matter 1 mks Impulse reaching the dendrites end of relay / Neurone 2 causes the synaptic vesicles, releases acetylcholine / transmitter substances; into the synaptic cleft;the acetylcholine / transmitter chemical diffuses across the cleft; and causes the depolarization of the motor neuron/ neurone br br Check on the diagram arrows show points towards neurone br br 1 mk i Name the type of response 1mk br br 10 Thigmotropism/Haptotropism; br br ii Explain how the response named in i br br above occurs. 3mks br br Contact with support; causes migration of auxins to the outside; causing faster growth on the side away from contact surface; Causing dendrils to curl around the support ; br br NB a ii is tied to i iii What is the importance of tactic responses to br br microscopic plants? 1mk br br Escape injurious stimuli/seek favourable habitat br br Rej. Seek mate and obtain food br br 11. Describe how the mammalian ear is adapted to perform its functions. 20mks br br The pinna is flap made of skin and cartilage; for collection and concentration of sound waves; Auditory canal/meatus is a tube lined with hairs which trap solid particles like dust; It has wax secreting cells; that secrete wax for trapping solids and insects entering the ear; br br The eardrum/tympanic membrane is thin with double br br layer of epidermis; It vibrates translating sound waves into sound vibrations; Sound vibrations are transmitted to ear ossicles; br br Ear ossicles are malleus, incus and stapes; they br br amplify and transmit vibrations to the oral window; The oval window is a thin membrane which transmits br br sound vibrations to the fluid of the inner ear; perilymph and Endolymph; br br Eustachian tube connects middle ear with pharynx equalizing air pressure in the ear with atmospheric pressure; to prevent distortion of the eardrum; The cochlea is highly coiled tube with system of canals and sensory cells to occupy a small space/increase the surface area for accommodating many sensory cells to detect sounds vibrations; and generate impulses transmitted to the brain; br br Auditory nerve transmits nerve impulses to the brain br br for interpretation; br br Semicircular canals are tubular cavities containing br br fluid; br br The canals are arranged at right angles to each other in the three planes of spaces; to detect changes in position of the body; the canals have ampulla: utriculus and sacculus; to detect position of body in relation to gravity; br br Utriculus has otoliths attached to sensory cells which generate impulses which are then transmitted to the brain through the auditory nerve; br br The perilymph and endolymph fluid in the inner ear br br absorb mechanical shock/transmit sound vibrations/protect delicate parts; Total 25 max 20 marks a br br 12 enter eye br br i Conjunctiva transparent allow light to br br ii Cornea transparent / curved allow light / refracts light br br entering eye; br br iii Aqueous / vitreous humour clear / allow light pass / br br refract light, hydrostatic pressure br br Maintain shape of eyeball. Contains sugars / proteins / br br salts provide nutrients to eye. br br iv Iris contractile controls light intensity / amount of br br light entering eye; v Ciliary body glandular secretes humuor vi Ciliary muscle contractile controls curvature of lens; vii Suspensory ligament fibrous holds lens in position viii Lens transparent / Biconvex allow light go through to retina / refract light / focus light. br br ix Retina rods - rhodopsin for dim light vision; br br - Iodopsin for bright light vision br br x Fovea centralis high concentration of cones for accurate vision xi Choroid layer blood vessels pigmented nutrition br br for - reduce light reflection / absorb stray light br br xii Sclera fibrous protection / give eye shape; xiii Optical nerves sensory neurone transmit impulse from retina to brain. xiv External eye muscle contractile move eyeball within socket xv Blind spot cone and rods absent no image is perceived br br Correction br br b i Short sightedness; lens br br biconcave / diverging br br ii Long sightedness; iii Astigmatism; iv Squinting; converging lens / convex lens use of cylindrical lens any 2 surgery br br identify correction 4mks br br 13. communication br br Nervous communication Endocrine Response br br - High speed of transmission- Low speed of br br transmission; br br - Rapid response - Impulse transmitted through neurone - Hormones br br - Response delayed br br transmitted in blood br br - Responses specific and localized to one - br br Responses affects several parts of the br br Target organ body; br br Note: Comparison should come out clearly to award. br br 14. a H Eustachian tube; br br J Semi-circular canals; br br b H Tube open/ connection to the pharynx and to the br br middle ear/ opens during swallowing/ yawning and vomiting to equalize the air pressure in the middle ear with the atmospheric air pressure; br br M pinna curved/ funnel shaped to receive or br br collect and direct sound waves into the ear; br br N cochlea long/highly coiled/ spiral in form to br br increase surface area for sound Perception; br br - Has sensory hairs/ cells which convert sound br br vibrations to impulses/ generate impulses; br br - Has endolymph to transmit vibrations; br br Mark one for each structure. Rej. If the adaptation is not tied to function. br br c Total deafness; d Endolymph; e Balance; acc body balance/ posture. 15 a Tactic response; br br b Move away from a harsh environment/move to favorable environment; br br c To absorb any moisture from Petri dish A/OWTTE br br 16 . a A reflex mechanism/ability of the eye to adjust to bring an image from near or far object into sharp focus on the retina; b Circular muscles of the iris contract; while the radial muscles relax; Ciliary muscles relax; increasing tension on suspensory ligaments; lens become thinner increasing the focal length; image focused onto the retina; SUPPORT AND MOVEMENT IN PLANTS AND ANIMALS br br Support is the ability of organisms to bear their weight and maintain their body forms. It involves holding body parts in their position and allow for movement. br br Movement is the displacement of parts of the body of an organism e.g. growth movements in plants and limbs in animals. br br Locomotion is movement of the whole organisms. br br Support and Movement in Plants br br This can be at cell level e.g. gametes in bryophytes and Pteridophytes or at organ level in tropic and nastic responses. br br Importance of Movement in Plants i. Enable plants to obtain resources such as sunlight, water br br and nutrients due to tropic and nastic responses. ii. Enhances fertilization in bryophytes and Pteridophytes iii. Enhance fertilization in flowering plants by growth of br br pollen tube towards the embryo sac. br br iv. Helps plants to escape harmful stimuli such as high br br temperature br br Importance of Support in Plants i. Hold flowers in position for pollination to occur. ii. Help plants to withstand forces of the environment such as br br gravity and air currents. iii. Fruits are held in appropriate position for dispersal to br br occur. Increase the efficiency of photosynthesis as the leaves are firm and arranged in mosaic pattern for maximum absorption of light and carbon iv oxide. br br iv. br br Arrangement of Tissues in Plants Diagrams Parenchyma. The cells are spherical or elongated. They are br br unspecialized cells forming the packing tissues. When turgid, they help in providing support in herbaceous plants. br br Collenchyma. Its underneath the epidermis. They are similar in appearance to parenchyma and they contain living protoplasm. They have deposition of cellulose to provide mechanical support. They are mainly found in young leaves and stems. br br Sclerenchyma. They appear as long fibres in stems. Cells are dead and they have lignin. Mainly found in stems and midrib of leaves. The walls are pitted to allow exchange of substances between cells. br br Xylem vessels and Tracheids. Xylem vessels are long tube like structures with lignified walls used for transporting water and mineral salts and also give plant mechanical support. Tracheids are long cells with tapering ends whose walls are lignified to give the plant mechanical support. Both xylem vessels ant tracheids are made of dead cells manly present in woody stems. br br Tendrils and Climbing stems. Some herbaceous plants br br support themselves by use of tendrils e.g. pumpkins, garden peas etc. Others obtain support by twinning round other hard objects such as stem of passion fruit, morning glory etc. br br Spines and Thorns. Some plants use spines and thorns to br br attach to solid objects for support e.g. in rose. Practical Activity 3 br br To Observe Wilting in Plants Support and Movement in Animals br br Animals have a firm and rigid framework for support called br br the skeleton. br br Importance of Movement in Animals br br 1. Enable searching of food, mate and shelter. 2. Move to avoid predators. 3. To colonize new areas 4. Move from areas with unfavourable conditions such as fire, br br earthquakes, flood etc. Types and Function of Skeletons br br 1. Hydrostatic skeleton It is found in soft bodied animals such as the earthworm. 2. Exoskeleton It is made of the external covering found in arthropods. Its made of waterproof cuticle which contains the protein br br Chitin secreted by the epidermal cells. br br Functions of the Exoskeleton i. Reduces water loss ii. Protection against microbial infections and mechanical br br injury br br iii. Support body tissues and organs. iv. Provide point for attachment of muscles allowing br br locomotion to take place. br br v. Enhance flight in insects by means of wings which are the br br flattened parts of the exoskeleton. br br vi. Enhance walking in insects using jointed appendages. NB/. br br 1. Exoskeleton has a disadvantage as it limits growth. To overcome this limitation it is periodically shed through moulting ecdysis . 2. Insects that jump or hop have powerful hind limbs. The femur of the hind limb has powerful antagonistic muscles. br br Diagrams 3 Endoskeleton. It is found in all vertebrates. Muscles are external to the hard framework. It is made of living tissues either cartilage or bone which br br increase in size as the animal grows and therefore need not to be shed as in exoskeleton. br br Functions of the Endoskeleton i. Supports the animals body ii. Gives the body its shape iii. Protects inner delicate organs such as the lungs, heart, liver br br etc from mechanical injury e.g. ribs. br br iv. Provide surface for muscle attachment facilitating br br movement. br br v. Production of blood cells i.e. the long and short bones vi. Acts as a reservoir of calcium and phosphate ions in the br br body br br Locomotion in Finned Fish Tilapia Diagrams Practical Activity 5 Practical Activity 6 br br How a finned fish is adapted to locomotion in water 1. Streamlined body/ tapered anteriorly and posteriorly; to br br minimize water resistance; br br 2. Inflexible head; to maintain forward thrust; br br 3. Overlapping scales facing posterior end; to bring about less br br resistance; Overlapping of scales also prevents wetting of the skin; br br 4. Slimy/oily substance to moisten scales; hence reduce br br resistance between water and fish; br br 5. Swim bladder; air filled cavity which controls/ brings br br buoyancy; and depth at which it swims; br br 6. Flexible backbone /series of vertebrae with Myotomes/ br br muscles blocks; which contract and relax alternately bringing about thrust/force; which propels fish forwards; br br 7. Pectoral and pelvic fins paired fins ; which bring about br br balancing effect; braking; and changing direction; they also control pitching i.e. control upward and downward movement; br br 8. Dorsal fin, caudal fin and anal fin unpaired fins ; to increase vertical surface area; and therefore prevent rolling from side to side; and yawing; br br 9. Tail fins/caudal fins that are long and flexible; for steering/ br br more force/ thrust; br br 10. Lateral line has sensory cells; which enables to perceive vibrations; hence can locate objects so that it escapes / changes direction; Support and Movement in Mammals Diagram of a human and rabbit skeleton br br The skeleton is divided into: br br Axial skull, sternum, ribcage and vertebral column. Appendicular consists of girdles and the limbs attached to br br them Axial Skeleton 1. Skull Made up of many bones fused together to form the br br cranium. br br The bones are joined together forming immovable joins br br called Sutures . br br Cranium encloses and protects the brain, olfactory organs, br br the eyes, middle and inner ear. br br Facial skeleton has a fixed upper jaw called maxilla and a br br movable lower jaw known as the mandible. br br At the posterior end, there are two smooth rounded br br projections called occipital condyles. These articulate with the first bone of the vertebral column atlas forming a hinge joint. This joint permits nodding of the head. 2. Ribcage and sternum Ribcage encloses the thoracic cavity protecting delicate br br organs such as the lungs and heart. br br Cage is made up of ribs that articulate with vertebral br br column at the back and sternum to the front. br br In birds, the sternum is modified to form the keel which br br gives a large surface area for attachment of flight muscles. br br Ribcage and sternum help during breathing because they br br offer the surface for attachment of the intercostals muscles. br br 3. Vertebral column Consists of bones called vertebrae that are separated from br br each other by cartilage called inter-vertebral discs. br br The discs absorb shock and reduce friction. It also makes br br the vertebral column flexible. br br There are five types of vertebrae in the vertebral column; 1. Cervical vertebrae 2. Thoracic vertebra 3. Lumbar vertebrae 4. Sacral vertebrae 5. Caudal vertebrae br br All the vertebrae have a common basic plan. Structure of a Vertebra Each vertebra is made up of the following parts. i. Centrum body . It supports the weight of the vertebra and the weight of the entire vertebral column.. ii. Neural arch. It encloses the neural canal. iii. Neural spine. Provides surface for muscle and ligament br br attachment. br br iv. Neural canal. It protects the spinal cord which passes br br through it. br br v. Transverse processes. Provides surface for muscle and br br ligament attachment. br br vi. Zygapophysis facets . These are smooth patches for br br articulation with the other vertebrae. The one in front and the other one behind . The front facets are called Pre - Zygapophysis while the back pair facets are called Post- Zygapophysis br br Diagram br br 1 Cervical vertebrae a Atlas First cervical vertebra Distinctive features. i. No Centrum ii. Broad and flat transverse processes. iii. Has vertebraterial canal in each transverse process for br br vertebral arteries to pass through. br br iv. Front facets are large and grooved to articulate with condyles of the skull to allow nodding on the head. br br v. Neural spine is very small. Diagram br br Functions br br i. Protect the spinal cord. ii. Provide surface for muscle attachment. iii. Allows head to nod. b Axis second Distinctive features. br br i. Centrum prolonged to from the odontoid process. ii. Has vertebraterial canal in each transverse process for br br vertebral arteries to pass. br br iii. Small wing like transverse processes. iv. Wide neural canal. Functions br br i. Protects the spinal cord. ii. Allows the head to rotate. Odontoid process forms a peg br br which fits into the neural canal of the atlas. br br iii. Provide surface for muscle attachment Diagram c The other cervical vertebrae. Distinctive features i. Short neural spine ii. Transverse process divided and broad. iii. Has vertebraterial canal in each transverse process for vertebral arteries to pass through. br br iv. Wide centrum br br Diagram br br Functions br br i. Provide surface for attachment of neck muscle. ii. Protect the spinal cord. iii. Supports the weight of the head. 2 Thoracic vertebrae Distinctive features br br i. Long neural spine pointing backwards. ii. Large centrum. iii. Short transverse processes. iv. Tubercular facets on each transverse for articulation br br with tuberculum of the rib. v. Two pairs of capitular demi-facets for articulation with br br capitulum of the rib. br br Diagram Functions br br i. Helps to form the rib cage. ii. Provides articulation for one end of each rib. iii. Protects the spinal cord. iv. Provides surface for muscle attachment. 3 Lumbar vertebrae Distinctive features i. Large broad centrum to offer support. ii. Broad neural spine. iii. Broad and long transverse processes. iv. Have extra processes like metapophysis, anapophysis and br br hypapophysis . br br Functions i. Protects the spinal cord. ii. Provides surface for muscle attachment. iii. Protect and support the heavy organs in the abdominal br br cavity. br br iv. Supports the heavy weight of the upper part of the body. br br 4 Sacral vertebrae Distinctive features 1. All sacral vertebrae fused to form sacrum 2. Transverse processes of first sacral vertebra large and wing br br like for articulation with pelvic girdle 3. Pairs of holes on the lower surface for the spinal nerves to br br pass through. br br 4. Sacrum is broader on the front side and narrow towards the br br tail. br br Functions br br 1. Protects alimentary canal on dorsal side. 2. Provides attachment to hip girdle 3. Protects the spinal cord 4. Provides attachment for the muscles br br Diagram Diagram br br Biology Form 1-2 Work Revision 1. A student set up materials in an experiment as shown below. br br Sugar solution m br br Fresh potato br br Boiled br br potato br br Water b If the experiment set up was left over-night, state br br observation in the set up A and B. 2mks c Account for the observations in each set up. br br 3mks br br d If another experiment C was set such that nothing is placed in the potato cup, state and explain the results that would have 2mks been obtained. 2. An experiment was carried out to investigate, haemolysis br br of human cells. The red blood cells were placed in different concentration of sodium chloride solution. The percentage of haemolysed cells was determined. The results were shown in the table below. br br Salt conc. g/100cm3 Red blood cells haemolysed br br 0.33 0.36 0.38 0.39 0.42 0.44 0.48 br br 100 91 82 a i On the grid provided plot a graph of haemolysed red blood cells against salt concentration. 6mks ii At what concentration of salt solution was the proportion of haemolysed cells equal to non-haemolysed cells? 1mk iii State the percentage of red blood cells haemolysed at salt concentration of 0.45. 1mk b Account for the results obtained at: i 0.33 salt concentration br br 3mks br br ii 0.48 salt concentration br br 3mks br br c What would happen to the red blood cells if they were placed in 0.50 salt solution. d Explain what would happen to onion cells if they were placed in distilled water. 3mks 3. Explain how various environmental factors affect the rate of transpiration in plants. 4. br br 3mks br br 20mks br br a State the meaning of the following terms. i Digestion 2mks ii Ingestion 2mks b Describe the process through which a piece of ugali undergoes in man from the time of ingestion up to the time of absorption. 16mks br br 6. The diagram below represents a unit of gaseous exchange in man. Study it carefully and answer the questions that follow. br br br br B A br br G H G D br br br br E br br br br a Name the blood vessel that brings blood to the lungs and br br the vessel which takes blood away from the lungs. br br 2mks br br b Name the structure above. 1mk c Label A and E. br br 2mks br br 198 d In what form is carbon IV oxide transported in structure br br labeled E . 1mk br br e Name the gas G . 1mk br br 6. Gastrin is a hormone produced by mammals. a i Where is the hormone produced? br br 1mk br br ii What is the function of gastrin? br br 1mk br br b What stimulateds the production of gastrin. br br 1mk br br c The diagram below shows part of the human intestine. br br br br i and B br br Identify the parts labeled A br br 1mk br br ii To which circulatory system does the part labeled B br br belong. d State any two adaptations of the human large intestine to 2mks its function. 7. The diagram below represents part of a xylem tissue. br br 1mk br br a i Name the br br parts labeled P and Q 2mks br br ii Give the function of the part labeled P . br br 1mks br br b State the function of the phloem tissue. br br 1mk br br c i State how the functioning of the phloem tissue is affected if the companion cell is destroyed. 1mk br br ii Give a reason for your answer. br br 1mk br br d State any two structural differences between phloem and 2mks xylem tissues. br br 199 8. In an experiment to determine the effect of exercise on the br br concentration of lactic acid in blood, the following data was obtained. Study the data and use it to answer the questions that follow. The lactic acid concentration was measured before, during br br and after the exercise. Time minutes Lactic acid conc. arbituary units a Using a suitable scale, plot a graph of the concentration of lactic acid against time. 6mks b From the graph you have drawn determine i The period of exercise . Explain. br br 0 10 20 25 30 40 50 60 70 80 90 100 br br 0.5 0.5 5 13 12 8 6 4 3 2 1 0.9 br br 2mks br br ii The time when oxygen debt occurred Explain. br br 2mks br br iii The duration it took to pay back the oxygen debt.Explain 2msk br br c On the same set of axes plot a hypothetical curve for oxygen intake during the experiment period of 90 minutes. br br 2mks br br d Why does lactic acid level usually continue to rise in the br br blood after exercise ceases. 2mks br br e Suggest the two importance of anaerobic respiration to animals. 2mks br br d What is oxygen debt? br br 2mks br br 9. What is the role of the liver in the maintance of a constant level of materials in the body. 10.The diagram below represents a simple respiratory pathway in cells br br 20mks a Name the process marked X and Y. 2mks br br b State two differences between process X and Y. br br 2mks br br c State the name of substance B and condition under which it 2mks is formed. d Explain how body size affects the rate of respiration in 2mks animals. 11. The diagram below represent the structure of a nephron. Study it and answer the questions that follow. br br X C C br br a i State the physiological process by which solutes are selectively re-absorbed back into blood at the part labelled B. br br 1mk br br ii How is the part labeled B adapted to carry out the physiological process named in 3 a i above. br br 1mk br br b In which part of the kidney is the part labelled A abundantly found. c On the diagram above , indicate the direction of flow of blood using arrows at the part labelled C. 1mk e State the functions carried out by the following hormones in the functioning of the nephron. i Aldosterone. 1mk br br 1mk br br ii Anti diuretic hormone. br br 1mk br br 12. The data below shows the rate of photosynthesis at different temperature in attached leaves of three East African plants. Crotolaria, Gynandropsis and Amaranthus species respectively which were grown outside with the same illustration while water and carbon IV oxide are not limiting factors in this experiment. Rate of photosynthesis was expressed interms of carbon IV oxide uptake in mg/mm2/hr at various temperatures as tabulated below. br br Rate of photosynthesis mg/mm2/hr br br Temperature oC br br Gynandropsis sp - 22 50 60 80 85 80 73 66 2 Crotolaris sp 20 40 49 64 48 45 42 31 15 - Amaranthus sp - 10 27 42 55 54 50 45 40 11 5 10 15 20 25 30 35 40 45 50 a Represent the results graphically rate of photosynthesis against temperature b Using the graph in a above indicate optimum temperature for the Gynandropsis and Amaranthus species. br br 2mks br br Gynandropsis Amaranthus c Give a reason why Gynandaropsis and Amaranthus could not function photosynthetically at 5oC. 1mk d What are the possible ecological habitats for the following plants. 2mks i Amaranthus ii Crotolaria e At what temperature was the amount of carbon IV oxide around the leaf of Gynandropsis highest? br br 1mk br br f What raw material is required in the light stage of photosynthesis. g Name the parts of chloroplasts in which the following stages of photosynthesis take place. 2mks i Light stage ii Dark stage br br 1mk h State one structural similarity and difference between chloroplast and mitochondria. Similarity Difference i What is the compensation point of photosynthesis? br br 2mks br br 1mk br br 13 a Explain why plants lack elaborate excretory organs like those found in animals. b Name five methods of excretion in plants. br br 3mks br br 5mks br br c State any six excretory products in plants and give economic uses. 14. During a laboratory investigation, a scientist extracted gastric juice from the mammalian stomach. He used it to carry out tests on a food sample B which was suspected to contain proteins. He divided the food sample B into three portions and treated them as below. br br 12mks br br I. On the 1st portion of B, he added Gastric juice and mixed them thoroughly before adding sodium hydroxide followed with copper II sulphate drop by drop. br br II. On the 2nd portion of B, he added boiled gastric juice and mixed them thoroughly before adding sodium hydroxide followed with copper II sulphate drop by drop. III. On the 3rd portion of B, he added Gastric juice, sodium bi-carbonate and mixed them thoroughl before adding sodium hydroxide followed with copper II sulphate drop by drop. a State the observations he made in each set up. br br 3mks br br - 1st portion - 2nd portion - 3rd portion br br b Why was the experiment on the 1st portion included in the tests? c Name the property of the chemical being investigated in 1mk these tests. d Account for the observations made in 2 a above. br br 1mk br br 3mks br br 15. The diagram below illustrates circulation in certain organs of the mammalian body. br br br br Heart br br Small Intestines B br br A Liver C br br 203 a Identify the blood vessels represented by A, B and C. br br 3mks br br b Explain why blood from the small intestines goes to the liver before it goes to any other organ of the body. br br 2mks br br c Compare the blood in vessels B and C. br br 1mk br br d Outline how a glucose molecule in vessel A finally reaches the heart. 1 6. The table below shows how the internal temperature two animals X and Y varied with the external temperature. The temperature was measured regularly and recorded for 12 hours in a day. Study the table and answer the questions that follow. br br 2mks a Using the same grid, draw graphs of external temperature, and internal temperature of animals X and Y Y-axes against time X-axes . br br 7mks br br b Account for the variation of internal and external temperatures for the animals X and Y. 2mks c Identify the classification of organisms whose internal temperature varies as X and Y d Explain two ways used by organism Y to make its internal temperature vary as shown despite of changes in external temperature. 4mks 18 a Give the functions of the skin in organisms. 6mks br br 2mks br br b How is the mammalian skin modified to enable it perform its functions? 19. The diagram below shows how gaseous exchange occurs across the gills in fish. br br l4mks i Give the term used to describe this flow. br br 1 Mark br br ii Explain the advantage of the above flow named in a i above. br br 2 Marks b What difference would be observed if water and blood flows across the gills in the same direction? 2 Marks br br c In which structures in the gills does gaseous exchange take place? 1 Mark d Name two organs in man which display the flow system named in a i . 2 Marks br br 20. An experiment was carried out to investigate the effect of different concentrations of Sodium Chloride on human red blood cells. Equal volumes of blood were added to equal volumes of salt solutions of different concentrations. The results were as shown below:- Set up br br Sodium Chloride concentration br br Shape of red blood cells at the of end experiment Normal Swollen br br Number of red blood cells at the of end experiment No change in number Fewer number br br A B 0.9 0.3 br br in a If the experiment was repeated with 1.4 Sodium Chloride solution, state the results you would expect with reference to:- i Number of red blood cells. 1 Mark br br ii Appearance of red blood cells when viewed under the 1 Mark microscope. Account for the fewer number of red blood cells in 0.3 Sodium Chloride salt solution. c Give the biological term which can be used to describe 0.9 Sodium chloride solution. 1 Mark d Define plasmolysis. br br 3 Marks br br 1 Mark B- Remain the same; br br iii A Surrounding the cube is a region with high br br concentration of water molecules while in the crystals, there are very few water molecules; The sugar crystals exert on Osmosis pressure by Osmosis water molecules move across the potato tissue, which acts as a semi-permeable membrane. The level rises; br br sugar br br B- No change since boiling denatures the membrane br br structure of potato cells; br br iv C- No water moves into the potato cup/remains the br br same; since there is no concentration gradient; 2 a i Graph. br br ii 0.402 0.01 iii 11 1 . br br b i All cells have been haemolysed; cells contains one hypertonic to salt solution; water enters cells by osmosis; cells swell and eventually burst. br br ii No cells were haemolysed; cell contents were isotonic the cell was equal br br to salt solutions aments of water entering to that leaving the cell ; no net movement of water into cells; br br c The cells would become crenated; the cell contents would be hypotonic to salt solutions; water would leave cells by osmosis; membranes would shrink. d Contents of Onion epidermal cells would be hypertonic to water; water would enter cells by Osmosis; cells would become turgid; 3. transpiration; high temperature increases the atmosphere to hold water and moisture; also heat increase internal temperature of the leaf 4 accept converse br br - Temperature;- High temperature faster rate of br br capacity of - Atmospheric pressure; Low atmospheric pressure, high br br rate of transpiration 2 br br - Humidity; Low humidity higher rate of transpiration; low humidity increases the saturation defiant; hence water moves form leaves to drier atmosphere; 4 br br - Wind; When it is windy the rate of transpiration is higher; wind sweeps away vapour that has accumulated at the surface of leaf; increasing saturation deficit; hence faster rate of transpiration 5 br br - Light intensity; High light intensity faster rate of br br transpiration high light intensity increase hence stomata opens; 4 br br photosynthesis rate - Amount of water in soil; More water in the soil br br increases the rate of transpiration; it wets the xylem is wet throughout ; 3 Max 20 4. a Define digestion and ingestion. br br xylem ensure br br i Digestion- It is break down of complex insoluble; food substance into simple soluble food substance; ii Ingestion- is introduction of food through the mouth br br into the digestive system; br br b Describe the digestion of Ugali. - br br Digestion of ugali begins in the mouth; ugali is chewed by the teeth to increase large surface area for action of salivary amylase/ptyalin; The food mixes with saliva produced by salivary glands; br br - Saliva contains mucus and enzyme ptyalin. Mucus moistens, softens and lubricates the food; ptyalin speeds up the conversion of starch to maltose; ugali is made into bolus in the mouth; br br - The bolus moves along br br the oescophagus and prestalsis/by contraction and relaxation of circular and longitudinal muscles into the stomach; - The digestion continues until ugali become acidic contain since carbohydrase/carbohydrate digesting enzymes no digestion of ugali takes place here. br br the stomach br br - Ugali now moves into duodenum by peristalsis in form of acidic chime; where it mixes with the bile the juice from liver and pancreatic from pancreases; bile being alkaline neutralizes the stomach acid; and provides a suitable alkaline medium for the enzymes to act on carbohydrates; - Pancreatic juice contains three enzymes out of the which enzyme amylase speeds conversion of starch to maltose; br br - When food reaches the ileum; it mixes with intestinal juice which contains several enzymes. Maltase speeds up conversion of maltose to glucose; br br - Lactose which speeds up conversion of lactose to glucose and galactose; sucrase which speeds up conversion of sucrose into fructose and glucose; br br - Absorption glucose, br br the end product of all carbohydrates diffuses through the epithelium of villi and capillary walls and enters into blood stream and is carried to the liver via hepatic portal veins; br br - Assimilation- in the liver excess glucose is converted br br into glycogen and stored; br br - - The rest of the glucose is carried by the blood tissues where is oxidized during tissue respiration to release energy; 21 max 18 mks Total 20mks br br a - Pulmonary artery - Pulmonary vein b Alveolus c A - cavity of alveolus E Red blood cell d Hydrogen carbonate ions; Carbamino haemoglobin; a i Walls of stomach; ii Stimulates the secretion / production of gastric juice; br br b Presence of food in the stomach; B Lacteal; c A Blood capillaries; d - Produces plenty of mucus to lubricate br br coarse/indigestible material during peristalsis; br br - Wide human accommodates /store indigestible food - Elongate to increase surface are for absorption of br br water. br br - has muscles to facilitate peristalsis when they contract; a i P Tracheids Q pits ii P - water conducting elements of xylem b Function of phloem translocation/ transport of organic br br 7. br br substances from the leaves to the of the plant; br br c i Translocation of food will not occur acc. Slow br br translocation br br ii Reason it contains a lot of mitochondria which br br provide energy for translocation; br br d cytoplasmic strands 4 Lack lignin deposits br br 8. br br a Photocopy scale 1m Labeling axes 1 Plotting 2m Curves 2m curves must be labeled rej. Dotted br br line for curves br br A GRAPH OF LACTIC ACID CONCENTRATION AGAINST TIME br br br br b i 10-15 minutes ; period of rapid increase in lactic acid br br concentration 2mks br br ii 10-20 seconds : period when lactic acid level starts br br to increase; 2mks br br iii 75minutes i.e. from 25th minutes to the 100minutes, this is the time lactic cid took to decrease from the highest level to normal; 2mks br br c It would have the same basic shape; but would peak br br slightly ahead of the lactic acid curve in time; br br e Because it is still diffusing out of the muscles, where it br br was made a few minutes earlier; br br e Allows for energy production even cases of oxygen deficiency; thus enables animals to survive active exercise and to inhabit even in areas with limited oxygen supply; br br f Oxygen debt is the amount of oxygen to get rid of the lactic acid; that has accumulated due to anaerobic respiration; 2mks br br 209 9. Regulation of blood sugar level; under the influence of insulin; and glucagons hormones . When there is excess sugar; the hormone insulin stimulate/causes liver cell to convert it to glycogen; some converted to fats/lipids for storage; br br When the blood sugar level is below normal: the hormone glucagon causes liver cells to convert glycogen to glucose; Regulation of amino acids; excess amino acids; are deaminated; by the liver cells leading to formation of urea; which is transported by the blood to the kidney; for elimination; Production of heat: the liver is involved in the thermoregulation due to many metabolic, activities; taking place in the liver cells a lot of heat is generated which is distributed to the entire/whole body; Detoxication of toxic substances; such as drugs and br br hydroxide peroxide br br Elimination of haemoglobin; and formation of bile; breakdown worn out red blood cells; the bile salts sodium tyrochocolate and sodium glycocholate; in the bile eEMULSIFYfats in the duodenum Storage of blood in its veins; thus regulating the volume of blood circulating in the body br br Elimination of sex hormones after they have performed their function/work; storage of vitamin AD and B12 some mineral salts; thus regulating their levels in the blood TOTAL 23 MAX 20 br br 10. a X - glycolysis Y Krebs cycle br br b br br Process X - occurs in cytoplasm - independent of oxygen - produces less energy - raw material is glucose - End products are energy, Process Y - occurs in mitochondria - Is oxygen dependent - produces more energy - Raw material is pyruvate - End products are energy, br br CO2, lactic acid or ethanol CO2 and water c lactic acid; under anaerobic conditions d small body size leads to alarge surface area to volume br br ratio; hence more loss of heat to the environment; leading to increased rate of respiration to replace the lost heat; 11. a i Active transport/diffusion Tied ii Numerous Mitochondria in its wall to generate energy/microvilli/coiling increase surface area/thin epithelium for quick diffusion. b Cortex c on the diagram d plasma proteins; Blood cells; accept specific examples e.g. albumins, red blood cells; e i Regulate re-absorption of Sodium salts; br br ii Regulate re-absorption of water br br 12. a Allocation of marks on graph b Gynandropsis opt To 30oC Amaranthus opt. to 25oC c At 5oC, the enzymes that catalyse the process of br br photosynthesis are inactivated. br br d Amaranthus Terrestrial; Crotolaria terrestrial; e 50oC; f water; g i Granum; ii Stroma h Similarity: Both have double membrane; 1mk Both br br have fluid filled matrix; Difference : inner membrane of mitochondrion is folded to form cristae while inner membrane of chloroplast is smooth; br br - chloroplast is biconcave shaped while mitochondria is oval/sausage shaped any 1x1 1mk br br i Point at which the rate of photosynthesis equals to the br br rate of respiration. 13. a plants wastes accumulate slowly; - plants produce less toxic wastes; - some excretory products are recycled by plants e.g. br br CO2, SO2 br br - plant tissues are tolerant to toxic wastes; - plant wastes are stored in temporary structures br br which fall off e.g. leaves any 3x1 3mks b Diffusion; br br - Transpiration; - Exudation; - Deposition of wastes/ leaf fall/ flower fall/ storage in br br bark; br br - Recycling; - Guttation ; any 5x1 5mks br br c br br Excretory products br br Uses 1. Caffeine; 2. Popain; 3. Tannin; 4. Nicotine; 5. Latex; 6. Quinine; 7. Atropine; 8. Morphine; 9. Colchine; 10. Cocai br br Body stimulant; Meat tenderizer; Leather tanning; Stimulant; insecticide; Manufacture of tyre/rubber products; Anti-malarial drugs; Increase heart beat; dilate eye pupil; Cancer treatment; Used in genetics to induce polypoidy; Anesthesia/painkiller/stimul ant; Pain killer; Stimulant; Any 6x2 12mks br br ne; br br 11. Cann br br abis; br br 12. Khat/ br br miraa; 14. a 1st portion. - Blue; colour was observed 2nd portion Purple; colour was observed 3rd portion Purple; colour was observed br br b A control experiment; c Proteins are highly sensitive to temperature and pH changes; award if either temp of pH is stated singly d peptones; br br 1st portion Enzyme pepsin broke down proteins into br br 2nd portion Enzyme pepsin works in acidic medium; not br br in basic medium 15. a A Hepartic portal vein; B Hepartic vein; br br C Hepartic artery; b So that any toxic substances absorbed together with br br food nutrients from the ileum be detoxified; br br - So that food substances e.g. glucose, amino acids can be br br regulated. Only the required quantity of glucose is left in circulation as excess is either stored as glycogen, fat and excess may be respired. Excess amino acids are deaminated; br br c B Deoxygenated C - Oxygenated d From the small intestines, it is transported to the liver through Hepartic portal vein; It is then transported to the heart through the hepartic vein; 16. a graph b X Lacks internal mechanisms to regulate its internal br br temperature br br Y Has internal means to regulate its internal temperature. hence able to maintain it within narrow range br br c X Poikilotherm d Blood vessels vasodilate when temperature is higher br br Y Endotherm br br than norm to allow for heat loss from blood through radiation, evaporation, etc; when temperature is lower, blood vessels constrict radiation, evaporation etc; - When temperature is higher, lies flat to allow for heat loss from the body since insulation layer of air is removed; when temperature is lower, hair strands erect to hold air which insulates the body against heat loss through radiation, evaporation etc. br br to prevent loss of heat from blood through br br 17. a Higher temperature; increases the kinetic energy; of br br water molecules which makes water turn into vapour on the leaf surfaces faster and hence increase rate of transpiration br br Higher light intensity; influences maximum opening of stomata which increases the surface area; over which transpiration occurs maximumly br br Wind; carries away moisture around the plant and create a higher saturation deficit; which then increases the rate of water loss/transpiration in plants. br br Higher relative humidity; reduces saturation deficit; which br br causes lowering of water loss/transpiration in plants. Higher amount of water in the soil; makes the plant to br br absorb excess water which increases the need for the plant to get rid of it through transpiration faster; br br If the leaf is broader and has numerous larger open stomata; the surface area over which water loss occurs is increased; causing increase in the rate of transpiration. br br award max. 12mks br br 18. a It protects the underlying tissues against mechanical injury, UV-light rays and entry of pathogens; Rej. germs br br As an excretory organs , it enables organisms to eliminate br br excess water, ions and traces of urea; br br As a sensory organ, it enables the organisms to be aware of deviations in pressure, touch and temperature from the external environment; br br It is a thermoregulator such that it enables the body to lose excess heat to lower its temperature back to norm or may enable the organisms to store it s heat if the temperature is lower and hence raise it back to the norm; It takes part in osmoregulation by enabling the body fluids br br to get rid of excess water or excess ions; br br It takes part in the regulation of the pH of body fluids by enabling the body to get rid of either Hydrogen ions or bi- carbonate ions; br br b Presence of the cornified layer; which tough and has keratin to enable it protect the underlying tissues from mechanical injury; It alsos has sebum; which is antiseptic and enables it to prtect the ody against entry of pathogesn. Presence of melanin; enables it to protect the underlying tissues against damage by t UV-light radiations. It has sweat glands with secretory cells; which absorb br br excess water, excess ions and traces fo urea from blood and secrete them into the sweat duct; br br Has the sweat pores; which open son the skin surface to allow for elimination of sweat containing excess water, excess ions and traces of urea; br br It has nerve endings; which enables it to detect any deviations in temperature, pressure and contact/touch; It has hair follicles; which stand erect when temperature is lower than normal to reduce heat loss from the body or lie flat to enable to body lose excess heat and lower temperature back to the norm when the internal temperature is higher; br br Has blood vessels; which vasodilate when temperature is higher than norm to enable the organisms lose than the norm to reduce heat loss from the body; i Counter current system; br br 19. a ii Maintain a diffusion gradient so that there is maximum uptake of oxygen; continue diffusing into blood and Carbon iv oxide into water; b Parallel flow lower diffusion gradient; so that less oxygen br br diffuse into blood/low rate of gaseous exchange br br c Gill filaments d Placenta Kidney 20 a i Remain the same br br ii Crenated br br b The solution is hypotonic to red blood cells hence the cells br br grains water; by osmosis; swelling until they burst. br br c Isotonic solution d Plasmolysis the process by which plant cells loss water by br br Osmosis shrink and become flaccid. br br BIOLOGY DIAGRAMS br br br br 215 br br 218 br br 219 br br 220 br br 221 br br M br br V W br br N Z br br 222 br br 223 br br 224 br br 225 br br R P br br Companion Cell br br Q br br A br br B br br 226 TOPICAL QUESTIONS FOR BIOLOGY br br FORM I TOPICS br br 1. a Define biology br br -the study of life/living things b List the branches of biology - Zoology study of animals - Botany study of plants - Microbiology study of microorganisms c Explain the importance of biology - helps to solve environmental problems - Helps to learn scientific skills - For entry into other professions/careers - To apply knowledge to everyday life situations - To classify organisms into their right groups - understanding living organisms d State the characteristics of living organisms - feeding/nutrition - Growth and development - respiration to produce energy - sensitivity/irritation/response - excretion getting rid of metabolic waste material - movement/locomotion - reproduction e State the main differences between plants and animals Animals Plants No chlorophyll Give parental care to young Plants dont care for their br br Contain chlorophyll br br young br br 2. a i What is a hand lens? - Convex lens mounted on a frame and used to magnify br br small objects for viewing. ii How is a hand lens used? - place the lens a short distance from the eye - Bring the object to be viewed near the lens until an br br enlarged and clear image can be seen. br br ii When is a hand lens used? br br - For reasonably sized objects such as insect wing, leg, br br flower parts. br br - Cannot be used for small objects such as cells, stomata. br br iv Explain how to calculate drawing magnification - drawing magnification equals to length of drawing divided by length of object or image length divided by actual length i.e. length of drawing or image length br br Length of object actual length br br b i what is classification? - Orderly arrangement of living organisms into various groups according to their similarities ii List the external features used to classify plants br br - rhizoids e.g. mosses - frond e.g. ferns - roots e.g. taproot, fibrous roots, modified roots - flowers - leaves - buds - seeds iii List the external features used to classify animals br br - horns e.g. cattle, goat, sheep, deer, gazelle etc - hooves e.g. cattle, sheep, donkey - mammary glands e.g. cattle, dog, sheep, cat - hair e.g. human, cat - Shell e.g. snail, Tortoise - spines e.g. hedge hog, porcupine br br c Give the reasons why classification is important - Placing/grouping living organisms into correct groups called taxa - Identification - arrange information about living organisms into orderly and sequential manner i.e. it is easy to study organisms in groups -helps in understanding evolutionary relationships - monitoring disappearance and appearance of organisms i.e. predict characteristics of organisms d i Name the taxonomic units of classification in descending order - Kingdom largest unit - Phylum animals /division plants - Class - Order br br - Family - Genus - Species smallest unit br br ii What is a species? br br - all organisms which can interbreed and give rise to fertile br br viable offspring br br iii Name the major kingdoms used in classification -monera -protoctista/protista -fungi -plantae -animalia e i Define the term binomial nomenclature - a scientific system of naming organisms using the generic/genus and specific/species names - e.g. for humans, Homo sapiens ii State the principles followed during binomial nomenclature br br - the first generic name should begin with a capital letter br br while the rest are small letters br br - the two names are printed in italics and if handwritten br br should be underlined each separately br br iii Give the advantages of using binomial nomenclature - no confusion about which organism is referred to - names are internationally accepted regardless of language - shows evolutionary relationship hence easy to understand - useful in naming many species unlike use of common br br names br br iv Name the types of classification br br - traditional using common names - scientific using binomial nomenclature 3. a i Define the term cell - it is the basic unit of organization of an organism i.e. the br br basic functional and structural unit of an organism. ii What is cell biology? br br - study of structure and functioning of a cell - also called cytology b i What is a microscope? - an instrument used to magnify objects and make them appear bigger. ii Name the types of microscope br br - the light microscope - the electron microscope br br iii State the purpose of using a light microscope br br - it magnifies and reveals the structure details of tiny objects br br such as the cell, that cannot be seen by the human eye directly br br - br br iv Draw a labeled sketch of a light microscope br br br br v State the functions of the labeled parts a. Eyepiece used to look through and to magnify the object b. Course adjustment knob raises or lowers body tube and focuses object roughly c. Fine adjustment knob raises or lowers body tube by small distances to bring image into fine focus d. objective lens brings image into focus and also magnifies object/image br br stage is a platform where object or specimen on slide is br br placed br br mirror reflects light through condenser and directs it to br br objective lens br br clips hold glass slide in position body tube holds eyepiece and revolving nose piece which br br has objective lenses br br limb or base support whole instrument arm for holding when carrying instrument br br 230 revolving nose piece holds objective lens in place enabling br br change from one objective lens to another e i Explain the procedure followed when using a microscope - put the microscope on the bench with the stage facing away from you viewer - turn the lower power objective to click in line with the eyepiece - Ensure that the diaphragm/iris is fully open - Adjust the mirror until the stage is illuminated with enough light - Place the slide containing the specimen on the stage for magnification - Draw the image and indicate magnification of the drawing. ii State the precautions that are necessary when handling a microscope br br always use two hands when carrying it never place a microscope too close to the edge of the br br bench or table br br do not touch the mirror and lens with wet or dirty hands clean dirty lenses using a special lens cleaning cloth clean other parts using a soft cloth or tissue paper low power objective must click into position before and br br after use. br br Do not wet any part of the microscope Clean and store well after use br br d i What is magnification? - The power of making an image larger ii Give the formula used to calculate magnification in a light microscope iii Give the reasons for each of the following steps when preparing a cross-section of a stem or leaf for examination under the microscope cutting very thin sections br br thin sections allow light to pass through making it easy to br br observe the tissue br br Using a sharp razor blade during the cutting br br sharp blade does not damage, deform, destroy or distort the br br surface of cell or tissue br br it makes thin sections Placing sections in water br br to maintain turgidity hence maintain shape of cell it prevents drying of the section br br Staining the sections with iodine before observing br br To make chloroplasts, starch containing structures, granules br br or plastids distinct. br br e i List the parts of a cell that can be seen under a light microscope br br a cell membrane br br b cytoplasm c cell wall e nucleus d vacuole br br br br ii Draw the general structure of a plant and animal cell iii List the parts of a cell that can be seen under an electronic microscope and state the functions of each part. Cell wall br br found in plant cells in addition to cell membrane made of cellulose which makes the plant tough allows gases, water and other substances to pass through br br Cell membrane br br permeable/selective to control movement of materials in br br and out of cells br br bound/encloses the cell contents also called plasma membrane or plasmallema br br Cytoplasm br br fluid medium where chemical reactions occur also where cell organelles are suspended br br Nucleus br br controls cell activities br br Nucleolus br br synthesizes DNA br br Vacuole br br 232 sacs filled with fluid called cell sap large in plants but small in animals act as reservoirs for food and harmful wastes which would br br otherwise interfere with the metabolism in cytoplasm br br Lysosomes br br store hydrolytic enzymes destroy worn out cell organelles, cells, pathogens digestion of food in unicellular organisms autolysis Golgi apparatus br br processing/packaging of synthesized materials transporting/secretion of packaged materials/cell materials br br e.g. glycoproteins and mucus br br production of lysosomes br br Ribosomes br br where protein synthesis takes place br br Mitochondrion br br synthesis of ATP/energy br br Chloroplasts br br where photosynthesis takes place br br Endoplasmic reticulum br br transport of cell secretions can be rough or smooth br br iv State the functions of cell sap br br stores chemical substances, sugar, salts br br maintains shape of the cell/provides mechanical strength plays a role in osmoregulation by creating an osmotic br br gradient that brings about movement of water br br e Compare plant and animal cells br br plant cells have chloroplasts lacking in animals animal cells have many small vacuoles while plant cells have a large central vacuole br br plant cell have cellulose cell walls lacking in animal cells cytoplasm in plant cell is in the periphery but in animal cell br br it is centrally placed br br plants store starch, oil and protein while animals store gats br br and glycogen br br animal cells have centrioles which plant cells do not have br br f Explain the meaning of each of the following br br i Cell br br - Basic unit of organization in an organism - Specialized animal cells include sperm, ovum muscle Specialized plant cells include epidermal, guard cell and palisade cell ii Tissue br br these are cells of a particular type grouped together to br br perform a certain function br br animal tissues include epithelium, blood, nerves, muscle, br br skeletal and connective tissues br br plant tissues include epidermal, photosynthetic, vascular, br br strengthening tissues br br iii Organ br br tissues combine together to form organs an organ is a complex structure with a particular function animal examples include heart, liver, kidney, lungs, brain, br br blood vessels, muscles, skeleton br br Plant organs include leaves, roots, flowers, and stem. br br iv Organ system br br organs are grouped together to form systems also called br br organ systems br br animal systems include excretory, digestive, respiratory, br br nervous, circulatory, endocrine hormones/glands , skeletal systems br br plant systems include transport system br br g i Name the structures which are present in plant cells but absent in animal cells - Chloroplast - Cell wall ii Name the structures which are present in animal cells but absent in plant cells Lysosomes Centrioles Pinocytic vesicles h Explain how to estimate cell size i Materials br br cell sizes are measured in units known as micrometers my required is a transparent ruler marked in millimeters 1m 1 mm br br 1000 focus so that the millimeter marks can be seen as thick dark br br lines br br estimate the diameter of field of view by counting the one millimeter spaces between the first mark and the last one across the field of view as shown below br br br br the diameter of the field of view above is estimated as 3.2 br br mm br br convert the diameter of the field of view from millimeters br br to micrometers i.e. 3. br br Estimate the fraction of the field of view occupied by the cell. This is done by estimating the number of cells places end to end that would fill the diameter of the field of view as shown below br br in the figure above, it is estimated that approximately six br br cells will occupy the diameter of the field of view therefore, one cell will occupy of the field of view its diameter is calculated as times the diameter of the br br field of view br br i In a drawing of a giraffe, the height of the head from the ground was recorded as 10cm. the drawing also showed a magnification of 0.02. calculate the actual height of the giraffe br br Drawing height 10cm 500cm Magnification i br br 0.02 br br In a class experiment to estimate sizes of cells a student observed and obtained millimeter marks on the field of view of a microscope as shown in the diagram below . br br 235 Millimeter marks br br - If the student counted 40 cells on the diameter of the field of view, what was the approximate size of the each cell in micrometers? Diameter of field of view 3 x 1000 75 m Number of cells 40 br br ii Under which of the following light microscope br br magnifications would one see a larger part of the specimen? X40 or x400? Give a reason br br x40 Smaller magnification gives a wider field of view hence a br br larger part seen. br br e. the study of the functions of a cell in relation to their br br a i Define cell physiology br br structure br br ii State the functions of the cell exchange of materials between the cell and the external br br environment br br physiological reactions e.g. photosynthesis production of energy through mitochondria b i Describe the structure of cell membrane - made up of three layers - Lipid portion sandwiched between two protein layers - Lipid portion enhances penetration of oil soluble substances Pores present to facilitate inward and outward movement of water soluble substances br br iii Give the properties of cell membrane semi-permeable sensitive to changes in temperature and pH Possesses electric charges. c i What is diffusion? br br movement of substances/molecules/particles/ions from a br br region of high concentration to a region of low concentration until equilibrium is reached br br iii State the factors affecting diffusion diffusion gradient/concentration gradient surface area to volume ratio temperature size of molecules state of the diffusing substance thickness of membrane and tissues iii Explain the roles of diffusion in living organisms br br gaseous exchange absorption of digested food in intestines movement of salts in plants movement of materials between blood capillaries and br br tissues br br removal of waste materials from bodies of small organisms air movement in intercellular spaces in plants br br iv Suggest an experiment to demonstrate diffusion to a beaker of water, drop crystals of potassium br br permanganate or copper sulphate br br leave to stand in a place without disturbing observe the spreading of molecules liquid is coloured uniformly due to diffusion br br d i What is osmosis? br br Movement of water or solvent molecules from a br br dilute/hypotonic solution to a more concentrated/hypertonic solution across a semi-permeable membrane. br br OR br br movement of solvent molecules from a region of their br br higher concentration to a region of their lower concentration through a semi-permeable membrane br br ii State the factors affecting osmosis br br concentration of the solution concentration gradient temperature iv Explain the roles of osmosis in living organisms helps to draw water into roots of plants helps in the passage of water from one living cell to another br br in the plant br br helps to keep plant cells turgid increasing support Helps in opening and closing of stomata. Folding of leaves in Mimosa pudica when touched Feeding in insectivorous plants v A group of students set up an experiment to br br investigate a certain physiological process. The set up is as shown in the diagram below. br br 237 After some time they observed that the level of sugar had risen. What was the physiological process under investigation? br br Osmosis br br Why was there a rise in the level of sugar solution? br br sugar solution is more concentrated than cell sap osmosis those cells become more concentrated and therefore draw br br water from neighbouring cells br br this process continues until the cells in contact with the br br water in the container draw it up causing a rise in the level of the sugar solution br br Suggest the results that the students would obtain if they repeated the experiment using cooked potato The level of sugar solution will not rise. br br What is the reason for your suggestion? br br boiling kills/destroys cells making them osmotically br br inactive br br vi Explain the following terms br br Hypnotic br br a solution whose concentration is lower than that of the cell br br Isotonic br br a solution whose concentration is the same as that of the br br cell Hypertonic br br a solution whose concentration is higher than that of the br br cell br br Turgor pressure br br As a cell gains water, its vacuole enlarges and exerts an br br outward pressure called turgor pressure. br br br br 238 Plasmolysis br br if a plant is placed in a hypotonic solution if loses water the protoplasm shrinks to an extent that it pulls away from br br the cellulose cell wall br br br br Wilting br br when a plant is turgid it can stand upright however, if the cells lose a lot of water, turgidity is reduced the plant then droops because the cells are flaccid the plant is said to wilt br br Haemolysis br br if red blood cells are placed in distilled water, the cells take br br up water by osmosis, swell and burst br br this is because it does not have any mechanism like the br br cellulose cell wall to prevent overstretching nor any means of removing excess water this is called haemolysis br br e A form one student placed red blood cells in different salt concentrations and obtained the following results:- There was a gain no change 0 zero and a loss - in the volume of the cells as show below:- br br 239 Briefly explain the results of the experiment br br in the first solution , red blood cell absorbed water by br br osmosis, swell and burst haemolysis hence the solution is hypotonic br br in the second solution, there was no change in size or structure as it was isotonic hence no osmotic gradient in the third solution the red blood cell lost water to shrink hence became crenated as the solution was hypotonic to the cell cytoplasm. br br f i What is active transport? br br movement of molecules and ions against a concentration br br gradient br br the substances move from a lower to a higher concentration br br gradient by use of energy br br ii State the factors affecting active transport br br oxygen concentration temperature change in pH glucose concentration enzyme inhibitors iii Why is oxygen important in the process of active transport? - Oxygen is required for respiration, which produces energy necessary for the process to occur. 2.0 the factors that affect the rates of the following process in living organisms. br br a. DIFFUSION. br br - Diffusion gradient which refers to the difference in concentration of molecules between the region of high concentration and the region of low concentration. Increasing the concentration gradient causes an increase in rate of diffusion and vice versa. -Surface area to volume ratio . is the ratio of total surface area exposed by an organism compared to its body volume. Small sized living organisms have a large surface area to volume ratio. The larger the surface area to volume ratio ,the high the rate of diffusion and vice versa. Small organisms like amoeba and paramecium can hence rely on diffusion for transport of substances into and within its body and removal of waste products -thickness of membranes. Molecules take longer to diffuse across thick membranes than across thin membranes hence the thin the membrane the higher the rate of diffusion. -Temperature. Increasing temperature increases the kinetic energy of diffusing molecules making them to spread faster. Increasing temperature increases the rate of diffusion and vice versa -size of molecules/molecular weight. Small sized molecules/molecules of low molecular weight move/diffuse faster hence the rate of diffusion is high where the molecules involved are small or have low molecular weight and vice versa . B. OSMOSIS -Temperature. Increasing temperature increases the kinetic energy of water molecules making them to spread faster. Increasing temperature increases the rate of osmosis and vice versa -concentration gradient/diffusion pressure deficit. Refers to the difference in concentration on either side of a semi- permeable membrane. The higher the osmotic pressure difference the higher the rate of osmosis. C. ACTIVE TRANSPORT OXYGEN CONCENTRATION. It is required for respiration/to oxidize respiratory substrates to release energy required for active transport. an increase in oxygen concentration causes a simultaneous increase to the rate of active transport upto a certain level. PH Enzymes being protein in nature are PH specific. Extreme change in PH affect the rate of respiration which is controlled by enzymes and may denature the enzymes reducing the rate of active transport. - GLUCOSE CONCENTRATION. is the main respiratory substrate for energy production. An increase in glucose concentration in cells increase the rate of respiration and hence the rate of active transport is increased upto a certain optimum level beyond which any additional increase in glucose concentration has no effect. TEMPERATURE. The process of respiration by which energy for active transport is generated is controlled by enzymes. Enzymes work best at temperatures of between 350c- 400c,usually called optimum temperature ranges. At very low temperatures enzymes are inactive lowering the rate of respiration hence low rates of active transport . increase in temperature above optimum above 400c denatures enzymes slowing down respiration and ac tive transport until it finally stops. ENZYMES INHIBITORS. They are substances which slow down by competing with the enzyme for the active sites in the substrate or stop by blocking the active sites of the enzyme the activity/funtioning of enzymes .this slows down or stops respiration and so is active transport. CONCENTRATION OF CARRIER MOLECULES IN THE CELL MEMBRANE. They are substances that bind to the ions being transported actively and carrying them across the membrane . increase in concentration of carrier molecules increases the rate of active transport upto a certain level and vice versa. 4. Explain briefly the role of osmosis in living tissues. In plants: Osmosis facilitates the absorption of water from the soil by plant roots, water is required for the process of photosynthesis. Turgidity of cells contributes to support in herbaceous plants and helps plant to maintain shape. Helps in closing and opening of stomata regulating the process of gaseous exchange and transpiration. It facilitates feeding in insectivorous plants like venus fly trap. In animals: Enables reabsorption of water from the kidney tubules back to blood stream facilitating the process of osmoregulation. It enables organisms in fresh water bodies like amoeba to absorb water. it is applied in food preservation. 5. explain what happens when plant and animal cells are put in hypotonic and hypertonic solutions. br br a. i plant cells in hypotonic solution. br br The concentration of the plant cell sap is hypertonic to the solution/water medium. the cell draws in water by osmosis through the cell wall, cell membrane into the cell cytoplasm. Water enters the cell vacuole by osmosis; it enlarges and exerts an outward pressure on the cell wall called turgor pressure. Increased turgor pressure pushes the cell cytoplasm against the cell wall until the cell wall cannot stretch any further. The cell becomes firm or rigid and is said to be turgid. As the cell wall is being stretched outwards, it develops a resistant inwards pressure that is equal and opposite to the turgor pressure and this is called wall pressure. ii. Plant cells in hypertonic solution. The plant cell sap is hypotonic to the solution medium. Water molecules are drawn out of the plant cells by osmosis into the hypertonic solution through the semi-permiable membrane of the plant cells. As a result the plant cell will start to shrink/less rigid and become flabby. The cell membrane/plasma membrane is pulled away from the cell wall and the cell is said to be flaccid. this process by which a plant cell lose water, shrink and become flaccid is called plasmolysis. However the shape of the plant cell is maintained by the tough rigid cellulose cell wall which prevents crenation in plant cells. b.i Animal cells in hypotonic solution. The concentration of water in the cytoplasm of the plant cells is hypertonic to the solution medium in the test. Water molecules are then drawn into the animal cell cytoplasm from the surrounding medium by osmosis through the semipermiable membrane. the cell swells as water is drawn into them by osmosis .as water continues to enter into the cell,the weak animal cell membrane bursts a process called lysis. in red blood cells this process is called haemolysis. However in unicellular organisms like amoeba and paramecium,bursting of their cells does not take place because they have specialized organelles called contractile vacuoles for removal of exces water out of their bodies/cells. ii. Animal cells in hypertonic solution. The concentration of the animal cells cell cytoplasm is hypotonic to the solution medium in the test. the surrounding hypertonic solution will draw water out of the animal cells by osmosis through the semi-permeable membrane. Continued loss of water causes the cells to be smaller in size and their membranes become wrinkled. This process will continue until the concentration of the cell sap and the surrounding medium is equal i.e isotonic.the process by which animal cells lose water and shrink is called crenation. 6. Explain briefly the role of active transport in living organisms. It is involved in active reabsorption of glucose and mineral salts in kidney tubules during formation of urine. it enables the absorption of digested food from the alimentary canal/small intestines into the blood stream. Excretion of waste products from body cells for eventual removal. Involved in transmission of nerve impulses within the nerve cells through the sodium pump which maintains a balance between sodium and potassium ions. It facilitates accumulation of substances in the body cells to offset osmotic pressure of organisms in dry and marine environment allowing them to absorb water by osmosis and avoid desiccation. In plants it enables plant roots to absorb water from the soil against the concentration gradient. Its involved in translocation of manufactured food in the phloem tissue within the plant body. Its involved in the opening and closing of the stomata through the sodium-potassium pump mechanism. iv Outline the roles of active transport in living organisms br br mineral salt intake by plants selective reabsorption of glucose and some salts by kidney br br tubules br br absorption of digested good by small intestines excretion of waste products from body cells reabsorption of useful materials in the blood stream or at br br the tissue fluid br br sodium pump mechanism in the nerve cells/neurons f. a i Define nutrition the process by which living organisms obtain and br br assimilate nutrients br br ii State the importance of nutrition br br for respiration to get energy for growth for development to repair and replace worn out and damaged parts and tissues br br b Differentiate the various modes of feeding br br i Autotrophism manufacturing food from simple organic substances types are photosynthesis and chemosynthesis ii Heterotrophism obtaining food from autotrophes and other organic br br substances br br types are holozoic, saprophytic and parasitic g. the process by which green plants build up organic br br a i Define photosynthesis br br compounds from carbon IV oxide and water in the presence of sunlight br br ii. State the importance of photosynthesis formation of sugars/glucose which is a source of energy purification of air CO2 is used, O2 is released storage of energy to be used later in respiration stores energy in wood, coal, oil to be used later to run br br industries br br Structural adaptation of the leaf to its function br br br br The leaf has a broad and flattened lamina to provide a large surface area for trapping optimum light for photosynthesis and allow maximum gaseous exchange. The leaf epidermis is thin one cell thick to reduce the distance across which diffusion of carbon iv oxide gas to palisade cells and oxygen gas from palisade cells takes place. The leaf has numerous stomata that allows easy diffusion of gases into and out of the palisade tissue. The leaf cuticle and epidermis are transparent to allow easy penetration of light to the photosynthetic tissue. The palisade cells are numerous,elongated and contain numerous chloroplasts to trapping optimum light for photosynthesis. The palisade tissue is just beneath the upper epidermis exposing them to trap optimum light for photosynthesis. The leaf has numerous leaf veins consisting of a. xylem vessels and tracheids for transporting water and dissolved mineral salts from the soil to the photosynthetic tissue b. phloem tissue for translocation of of manufactured food from the leaf to storage organs and other parts of the plant . br br 245 Numerous and large air spaces in the spongy mesopyl layer for optimum gaseous exchange with the photosynthetic tissue. Phylotaxy which is regular arrangement of leaves on the stem minimizes overshadowing and overlapping exposing all leaves to light for photosynthesis. The prominent midrib and leaf veins reduces chances of rolling of leaves maintaining a large surface area for trapping optimum light for photosynthesis. br br br br C Describe the structure and function of chloroplast br br i Structure br br 246 ii Function structure in which photosynthesis takes place iii Adaptations has numerous/many grana to provide large surface area for br br packing many chlorophyll pigments br br have numerous chlorophyll pigments which trap br br sunlight/light for photosynthesis br br has stroma/third matrix which contain certain enzymes that br br catalyze photosynthetic reactions br br d i Give a word equation for photosynthesis Carbon iv Oxide water sunlight sugar oxygen NB 6CO2 6H2O C6H1206 6O2 . Describe briefly the process of photosynthesis in plants. The process of photosynthesis takes place in green plants allowing them to make their own food. The process is controlled by enzymes and involves a series of reactions that take place in chloroplasts. The raw materials required are water and carbon iv oxide.the process takes place in two consecutive stages i.e Light reaction stage Its also called the light dependent stage as it requires light energy . the reactions take place in the granna of the chloroplast. light energy from the sun is trapped by chlorophyll in the chloroplast and converted into chemical energy. This energy splits water molecules into hydrogen ions and oxygen atoms a process is called photolysis. The oxygen atoms are released as aby product or used up in the process of respiration. The hydrogen ions formed are used in the dark stage of photosynthesis. Water hydrogen ions oxygen atoms 2H2O 4H o2 g Some of the light enrgy is used to combine a molecule called adenosine diphosphate ADP with a phosphate group to form the rich energy molecules called adenosine Tri-Phosphate ATP ADP P ATP Dark reaction stage Its also called the light independent stage of photosynthesis since light is not required because it can take place both in presence and absence of light. the reactions are controlled by enzymes. the hydrogen atoms released in the light stage are combined with carbon iv oxide to form simple sugars mainly glucose. The process uses energy from ATP. This is reffered to as carbon iv oxide fixation. The reactions take place in the stroma of chloroplast. The excess glucose is converted into starch or lipids for storage. The general process of photosynthesis can be summarized by the following word and chemical equitions. Water carbon iv oxide light chlorophyll glucose oxygen 6H2o 6co2 C6H12O6 6O2 9. Factors that cause high rate of photosynthesis. High water availability in the soil. Water a raw material for photosynthesis is split in presence of light to provide the hydrogen ions required in carbon iv fixation. When water is readily available more hydrogen ions are produced hence high rate of photosynthesis. High light intensity. Light splits water molecules to hydrogen ions and oxygen atoms. Increasing light intensity increases the rate of photosynthesis up to a certain level beyond which other factors become limiting and rate of photosynthesis becomes constant. rate br br of photosynthesis Day length. Long day length especially at high latitudes temperate regions provides more light for photosynthesis causing an increase in the rate of photosynthesis. Light quality. The preferred wavelengths for photosynthesis range between 400nm-700nm. the rate of photosynthesis is higher in red and blue light and lower in all other types of light. Concentration of carbon iv oxide. Its a raw material required to combine with hydrogen ions to form simple carbohydrate molecules. Increasing the concentration of carbon iv oxide increases the rate of photosynthesis up to an optimum level beyond which other factors limit the rate of photosynthesis. f Give the differences between the light and dark reactions during photosynthesis Light reactions Dark reactions br br occurs in grana h. substances which make up cells, tissues and organs of the br br occurs in stroma br br a i What are chemicals of life? br br living system br br they combine to form organic compounds br br ii What are organic compounds? br br compounds that contain the element carbon iii List the organic compounds proteins carbohydrates lipids fats and oils vitamins enzymes nucleic acids DNA and RNA br br b i What are carbohydrates? - Compounds of carbon, hydrogen and oxygen - The elements are in the ratio of I carbon: 2 hydrogen: 1 oxygen ii Name the groups of carbohydrates br br monosaccharides simple carbohydrates e.g. glucose, br br fructose and galactose br br disaccharides formed when two monosaccharides br br combine e.g. maltose, sucrose, lactose br br polysaccharides composed of many monosaccharides and br br disaccharides e.g. starch, glycogen, cellulose br br iv State the general functions of carbohydrates production of chemical energy storage of starch plants and glycogen animals commercial uses e.g. manufacture of paper, textiles c i what are proteins? br br compounds of carbon, hydrogen and oxygen and in addition nitrogen, and sometimes sulphur and or phosphorus br br building blocks are called amino acids br br ii Name the types of amino acids br br essential amino acids which must be supplied in food since br br they body cannot synthesize them br br Non-essential amino acids which body can synthesize. iv State the classes of proteins first class proteins which supply all the essential amino br br acids br br second class proteins which lack at least one amino acid v Give the functions of proteins structural compounds e.g. muscles, hair, hooves, and br br feathers br br as enzymes e.g. pepsin, trypsin hormones e.g. insulin and glucagons antibodies part of haemoglobin molecule actin and myosin in muscles collagen in bones and cartilage pigments in rods and cones for coordination components of blood i.e. plasma proteins br br d i What are lipids - Fats and oils - They contain carbon, hydrogen and oxygen - However, they contain a higher proportion of carbon and hydrogen but less oxygen that in carbohydrates ii Name the types of lipids oils liquid under room temperature fats solid under room temperature iii What are the building blocks of lipids? br br fatty acids and glycerol v State the functions of lipids production of energy source of metabolic water structural compound e i What are enzymes? br br a chemical compound, protein in nature, which acts as a br br biological catalyst br br ii State the properties of enzymes are highly specific in nature they are not used up during chemical reactions work within specific range of temperature work within specific range of pH enzyme controlled reactions are reversible iii State the factors that affect enzyme action br br temperature substrate concentration pH of the medium enzyme concentration presence of inhibitors and co-factors v Name the types of enzyme inhibitors competitive inhibitors non- competitive inhibitors vi What are the functions of enzymes? enable cellular reactions to take place at a reasonably faster br br rate br br Control cell reactions therefore no violent incidences occur br br in cells that might burn them. br br i. a Explain the various types of heterotrophic nutrition i Holozoic Mode of feeding by animals where solid complex food br br substances are ingested, digested and egested. br br ii Saprophytism feeding on dead organic matter iii Parasitism feeding from another organism but not killing it iv Symbiosis an association in which organisms of different species br br derive mutual benefit from one another br br b Differentiate between omnivorous, carnivorous and herbivorous modes of nutrition i Herbivorous herbivores feed exclusively on vegetation ii Omnivorous omnivores are animals which feed partially on plant br br materials and partially on flesh e.g pigs br br iii Carnivorous Carnivores feed on flesh alone e.g. lion br br c i What is dentition? br br Refers to the number, arrangement and kind of teeth in an br br animal ii Distinguish between the terms homodont and heterodont homodont have same kind , type, shape and size of teeth which perform similar function e.g. fish, reptiles and amphibians br br Heterodont have different kind, type, shape and size of br br teeth which perform different functions as those found in mammals. br br iv Name the types of teeth found in mammals Incisors Canines Pre-molars Molars br br d Describe the adaptations and functions of various types of mammalian teeth br br br br Incisors chisel shaped/wedge shaped found in the front of the br br buccal cavity used for cutting i Canines next to incisors very sharp and pointed located at the sides of jaws used for tearing food ii Premolars next to canines but before br br molars br br have cusps and ridges on br br their surface br br used for crushing and grinding iii Molars found at the back of the jaw have cusps and ridges on their surface absent in young mammals but appear later when permanent br br teeth grow br br used for grinding and crushing br br e i Draw a labeled diagram to represent internal structure of a mammalian tooth. br br 252 ii State the functions of the labeled structures labeled Dentine br br main constituent of teeth like bone in structure but contains no cells br br Enamel br br protects tooth from mechanical/physical injury the hard covering of the exposed part of teeth br br Crown br br portion of tooth above the gum covered with dentine br br Root br br part imbedded in the jaw below the gum covered by substances called cement cement is hard and bone-like br br Cement br br bone-like substance covering root and enamel of br br mammalian tooth br br Neck br br region at the same level with the gum forms a junction between the crown and root covered by enamel br br Pulp cavity br br at centre of tooth within dentine has blood vessels for transporting nutrients/food and gases has nerves for sensitivity f i What is dental formula? br br formula indicating the number of each kind of teeth for a br br given species of mammal only half the jaw is included the number in the upper jaw of one side is written above br br that in the lower jaw of one side br br the categories of teeth are given in the order incisors, br br herbivore e.g. sheep I 0 Omnivore e.g. human I . c1 br br /3, c 0 br br /1, pm , m3/3 30 /3 32 /1, pm2/2, m 3 br br iii How would one use dental formula to identify the following? Herbivores br br presence of diastema/gap between incisors and premolars free movement of tongue absence of incisors in upper jaw absence of canines presence of hard pad closely packed molars br br br br Carnivore br br presence of canines presence of carnassial teeth presence of incisors in upper jaw/absence of diastema/gap br br between incisor and premolar br br iv State the functions of the following structures in br br mammals br br Carnassials br br tearing flesh from bones br br Pad of gum br br provides grasping surface for lower incisors br br g Name the common dental diseases br br dental caries periodontal pyorrhea and gingivitis j. a i What is digestion? breakdown of complex food particles by enzymes to simple br br substances which can be absorbed br br ii Explain the types of digestion Intercellular br br 254 Digestion that takes place in food vacuoles inside cells. br br Extra cellular br br digestion that takes place outside cells e.g. in the digestive br br tract br br b i Draw human digestive system br br br br 255 br br ii Describe the process of digestion in the various parts of the human digestive system Mouth br br contains teeth for chewing has tongue for mixing food with saliva has salivary glands for chemical digestion, secretion of br br enzymes and mucus secretion br br starch is acted on by salivary amylase enzymes to produce br br maltose br br the tongue rolls food into a bolus which is carried into the br br stomach by peristalsis br br peristalsis is movement of food along the gut by waves of br br contraction br br it facilitates rapid digestion due to its mixing action br br Oesophagus br br also called gullet br br 256 forms a passage for food by peristalsis connects the mouth to the stomach br br Stomach br br has gastric glands which secrete gastric juices these juices contain hydrochloric acid HCL , mucus, and br br the enzymes pepsin, rennin and lipase br br HCL produces an acidic medium for enzyme action Proteins are acted upon by pepsin to produce peptides Caseinogen is acted upon by rennin to produce casein Fats are acted upon by lipase to produce fatty acids and br br glycerol br br Mucus lubricates the stomach and prevents autolysis of br br stomach mucus protects stomach br br Duodenum br br the first u-shaped part of the small intestine food in the stomach is now in a semi-liquid form called br br chime br br chime leaves the stomach by peristalsis into the duodenum there, the liver produces bile pigments, bile salts and br br sodium hydrogen carbonate br br the stomach is usually alkaline to neutralize chime which is br br acidic br br bile salts emulsify fats bile comes from the gall bladder through the bile duct sodium hydrogen carbonate provides the correct pH/alkaline br br pancreatic juices are released by pancreas into the br br duodenum br br the juices contain trypsin, chemotrypsin, amylase, lipase br br and protease br br proteins are acted upon by trypsin to form polypeptides and br br amino acids br br starch is broken down to maltose by amylase br br Ileum - produces intestinal juices - Intestinal juice contains maltase, sucrase, lactase, erepsin, lipase, and several other peptidases - Maltose is broken down to glucose and galactose by lactase - Sucrose is acted upon by sucrase to glucose Polypeptides are broken down into amino acids by erepsin - Mucus secretion is to protect the ileum wall from digestion/autolysis Colon - Commonly called the large intestine - Wider than the ileum - has several mucus-producing cells Highly folded for water absorption - Also prepares food for egestion - egestion is the process by which the insoluble parts of food are discharged from the body in form of faeces. Rectum - Muscular and enlarged - it produces mucus - used for storage and removal of faeces Anus - found at the exterior end of the rectum The rectum opens into the anus - The anus has anal sphincter to control egestion - Anus is used for egestion of faeces c Explain how mammalian intestines are adapted to perform their function - The mammalian intestines are relatively long and coiled. This allows food enough time and increases surface area for digestion and absorption of products of digestion - The intestinal lumen inner wall has projections called villi to increase surface area for absorption - The villi have projections called micro-villi which lead to further increase of surface area for absorption - The walls have glands which secrete enzymes for digestion e.g. maltase, sucrase, lactase, peptidase and enterokinase. - Goblet cells mucus secreting cells or glands produce mucus which protects the intestinal wall from being digested and reduces friction. - Intestines have openings of ducts which allow bile, a pancreatic juice into the lumen - The intestines have circular and longitudinal muscles whose contraction and relaxation peristalsis leads to mixing of food with enzymes juices helps push food along the gut. - The intestines are well supplied with blood vessels that supply oxygen and remove digested food. - Intestines have lacteal vessels for transport of lipids fats and oils - Intestines have thin epithelium to facilitate fast/rapid absorption/diffusion d What is the function of hydrochloric acid in digestion? - kills bacteria - activates trypsinogen to trypsin which digests proteins to peptones and peptones to soluble amino acids - provides acidic medium for gastric enzymes e i What is assimilation? - The process by which digested food is taken up by cells and used in the body for various purposes. ii State the uses of digested food in the bodies of animals - Protection - Repair - Growth - Energy production f Name the types of food substances in the food that do not undergo digestion in human digestive system br br mineral salts water roughage vitamins k. Explain the importance of the following food br br substances in human nutrition br br Vitamins are organic chemical compounds essential for a healthy br br body br br are obtained from fresh fruits and vegetables some are synthesized in the body e.g. vitamin K they are destroyed by overcooking food they protect the body against diseases, play regulatory br br mechanisms in the body and act as co-enzymes br br insufficient amounts lead to deficiency diseases e.g. rickets, br br scurvy, beriberi a Mineral salts are important in organic compounds containing elements br br which are essential for normal body metabolism br br those required in large quantities are called macro-nutrients while those required in small quantities are called micro- nutrients or trace elements br br They are used in bone and teeth formation. In osmotic br br balance and neurotransmission br br insufficient amounts lead to anaemia, rickets, goiter Excess amounts lead to high blood pressure, and dental br br disorders. b Roughage composed of cellulose and plant fibers digested by cellulose contained by gut microorganisms provides grip essential for peristalsis lack of roughage leads to slow movement of food leading br br to constipation br br roughage adds bulk to food for peristalsis to take place c Water used in transport in the body, universal solvent, hydrolysis insufficient leads to dehydration l. Explain the factors that determine energy requirements br br in humans br br a Basal Metabolic Rate BMR this is the energy required when the body is completely at br br rest br br used to carry out breathing, heartbeat, circulation of blood br br and other basic reactions br br also used in maintaining body temperature at constant all movements or physical work e.g. walking, eating br br required more energy. br br b Occupation means activity occurring everyday everyday activity determines energy requirement People doing heavy work like digging require more energy br br than office workers. br br c Age children carry out many activities and also have more cell br br division than adults br br their BMR is therefore higher than for adults as they grow older, they become less active and their energy requirements decrease br br d Body size small bodied people have a large surface area to volume br br ratio br br their bodies lose more heat energy to the surrounding they therefore require more energy-giving foods this is the opposite for big bodied people e Sex most males are more muscular than females they also do heavier work than females hence require more br br energy br br females do lighter work hence require less energy f Climate Observation Conclusion - colour changes to blue black/dark blue - colour changes to Green to yellow to orange to brown to red - colour changes to Green to yellow to orange to brown to red -- colour changes to purple/violet DCPIP decolorized - translucent mark - white emulsions br br Present br br Present br br Present FORM TWO TOPICS br br 1. a i Define transport br br movement of substances from one part of the body to br br another br br ii Explain the necessity of transport in plants and animals make nutrients move from one point to another movement of respiratory gases i.e. oxygen and carbon IV br br oxide br br elimination of metabolic wastes br br movement of hormones movement of water movement of salts movement of enzymes br br b i Describe the structure and function of root hair br br root hairs are found near the root tip they are cells with elongated finger-like projections which br br are in contact with soil particles br br they are permeable to water and mineral salts hence are br br used to absorb water and mineral salts br br There large number offers a large surface area for br br absorption of water and mineral salts. br br ii State ways in which the root hairs are adapted to their functions br br the root hair is long/narrow/numerous to increase surface br br area for absorption of water and mineral salts br br many mitochondria in cytoplasm to supply energy for br br active transport of mineral salts br br are thin walled to speed up rate of absorption of water and br br mineral salts br br c i Compare the internal structure of a dicotyledonous root and a monocotyledonous root Dicot root br br br br Monocot root br br ii State the similarities and differences between a dicotyledonous and monocotyledonous root Similarities br br 262 both used for anchorage and absorption of water and br br mineral salts br br both have root hairs, epidermis, pericycle, cortex, br br endodermis and vascular bundles xylem and phloem br br both may be used to store food/storage organs br br Differences Monocotyledonous Dicotyledonous br br phloem and xylem are arranged in ring form alternately pith present br br phloem lies between radial rays of central xylem star shaped br br pith absent br br i ii Compare the internal structure of a monocotyledonous and dicotyledonous stem Monocotyledonous Dicotyledonous br br br br v Give the similarities and differences between a monocotyledonous and dicotyledonous stem br br Similarities br br both are used for protection both conduct water, salts and food both have epidermis, cortex, pericycle and vascular bundles br br Differences Monocotyledonous Dicotyledonous br br vascular bundles are many and scattered some have hollow pith br br vascular bundles are few and arranged in a concentric ring near the epidermis br br or pith is absent no cambium layer therefore cannot undergo secondary growth br br pith large and well br br developed br br presence of cambium therefore undergoes secondary growth cortex has several layers of cells br br very little cortex br br 263 has root hairs no cuticle xylem and phloem no root hairs cuticle present xylem and phloem br br arranged alternately in xylem, the small arranged on the same radii br br in xylem, the smallest vessels are towards the inside br br vessels are towards the outside br br cortex is the widest br br pith is the widest tissue c i Name the transport structures of a flowering plant br br tissue br br xylem vessels and tracheids transport water and mineral br br salts from the soil br br Phloem vessels translocate manufactured food from leaves br br to other parts of the body. br br ii State the ways in which xylem vessels are adapted to their function br br lignified/thickened to prevent collapsing narrow to facilitate capillary no cross walls for continuous flow/column of water have bordered pits for lateral movement of water d i Why do flowering plants need water? photosynthesis transport turgidity which helps in plant support solvent i.e. medium for chemical reactions cooling effect during transpiration seed germination br br ii Describe the movement of water from the soil to the leaves of a tall plant Soil br br water exists as a thin film in the soil, between soil particles the concentration of cell sap of root hair is greater than that of the surrounding solution in the soil, thus drawing the water molecules across the cell wall and cell membrane into the root hair by osmosis br br water drawn into the root hair cell dilutes the cell sap br br making it less concentrated than that in the adjacent cortex cells of the root due to osmotic gradient water moves from the root hair cells into the cortex by osmosis, from cell to cell by osmosis, across the endodermis by active transport into xylem vessels of the root that conduct water into xylem vessels of the stem into xylem vessels of the leaves br br Stem br br Once in the stem water moves up the plant aided by the br br narrowness of the xylem vessels capillary , root pressure, attraction of water molecules to each other cohesion . Attraction of water molecules to the walls adhesion br br from the stem water enters the xylem of leaves water moves in the xylem vessels of the stem in a br br continuous uninterrupted water column up to the tree leaves br br Leaves br br once in the leaves water moves into the mesophyll cells by br br osmosis br br as water vaporizes from the spongy mesophyll cells their sap becomes more concentrated than the adjacent cells br br as the result water flows into the cell from other br br surrounding cells which in turn takes in water from xylem vessels within the leaf veins this creates a pull suction force called transpiration pull br br that pulls a stream of water from xylem vessels in the stem and roots br br The transpiration pull maintains a continuous column of br br water from the roots to the leaves. br br iii Name the process by which mineral salts enter into a plant br br active transport diffusion vi Explain the forces that make water and mineral salts br br move through a plant br br mineral salts are taken up due to diffusion because of the br br concentration gradient between the mineral ions in sap and those in soil solution br br active transport involves energy in form of ATP due to respiration which forces mineral salts through a plant against a concentration gradient br br water moves by osmosis through a semi-permeable membrane of root hairs and between cells of stem br br in stem water moves by cohesion attraction of water br br molecules to each other br br it also moves by adhesion attraction of water molecules to br br walls br br capillarity is due to narrowness of xylem vessels transpiration pull occurs when water vapour evaporates br br from sub-stomatal chambers into the air br br root pressure is a force that pushes water up the stem from br br the roots and causes guttation /exudation br br vii Explain the uptake of mineral salts by plants plants require mineral salts for metabolism and proper br br functioning of their bodies br br mineral salts are taken up from the soil into the root hairs in form of solution by active transport which requires energy active transport involves substances called carriers taken up together with water and are then carried to the stems and leaves br br the main process involved in uptake and movement of br br mineral salts is active transport br br e i What is transpiration? loss of water from plant to the atmosphere br br ii Name the sites through which transpiration takes place in a plant br br stomata stomatal transpiration lenticels lenticular transpiration cuticle cuticular transpiration iii State the importance of transpiration to plants br br cooling the plant transport of water transport of mineral salts excretion of excess water from plants excess transpiration causes wilting v Explain the structural factors that affect the rate of br br transpiration in plants br br number of stomata i.e. the more the stomata the higher the br br rate and vice versa br br turgidity of the guard cells which control the opening and closing of stomata when they are open transpiration rate is high br br size of leaves where the larger the surface area the higher br br the rate of transpiration leaf fall leads to lower rate of transpiration and also drying br br of leaves reduces rate of transpiration br br Thin cuticle reduces distance through which water br br vaporizes hence increase transpiration rate. Absence of cuticle also increase rate of transpiration br br vi explain the environmental factors that affect rate of br br transpiration in plants br br high temperature increases rate of transpiration and low br br temperature reduces the rate br br humidity when high increases rate and when low reduces br br the rate br br transpiration rate is higher in moving air wind than in still br br air br br high light intensity increases internal temperature hence br br higher rate of evaporation leading to higher rate of transpiration br br availability of water in the soil leads to more absorption br br hence more loss to the atmosphere br br atmospheric pressure when high leads to more evaporation br br and when low leads to low rate evaporation of water br br vii State the structural differences between xylem vessels br br and sieve tubes br br sieve tubes have cross wall while xylem vessels have none xylem vessels are lignified while sieve tubes are not Sieve tubes have cytoplasm elements while xylem vessels br br have none. br br viii State the adaptations of plants which enable them to reduce water loss br br thick waxy cuticle reduced leaf size/thorns/spines shedding of leaves Sunken stomata. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporation br br rolling of leaves ix State the factors that cause increase in the rate of br br transpiration from leaves br br increased light intensity low relative humidity temperature x Explain how drooping of leaves on a hot sunny day is br br advantageous to a plant reduces surface area exposed to sun reducing cuticular br br transpiration br br f Explain how aquatic and terrestrial plants are adapted br br to deal with problems of transpiration br br a. Mesophytes br br they grow in soils with enough water water loss is perfectly balanced by absorption of more from br br the soil br br no special adaptations b. Xerophytes br br they grow in dry conditions root grow very deep to absorb water succulent/fleshy leaves to store water few stomata which are sunken thickened waxy cuticle leaves are hairy and often folding some leaves are needle-like/spines or scales leaf surfaces are reduced i.e. small leaves all these adaptations are to reduce water loss br br c. Hydrophytes br br plants that grow in water presence of sclereids leaves are broad leaves have many stomata on upper side only none on the br br lower surface br br some leaves float on water absence or reduced leaf cuticle large air spaces some leaves are submerged poorly developed or reduced vascular bundles g i What is translocation transfer of manufactured food substances to the parts where they are required br br ii Name the tissue which is responsible for translocation of manufactured food in flowering plants br br phloem tissue br br iii Name the processes that bring about the translocation of manufactured food -active transport Diffusion Mass flow Cytoplasmic streaming iv Draw a labeled diagram to represent phloem tissue br br br br vi State the functions of the labeled structures br br cytoplasmic strands br br translocation Companion cell br br supply nutrients to sieve tube element supply energy for translocation regulates activities of tube cells/elements br br Sieve tubes element br br conduct food down the stem vii name the compounds that are translocated in phloem sugars amino acids hormones e.g auxins oils/lipids resins vitamins Describe an experiment you would carry out in order to demon-strate that phloem transports manufactured food substances in a plant a. Ringing experiment cut a ring in the bark including the phloem from the stem of br br a woody plant br br phloem is found next to or just beneath the bark observe daily for some time more than three weeks a swelling of the bark appears above the ring this is due to accumulation of food from leaves br br 269 the bark of a second similar plant is removed carefully br br leaving the phloem intact a swelling does not appear ii Use the radioactive tracers br br plant is exposed to carbon containing radio-active carbon br br C14 br br C14 is found in the end products of photosynthesis It is finally detected in phloem C14 is found to move in both directions iii Collecting exudate from stylets of aphids br br aphids feed on certain plant phloem using their stylets aphid mouthparts are dissected using a sharp razor exudates from the mouthparts are collected and then br br analyzed br br sucrose is found to be a major component of the exudates this proves that phloem translocates manufactured food br br substances br br h Describe an experiment you would carry out to br br demonstrate that xylem transports water br br i. Either cut a stem of a young plant or twig of a tree under water or else uproot a young herbaceous plant and wash the soil br br gently br br put some water in a beaker and add a dye i.e. eosin or red ink and place the cut stem or young plant in a beaker leave for time e.g. between 20 minutes and one hour cut a thin section of stem or leaf mount it on a slide and examine under a microscope observe and note the distribution of the dye or ink the dye appears only in the xylem vessels ii. OR use radio-active tracers, C14 in form of carbon ring a plant then put it in a container containing radio- active phosphorous solution br br The radio-active phosphorus is later detected in the leaves. 2. a i List the components of animal transport br br systems br br system of blood vessels in which materials are circulated br br round the body br br blood, a fluid medium which contains dissolved substances br br and cells the heart, a pumping mechanism which keeps blood in br br circulation br br ii Distinguish between closed and open circulatory systems closed system has blood vessels through which blood br br moves eg vertebrates br br open system has no blood vessels hence blood is in direct br br contact with tissues e.g arthropoda br br iii What are the advantages of the closed circulatory system over open circulatory system? Closed system has continuous vessels hence able to br br generate high pressure br br Circulates blood over longer distance Circulates blood at a faster rate Efficient transport of nutrients and waste products Animals are more active br br iv Distinguish between single circulatory system and double circulatory system Single circulatory br br blood passes through the heart once in a complete circuit of br br the body Double circulation -blood enters the heart twice in a complete circulation - Pulmonary circulation from the heart to lungs and back - Systemic circulation from the heart to body systems and back b i describe the general layout of the transport system in mammals br br blood which is a fluid tissue of the body carrying food br br substances, oxygen, carbon IV oxide and metabolic wastes arteries which are elastic tubes carrying blood from the br br heart to cells br br veins which are blood vessels carrying blood away from br br the cells to the heart br br capillaries which are extremely numerous and are microscopic channels connecting arteries to veins ii Describe the structure and function of the mammalian heart br br the heart is a four-chambered hollow muscle located in the br br thoracic cavity br br it consists of two small receiving chambers, the br br atria auricles and two larger pumping chambers, the auricles br br 272 br br the left ventricles is the most powerful and has the thickest br br walls br br this is because it is the chamber which pumps blood br br throughout the body br br each time it contracts, blood is forced out into the elastic br br arteries aorta br br blood moves on to the capillaries from capillaries blood moves to veins and back to the heart br br through the vena cava br br 273 from vena cava it enters into right auricle which contracts br br and pumps blood into the right ventricle br br right ventricle pumps blood into the lungs through the br br pulmonary artery br br blood releases carbon IV oxide to lungs and picks oxygen br br then returns to left auricle br br left auricle pumps blood into left ventricle left ventricle then pumps blood into the aorta and into br br arteries, starting the process all over again br br both auricles contract simultaneously while both iii Explain how the mammalian heart is adapted to performing its functions br br the heart is made of muscles that contract and relax br br synchronously without requiring nervous stimulation br br nerve supply however, determine contraction strength and br br frequency br br the heart is divided into four chambers The right atrium is connected to the right auricle. It br br receives blood from the whole body. br br The blood is pumped from the left atrium to the right br br ventricle br br To avoid flow back into the right atrium, a valve is present br br between the two chambers the tricuspid valve br br The right ventricle pumps blood to the lungs This is facilitated by the presence of pulmonary artery A valve is also present to avoid blood flowing back from the pulmonary artery to the right ventricle br br Blood from the lungs enters the heart through the br br pulmonary vein into the left atrium. br br When the left atrium contracts, blood flows into the left br br ventricle br br Blood will not flow back into the left atrium because of the br br presence of bicuspid valve mitral br br The left ventricle is connected with the aorta and when it br br contracts, blood flows into the aorta for distribution into the whole body br br The heart muscle surrounding the left ventricle is thicker than that surrounding the right ventricle to be able to generate enough pressure to push blood to the whole body A pace-maker is present in the heart muscle to initiate and br br synchronise contractions. For the heart muscle to be well nourished and be provided with enough oxygen and carbon IV oxide removal, it is supplied with blood by the coronary arteries and drained by the coronary veins br br iv Explain why blood leaving the lungs may not be fully oxygenated br br under ventilation of the lungs blockage of alveoli air sacs high cardiac frequency i.e. high rate of pumping of blood in br br the heart br br e Describe the structure and functions of the blood vessels br br i. Arteries carry away blood from the heart carry oxygenated blood except pulmonary artery which br br takes blood from the heart to lungs for oxygen br br have thick, muscular walls are elastic have narrow lumen all these adaptations are required to withstand high pressure br br caused by heartbeat br br ii. Capillaries link arterioles and venules to arteries and veins small in diameter to increase pressure resistance for br br materials to filter out br br thin walled as they consist of a single layer of cells to allow br br diffusion of substances e.g leucocytes to tissues thin walled to allow presence of intercellular spaces large number i.e. numerous to provide a large surface area for exchange of materials br br have sphincter muscles at the junction of the arterioles and br br capillaries to control movement of blood into them lie close to the body for easy exchange of materials iii. Veins carry blood back to the heart all carry deoxygenated blood except pulmonary vein that br br carries blood from the heart to lungs br br have thinner walls than arteries have valves to prevent backflow of blood have wide lumen g i State the ways in which the composition of blood in br br the pulmonary arterioles differs from that in the pulmonary venules Pulmonary arterioles deoxygenated high carbon IV oxide low oxygen more nutrients br br ii Give the reasons why pressure of blood is greater in the arterioles than I the veins of mammals br br blood is pumped to the arteries by the heart at high pressure blood pressure in veins is reduced by capillary resistance arteries have narrow lumen which maintains high br br pressure/veins have wide lumen which reduces pressure arteries have more/thicker muscular walls which generate pressure/veins have less/thinner muscular walls which reduce pressure br br iii Name the common heart diseases in humans br br thrombosis antheroma arteriosclerosis varicose veins cerebral vascular thrombosis h i State the functions of mammalian blood transport of substances defense against diseases clotting temperature regulation br br ii Describe how mammalian blood components carry out their functions Plasma br br transport dissolved food substances like glucose, amino br br acids, fatty acids and glycerol from small intestines to liver and other body tissues br br transports hormones, enzymes from secretory glands to tissues when required br br transports carbon IV oxide to lungs and urea from tissues to br br the kidneys distributes heat bathes the tissues allowing for exchange of materials contains protein fibrinogen and pro-thrombin which take br br part in blood clotting Red blood cells Erythrocytes br br transports oxygen from the lungs to body tissues in form of br br haemoglobin transport carbon IV oxide from body tissues to the lungs in br br form of bicarbonates White blood cells leucocytes br br engulf foreign bodies produce antibodies for defense against disease produce antitoxins which neutralize bacterial toxins br br Blood platelets thrombocytes br br produce an enzyme called thrombokinase/thromboplastin br br necessary for blood clotting br br prevents loss of blood, water and mineral salts br br iii State the ways in which the red blood cells are adapted to their functions br br many per unit volume hence carry more oxygen and carbon br br IV oxide br br biconcave in shape to provide large surface area for br br absorption of oxygen and carbon IV oxide br br absence of nucleolus hence more haemoglobin to carry br br sufficient oxygen and carbon IV oxide br br alter shape to be able to pass through the narrow lumen of capillaries to deliver or supply oxygen and carry away carbon IV oxide br br have haemoglobin with high affinity for uptake of oxygen br br and carbon IV oxide br br iv State the structural differences between a red blood cell and a white blood cell. Red blood cells white blood cells Explain how oxygen and carbon Iv oxide are transported in the blood Oxygen br br oxygen concentration is higher in lungs alveoli that in br br blood br br oxygen in the alveoli dissolves in the film of moisture and diffuses through thin epithelial and capillary walls into plasma and red blood cells br br the oxygen combines with haemoglobin to form br br oxyhaemoglobin br br blood then becomes oxygenated blood from lungs then travels to all body tissues where the br br oxyhaemoglobin breaks down to form oxygen and haemoglobin br br haemoglobin is transported back to the lungs to collect br br more oxygen while the oxygen in capillaries diffuses into body cells for respiration br br respiration produces carbon IV oxide br br Carbon IV oxide br br carbon IV oxide produced during respiration diffuses out of br br cells into blood plasma and red blood cells due to concentration gradient br br carbon IV oxide and water form carbonic acid carbamino br br compounds with haemoglobin br br in the presence of carboxyl anhydrase enzyme, hydrogen br br carbonate is carried in blood to the lungs br br in the lungs the hydrogen carbonate dissociates to liberate carbon IV oxide which diffuses into alveolar cavity due to concentration gradient br br from alveolar space carbon IV oxide is expelled during br br expiration br br Most carbon IV oxide is transported from tissues to lungs within the red blood cells and not in the blood plasma. Give the advantages of this mode of transport. br br - PH of blood is not altered/homeostasis is maintained - Within the red blood cell is an enzyme, carbonic anhyrase which helps in fast loading combining and offloading of carbon Iv oxide i i what is blood clotting? process in which blood components clump together to br br prevent loss of blood from an injured/cut vessel ii Name a protein, vitamin, an enzyme and a mineral element involved in blood clotting Protein fibrinogen/prothrombin Vitamin - k/quinine Enzyme thrombokinase/thromboplatin/thrombin Mineral element calcium iii Describe the blood clotting process br br enzyme thromboplastin produced in the platelets of br br damaged tissues converts plasma protein prothrombin into thrombin in the presence of calcium ions br br thrombin converts another plasma protein fibrogen into br br fibrin in the presence of vitamin K br br fibrin is insoluble fibrin forms fibres which form a meshwork that forms a br br clot br br prothrombin thromboplastin thrombin br br calcium ion br br Fibrinogen thrombin fibrin clot br br vitamin K br br iv State the role of blood clotting on wounds prevents blood/body fluids from being lost conserves water and salts prevents entry of microorganisms/pathogens regulates body temperature enables wound to heal faster br br v Explain why blood flowing in blood vessels does not normally clot - Presence of anticoagulant in blood j i. list the major types of human blood groups O, with neither B nor A antigen AB, with both A and B antigens A, with type A antigen B, with type B antigen iii. explain the meaning of : Universal donor a person who can donate blood to any other blood group br br without agglutination/clumping br br this is usually blood group O however this person cannot receive blood from other blood br br groups except group O br br Universal recipient can receive blood from all blood groups without br br agglutination br br this is usually blood group AB however, can only donate blood to group AB br br iii What is the difference between rhesus positive and Rhesus negative blood samples? br br rhesus positive blood has the Rhesus Rh antigen rhesus negative lacks the Rhesus antigen br br vi What is blood transfusion? - Introduction of blood from one person to another v Under what conditions would blood transfusion be necessary in people? during accidents during surgery in hospitals bleeding mothers when giving birth vi How can low blood volume be brought back to normal? transfusion taking fluids eating iron rich food/taking iron tablets How may excessive bleeding result in death? Anaemia/low blood volume/loss of iron/low red blood cells br br count/low haemoglobin leading to low oxygen, loss of nutrients and dehydration. br br State the precautions that must be taken before blood transfusion blood must be disease free sterilized equipment must be used blood of the recipient and that of the donor must b compatible to both ABO and rhesus factor br br Fresh blood must be used. br br j i What is immunity? - Resistance to disease by organisms ii Distinguish between natural and acquired immunity br br natural immunity is inherited/transmitted from parent to br br offspring/inborn/innate br br Acquired immunity is developed after suffering from a br br disease or through vaccination. br br iii What are allergic reactions? br br Excessive sensitivity and reaction of an individual to certain substances in environment e.g. dust, pollen, perfumes, smoke etc. vi How does an allergic reaction occur? the substances act as antigens an antigen-antibody reaction occurs on surface of cells the cells release a substance called histamine the histamine causes irritation, itching and may stimulate br br nasal discharge br br vii State the role of vaccination against certain diseases br br protect body against infectious diseases prevent spread/transmission of certain diseases diseases for which vaccination is given include br br tuberculosis, poliomylitis,measles, whooping cough, diphtheria br br 3. a i What is gaseous exchange? br br The continous exchange of oxygen and carbon Iv oxide br br between the organism and environment. br br ii Why is gaseous exchange important to organisms? to supply oxygen necessary for energy production to remove carbon IV oxide produced during respiration To remove water vapour. br br b i name the structure used for gaseous exchange by plants br br stomatal pores/stomata lenticels cuticle pneumatophores ii Briefly describe the structure of stomata are minute pores found in leaf epidermis each consists of a slit-like opening Each is bordered by two large, bean-shaped guard cells. Guard cells contain chloroplasts, unlike the other epidermal br br cells which enable photosynthesis to occur br br Inner walls of guard cells are thicker than the outer cells br br iii State the factors which affect stomatal opening br br water which when low stomata close and when high br br stomata keeps open br br light as stomata open in bright light and close in darkness temperature br br iv Name the theories suggesting the mechanism of opening and closing of stomata br br interconversion of starch and sugar pH theory mineral ion concentration v Describe the mechanism of opening and closing of stomata br br stomata close at night and open during daytime This comes about due to changes in turgidity as a result of br br pH changes in guard cells. br br In the dark carbon Iv oxide accumulates in the intercellular br br spaces br br This raises concentration of carbonic acid The pH drops pH lowered Enzymes convert sugar into starch in guard cells Osmotic pressure in guard cells is lowered Water moves out of guard cells by osmosis making cells br br lose turgidity hence become flaccid br br The stomata close During day time there is photosynthesis hence the br br production of sugar, carbon IV oxide concentration is lowered, pH increases, guard cells become turgid causing stomata to open. br br During the day potassium ions concentrate in guard cells, raising their osmotic pressure and causes then to open In the night the concentration of potassium ions decreases increasing osmotic pressure in guard cells therefore causes stomata to open. br br vii What is the advantage of having stomata open br br during daytime and having them closed at night? opening in the daytime allows diffusion of carbon IV into br br the leaf for photosynthesis to take place and allows diffusion of oxygen out of the leaf br br transpiration also takes place, thus cooling the leaf and br br facilitating uptake of water and mineral slats br br Closing in the night is to conserve water in the plant br br especially when there is not enough water available in the soil. c i State the ways in which leaves of plants are adapted to gaseous exchange br br presence of stomata for faster gaseous exchange intercellular spaces/air spaces in the leaf for br br movement/circulation of air br br film of moisture around the surface of cells for easy br br diffusion br br broad/flattened shape to increase surface area thin lamina to reduce distance of diffusion br br exposed to air for easy diffusion br br ii Describe how gaseous exchange takes place in terrestrial plants br br Gaseous exchange takes place in spongy mesophyll During the day air diffuses into large air spaces of spongy br br mesophyll through stomata br br The carbon iv oxide in the air diffuses into the br br photosynthesis oxygen is produced br br Some of the oxygen diffuses out of the leaf through stomata During the night air diffuses out of air spaces of spongy br br mesophyll br br The air dissolves into film of moisture The oxygen in the air diffuses into cells and is used in respiration during which carbon iv oxide is produced br br The carbon iv oxide diffuses out of the leaf through stomata br br due to diffusion/concentration gradient br br At night carbon iv oxide accumulates in the leaf since br br photosynthesis does not take place br br Some gaseous exchange also takes place through cuticle Gaseous exchange occurs through epidermis of young br br leaves and stems br br The cork cells at lenticels are loosely packed Gaseous exchange takes place between cork and br br atmosphere within the loosely packed cells iii State the ways in which floating leaves of aquatic br br plants are adapted to gaseous exchange br br stomata found only on upper dermis to allow efficient br br gaseous exchange br br presence to aerenchyma tissues/large air spaces to enable it br br float/buoyancy/storage of air br br absence of cuticle to enhance gaseous exchange iv How is aerenchyma tissue adapted to its function? has large airspaces which store gases/for gaseous br br exchange/buoyancy br br v Explain stomatal distribution in plants of different br br habitats br br land plants have their stomata mainly on the lower side to reduce water loss but if on both sides then upper side has very few br br water plants, floaters, have stomata on upper side to br br enhance water loss in dry areas, plants have leaves with sunken stomata to br br reduce water loss by transpiration br br Plants in wet areas have stomata equally distributed on both br br sides. br br d i List the types of respiratory surfaces of animals br br cell membrane in unicellular organisms e.g. amoeba gills in fish tracheal system skin, buccal cavity and lungs in amphibians lings in mammals br br ii State the characteristics of respiratory surfaces in animals br br moist thin walled/thin membrane/thin surface Highly/richly vascularised/numerous blood vessels/well br br supplied with blood vessels. br br Large surface area br br iii Describe gaseous exchange in protozoa br br example is amoeba small and have large surface area oxygen diffuses into the organism and carbon IV oxide br br diffuses out into water br br simple diffusion of gases is enough to meet its respiratory br br requirements br br e i Make a labeled drawing of a fish gill br br br br ii How is a fish gill adapted to its function? large surface area due to many filaments extensive vascularisation due to capillaries, for gaseous br br exchange br br thin filaments to facilitate diffusion of gases presence of rakers to filter solid particles gill bar is bony, hard and firm to support the filaments and br br rakers and for attachment of filaments and rakers br br iii Discuss gaseous exchange in bony fish br br example is tilapia br br 284 the mouth opens and the floor of the mouth is lowered so that the volume in the mouth is increased and pressure is lowered br br water then enters into the mouth cavity the mouth is closed and the floor of the mouth raised so that br br the volume is reduced br br this raises the pressure, forcing water over gills and out br br through the operculum br br As water passes over the gills oxygen diffuses due to br br concentration gradient partial pressure into the blood stream. br br In the body tissues, carbon IV oxide diffuses into the blood due to concentration gradient, and is transported to the gills and diffuses out into the water. br br iv What is counter-flow system? br br Where water in which the fish lives flows in opposite br br direction across the gill. br br vi What is the advantage of counter-flow system? maintains a diffusion gradient so that there is maximum br br uptake of oxygen br br oxygen continues diffusing into blood and carbon iv oxide br br into water br br f i Describe the mechanism of gaseous exchange in terrestrial insects br br example is cockroach air in the atmosphere contains oxygen air is drawn into the body of the insect through the spiracles due to movement of abdominal muscles br br these movements cause the opening of spiracles air moves through the trachea to tracheoles oxygen moves from the tracheoles into body cells by br br diffusion due to concentration gradient br br carbon iv oxide in the tissues diffuses into tracheoles due to br br concentration gradient br br From tracheoles carbon IV oxide moves into trachea and br br out through the spiracles into the air. br br ii State how traceholes are adapted to gaseous exchange br br thin walls of tracheoles moist surface large surface area due to numerous tracheoles br br g i What is breathing? Any process which speeds up the rate of gaseous exchange br br between an animal and its surrounding. br br ii Name the structures in humans that are used in gaseous exchange nose larynx epiglottis trachea lungs pleural membrane pleural cavity diaphragm muscles br br iii Describe the mechanism of gaseous exchange in a mammal Breathing in br br external intercostals muscles contract while internal br br intercostals muscles relax, raising the ribcage upwards and outwards br br muscles of the diaphragm contract hence it flattens the volume of the thoracic cavity increases while pressure br br decreases br br higher air pressure in the atmosphere forces air into lungs br br through the nose br br Breathing out br br external intercostals muscles relax while internal intercostals muscles contract, moving the ribcage downwards and inwards br br muscles of the diaphragm relax hence the diaphragm br br assumes dome shape br br the volume of the thoracic cavity decreases while pressure br br increases br br the higher pressure forces air out of the lungs through the br br nose iv Explain how mammalian lungs are adapted to gaseous exchange br br large number of alveoli that increase surface area moist inner surface of alveoli for dissolving oxygen/gases br br to facilitate exchange of gases through alveolar cavities and blood br br thin walls of alveoli to allow efficient/faster diffusion of br br gases rich capillary/blood supply on alveolar surface to transport oxygen away from the lungs and carbon IV oxide to the lungs br br v Name the features of alveoli that adapt them to their function br br have large surface area/spherical shaped numerous/many to increase surface area one cell thick moist surface for air to diffuse highly vascularised/numerous capillaries vii How is the trachea of a mammal suited to its br br function? br br has a ring of cartilage which keeps it open at all times cilia that move mucus/particles to the top of the trachea i.e. br br into larynx for removal br br mucus to trap dust, solid particles and microorganisms hollow for passage of air viii State the advantages of breathing through the nose br br rather than through the mouth br br nose has hairs to filter solid particles it has mucus lining to trap dust particles the nose has cells sensitive to smell for survival it warms the air before it reaches the lungs ix Give the conditions under which the carbon iv oxide br br level rises above normal in mammalian blood vigorous exercise emotions/stress disease infection x Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it rises br br heartbeat/cardiac frequency increases to pump blood faster carbon iv oxide from the tissues and supply more oxygen ventilation rate/rate and depth of breathing increases to take more oxygen and remove carbon iv oxide from the lungs br br arterioles to take in more oxygen and remove carbon iv br br oxide from the lungs br br arterioles dilate leading to faster flow of blood to and from br br body tissues br br h i Describe the factors which control the rate of breathing in humans breathing movements usually occur unconsciously it is controlled by the medulla oblongata part of the brain br br situated at the breathing centre medullar oblongata is in the brain respiratory centre transmits impulses to the diaphragm br br through phrenic nerves br br carbon iv oxide concentration in the blood determines the br br breathing rate br br if carbon iv oxide is less, the brain is triggered to decrease br br breathing rate br br cardiac frequency decreases and the arterioles constrict therefore carbon iv oxide level is raised this brings back to normal level of breathing and carbon iv br br oxide level increases/is more the brain is triggered to increase breathing rate br br cardiac frequency is increased there is vasodilation of arterioles carbon iv oxide level falls therefore the normal level is attained and carbon iv oxide is br br removed faster br br ii Name the respirator diseases br br asthma bronchitis whooping cough pneumonia tuberculosis br br 4. a i Define respiration br br the oxidation/breakdown of food within cells to release br br energy br br ii Explain the significance of respiration in living organisms br br it yields energy ATP this energy enables organisms to move, grow, excrete and br br reproduce br br iii Where does respiration take place? br br in the mitochondria br br b i Draw and label a mitochondrion br br 288 br br ii State the most important function of mitochondria br br to produce Adenosine triphosphate ATP which is the br br energy source of the whole cell br br iii Give the functions of the labeled parts Outer membrane br br controls what enters and what leaves mitochondrion br br Cristae br br also called inner membrane increase surface are for attachment of enzymes this is where cellular oxidation reactions occur br br Matrix br br enzymes are located here other reactions occur here br br c Explain the roles of enzymes in respiration br br they catalyse reactions i.e. speed up respiration br br d i What is aerobic respiration br br respiration in the presence of oxygen br br ii Give a word equation for aerobic respiration br br glucose oxygen - water carbon iv oxide energy br br iii What are the end products of aerobic respiration? br br energy carbon iv oxide water br br e i What is anaerobic respiration occurs in the absence of oxygen br br 289 e.g. yeast and certain bacteria release energy in the absence br br of oxygen br br ii What are obligate anaerobes? br br are completely independent of oxygen br br iii What are facultative anaerobes? br br can survive both in the presence and absence of oxygen also called partial anaerobes br br iv State the word equation representing anaerobic respiration in plants - Glucose ethanol carbon iv oxide energy v Name the end products of anaerobic respiration in plants br br alcohol/ethanol carbon iv oxide energy br br g i Give a word equation of anaerobic respiration in animals - Glucose lactic acid energy ii Name the end products of respiration in animals when there is insufficient oxygen supply br br lactic acid energy br br iii Why is there a high rate of lactic acid production during exercise? br br the demand for oxygen is more than supply leading to br br anaerobic respiration br br iv Why does lactic acid level reduce after exercise? br br lactic acid is oxidized to form carbon iv oxide and water some is converted to glucose some is converted into glycogen v State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat br br lactic acid is poisonous to tissues and must be removed to increase supply of oxygen to tissues State the economic importance of anaerobic respiration brewing of alcohol biogas production compost manure formation silage formation baking bread production of dairy products fermentation of milk sewage treatment h i What is respiratory quotient RQ ? br br ration of carbon IV oxide produced to oxygen consumed br br RQ volume of CO2 produced br br Volume of oxygen consumed br br ii Why are respiratory quotient important br br their calculation assists in identifying the kind of substrate br br being used in respiration br br iii Name the respiratory substrates br br carbohydrates fats proteins br br iv Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration? - Some energy locked up in intermediate products like ethanol in plants and lactic acid in animals br br substrate is completely oxidized in aerobic respiration br br iv Explain the disadvantages of anaerobic respiration br br Less energy produced in anaerobic respiration since food is br br partially oxidized while in aerobic respiration food is completely oxidized. br br Some metabolic wastes accumulate in cells affecting br br cellular functions br br Ethanol produced in plants poisons the tissues while lactic acid produced in animals causes muscle fatigue/muscle cramp and may stop muscle contraction br br Such intermediate wastes are not produced in aerobic br br respiration br br v Mention the types of experiments carried out for respiration germinating seeds which yield energy in form of heat animals produced heat when they respire yeast cells respire to produce heat br br 5. a i Define the following terms Excretion br br the process by which organisms get rid of waste products which result from chemical process which occur in living cells Secretion br br the process by which organisms produce substances which br br are useful to the body, by glands br br Egestion br br removal of indigestive materials from the body br br Homeostasis br br maintenance of constant internal environment br br ii Explain why excretion is necessary in plants and animals -products of excretion are usually harmful while some are toxic - if allowed to accumulate in the cells they would destroy tissues and interfere with normal metabolism - They are therefore removed through excretion b i Describe how excretion takes place in green plants carbon IV oxide, oxygen and water diffuse through the br br stomata, lenticels and hydathodes br br some toxic wastes are converted into non-toxic substances these are deposited in certain tissues of the plant or stored br br in aging structures br br resins and tannins are exuded through the bark of stem or br br lost during leaf fall br br ii Why do plants lack complex excretory structures like those of animals? br br plants have lower rates of metabolism plants excrete non-poisonous products derived from br br carbohydrate metabolism unlike animals which produce toxic wastes derived from protein metabolism br br plants re-use some of their wastes like nitrogenous wastes br br used in protein synthesis br br plants store waste products in roots, fruits and leaves ii State the excretory products of plants and some of their uses to humans br br caffeine from tea and coffee is used in medicine and as a br br stimulant which is harmful to humans br br quinine used for treating malaria cocaine derived from leaves of cocoa plant used as a br br stimulant by addicts or as a local anesthesia, also causes damage to the brain, may cause addiction if not well used and is an illegal drug Nicotine got from leaves of tobacco plant stimulates the central nervous, may cause addiction if much is used or consumed. It is used to make cigarettes, cigars and is poisonous. It is a precursor of lung cancer Cannabis sative bhang is used to make drugs Gum derived from glues is used for sticking substances br br and making certain jellies br br Rubber , a product of latex, got from rubber plant is sued to br br make tyres and synthetic fibres br br Morphine from opium poppy plant is a narcotic and illegal br br drug as it causes addiction br br Khat and miraa are used as stimulants Colchicines used in inducing polyploidy, cancer therapy, br br treatment of gouts in small quantities br br Papain used as meat tenderizer br br c i Describe excretion in unicellular organisms -examples are amoeba and paramecium -They have to remove waste products such as carbon IV oxide and nitrogenous substances e.g urea and ammonia - These diffuse from the body surface into the surrounding water - Diffusion is due to large surface area ii List excretory organs and products of mammals br br kidney excretes urea, water and salts skin excretes water, slats and urea lungs excrete carbon IV oxide and water liver excretes bile salts d i Draw and label a mammalian skin br br br br ii Explain how the mammalian skin is adapted to its functions br br the skin is made up of dermis and epidermis br br Epidermis br br it is made up of three layers the outermost layer, cornified layer is made up of dead cells that prevent entry of microorganisms, prevent physical damage and dessication br br granular layer made of living cells gives rise to cornified br br layer br br malpighian layer is made up of actively dividing cells that give rise to new epidermal cells/granular layer it contains melanin that protects the body against ultra violet rays radiations br br Dermis br br has several components Has sweat gland which produce sweat through sweat pores on the skin and the sweat evaporates cooling the body by lowering body temperature. When it is cold, no sweat is produced, conserving water br br sweat contains water, sodium chloride, uric acid and urea br br hence the skin acts as an excretory organ br br Has hair. The hair stands erect to trap air when temperature is low to reduce loss/insulation. It lies flat to allow heat loss when temperature is high. br br 294 Has nerve endings which are sensitive to stimuli such as br br heat, cold, pain, pressure and touch br br Has subcutaneous fat/adipose fat that insulates the body br br against heat loss br br Has arteries and capillaries blood vessels that supply food br br and oxygen and remove excretory products. Arterioles vasodilate when temperatures are high to lose heat by radiation, and convention. Arterioles constrict when temperatures are low to conserve heat i.e. reduce heat loss Has sebaceous glands which secrete sebum, and antiseptic and water repellant that prevents drying and cracking the skin by making the skin supple e What is the role of lungs in excretion? br br during respiration oxygen is used up in the body cells to br br produce energy br br carbon IV oxide is produced as a by-product the carbon IV oxide must be eliminated from the body elimination is through the lungs also, water vapour is formed and must be removed this removal is through the lungs the lung is therefore considered as an excretory organ as it removes carbon IV oxide and water vapour which are by- products of respiration f State the functions of the liver i. Excretion br br in this function the liver is aided by the kidney deamination i.e. excess amino acids converted into urea and br br uric acid which is transported to skin and kidney for removal br br detoxification where harmful substances are converted into harmless ones in the liver and transported to kidneys for removal br br breakdown of worn out blood cells and haemoglobin and the residue excreted through the kidney to give urine a yellow tinge br br Breakdown of sex hormones after they have performed their function and the wasted are released through the kidney and bile. br br ii Homeostasis br br regulation of blood glucose the normal amount of glucose in blood is about 90mg/100 br br increase in blood sugar is detected by cells of the pancreas br br which secrete insulin br br insulin stimulates the liver to convert excess glucose to br br glycogen br br further excess glucose is converted to fats until the normal br br blood sugar level is attained br br Excess glucose is oxidized to carbon IV oxide, water and br br energy. Excess glucose is also used in respiration decrease in blood sugar level below normal level is br br detected by the pancreas, which secretes glucagon which stimulates the liver to convert glycogen to glucose until the normal sugar level is attained br br fats, amino acids are converted to glucose it also leads to reduced oxidation of glucose br br Deamination br br excess amino acids are deaminated by the removal of br br amino group br br the amino group is converted to ammonia ammonia combines with carbon IV oxide to form urea urea is excreted in urine through the kidney br br Detoxification br br poisonous substances are converted to less harmful br br compounds Thermal regulation br br maintenance of body temperature heat is generated in the liver by chemical activities the heat is distributed br br g i Draw a labeled diagram of mammalian nephrone br br br br 296 br br ii Describe how the human kidney functions br br the afferent arterioles, which is a branch of the renal artery, br br supplies blood to the glomerulus br br the afferent arteriole has a wider diameter than the efferent br br arteriole br br this difference in diameter of afferent and efferent vessels br br causes high pressure leading to ultra filtration br br the walls of the blood capillaries are one cell thick hence br br glucose, amino acids, vitamins, hormones, salts, cratinine, urea and water filter into Bowmans capsule to form glomerular filtrate br br white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary walls hence remain in blood capillary br br the filtrate flows into proximal convoluted tubule where amino acids, vitamins and all glucose are selectively reabsorbed back into the blood stream br br many mitochondria provide energy for reabsorption of br br these substances against a concentration gradient by active transport br br the glomerular filtrate flows into the loop of Henle br br 297 water in the descending loop moves by osmosis into the br br blood capillaries br br sodium chloride is actively pumped from the ascending arm br br of the loop of Henle into the blood capillaries br br the glomerular filatrate flows into the distal convoluted br br tubule br br water and salts are reabsorbed from distal convoluted br br tubule into blood capillaries br br the glomerular filtrate flows into collecting tubule duct from where more water is reabsorbed into blood stream br br antiduretic hormone influences the amount of water reabsorbed depending on osmotic pressure of blood br br the glomerular filtrate from collecting duct, now referred to as urine, is emptied into pelvis and ureter into bladder and out of body through urethra br br urine consists of excess water, slats and nitrogenous wastes iii State the adaptations of proximal convoluted tubule to its function br br folded to increase surface area for absorption thin epithelium to reduce distance of diffusion micro-villi on inner lining to increase surface area for br br absorption br br folded to reduce speed of flow for efficient absorption numerous mitochondira to provide energy for reabsorption dense capillary network to transport reabsorbed products iv Name the common kidney diseases br br nephritis kidney stones renal calculi cystitis oedema kidney failure br br 6. a i Why is homeostatic control necessary? br br this provides a constant internal environment so that the cells of the body have the optimum best condition for their survival br br ii What is internal environment? br br immediate surrounding of body cells refers to tissue fluid within an organism br br b i Why is constant body temperature maintained by mammals? br br most enzymes in the body function within a narrow range br br of temperature high temperature denatures enzymes low temperature inactivates and inhibits enzymes br br i i Explain the advantage gained by possessing a constant body temperature br br animals remain active despite fluctuations in environmental br br temperature br br higher chances of survival in various environments ie they br br colonize various environments br br chemical processes in their body continues at an optimum br br rate br br iii How do mammals regulate body temperature? br br the body temperature of a mammal is kept constant to maintain this temperature the mammal must be able to br br balance its heat loss against the heat gain br br body temperature is controlled by the hypothalamus, a br br specialized part of the brain br br changes in the temperature within the body and the surrounding are detected by the hypothalamus br br it transmits impulses to the skin and the blood stream in br br response to temperature changes br br hypothalamus acts as a thermostat for the body a mammal loses heat by breathing out, urine, feaces, skin br br by radiation and by evaporation of sweat. br br A mammal generates heat by the activity of its muscles, by general metabolism in respiration, or chemical activities In hot conditions the hypothalamus stimulates responses that increase heat loss from the body hence lowering the body temperature br br Such responses include sweating, vasodilation, keeping its hair flat on the surface of skin and reduction of metabolic rate br br In cold conditions the hypothalamus stimulates responses that generate heat gain in the body and reduce heat loss to the environment br br Such responses include shivering, vasoconstriction, raising its hair to trap a layer of air around the skin because still air is a good insulator of heat and by generation of heat by increasing metabolic rate. br br iv Why does body temperature of a healthy person rise up to 37oC on a hot humid day? sweat evaporation is reduced hence cooling is less therefore more heat is retained in the body causing temperature to rise br br v Name the structures in the human body that detect external temperature changes br br temperature receptors end bulb corpuscles e.g. bulb of br br Krause warmth and organ of Ruffinni cold br br heat thermal receptors br br vi State the advantages that organisms with small surface area to volume ratio experience over those with larger br br heat loss slow hence their body temperature can increase to br br intolerable levels br br Heat gain from surrounding slower hence may remain br br inactive for a long time. br br Need specialized and complex transport system and also br br gaseous exchange system br br Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes. surface area to volume ratio is higher in smaller individuals than larger ones, therefore smaller heat is lost faster by smaller ones than larger ones br br they therefore require more energy per unit body weight to br br maintain body temperature c i What is the meaning of osmoregulation? br br mechanism which regulates osmotic pressure of internal br br environment of an organism br br the regulation/maintenance of salt/solute-water balance of br br an internal environment br br ii State the importance of osmoregulation - Maintenance of constant level of water and slats osmotic pressure for optimum/suitable conditions for metabolism suitable for cellular functions iii State the ways by which desert mammals conserve water br br fewer glomeruli longer loop of Henle excretion of dry feaces or concentrated urine hump for fat to be metabolized to give metabolic water for br br use br br nocturnal, burrowing, aestivate or hibernate sweat glands few or absent more ADH vasopressin iv Explain why some desert animals excrete uric acid rather than water br br uric acid is less toxic than ammonia, hence elimination of uric acid requires less water than ammonia therefore more water conserved br br uric acid being less toxic is safer to excrete where there is br br less water/desert br br v Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine br br the concentration of salts in the blood rises leading to production of more ADH hence higher rate of water reabsorption by kidney tubules br br vi Explain how marine fish regulate their osmotic pressure swallow plenty of sea water to increase amount of water in br br the body br br have chloride excretory cells in their gills to remove excess br br salts br br eliminate nitrogenous wastes in form of trimethalamine br br oxide which requires little water for elimination br br few/small glomeruli thus slow filtration rate in the kidneys retain nitrogenous wastes in form of urea to raise osmotic br br pressure of body fluids br br d i What is the biological significance of maintaining a relatively constant sugar level in a human body? br br body cells are surrounded by tissue fluids that are isotonic/same osmotic pressure as cytoplasm br br if sugar level is high/hypertonic, cell will lose water by br br osmosis to the surrounding, thus increasing the concentration of the contents br br this changes the physiology of the cell if the blood sugar is lower than the normal, the cytoplasm gains water by osmosis, diluting the cell contents, thus altering the physiology of the cell ii Discuss the role of the following hormones in blood sugar control Insulin br br insulin is produced when there is increase in blood sugar br br concentration br br it converts glucose to glycogen which is in the liver or br br muscle thus lowering sugar level br br Glucagon when glucose level decreases glucagon is produced, which causes the breakdown of glycogen to glucose thus raising blood sugar level br br e Explain the part played by antidiuretic hormone in homeostasis br br Produced when there is less water high osmotic pressure above normal level of salt concentration in the blood. It acts on kidney tubules nephron thus increasing water br br reabsorption from tubules to the blood stream, thus restoring osmotic pressure br br When there is more water lower osmotic pressure or br br decreased salt concentration in blood, little or no ADH is produced, less water reabsorbed hence water loss in urine more dilute urine hence raising the osmotic pressure in body fluids/blood br br f What is the role of blood clotting in homeostasis? br br when a blood vessel is cut, there is exposure of blood br br platelets to the air br br this triggers fibrinogen to be converted to fibrin the fibrin forms a clot that prevents body fluids e.g. blood br br from being lost br br therefore the clot conserves water and salts in the body g Describe the role of the following hormones in homeostasis br br i. Aldosterone br br concerned with regulation of ionic balance secreted by the cortex of adrenal glands it increases sodium ion uptake by the gut and promotes the reabsorption of sodium ions and therefore water in the kidneys br br this is accompanied by elimination of potassium ions this raises the overall level of sodium and lowers the br br overall level of potassium in the blood br br as sodium ions are absorbed in the blood, chlorine ions follow so as to neutralize the effect of sodium ions br br the production of aldosterone is regulated by the br br concentration of sodium ions which has an inhibiting effect, and a fall in sodium ions has a stimulating effect on the adrenal cortex br br the flow of aldosterone is stimulated by the adreno-cortic- tropic hormone ACTH produced in the anterior of the pituitary gland br br however, the main method of control is dependent on the fact that adrenal cortex itself is somehow sensitive to the relative concentration of potassium and sodium in the blood br br ii. Adrenaline br br produced by adrenal glands in high concentrations, it increases hydrolysis of glycogen br br and increases blood sugar br br it is usually released in emergency cases to increase br br glucose level for respiration br br this releases energy for the emergency br br h i Distinuish between diabetes mellitus and diabetes insipidus br br diabetes mellitus is a condition resulting from insufficient br br production of insulin causing hyperglucaemia and presence of glucose in urine br br diabetes insipidus is a condition whereby less or no br br antidiuretic hormone is secreted hence a high volume of water is passed out in urine in a condition called diuresis ii How can high blood sugar level in a person be controlled? br br administer insulin br br iii Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowmans capsule? glucose molecules are actively reabsorbed in the proximal br br convoluted tubules br br iv When is glycogen which is stored in the liver converted into glucose and released into the blood? after activity/when blood sugar glucose falls below br br normal br br when glucagon stimulates the liver/when glucagon is produced after strenuous/vigorous activity during starvation br br v How would one find out from a sample of urine whether a person is suffering from diabetes mellitus? test or react urine in Benedicts solution positive result i.e. orange or red precipitate Positive result is an indication of diabetes mellitus. FORM III TOPICS br br 1. a i What is meant by the term binomial br br nomenclature? br br scientific system of naming organisms using the generic genus and specific species names br br ii State briefly the general principles of classification of living organisms br br scientific names must be in Latin or should be latinised family names are formed by adding the suffix idea to the stem of the genus e.g. the genus Rana become Ranaidea br br generic names should be a single unique name br br b State the main characteristics of the five kingdoms of organisms br br i. Monera e.g. bacteria unicellular single celled prokaryotic genetic material not surrounded by membrane cell wall without cellulose lack most organelles small in size microscopic br br ii. Protista protoctista br br single celled unicellular eukaryotic most cell organelles present when cell walls are present have no cellulose e.g. protozoa and algae usually microscopic iii. Fungi br br have hyphae which form mycelia absence of chlorophyll have rhizoids lack roots, leaves, stem have spore forming structures sporangia e.g. mucor, rhizopus iv. Plantae most are green/contain chlorophyll autotrophic/feed by photosynthesis cells have cellulose cell walls respond slowly to stimuli tropism lack locomotion are stationary indefinite growth at meristems lack specialized excretory structures v. Animalia cells do not have cell walls most carry out locomotion heterotrophic fast response to stimuli tactic have specialized excretory structures c Describe the economic importance of: br br i. Fungi some cause decay to our food some cause diseases to humans and animals e.g. ringworms may be used as food e.g. mushrooms, yeast some are used in production of antibiotics e.g. penicillin, br br chloromycin, streptomycin br br yeast is used in brewing industry, baking and source of br br vitamin B br br many cause diseases to our crops e.g. late blight important in recycling nutrients in soil since they cause br br decay of organic matter br br mycorrhizal association in forest development may help in br br water intake/absorption help in nitrogen fixation Bacteria are useful in the manufacture of antibiotics silage formation, fermentation of cheese, butter, milk yoghurt curing of tea, tobacco and retting flax formation of vitamin B12 and K enzymes such as amylase and invertase hormones such as insulin vinegar, acetic acid, lactic acid, citric acid in septic tanks and modern sewage works make use of bacteria br br biogas production saprophytic bacteria are used in compost decomposition or br br cause decay br br symbiotic bacteria are used in compost decomposition or br br cause decay br br symbiotic bacteria in herbivores/ruminants help in br br digestion br br some diseases in animals/humans and plants are caused by br br bacteria br br many bacteria cause food spoilage/decay br br nitrifying and nitrogen fixing bacteria increase soil br br fertility/make nitrates available br br denitrifying bacteria reduce soil fertility/convert nitrates br br into nitrogen/reduce nitrates br br d State the main characteristics of the following division of kingdom plantae i. Bryophyte e.g. mosses and liverworts presence of rhizoids lack of vascular tissues lack phloem and xylem body parts not differentiated into root, stem, leaves capsule or seta gametophyte generation dominant. ii. Pteridophyta e.g. ferns has true roots, stems and leaves fond with sori on under-surface vascular tissues present sporophyte generation is dominant iii. Spermatophyte photosynthetic well differentiated into roots, stems and leaves well developed vascular system seed bearing plants br br e Name sub-divisions of spermatophyte and state the characteristics of each class br br i. Gymnospermae cornifers naked seeds exposed are all woody trees reproduce by means of cones show xerophytic characteristics xylem have tracheids but lack vessels phloem lacks companion cells single fertilization pollen lands directly on ovules ii. Angiospermae flowering plants reproduce by flowers seeds enclosed in fruits flowers bisexual hence double fertilization herbaceous pollen grains land on stigma of pistil xylem contains vessels phloem contains companion cells ovules contained in ovary iii. Name the classes and state characteristics of br br angiospermae br br Dicotyledonae br br two seed leaves network venation of leaves regularly arranged vascular bundles tap root system broad leaves secondary growth occurs br br Monocotyledonae one seed leaf parallel venation of leaves irregularly arranged vascular bundles fibrous root system narrow leaves sheath like leaf stalk petiole no secondary growth br br iv State the importance of plants br br balancing carbon IV oxide and oxygen in the atmosphere br br during photosynthesis and respiration br br influence water cycle reduce soil erosion by bind soil particles together useful products e.g. food, medicine, timber, paper and br br clothing br br habitat e.g. forests and grassland for animals which may br br also be tourist attraction br br earn money from sales of products aesthetic value/beauty e.g. flowers, shade/shelter, live br br fences, windbreaks br br Some are harmful e.g. poisons, weeds, injurious stinging nettles, thorns , water hyacinth. br br f i Give the general characteristics of phylum arthropoda br br jointed appendages presence of exoskeleton triploblastic and coelomate segmented body bilateral symmetry similar halves ii. State the characteristics of the following classes of br br arthropoda Diplopoda br br the millipedes two pairs of legs per segment many segments terrestrial habitat body cylindrical and long herbivorous one pair of antennae br br Chilopoda br br the centipedes one pair of legs per segment many segments terrestrial habitat body long and ventro-dorsally flattened carnivorous last pair of legs pointing backwards with poison claws br br called maxillipedes one pair of antennae br br Insecta br br three body parts i.e. head thorax, abdomen six legs/three pairs of legs a pair of compound eyes presence of wings a pair of antennae br br Crustacean br br two body parts segmented body have pincers modified legs to catch prey have hard exoskeleton a pair of compound eyes br br Arachnida br br body divided into two parts abdomen and cephalothorax simple eyes eight legs four pairs of legs br br iii State the economic importance of insects Beneficial effects food supply important in food chains pollinators biological control of pests and other organisms aesthetic value contribute to decomposition e.g. litter feeders like beetles br br Harmful effects br br pests vectors dirt and disease carriers injurious e.g. stings and bites br br g i State the general characteristics of chordate br br notochord dorsal slits pharyngeal cleft during development bilateral symmetry triploblastic three layer body-ectoderm, mesoderm and br br endoderm br br clear cut head formation multilayered epidermis post anal tail closed circulatory system segmented muscle blocks myotomes single pair of gonads br br Give the characteristics of the following classes of chordate Pisces br br presence of fins for locomotion two chambered heart presence of overlapping scales presence of gills or operculum for gaseous exchange presence of lateral line for protection streamlined body poikilothermic body temperature varies with that of br br environment br br Amphibian br br partially live in fresh water and partially on land poikilothermic pentadactylous with two pairs of limbs webbed feet for locomotion in water body streamlined heart is three chambered moist skin for gaseous exchange br br skin is dry oviparous lay eggs no pinna external ear three chambered heart 9crocodile has four chambers skin not glandular no mammary glands br br Aves br br the birds homoeothermic constant body temperature four chambered heart streamlined body for locomotion in air skin dry and covered by feathers scales on legs hollow bones oviparous lay eggs mouths modified into beaks br br Mammalian br br hair on the body homoeothermic viviparous give birth to live young except a few have mammary glands glandular skin e.g. sweat glands, sebaceous glands four chambered heart pinna external ear two pairs of pentadactyl limbs presence of diaphragm have salivary glands i i What is a dichotomous key? A biological device tool which enables one to identify an organism by progressively opting between two alternative observable characteristics br br ii. State the necessity of using a dichotomous key used to identify organisms quickly and accurately by following the statements in the key we are able to identify each organism on the basis of a characteristic which is not to be found in other specimens br br iii. List the rules followed in constructing a br br dichotomous key use observable characteristics only start with major characteristics, placing organisms into two br br groups at each stage use a single characteristics at a time use contrasting characteristics at each stage e.g 1 a short, br br 1 b tall br br avoid repeating the same characteristics br br iv Describe the procedure of using a dichotomous key. Make a list of major features of the characteristics to be identified br br look at the features of similarities look at the features of differences between the organisms we can then be able to identify the organisms by br br distinguishing one from another br br the key uses a method of elimination by following statements that are correct only for the organism iv You are provided with a specimen kale leaf. Use the dichotomous key below to identify the taxonomic group to which the specimen belongs. Show the steps number and letter in the key that you followed to arrive at the identify of the specimen 1 a leaf broad b leaf narrow go to 2 Araicaria 2 a leaf parallel veined b leaf net-veined 3 a leaf with one lobe simple b leaf with many lobes compound Grevellea Kalanchoa 4 a leaf fleshy go to 5 b leaf not fleshy 5 a leaf petiole modified to form sheath b leaf petiole not modified to form sheath Brassica 6 a leaf purple b leaf green steps 1a, 2b, 3a, 4b, 5b Identify Brassica v You have been provided with four animals labeled K mature adult housefly , L mature adult grasshopper, M maize flour beetle and N worker termite use the dichotomous key below to identify the specimens. Write down in the correct order, the steps number and letter in the key that you followed to arrive at your answer. Dichotomous key 1 a animal with wings b animal without wings 2 a with two pairs of wings br br Cynodon br br go to 3 go to 4 br br go to 6 br br go to 2 br br go to 7 go to 3 b with one pair of wings 3 a with membranous wings b hind pair of membranous wings 4 a with long abdomen b medium sized abdomen 5 a wings with coloured scales b wings without scales 6 a forewings hard and shell-like b forewings hard but not shell-like 7 a body horizontally flattened b body laterally flattened Identify the orders o the various specimens as per the table below Specimen K-housefly L- grasshopper M- beetle M-termite br br Diptera go to 4 br br go to 6 br br Odontata br br go to 5 Lepidoptera hymenoptera coleopteran br br Orthoptera br br Isoptera Symphonoptera br br Order Diptera Orthoptera Coleoptera Isoptera Steps followed 1a,2b 1a, 2a, 3b, 6b 1a, 2a, 3b, 6a 1b, 7a 2 a Define the following ecological terms br br i. Ecology br br study of the interrelationships between organisms and their br br environment br br ii. Environment br br surrounding of the organism i.e. biotic or a biotic factors br br iii. Habitat br br A specific locality home of a living organism with a set of br br factors conditions in which an organism lives. br br iv. Ecological niche br br Role of an organism in its habitat e.g. feeding relationship br br v. Population br br Number group of organisms of a species occupying a br br given habitat br br vi. Community br br Refers to different species of plants and animals organisms in a given habitat area co-existing or interacting living with each other and the environment in which they live br br vii. Ecosystem br br A community of organisms interacting with one another br br and the environment in which they live br br viii. Biosphere The earth and its atmosphere where living organisms are br br found br br ix. Autecology br br Study of a single individual species of plants or animals within a community, ecosystem, habitat or environment. br br x. Synecology br br Study of natural communities plants and animals or br br populations interacting within an ecosystem. br br xi. Carrying capacity br br maximum number of organisms an area can support br br without being depleted br br xii. Biome br br geographical area with particular climatic conditions and br br flora and fauna br br it constitutes many ecosystems br br xiii. Biomass br br dry weight mass of a living organism in a given area units of measurement are kg/m2/year br br b i What are abiotic factors? br br non-living components of the ecosystem br br ii Explain how abiotic factors affect living organisms Wind br br this influences rate of water evaporation from organisms therefore it affects distribution of organisms e.g. wind increases rate of transpiration and evaporation of water from the soil br br wind is an agent of soil erosion, may break and uproot trees may aid in the formation of sand dunes which can form habitats for some desert plants wind disperses fruits, seeds, spores wind forms waves in lakes and oceans which enhances br br aeration of water which replenishes oxygen concentration necessary for life br br wind is an agent of pollination br br Temperature br br influences rate of enzyme action in photosynthesis and br br other metabolic reactions in plants and animals br br organisms function within a narrow range of temperature it affects distribution of organisms changes in temperature affect rate of photosynthesis and br br biochemical reactions e.g. metabolism and enzyme reaction br br temperature increases rate of transpiration Light br br needed by green plants and photosynthetic bacteria which br br are primary producers br br animals depend on plants directly or indirectly for food main source of light is the sun light is necessary for synthesis of vitamin D in certain br br animals br br some plants need light for flowering seeds like lettuce need light for germination br br Humidity br br amount of water vapour held by the air affects the rate at which water is lost from organisms body br br by evaporation and stomatal transpiration br br when humidity is low the rate of transpiration increases humidity influences distribution of organisms br br PH br br each plant requires a specific PH in which to grow acidic, br br neutral or alkalinic br br pH affects enzyme reaction in metabolism br br Salinity br br some ions are needed for plant and animal nutrition osmoregulation implants and animals is affected by salinity br br Topography br br altitude affects light, atmospheric pressure and light Slope influences surface runoff, wind erosion, etc. mountains affect distribution of organisms which differs in br br leeward side and windward side br br mountains affect distribution of organisms which differ on br br lowlands and on highlands br br mountains also form physical barriers to migration of organism and may cause isolation of species br br background may offer camouflage to some organisms br br hence protection from enemies br br Rainfall water or precipitation br br amount and distribution of rainfall affect vegetation type this consequently affects distribution of animals e.g. polar region water frozen hence only well adapted organisms survive br br fewer organisms found in deserts where rainfall is less Water is required for seed germination, raw material for br br photosynthesis, solvent for mineral salts. Provides turgidity for plant support, medium for transport, disperses fruits, seeds and spores br br Pressure br br the weight atmosphere exerts upon the earth varies with altitude 9the higher the altitude the less the br br pressure br br this variation implies change in density which directly br br means less oxygen for respiration and less carbon iv oxide for photosynthesis and this affects distribution of organisms br br Mineral salts trace elements br br these affect distribution of plants in the soil plants thrive best where elements are available Plants living in soil deficient in a particular element must br br have special methods of obtaining it. br br They harbor nitrogen fixing bacteria and others have br br carnivorous habit br br Plant distribution influences animal distribution br br c i What are biotic factors? br br refers to living organisms in an area biotic environment of an organism constitutes all organisms around it, which it relates or interacts with in various ways br br ii Give examples of biotic factors affecting ecosystems br br feeding relationships predation competition diseases and pests human activities br br d Discuss how the various biotic factors affect living organisms br br i. Competition organisms compete with one another for food, light, water, mates and shelter br br organisms must live together for competition for available br br resources br br those which cannot cope either structurally or behaviorally br br will migrate or die br br those remaining, due to better adaptations will increase in br br population br br competition between members of the same species is called br br intra-specific competition e.g. for mates br br Competition between members of different species is inter br br specific competition e.g. for food and space. ii. Predation this is predator-prey relationship predator feeds on prey hence both control the others br br population br br Distribution of predator and prey is important as predator br br cannot survive without prey br br It there is no predator the prey will increase in population beyond carrying capacity hence die due to environment depletion iii. Parasitism an association where an organism lives in or on another br br living organism obtaining food and other benefits from it, causing harm to it without necessary killing it br br parasites may kill host they deprive host of food make host weak by introducing diseases make reproductive ability of host low hence host becomes br br susceptible to predation iv. Diseases and parasites make organisms weak and susceptible to predation kill organisms and reduce their population v. Symbiotic and association of organisms of different species where br br both benefit from the association i.e. there is mutual benefit br br vi. Human activities these are human factors which have an influence on the br br biosphere br br examples are road construction, industrialization, br br deforestation, agriculture, pollution, poaching, fishing conservation, population control affect ecosystem and balance of nature Saprophytism saprophytes are organisms which obtain organic matter in solution from dead and decaying tissues of plants and animals br br they include saprophytic bacteria and fungi they make available carbon, nitrogen and other elements br br form dead to living organisms br br they are useful in recycling nutrients in nature br br e i What is nitrogen cycle? br br The process by which nitrogen in the air is made available br br plants and animals and eventually returns to the air. ii Draw a simplified diagram representing the nitrogen cycle br br br br iii Describe the nitrogen cycle br br during thunderstorms/lightning nitrogen gas combines with br br oxygen to form nitrogen oxides br br nitrogen oxides dissolve in water to form nitric acid acid is deposited in the soil by rain nitric acid combines with chemical substances to form br br nitrates or nitric acid dissociates to form nitrates which are absorbed by plants br br symbiotic bacteria Rhizobium which are found in root nodules of leguminous plants fix free nitrogen to nitrates br br free living bacteria clostridium and Azotobacter fix br br nitrogen to nitrates br br nostoc algae Anabaema chlorella fix nitrogen to nitrates plants use nitrates to form plant proteins animals feed on plants and convert plant proteins into br br animal proteins br br plants and animals die and are decomposed by putrefying br br bacteria, fungi saprophytes br br decomposing plants, animals and nitrogenous wastes release ammonia which is converted to nitrites by Nitrosomonas and nitrococcus bacteria br br nitrites are converted to nitrates by nitrobacter bacteria nitrates in the soil can be converted to free nitrogen denitrification by some fungi, pseudomonas and theobaccilus bacteria generally called denitrifying bacteria br br iii. Nitrogen in the atmosphere cannot be directly utilized by plants. State two ways by which this nitrogen is made available for plant use br br fixation by microorganisms Rhixobium, Axotobacter fixation by electrical discharge in atmosphere i.e. br br conversion by thunderstorm or lightning br br 317 f i Describe how energy flows from the sun through the various trophic levels in an ecosystem br br energy from the sun is trapped by green plants during photosynthesis, producing chemical energy9food or carbohydrates br br green plants are producers and occupy the first trophic level green plants are eaten by herbivores called primary producers as they occupy the second trophic level br br herbivores are eaten by carnivores, secondary consumers, br br which occupy the third trophic level br br when organisms 9plant and animals die, fungi and bacteria which are saprophytic organisms feed on them thus causing them to decompose into simple substances e.g. mineral salts br br these organisms are called decomposers and detrivores decomposer feed on dead organic matter hence cause decomposition and decay which releases nutrients for plants, linking biotic and a biotic components at all levels energy is lost through respiration br br Give the reasons for loss of energy from one trophic level to another in a food chain br br insufficient utilization of food resources wastage e.g by br br defalcation br br through respiration through excretion e.g. urination and sweating br br Why are green plants referred to as primary producers in an ecosystem? - They utilize the energy from the sun to manufacture food for themselves and for subsequent trophic level consumers and other organisms vi . Explain the following terms giving suitable examples Food chain br br a nutritional sequence between producers and consumers through which energy flows in a straight line i.e. linear representation of feeding relationship between different organisms in an ecosystem br br if one consumer or the producer is removed the food chain br br is broken br br arrow points to the direction of energy flow e.g. green plant br br herbivore carnivore decomposer br br br br Food web br br 318 complex feeding relationship where a consumer feeds on more than one type of food while several herbivores feed on one type of plant br br it is an interrelationship of many food chains consumers are usually fewer than producers to ensure br br survival of both br br br br Pyramid of numbers br br this is a diagrammatic representation of numbers of organisms at each trophic level in a food chain usually there are more producers than consumers hence producers herbivores carnivore the reason for the pyramid is because herbivores feed on many plants producers as carnivores feed on many herbivores br br sometimes this may not be true e.g. when many caterpillars br br feed on one tree or parasites on a herbivore this gives an inverted pyramid of numbers br br Pyramid of biomass br br refers to diagrammatic representation total dry weight of organisms at different trophic levels in a food chain br br producers have greater biomass than any level of br br consumers progressively br br size of organisms in successive e trophic levels increases amount of individuals decreases in successive levels br br Account for the decrease of biomass in the successive trophic levels br br 319 fixed energy which supports living matter decreases at each successive trophic level since energy is lost by respiration and indigested unconverted materials hence less biomass supported at each level br br h i Describe the three characteristics of a population growth br br increase in numbers decrease in numbers/growth rate change in numbers br br Dispersion br br spread or distribution of organisms in a habitat br br Density br br the number of individuals per unit area br br ii Explain how the following methods are used to estimate population of organisms quadrat method br br identify the study area throw or mark out the quadrat in the area of study at br br random br br identify or label the various species of plants in the quadrat count plants of each species record the numbers repeat the process work out the average per quadrat for each species calculate the total number of different species in the area or br br calculate the population for the total area of habitat br br Line transect br br a string is stretched along an identified area all plants touching the string are counted br br Belt transect br br preliminary study of the study area to estimate size or make a sketch map br br two parallel lines strings or ropes running for a br br determined distance and width br br count the number of organisms in the transect calculate the area covered by the transect calculate the number of organisms being investigated per br br unit area br br repeat this process at least three times in other parts of the br br study area br br find the mean number of organisms per unit area from all br br the belt transects from this figure calculate the total population of the desired br br organisms in the study area. br br Capture-recapture method e.g. grasshoppers or fish capture the grasshoppers count and mark using permanent ink record release and allow time recapture and count the marked and unmarked total population is equal to the number of marked and br br unmarked grasshoppers in the second sample multiplied by the number of marked grasshoppers in the first sample divided by number of grasshoppers marked in the second sample that were recaptured br br 2. a Describe the adaptations of plants to various br br habitats br br i. Xerophytes grow in areas with scarcity of water roots grow deeply and extensively widely spread to br br ensure access to water br br thick succulent stems, roots and leaves for water storage photosynthetic stems take place of leaves which would lose br br a lot of water br br Leaves are needle-like reduced to spines , scaly, have br br sunken stomata. Some have curled rolled leaves. Some have thick waxy cuticle, reduced number of stomata to reduce water loss by transpiration some shed leaves during dry season to reduce water loss presence of thorns for protection short life cycle to ensure survival reversed stomatal rhythm ii. Hyrophytes br br grow in places with plenty of water waterlogged aerenchyma a tissue airspaces and large intercellular spaces and long fibrous roots for buoyancy floating in water br br poorly developed support tissues sclerenchyma because br br water provides the necessary support br br upper epidermis of leaves have more stomata than lower epidermis for gaseous exchange or for increased rate of transpiration br br poorly developed conducting tissues xylem and phloem br br because plants obtain water by diffusion br br iii. Mesophytes br br grow in well watered soils common plants no special adaptations, but depending on particular habitat, br br may have some adaptations br br in forests they grow fast, tall to capture light. Have br br climbers while some are adapted to carry out photosynthesis in low light intensities those that form undergrowth br br in places with adequate water they form broad leaves, thin br br cuticle and many stomata on both leaf surfaces in direr regions they possess more stomata on the lower leaf br br surface and are deep rooted roots for support drip off rain water br br some are shallow rooted and develop buttress and prop br br iv. Halophytes br br plants that grow in very salty soil where the salt concentration is higher than that in the plant br br have root cells which concentrate a lot of salts in them and br br enable then to take in water by osmosis br br succulent roots to store water have pneumatophores breathing roots to take in oxygen some have buttress roots for support secrete excess salt by use of salt glands have large airspaces in leaves and stems for buoyancy and to store air br br capable of photosynthesis at low light intensities e.g. mangrove br br b i What is pollution? br br any process which leads to adverse or harmful changes in br br the environment br br ii Explain the various human activities that have caused pollution Causes and effects of air pollution br br sulphur iv oxide, hydrogen sulphide, chlorine, oxides of nitrogen produced by industries, sewage, decomposing organic matter and fumes affect gaseous exchange, makes acid rain and damage plant leaves br br aerosols, herbicides, insecticides agrochemicals , paint spays, acaricides and CFCs sprayed to control diseases, pests and weeds affect respiratory organs of animals. The chemicals are residual and persistent not easily broken down and bring depletion of the ozone layer br br smoke and fumes produced in areas with heavy industries, motor vehicles, fires which burn fuel, oil, wood and coal cause carbon ii oxide, poisoning affect respiratory systems and affect visibility br br particles in smoke and fumes settle on leaves and stop br br photosynthesis br br carbon iv oxide causes green house effect which causes br br temperature inversion as a result of heating the lower layers of atmosphere br br sound and noise produced incessantly by machines, br br aeroplanes and heavy vehicles affect hearing in animals dust from cement factories, quarries, dust roads settles on br br leaves limiting photosynthesis br br removal of vegetation interferes with carbon cycle radio-active emissions from nuclear reactors, mines and br br bombs cause cancer, mutations and death. Control of air pollution br br use of lead free petrol in motor vehicles, air craft, br br aeroplanes and petroleum engines uses of smokeless fuels and electricity filtration, dissolution and use of chemicals to remove br br harmful gases br br factories should be erected far away from residential areas use of tall chimneys reduce volume or intensity of sound e.g. by use of ear br br muffs br br concords should fly at higher altitudes and aeroplanes to br br fly high up br br State the causes, effects and methods of controlling and prop roots for support water pollution Causes and effects br br agrochemicals e.g. fertilizers cause eutrophication leading br br to increase in animal population br br Silting makes water surfaces shallow and silt clogs stomata br br and gills of fish reducing rates of photosynthesis and gaseous exchange. It also leads to reduction of algae which causes reduction of consumers i.e. animal population industrial and domestic wastes contain toxic materials which kill producers and other organism while oily substances in wastes may clog gills of fish and may change pH of water oxygen solubility is also reduced by oily surfaces br br Untreated sewage and effluents where decomposition or organic matter in sewage reduces oxygen supply and sewage provides food for bacteria increasing their population and demand for oxygen thus depriving fish of oxygen. br br Human feaces causes eutrophication, carbon IV oxide br br produced by decomposition of faecal matter changes pH of water interferes with photosynthesis and may clog fish gills or block light penetration which interferes with producers thereby decreasing productivity. br br Dumping of chemicals from industries with toxic pollutants br br which kill organisms br br Spillage of oil and chemicals block oxygen and kill br br organisms br br Discharge of water from industries into water body where high temperatures reduce amount of oxygen in the water causing organism to suffocate and die br br Untreated sewage may lead to outbreak of epidemics br br Control of water pollution -pollution caused by domestic effluents may be controlled by treating domestic waste, using biotechnology, banning the use of phosphate-based detergents, using plastic pipes instead of those made from lead, recycling gabbage, using biodegradable detergents. Pollution caused by industrial waste may be controlled by treating/cooling industrial waste, carrying out environmental impact assessment before establishing industries Oil spillage may be controlled by cleaning spilled oil biotechnology and penalizing the industry individual or companies which cause oil spills/water pollution Pollution caused by agrochemicals may be controlled by using mechanical control of weeds, biological control of weeds and pests, biodegradable organic fertilizer herbicides, insecticides pesticides, organic farming educate farmers on the use of correct amount of agrochemicals silting may be controlled by appropriate farming practices, contour farming, reafforestation, building gabions and terracing br br iv State the causes /effects and control methods of soil pollution Causes and effects br br Air pollutants e.g. sulphur IV oxide fumes from sulphuric acid with rain water. The acid rain alters soil pH therefore affecting plants that cannot tolerate acidic soil most aerosols sprayed to control pests and diseases br br precipitate in the soil and are taken up by plants which make its concentration many times higher, increasing the toxicity in the plants which absorb them br br petroleum products due to spillage by oil tankers making it impossible for plant roots to obtain oxygen in oil saturated soils, therefore plants are killed br br agrochemicals and inorganic fertilizers contain heavy br br metals that are not used up by plants and eventually soil microorganisms cannot inhabit the soils br br organic matter slows down, life ceases and soil becomes br br exhausted br br community, household wastes and industrial wastes disposal is a major problem in big towns and cities. commodities packaged in metal tins, rubber, plastic containers, scrap metal, glass bottles, different types of paper are nuisance to the environment, rendering it useless for agricultural purposes Control of soil pollution br br use of organic farming techniques biological control of pests, diseases, parasites recycling of non-degradable containers or burying them br br safely after use br br controlled burning of garbage treatment of human and industrial waste for safe disposal avoid spilling chemicals and oil when used br br v Define biological control give suitable examples br br using a living organism to regulate, control or reduce the br br population of another organism e.g beetles to feed on water hyacinth, fish to feed on mosquito larvae. br br vi What is eutrophication? br br enrichment of water bodies with nutrients due to discharge br br of sewage leading to rapid growth of surface plants viii What are the effects of eutrophication? enrichment of water bodies with nutrients due to discharge br br of sewage leading to rapid growth of surface plants br br vii What are the effects of eutrophication? - The plants block light from reaching plants underneath hence no photosynthesis The plants die and decompose leading to lack of oxygen hence animals also die c Describe the symptoms, mode of transmission and control of cholera, typhoid malaria and amoebic dysentery in humans Disease Causative br br Transmissio n Contaminate d food or water Spread by flies form faeces Symptom s Intestinal pain Diarrhea Vomiting Dehydrati on br br Control br br agent Cholera Vibrio br br Proper hygiene e.g. boiling drinking water Vaccination proper sanitati on vaccina tion br br cholerae bac terium br br Typhoid Salmonella br br contami nated food or water spread by flies from faeces br br typhi bacterium fever rashe s diarr hea bloo d from bowe ls - fever Joint pains Vomiting Headache Anaemia br br killing mosqui to killing the mosqui to larvae drainin br br g stagnan t water clearin g bushes treatme nt sleep under mosqui to net sanitati on person al hygien e cook food well treatme nt using drugs br br Amoebi c dysenter y amoebi asis br br Entamoeba hystolytica bacterium br br - contaminated food or water due to improper disposal of faeces - intestinal pain Diarrhea Vomiting Dehydrati on br br d Discuss Ascaris lumbricoides under the following sub- headings br br i. Mode of transmission through ingestion of contaminated food live in intestines ii. Effects of parasite on the host inflammation of lungs pneumonia produce toxic substances intestinal obstruction iii. Adaptations thick cuticle which protects it against digestion lays many eggs to ensure survival mouthparts for sucking partly digested food lack of elaborate alimentary canal tolerant to low oxygen concentration two hosts to ensure survival eggs have protective cover to ensure survival in adverse br br environments br br iv. Control and prevention proper sanitation wash hand after defaecation and before eating br br e Discuss schistosoma under the following sub-headings br br i. Mode of transmission through contaminated water in swamps, etc ii. Effects on host bleeding in lungs blood stained urine unthriftiness iii. Adaptations has two hosts to increase chances of survival eggs have a hook like structure which raptures the walls of br br intestine or bladder br br lay large number of eggs to ensure survival larvae have a sucker for attachment on human skin which it br br digests br br larva has a tail which it swims with in search of host in br br water br br prolonged association between male and female to ensure br br that fertilization takes place br br adults can tolerate low oxygen concentration in the animal br br tissues br br adult worm secretes chemicals against antibodies larvae and eggs have glands that secrete lytic enzymes to br br soften the tissues that ease penetration br br larvae are encysted so as to survive adverse conditions iv Control and prevention br br proper use of toilet facilities boiling water before use avoid bathing/washing in infected water Use of molluscicides chemicals that kill snails/biological br br control/clearing water weeds on which snails feed. br br Drainage of stagnant water br br 3. Wearing gum/rubber boots br br a i What is reproduction? br br process by which living organisms give rise to new br br members of their own species which resemble the parents br br ii Why is reproduction important? br br for continuity of species/ to ensure survival of species maintaining life of species replace dead individuals br br iii Name the types of reproduction sexual which involves fusion of male and female gametes asexual in which no gametes are involved but parts of a br br mature organism develops into new individuals br br b i What is cell division? br br process by which cells are formed from pre-existing cells br br ii What are chromosomes? br br Threadlike structures found in nucleus of a cell. The units called genes Genes are factors that cause inheritance or determine br br characteristics of offspring br br c i What is mitosis? br br A type of cell division that occurs during growth leading to br br increase in number of cells br br all cells maintain the same chromosome constitution i.e. the br br diploid state br br ii Describe the five stages of mitosis Interphase br br br br replication of organelles duplication of DNA production of energy ATP for cell division br br Prophase br br stage of dehydration chromosomes shorten and thicken chromosome replicates into two chromatids chromatids joined at centromere formation of spindle fibers br br Metaphase br br chromosomes move to equator early metaphase chromosomes line up at the equator homologous chromosomes do not associate br br 329 br br Anaphase br br chromatids separate move to opposite ends poles of the cell br br Telophase br br chromatids reach the poles formation of two daughter cells occurs i.e. cytoplasmic br br division br br ii State the significance of mitosis br br ensures each daughter cell has same number and kinds of br br chromosomes as daughter cells br br gives rise to new cells responsible for growth br br d i What is meiosis? br br division of diploid cells to form gametes which are haploid br br ii State the significance of meiosis br br gives rise to gametes source of variation br br iii Give a summary of the stages of meiosis First meiotic division Interphase br br cell is in non-dividing condition br br 330 chromosomes appear threadlike br br br br Prophase I br br chromatic material shorten and thicken double stranded chromosomes appear bivalent double stranded chromosomes pair and twist round each br br other synapsis br br point of contact of chromosomes is called chiasma br br Metaphase I br br paired homologous chromosomes line up at the equator br br Anaphase I br br paired homologous chromosomes move to the poles br br Telophase I br br paired homologous chromosomes reach the poles two new nuclei are formed br br Second meiotic division Prophase II br br chromosomes shorten, thicken and become visible, stage of dehydration br br Metaphase II br br movement of chromosomes to equator br br 331 br br Anaphase II -chromatids of each chromosome separate to the poles br br Telophase II br br reach the poles four haploid daughter cells are formed br br iv Give the similarities between mitosis and meiosis br br both take part in cells both involve division cell multiplication br br v What are the differences between mitosis and meiosis? Mitosis Meiosis br br maintenance of reduction/halving of br br chromosome number diploid br br chromosomes haploid occurs in reproductive cells/gonads/produces gametes br br takes place in somatic br br cells/growth br br no crossing over/no crossing over takes br br variations br br place/variation occurs results into 4 daughter results into 2 daughter br br cells br br cells there is no pairing/no br br synapsis/no bivalent formed paring/synapsis/bivalen t br br a one division process br br a two division process of four stages each of four stages br br d i What is asexual reproduction br br formation of new individuals as a result of the fusion of br br two gametes br br fusion is called fertilization br br 332 ii What is the significance of sexual reproduction in living organisms? br br leads to genetic variation e.g. cross breeding which gives br br rise to hybrids br br iii State the advantages of sexual reproduction br br genetic variation greater adaptability to environment by offspring few bad or good traits inherited/retained greater amount of dispersal is possible may result in stronger offspring br br iv Give the disadvantages of sexual reproduction br br less certainty in egg and sperm meeting low rate of survival sex-linked diseases easily transmitted br br e i What is asexual reproduction? br br formation of new organisms without fusion of gametes occurs with only one parent parts of organism develop into new individual ii State the advantages of asexual reproduction retention of useful characteristics/genes/traits offspring establish faster/shorter life cycle better chances of survival because of suitable environment br br iii Give the disadvantages of asexual reproduction br br lack of genetic variation lowered resistance to disease loss of hybrid vigor competition for resources due to overcrowding iv Explain how reproduction occurs by the following methods of asexual reproduction Sporulation br br formation of spores spores are small haploid cells produced by plants spores give rise to new haploid organisms includes moulds, ferns, bryophytes, pteridophytes br br Budding br br where an outgrowth arises from a parent and drops off to br br develop into a new organisms br br hereditary material in the daughter cell and parent are br br exactly the same br br occurs in organisms such as hydra, jelly fish, sea anemones, br br yeast and some fungi br br Binary fission a cell splits into two new cells of equal size each daughter cell grows into anew organism Occurs in organisms such as amoeba, euglena, br br paramecium, some fungi and bacteria. br br f i What is a flower? br br this is the reproductive structure which bears the br br reproductive parts of a plant it produces seeds and fruits br br ii Draw a longitudinal section of a labeled diagram of a flower br br br br iii Give the functions of the parts of a flower Receptacle br br expanded end of stalk which bears floral parts br br Calyx br br consists of sepals usually green protect flower in bud br br Corolla br br consist of petals often colored or scented to attract insects br br Androecium br br male part of flower consist of stamens each stamen consists of an anther containing pollen sacs another produces pollen grains which contain male gametes br br Gynaecium br br female part of flower consists of one or more carpels each carpel contains one or more ovules in an ovary style bearing a stigma extends from ovary ovary contains female gametes which when fertilized br br become seeds br br iv What is inflorescence? br br a group of flowers borne on the same branch main stalk br br v Explain the meaning of the following terms which describe flowers Hermaphrodite br br 334 one with both stamen and carpel most flowers are hermaphrodite/bisexual br br Unisexual br br have only one of carpel or stamen i.e. either male or female br br Carpelate br br also called pistilate contains only carpels hence a female flower br br Staminate br br also called male flower contains only stamens br br Dioecious plants br br have pistilate and staminate flowers on different plants e.g. br br pawpaw Monoecius plants br br have pistilate and staminate on one plant however, pistilate and staminate occur at different plants br br e.g. maize br br Complete flower br br Has all four parts i.e. Calyx, corolla, androecium and br br gynoecium Incomplete flower br br does not have all four parts at least one is missing br br vi Explain the meaning of the following types of ovary Superior br br ovary occurs above other floral parts on the receptacle br br Inferior epigynous br br other floral parts arise above ovary on the receptacle br br g i What is pollination? br br transfer of pollen grains from anther of a stamen to stigma br br of a flower br br ii Explain the types of pollination br br self pollination takes place when mature pollen grains of a br br flower fall on the stigma of the same flower br br cross pollination takes place when pollen grains of a flower fall on the stigma of another flower of the same species br br iii State the advantages of pollination br br healthy offspring leads to variation greater chances of dispersal iv List the agents of pollination br br wind water insects br br v How are flowers adapted to wind and insect pollination? Insect pollinated flowers entomophilus br br are scented to attract insects have stick stigma for pollen grains to stick on are brightly coloured to attract insects presence of nectar to attract insects have nectar guides to guide insects to the nectarines have nectarines to secrete nectar stigma/ anthers located inside the flower/tubal/funnel br br shaped corolla to increase chances of contact by insects sticky/spiny/spiky pollen grains which stick on the body of br br insects and on stigma br br large/conspicuous flowers easily seen by/attract insects anthers firmly attached to the filament for insects to brush br br against them br br landing platform to ensure contact with anthers and stigma mimicry to attract male insects Wind pollinated flower anemophilus br br anthers/stigma hang outside the flower to increase chances br br of pollination br br the style/filament is long to expose stigma/anthers stigma is hairy/feathery/branched to increase surface area br br over which pollen grains land/to trap pollen grains br br pollen grains are smooth/dry/light/small to be easily carried br br by wind br br large amount of pollen grains to increase chances of br br pollination br br anthers loosely attached to filaments to enable them to br br sway to release pollen grains br br pollen grains may have structures which contain air to br br increase buoyancy br br flowers have long stalks holding them out in the wind vi State the ways in which plants prevent self-pollination br br protandry anthers/stamens mature first protagyny pistils mature first monoecism where male and female parts are on same plant br br but different parts dioecism where male and female parts are on different br br plants br br incompatibility self sterility heterostyly styles at different heights br br vii Give the characteristics that ensure cross pollination takes place in flowering plants br br presence of special structures that attract agents of br br pollination br br protandry/dichogamy protagyny/dichogamy monoecism self sterility heterostyly viii State the advantages of cross pollination hybrid vigour less prone to diseases promotes genetic variation greater evolutionary potential br br h i What is fertilization? - Fusion of male and female gametes to form a zygote ii Describe how fertilization takes place in a flower br br this follows pollination pollen grain is deposited on the stigma pollen grain sticks to the surface of the stigma the surface of the stigma produces a chemical substance which stimulates the pollen grain to produce a pollen tube/to germinate br br the pollen tube grows through the style tissues on which it br br feeds until it enters the ovary br br the generative nucleus divides into two giving two male nuclei br br embryo sac contains eight nuclei i.e. two synergids, egg br br cell, two polar nuclei and three antipodal cells the pollen tube enters the embryo sac through the br br micropyle and one of the male nucleus fuses with the egg cell/ovum to form a zygote br br the other male nucleus fuses with the two polar nuclei to form the triploid nuclei/endosperm food storage used by developing embryo br br the pollen tube nucleus in the pollen tube disintergrates br br soon afterwards br br this process is referred to as double fertilization br br zygote grows into an embryo containing plumule, radicle br br and cotyledons br br br br iii What is double fertilization? br br there are two male nuclei entering embryo sac one fuses with the ovum to form a zygote, while the other br br fuses with the polar nuclei to form a triploid primary endosperm nucleus br br therefore there are two fusions at fertilization iv Name the changes that Occur in a flower after fertilization br br petals, stamen, calyx and style wither ovary wall changes into pericarp intergument changes into seed coat/testa zygote changes into embryo by mitosis primary endosperm nucleus changes into endosperm whole ovule changes into seed ovary develops and grows into fruit under the influence of br br gibberrellic hormone br br j i Distinguish between a fruit and a seed a fruit is a fertilized ovary and has two scars a seed is a fertilized ovule and has one scar br br ii How is a seed formed? br br after fertilization, zygote grows into an embryo, primary br br endosperm nucleus developed into endosperm, interguments harden to form testa, hence the whole ovule becomes the seed br br the seed loses water to become drier the seed has plumule, radicle, seed leaves called br br cotyledons, a microphyle and a scar br br iii Draw a labeled diagram of a seed br br 338 iv Describe the main parts of a seed Testa br br also called seed coat a tough outer covering which protects the seed from br br insects, bacteria etc br br segment is the membrane inside the testa br br Hilum br br a scar spot where the seed was attached to the fruit or pod br br Micropyle br br small hole through which water and air enter the seed br br Radicle br br embryonic root grows into the shoot system br br Cotyledons br br embryonic leaves store food for the germinating seed i.e. for plumule and br br radicle br br when plumule and radicle grow, they use food stored in the br br cotyledon br br in some seeds food is stored in the endosperm br br v Draw a labeled diagram of a fruit br br br br vi How is a fruit formed? br br one of the organs that remains on the plant after pollination br br and fertilization is the ovary br br within the ovary, the developing embryo produces special br br chemical substances that stimulate the young ovary br br these substances also signal the start of the formation of the br br fruit, which is a mature ovary br br the fruit may contain one or more seeds during fruit formation the ovary increases in size while br br ripening or maturing br br a true fruit is formed from the ovary of a flower after br br fertilization br br 339 it has two scars style scar and stalk scar and contains seeds some seeds are not formed from the ovary of a flower some other parts of a flower develop to form a fruit such fruits are called false fruits br br vii Explain the importance of fruits in the survival of plants protect the seed against dessication, predators and adverse br br conditions br br aid in seed dispersal by attracting agents of dispersal stores food for the plant vii. Distinguish between parthenogenesis and br br parthenocarpy br br parthenogenesis is development of new animals from br br unfertilized eggs br br parthenocarpy is development of a fruit without br br fertilization br br iv State the differences between a seed and fruit Seed Fruit br br fertilized ovule attached to placenta through funicle fertilized ovary attached to branch through a stalk br br one scar called hilum has seed coat/testa seed wall br br two scars style scar br br and stalk scar br br has fruit wall/pericarp fruit wall is undifferentiated br br differentiated br br j. i What is placentation? br br arrangement of ovules within the plant ovary br br ii Explain the following types of placentation Marginal br br br br placenta appears as one ridge on ovary wall ovules are attached to placenta in rows e.g. peas in a pod br br Basal br br placenta formed at the base of the ovary with numerous br br ovules attached to it br br 340 Parietal br br br br edges of carpels fuse together dividing walls disappear, leaving one loculus have numerous seeds e.g. passion fruit placenta of each carpel appears as ridges on ovary wall br br Axile br br edges of carpels fuse br br together to form a single central placenta br br numerous ovules arranged on placenta ovary divided into a number of loculi by walls of the carpel br br e.g. br br Free central placentation br br edges of carpels fuse together dividing was disappears leaving one loculus placenta appears at base of ovary has numerous ovules k i How are fruits grouped? Simple fruits formed from a single flower or one ovary e.g. mango br br Aggregate fruits br br consists a group of ovaries that appear on a common br br receptacle e.g. strawberry br br Multiple compound fruits br br formed from several flowers whose ovaries fuse together br br after fertilization br br 341 form a bunch e.g. pineapple, figs are always false fruits ii What are succulent fruits? also called fleshy fruits all or part of pericarp fruit wall becomes juicy br br iii Give types of juicy fruits -Berry br br br br has many seeds whole pericarp is succulent e.g. orange, tomato, pawpaw br br Drupe br br only one seed pericarp divided into three layers i.e. epicarp, br br mesocarp juicy and endocarp hard br br e.g. mango and coconut br br Pome br br juicy part is swollen receptacle is usually a false fruit example is a pear iv What are dry fruits? br br have a pericarp that is dry, hard and woody either dehiscent or indehiscent called dry because they are not succulent br br v What are dehiscent fruits? br br split open when ripe to release seeds contain many seeds br br vi Give types of dehiscent fruits Legumes br br split along two edges are usually pods e.g. beans, peas, crotolaria br br Follicle br br split on one side only e.g. Sodom apple br br 342 Capsule br br has several lines of weakness/sutures open in many places e.g. castor oil, cotton br br vii What are indehiscent fruits? br br non-splitting fruits usually one seeded only ix Give main types of indehiscent fruits br br Nut br br pericarp woody, hard and thick e.g. cashew br br Achene br br has thin, tough pericarp e.g. sunflower l i What is seed and fruit dispersal? spreading of seeds and fruits away from parents so as to settle where conditions are suitable for their germination br br ii Why is dispersal of seeds and fruits necessary? br br prevent overcrowding reduces competition for space, nutrients and light colonization of new areas is made possible to increase chances of survival to prevent inbreeding to avoid extinction due to over competition for the br br necessities br br iii Explain how seeds and fruits are adapted to various methods of dispersal Adaptations for wind dispersal br br they have wings, feathers or hair-like structures to increase br br surface area for wind to carry them easily/buoyancy seeds/fruits are loosely attached on the stalks so that they br br can easily be released and carried away by wing br br seeds/fruits are generally light and small sized to be easily br br carried by wind br br some seeds/fruits have parachute-like structures to be easily br br carried b wind br br some have censor mechanism where seeds and fruits are br br borne on long stalks that are loosely attached which allows swaying so that movements of capsule by wind releases the seeds br br Water dispersal seeds br br seed/ mesocarp has air spaces thus light/buoyant to float br br hence carried by water br br they have waterproof cover and tough pericarp protects br br seeds from getting soaked fibrous and spongy mesocarp to easily float br br Animal dispersal seeds br br presence of hooks for attachment to animals thus carried to br br other parts br br fruits are brightly coloured, succulent and scented to attract br br animals br br seed coats are hard and resistant to digestive enzymes hence seeds are dropped away from mother plant large in size or borne on clusters to be easily seen br br Self dispersal/explosive self opening seeds they have lines of weakness called sutures for violent opening thus scattering seeds away from parent plant br br 5. a i Distinguish between external and internal br br fertilization in animals br br in external fertilization fusion of the male and female br br gametes takes place outside the body of the female e.g. amphibians and fish br br in internal fertilization union of gametes occurs inside the br br body of the female br br ii State the advantages and disadvantages of external fertilization Advantages br br large numbers produced therefore many offspring per br br breeding season br br female does not suffer gestation stress mother does not need to care for the young except in a few br br species br br the surviving individuals are highly selected for better survival br br Disadvantages br br many predators surround the eggs before and after br br fertilization br br fewer chances of fertilization/a lot of gametes wasted embryo development at mercy of environment large numbers of female gametes are required therefore br br female gets much exhausted br br iii State the advantages and disadvantages of internal fertilization Disadvantages br br number of gametes fewer hence less number of offspring less adapted for sudden change of environment after birth br br in mammals females suffer gestation stress br br Advantages br br more chances of fertilization fewer predators of oval/fertilized egg protected in females br br body br br stable internal environment fewer gametes required br br iii Give a reason why it is necessary for frogs to lay many eggs br br to increase chances of survival/fertilization iv Compare external and internal fertilization External Internal br br occurs in water outside the bodies of animals br br occurs inside the body of the female animal fewer eggs released br br many eggs are laid usually less contact between male and female br br from ovary br br very close contact in form of copulation between male and female both fertilized eggs exposed to danger br br Fertilized eggs are br br enclosed hence highly protected inside females body. br br b i Draw and label the human male reproductive system br br br br 345 br br ii Describe how the mammalian male reproductive system is adapted to perform its functions Penis br br is highly vascularised/spongy has a sensitive glands becomes erect to allow entry into the vagina br br Scrotum br br contains the testes outside the body on whose walls the br br process of spermatogenesis takes place br br the process is favored by lower temperature it contains sertoli cells which nourish sperms until they are br br mature Epididymis br br long and coiled for the purpose of sperm storage br br Vas deferens muscular upon contraction pushes sperms out and allows ejaculation br br Gametes br br 346 produced in large numbers to increase chances of br br fertilization br br the sperms have a tail for swimming/large number of br br mitochondria to provide energy/allow swimming to reach the egg Accessory glands br br are seminal vesicle, Cowpers gland and prostate gland they produce seminal fluid to provide a medium/ nutrients br br for sperms to swim br br iii How is the sperm adapted to perform its function? acrosomes contain enzymes to digest egg membrane nucleus contains genetic material mitochondria produce energy to move the tail back and br br forth br br the lashing movement of the tail enables the sperm to move/propulsion in fluid medium towards the egg br br it is streamlined for faster/easier movement/swimming to br br meet the egg br br c i Draw and label the human female reproductive system br br br br 347 br br 348 br br 349 ii Describe how the various structures of the human female reproductive system are adapted to their function Ovaries br br have several graafian follicles that develop and burst open br br to release/produce mature ova br br secretes sex hormones oestrogen which initiate/control br br development of secondary sexual characteristics br br produce hormones oestrogen and progesterone which prepare the uterus for implantation and subsequent nourishment of the embryo br br Oviducts fallopian tube br br are thin narrow and tubular to increase flowing speed of br br semen containing sperms br br are funnel shaped on the end next to ovary which enables br br them to receive the ovum br br their lining contains cilia which propel the ovum towards br br the uterus br br has peristaltic muscles that enable movement of zygote/ovum to the uterus for implantation br br is fairly long to increase surface area for fertilization br br Uterus br br is muscular for protection of developing embryo has elastic wall that allows growth and development of br br foetus/embryo br br has a highly vascularised endometrium that provides nutrients/gaseous exchange to developing embryo br br Cervix has valves that close the lower end of the uterus to ensure br br continued pregnancy during gestation period br br is capable of dilating has narrow entrance/neck-like entrance to uterus that br br enables quick swimming of sperms to uterus br br has suction mechanism that draws up/pulls sperms into br br uterus br br has a W shape that fits well with the glands of the penis br br to ensure sperms are deposited at the right point br br Vagina br br is elastic and muscular to enable good accommodation or penetration of the penis thus proper deposition of sperms and for easy parturition allows menstrual flow br br has sensitive labial walls which secrete/produce lubricating br br substances that ensure/enable/facilitate good coition capable of considerable enlargement, due to elastic muscles, to accommodate baby during parturition br br Clitoris br br has sensitive cells for orgasm br br iii Explain how the ovum is adapted to its function br br nucleus contains genetic material ventelline membrane encloses plasma membrane which br br encloses yolky cytoplasm br br yolky cytoplasm provides nourishment jelly coat protects ovum against dehydration br br iv Explain the differences between sperm and ovum Sperm Ovum br br long with a tail and br br spherical large stationary a lot of food stored in yolky cytoplasm lacks acrosome a lot of cytoplasm br br head small locomotory stores little food has acrosome tip with br br lytic enzymes br br nucleus prominent but cytoplasm negligible br br d i Explain the process of fertilization br br a process whereby the egg and sperm are brought together br br and fuse to form a zygote occurs in the fallopian tube after copulation sperm head penetrates the outer coat of the ovum while the br br tail remains outside br br penetration is due to reaction of acrosome acrosome digests the vitelline membrane thereafter a zygote is formed zygote which is diploid undergoes rapid cell division to br br form a mass of cells called blastocyst br br after fertilization a membrane forms around the ovum to br br prevent further entry of sperms br br blastocyst eventually develops into an embryo br br 352 br br i Explain the process of implantation br br this is the embedding and attaching of the embryo in the br br uterine wall/endometrium br br implantation marks the beginning of pregnancy sometimes implantation occurs in the oviduct wall which is abnormal and results in ectopic pregnancy which is fatal br br the outer wall of the blastocyst develops fingerlike projections which project into the uterine wall for attachment br br the projections are called villi br br 353 the villi and endometrium develop into an organ that is br br called the placenta br br the embryo is attached to the placenta through a cord called br br the umbilical cord br br br br iii br br 354 br br State the functions of umbilical cord br br it contains blood vessels umbilical artery, iliac arteries and br br umbilical veins br br it joins the placenta to the embryo passage for nutrients from the mother passage of excretory substances from foetus to mother for br br final discharge gaseous exchange passage of antibodies from mother to foetus, for protection br br of foetus against diseases iv State the role of placenta br br exchange of gases between mother and foetus exchange of nutrients and nitrogenous wastes anchorage/attachment of foetus produces hormones oestrogen and progesterone br br e i What is gestation period? br br time taken from fertilization to birth/pregnancy br br ii Explain the functions of the membranes associated with placenta Chorion br br surrounds the embryo has fingerlike projections that attach embryo to the uterus br br Amnion br br contains amniotic fluid fluid surrounds embryo br br 355 protects embryo from mechanical injury by acting as shock br br absorbers br br fluid also protects embryo from dehydration distributes pressure equally over embryo br br Yolk sac br br surround the yolk produces blood cells for embryo until its own liver is able br br to perform the task br br Allantois br br present only for a short time removes and store waste material it eventually becomes the umbilical cord br br iii Explain the events that take place to facilitate parturition br br near birth the placenta produces less progesterone oxytocin hormone is produced by posterior lobe of pituitary br br gland br br because progesterone level has decreased the uterus br br becomes sensitive to oxytocin br br oxytocin causes the contraction of the uterus myometrium these contractions are called labour pains just before parturition the head turns downwards the contractions eventually push the baby through the br br vagina br br amnion breaks and amniotic fluid is released oxytocin dilates the cervix foetus is expelled through cervix with head coming out first finally the whole infant comes out the umbilical cord is cut and the placenta is expelled as afterbirth br br iv State the reasons why later in pregnancy the ovary will b e removed without disturbing the pregnancy br br corpus luteum in the ovary secretes progesterone which maintains pregnancy and development of foetus after conception br br after four months pregnancy is maintained by progesterone br br from the placenta br br f i What are secondary sexual characteristics - Characteristics physiological and anatomical that start developing at puberty due to the influence of male and female hormones ii State the main secondary changes in Boys br br deepening of the voice br br growth of hair on face, pubic part, chest, legs penis and testes become bigger muscular development sperm production begins at puberty and may continue br br throughout life br br Girls br br growth of hair on pubic part and armpits widening/enlargement of hips development of breasts menstrual cycle starts as ovaries mature body acquires extra fat br br iii Describe the role of hormones in secondary sexual characteristics inBoys Follicle stimulation hormone FSH br br from pituitary stimulates production of androgens male hormones mainly br br testosterone by testis br br Testosterone br br secondary sexual characteristics br br Girls FHS br br from pituitary development of follicles stimulates oestrogen production by ovary br br LH br br from pituitary ovulation stimulates release of progesterone by ovary br br Oestrogen br br stimulates release of LH secondary sexual characteristics br br Progesterone br br also from placenta sustains pregnancy as it inhibits prolactin and oxytocin br br during pregnancy br br Prolactin ii Describe the role of hormones in the human menstrual cycle br br it is controlled by sex hormones which are responsible for br br the onset of secondary sexual characteristics and also control of the menstrual cycle br br the onset is signaled by discharge of blood/menses 14 days br br following the start of menstruation br br anterior lobe of pituitary gland secretes follicle stimulating br br hormone FSH br br Follicle stimulating hormone causes graafian follicle to develop in the ovary. It also stimulates tissues of the ovary/wall theca to secrete oestrogen br br oestrogen causes repair/healing of uterine wall oestrogen stimulates anterior lobe of pituitary to produce br br luteinising hormonge LH br br LH causes ovulation. It also causes graafian follicle to br br change into corpus luteum. LH stimulates corpus luteum to secrete progesterone br br Progesterone causes proliferation/thickening of uterine wall Oesterogen/progesterone inhibits the production of FSH by anterior lobe of pituitary, thus no more follicles develop and oestrogen production reduces br br In the next two weeks progesterone level rises and inhibits br br production of LH from anterior lobe of pituitary br br The corpus lutetium stops secreting progesterone and br br menstruation occurs when the level of progesterone drops br br Anterior lobe of pituitary starts secreting FSH again. br br iii What is menopause? br br end of ovulation in women occurs after age of 45 years does not occur in males br br h Explain the symptoms, methods of transmitting and prevention control of the following sexually transmitted diseases i Gonorrhea - caused by a bacterium called Neisseria gonorrhea - transmitted through sexual intercourse, - infects urethra and vaginal tract epithelia - Symptoms include pain, discharge of mucus and bad smell females - Effects include sterility, heart diseases, blindness of foetus and arthritis - Treatment by antibiotics - Control and prevention by proper sexual conduct ii Herpes br br notably Herpes simplex and H. genitalis caused by virus which attacks genitalia symptoms are painful sores in genitalia, skin lesions transmitted in saliva, sexual intercourse and injection by br br drug addicts no treatment br br iii Syphilis br br caused by bacterium called Treponema palladium symptoms are painless wounds in genitalia attack genitalia, nervous system, lips treated by antibiotics br br iv Trichomoniasis br br caused by plasmodium called Trichomonas attacks reproductive tract symptoms are itching and discharge of pus from the br br genitals br br treated by antibiotics br br v Hepatitis - Viral disease Affects the liver Transmitted through sexual intercourse No known treatment vi Candidiasis br br caused by fungus called Candida albicans transmitted through sexual intercourse symptoms include itching urethra, and vaginal discharge br br odourless br br controlled by personal hygiene, early treatment and br br responsible sexual behavior br br vii HIV/AIDS br br caused by HIV virus transmitted by sexual intercourse, blood transfusion, sharing piercing instruments from infected mother to foetus, infant and baby br br symptoms include fever, swollen lymph nodes, night sweating, cough, weight loss, fatigue, loss of appetite, diarrhea, headache, a opportunistic infections and tumors br br Control by responsible sexual behaviour, education, br br screening blood for transfusion and using sterile piercing instruments. br br 6. a Define the terms br br i Growth an irreversible change in size of a cell, organ or whole br br organism br br growth is due to synthesis of protoplasm or extracellular br br substances br br ii Development refers to a series of changes which an organism goes br br through in its lie cycle br br during development both qualitative and quantitative br br changes take place involves differentiation br br iii Differentiation refers to changes in which the cells of the body undergo and become specialised to perform specific functions br br b i Differentiate growth in plants and animals Plants Animals br br confined to shoots/root br br occurs all over the body intercalary different parts grow at br br tips apical br br have definite growth regions meristems br br different rates allometric maximum growth on maturity definite br br often br br indefinite/continuous br br growth results in br br no branching affected by nutrients br br branching br br affected by light, br br auxins, hormones and temperature ii List the processes involved in growth br br assimilation cell enlargement cell division by mitosis iv List the parameters used to measure growth height/length dry weight number of individuals volume leaf area of plant br br iv Name the patterns of growth in organisms br br - allometric and isometric br br - limited and unlimited - discontinuous growth br br c i Name the different types of growth curves br br - sigmoid curve normal growth curve - intermittent growth curve br br ii Draw a sigmoid growth curve and explain its different phases/stages br br br br A-lag phase - Slow growth rate at first Organism adapting to the environment B-exponential phase br br - organisms already adapted - first growth due to birth rate that is higher than death rate br br C- Stationery phase plateau - Birth rate equals death rate equilibrium Lack of nutrients, accumulation of toxic waste products D-phase of decline br br - due to depletion of nutrients, accumulation of toxic wastes, br br lack of space br br - some individuals old hence not reproducing - death rate higher than birth rate br br iii Draw an intermittent curve and explain the various stages br br A-growth B-no growth C- moulting/ecdysis br br - seen in arthropods - growth in in arthropods is intermittent takes place during some time only because their hard cuticles exoskeleton does not expand to cause growth br br - the cuticle must be shed off first to allow further growth - the shedding is called ecdysis or moulting br br 361 - when moulting has taken place animal grows but growth br br stops when the exoskeleton hardens again br br d i What is seed dormancy? br br - A state where a viable seed is incapable of germinating br br when all conditions are favourable. br br ii State the biological importance of seed dormancy br br - gives embryo time to reach maturity - gives time for dispersal - allows plant to survive adverse conditions iii State the factors which cause seed dormancy Internal factors br br - presence of abscisic acid/ABA/ presence of germination br br inhibitors br br - embryo not fully developed - absence of hormones/enzymes/inactivity of hormones/enzymes/gibberellins/cytokinins br br - impermeability of seed coat br br External factors br br - unsuitable temperature - absence of light - lack of oxygen - lack of oxygen - lack of water br br iv Give the conditions necessary to break seed dormancy - scarification/scratching to make seed coat impermeable - vernalisation/cold treatment in some seeds like wheat - burning/nicking/expose to heat e.g. wattle seeds - destruction of germination inhibitors e i What is seed germination? br br - process by which a seed develops in a seedling br br ii What is viability br br - ability of a seed to germinate br br iii Discuss the various conditions necessary for the germination of seeds Water br br - medium for enzymatic activity - hydrolysis of food into simpler substances - medium of transport - softens the seed - acts as a solvent br br Air br br - in form of oxygen br br - oxygen is used for respiration/oxidation of food to release br br energy br br Suitable optimum temperature br br - activates enzymes involved in mobilization of food br br reserves br br Enzymes br br - breakdown and subsequent oxidation of food - conservation of hydrolyzed food products into new plant br br tissues br br Viability br br - only viable seed are able to germinate and grow br br iv Name and describe the types of germination Epigeal br br br br cotyledons are brought above the ground level during germination due to elongation of hypocotyls br br Hypogeal br br - the cotyledons remain below the surface during br br germination due to elongation of epicotyl e.g. maize v Name the part of the bean seed that elongates to bring about epigeal germination hypocotyl vi Account for the loss in dry weight of cotyledons in a germinating bean seed br br - food stored is mobilized/used up for respiration and growth br br vii Describe the physiological changes that occur in a seed during germination br br - in presence of oxygen, optimum temperature and water, food reserves in the seed are hydrolysed or broken down into soluble diffusible form by enzymes - soluble food diffuses to the growing embryo - oils and carbohydrates provide energy - simple sugars converted to cellulose to form cell wall br br 363 - amino acids make protoplasm - seed develops plumule and radicle hence germinates viii Explain the biological significance of cotyledons being brought above the ground in epigeal germination br br - cotyledons have inadequate food - they are brought above the ground to acquire chloroplasts to carry out photosynthesis before the formation of foliage leaves to supplement food supply required for growth during germination br br f i Distinguish between primary and secondary growth Primary growth br br - occurs at the apical shoot and tip apices regions where br br meristematic cells occur br br - causes plant elongation since cells divide by mitosis br br Secondary growth -occurs at the cambium meristems Increases width girth of the stem ii What are meristems br br - dividing cells - meristem means they are dividing br br iii State the characteristics of meristematic cells br br - dense cytoplasm - thin cell walls - absence of vacuoles/cell sap br br iv State the location and function of the following meristematic tissues Apical meristem br br - located at tips of roots and shoots - increase length of stem and roots/primary growth Intercalary meristem br br - found at bases of internodes - responsible for elongation of internodes and increase in leaf br br sheath in grasses br br Lateral meristems br br - found near the periphery of stem and root - responsible for secondary growth/growth in girth of stem br br and root/lateral growth br br - called cambium and constitute vascular and cork cambium br br v Describe primary growth br br - occurs at tips of shoots and roots in the meristematic tissues br br of apical meristem br br - at the apex there is a zone of cell division/mitosis - cells elongate at elongation zone br br - the elongated cells differentiate at the region of differentiation resulting in increase in size br br - in the stems meristems give rise to leaf premodia which br br envelop the apex to form a bud br br - the bud protects the delicate inner cells - in roots the meristem is protected by root cap - after cells differentiate the form permanent tissues br br vi Describe secondary growth in plants - also called secondary thickening - only occurs in dicotyledonous plants that have cambium - monocotyledonous plants do not undergo secondary growth br br because they lack intervascular cambium br br - cambium cells divide to produce more cells on either side br br of the cambium br br - cells produced to the inside become secondary cambium - cells produced to the outside become secondary phloem - division of cambium cells occurs yearly producing new br br rings of secondary phloem and secondary xylem each year br br - intervascular cambium cambium between vascular br br bundles divide to form secondary parenchyma, thereby increasing growth of medullary rays br br - much more xylem is formed than phloem, thus pushing br br phloem and cambium ring outward br br - the rate of secondary growth is depended on seasons rains resulting in annual rings br br - cork cambium is located beneath epidermis ad is br br responsible for secondary thickening of the bark of perennial plants br br - cork cambium divides to form new cork bark tissues to br br accommodate increased growth on outside and secondary cortex on the inside br br - Cork cells cells of the bark are loosely parked at some br br points to form lenticels for gaseous exchange. vii State the significance of secondary growth br br - increase girth or circumference of trees - annual rings which show seasonal growth can be used to br br tell the age of trees br br g i Describe one method which can be used to measure the average growth rate of a single leaf of a plant EITHER br br - chose/identify a young leaf just unfolded - use the same leaf throughout - measure total length of whole leaf br br - record - repeat at regular intervals until no more change br br occurs/constant length br br - average rate of growth is equal to total increase in length br br divided by the period taken to achieve full length br br Average rate of growth total increase in length br br period taken to achieve full length br br OR br br - choose/identify a young leaf just unfolded - use the same leaf throughout - trace the outline on a graph paper and work out the area - record - repeat at regular intervals until regular area - average rate of growth equals to total increase in area divided by the period of time taken to achieve full area br br Average rate of growth total increase in area br br period of time taken to achieve final area br br i Describe how the growth of a root can be determined Materials br br - fine thread, marking ink, germinating bean seedlings, br br blotting paper, ruler marked in millimeters, pins, cork, a boiling tube and moist cotton wool br br Procedure br br - dry seedlings using blotting paper - place inside against the ruler marked in mm - dip the fine thread in waterproof ink - mark the radicle at equal intervals - pin the seedling to the cork - suspend the seedling into the boiling tube containing moist cotton wool br br - allow the seedling to grow for two days/some time observe the intervals with the marks - record your observations the widest intervals are found in the region just behind the tip indicating/showing region of greatest growth br br iii A boy hammered a nail in the bark of a tree at a height of 1.5metres above the ground. Four years later, the nail was found at the same height although the tree had grown 3 meters taller. Explain the above observation The nail was hammered at a point where vertical growth had stopped/further growth was confined to increase in width/diameter. Vertical growth is confined to tips/apex/vertical apical meristem h i Describe the role of hormones in growth and development of plants indole acetic acid/IAA/ auxins Cell division/increase in cell division Tropic responses Cell elongation/increases in ell elongation Development of abscision layer Growth of ovaries into fruits/parthenocarpy/initiates flowers Inhibits growth of lateral buds/produces apical dominance Stimulates adventitious/lateral roots Gibberellins Gibberellic acid/GA3 Promote cell elongation/rapid cell division/increase in length of the internodes Promote fruit formation without fertilization/parthenocarpy Reduces root growth Breaks seed dormancy/promotes germination Cytokinnins Kinnins/Kinnetin/Zeatin br br - breaks dormancy - promotes flowering - promotes cell division - stabilizes protein and chlorophyll - promotes root formation on a shoot - low concentration encourages leaf senses - normal concentration increases cell enlargement in leaves - stimulates lateral bud development br br Ethylene ethynelC2H4 - accelerates ripening in fruits - encourages fruit fall/leaf fall - induces thickening in stern/inhibits stem elongation - promotes flowering in pineapples - promotes germination in certain seeds br br Abscisic acid ABA abscisin hormone/dormin br br - causes bud dormancy - encourages fruit/leaf fall - high concentration causes closing of stomata - causes seed dormancy - inhibits cell elongation br br Traumatin br br - heals wounds by callous formation br br Florigen br br - promotes flowering br br ii State the applications of plant hormones in agriculture - induce root growth in stem cuttings - selective weed killers - encourage sprouting of lateral buds - breaking seed dormancy - induce parthenocarpy - accelerate ripening of fruits - promote flowering - cause dormancy br br iii Explain apical dominance br br - a phenomenon whereby production of auxins by a growing br br apical bud of a shoot inhibits growth of lateral buds - this inhibition is due to high concentration of auxins br br indoleacetic acid/IAA in apical bud br br - removal of terminal/apical bud causes development and br br sprouting of several buds which later develop into branches br br - applied in pruning coffee, tea and hedges - this leads to more yield br br iv Describe the role of hormones in the growth and development of animal somatotrophin growth hormones br br - from anterior pituitary - promotes cell division - overproduction causes gigantism - underproduction causes dwarfism br br Thyroxine br br - promotes growth and metamorphosis - underproduction leads to a child becoming a cretin br br mentally retarted br br Androgens br br - in males - growth of male reproductive organs Oestrogen br br - in females - growth of female reproductive organs br br Ecdysone br br - in arthropods - moulting ecdysis br br t i What is metamorphosis? br br - change in form during which there are changes in structure br br and function in body of organism br br - prepares organism for life in a different habitat radical changes in the body during the life cycle of an organism called holometabolous development br br example is egg larva pupa adult imago occurs in animals such as butterfly and bee br br br br iii What is the significance of each of the four stages in complete metamorphosis? Larval stage br br - feeding takes place - larva is quite different from adult - larva sheds its cuticle exoskeleton several times to emerge br br as pupa br br - dispersal stage avoids overcrowding br br Pupa br br - enclosed in a case called puparium cocoon - no feeding - organ formation takes place br br Adult br br - emerges from puparium - reproductive stage of the life cycle iv Describe incomplete metamorphosis - called hemimetabolous development - changes are gradual - eggs develop into nymphs which develop into adults - nymph resembles adult but are sexually immature - a nymph moults several times as some parts develop before br br it becomes an adult br br - stage of development between one moult and another is br br called instar br br - occurs in insects such as locust and cockroach br br v Name the hormones that control metamorphosis in insects br br - brain hormone responsible for moulting because it br br simulates production of ecdyson moulting hormone br br - ecdysone moulting hormone causes moulting - juvenile hormone causes moulting in larvae br br 369 vi State the advantages of metamorphosis in the life of insects br br - the adult and larvae exploit different niches - do not compete for food - pupa cam survive adverse pupa can survive adverse br br conditions eg-feeding stage br br - dispersal prevents overcrowding FORM IV TOPICS br br 1. a i Define the term genetics the study of heredity inheritance and variation or study of mechanisms by which characteristics are passed from parents to offspring br br iii List some characteristics which are inherited br br size height/length colour/type shape yield br br iii State the importance of genetics br br helps to explain differences between organisms of the same br br species br br helps to explain the transmission of characters from br br generation to generation improvement in livestock improvement in crops can be used to treat some difficult diseases b i Explain the meaning of the following terms Heredity br br the resemblance among individuals related by descent transmission of traits from parents to offspring br br Trait br br also called character A character of the organism e.g. type of ear, colour of eyes, br br height, yield etc. br br Gene br br unit of inheritance it is the heredity factor which transmits traits from parents br br to offspring br br genes are located at fixed points on chromosomes each point is called a locus loci Allele br br genes can exist in a series of alternative forms at a br br particular locus br br allele refers to alternative forms of genes controlling a br br particular characteristic br br Chromosomes br br threadlike structures found in nuclei of all plants and br br animals br br they carry genes which are hereditary materials they consist of substances called DNA and proteins called br br histosones br br DNA br br deoxyribonucleic acid substances that make up chromosomes double helix strand molecule that contains genes DNA consists of nucleotides A nucleotide consists of an inorganic phosphate, ribose br br sugar and a base br br There are four bases in a DNA molecule i.e. Adenine A , br br guanine G , thymine T and cystosine C br br Ribose sugar has four bases attached to it i.e. adenine, br br cystosine, guanine and thymine br br Adenine pairs with thymine while guanine pairs with br br cystosine br br Nucleotide initiates and controls protein synthesis br br ii List the types of chromosomes br br somatic body chromosomes also called autosomes sex chromosomes related to reproduction c i What is variation? br br sequence of differences occurring among individuals of the br br same species br br ii State the causes of variation in organisms br br random assortment of genes during meiosis crossing over fertilization doubling of chromosome numbers mutation environmental conditions iii Name the types of variation br br Continuous variation differences not clear cut e.g. height, br br length, weight, skin colour, intelligence etc. They are quantitative and show intermediates discontinuous variation differences are clear cut e.g. br br ability to roll tongue, ABO blood grouping system, RH factor, patterns of fingerprints, and ability to taste PTC. They are qualitative and have no intermediates br br iv Explain the following terms Acquired characteristics br br they are as a result of adaptations due to the environment br br and are not inherited Inherited characteristics br br are passed down to offspring during sexual reproduction br br Genotype br br genetic constitution of an individual/genetic makeup br br Phenotype br br characteristics of an individual observed or discernible by br br other means i.e. observable character br br Dominant gene character br br expressed in the phenotype when homozygous or br br heterozygous br br Recessive gene br br only expressed in homozygous state br br Homozygous br br when two alleles are identical e.g. LL,ll br br Heterozygous br br when two alleles are different at a particular locus e.g. Ll br br F1 and F2 br br F1 means first filial generation i.e. the first generation br br produced when two varieties can be crossed br br F2 means second generation i.e. product of offspring or from F1 generation br br d i Explain Mendels first law of inheritance br br also called law of segregation it states that genes are responsible for the development of br br individual characters br br these characters are transmitted individually without any br br alterations br br Only one character from a contrasting pair can be carried in br br a gamete, hence only one character can be inherited. br br ii Give an example of this law br br In an experiment, Drosophila fruit fly with long wings br br were crossed with those having short wings. Assume letter L denotes gene for wing size. The gene for long wings is dominant to that for short wings the genes for dominant are LL and for recessive ll. State the expected results for the first cross br br iii What is monohybrid inheritance? br br when inheritance of one character is studied one at a time br br e.g. wing size only br br the F2 generation when selfed always gives a phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 in a complete dominance br br v What is complete dominance? refers to where only one dominant character is expressed br br while the other character which is recessive is not expressed in the heterozygous state e.g. the case of wing size above br br e i What is meant by co dominance? br br When genes produce independent effects when br br heterozygous/none of the genes is dominant over the other/where two or more alleles does not show complete dominance/recessiveness due to the failure of any allele to be dominate in a heterozygous condition. br br ii Give an example of co dominance In a certain plant species, some individual plants may have only white, red or pink flowers. In an experiment a plant with white flowers was crossed with a parent with red flowers. Show results of F1 generation. Use letter R for red gene and W for white gene. If the plants form F1 were selfed, work out the phenotype ratio for the F2 generation Phenotypic ratio 1red:2pink:1white Genotypic ratio 1:2:1 f i What is a test cross? - A cross between an individual showing a character for a dominant gene that is homozygous or heterozygous with a homozygous recessive individual OR a cross between individual organism of unknown genotype br br with a homozygous recessive individual ii State the importance of a test cross in genetics br br helps in determining the genetic constitution/genotype of br br an organism br br iii What are multiple alleles? br br a set of more than two alleles that may determine a br br character example is blood group which can be determined by any br br two of three alleles i.e. A,B and O br br iv Explain the inheritance of ABO blood groups br br in humans blood groups are determined by three alleles i.e. br br A,B and O br br it is only possible to have two genes at a time genes A and B are co-dominant while gene O is recessive br br to genes A and B br br Give a worked example using parents with heterozygous blood groups AO and BO br br vi Explain the inheritance of Rhesus factor Rh in br br human beings br br in humans blood is either Rh positive or Rh negative people who have Rh antigen are Rh ve while those br br without Rh antigen in their blood are Rh -ve br br Rh ve is due to a dominant gene while the recessive gene br br causes lack of Rh factor. When a person who is homozygous dominant marries a person who is homozygous recessive the result is as shown below Let the gene for dominant Rh factor be R while gene for recessive be r br br vii How is sex determined in human beings? there are two sex chromosomes in humans, x and y males are xy and females are xx in females all ova have x chromosome in males 50 of sperms contain x chromosomes while 50 of sperms contain y chromosome br br when a sperm containing x chromosome fuses with an br br ovum this results into a girl br br when a sperm containing y chromosome fuses with an br br ovum the result is a boy an example is given below br br g i What does the term linkage mean? - These are genes which occur together on a chromosome and are passed to offspring without being separated ii Define the term sex-linked genes br br genes carried in the sex chromosome that are transmitted br br along with genes that determine sex iii What is meant by the term sex linkage? genes are located on the sex chromosome they are transmitted along with those that determine sex br br iv Name the sex-linked traits in humans colour blindness haemophilia Hairy ears. pinna, nose Baldness Duchene muscular dystrophy DMD muscular wasting br br v Give an example of a sex linked trait in humans on: Y Chromosome br br tuft of hair sprouting from pinna/baldness br br X Chromosome br br colour blindness/haemophilia br br vi In humans red-green colour blindness is caused by a recessive gene C, which is sex-linked. A normal man married to a carrier woman transmits the trait to his children. Show the possible genotypes of the children. Let C represent the gene for normal colour vision dominant Let c represent the gene for colour blindness Parental phenotype Norman man x carrier woman br br viii State the importance of sex linkage possible to determine sex of day old chicks ix Haemophilia is due to a recessive gene. The gene is br br sex-linked and located on the x chromosome. The figure below shows sworn offspring from phenotypically normal parents br br What are the parental genotypes? br br XY and XhX br br Work out the genotypes of the offspring h i What is mutation? sudden change in the structure of DNA at a particular br br locus/chromosome/gen ii Describe how mutations arise br br mutations arise due to alterations in normal number of br br chromosomes br br change in a portion of a chromosome affecting one or more br br genes br br by chromosomal aberration e.g. br br dleltion/duplication/substitution/inversion/translocation/cro ssing over br br caused by mutagenic agents e.g. radiation x-rays, ultra violet light, gamma rays and chemicals e.g. mustard gas/colchicines br br iii State the factors that may cause mutation br br these are chemicals and radiations Radiations X-rays Ultra violet rays Chemicals - colchicines Cyclamate Mustard gas Nitrous acid behaves like guanine Acridone orange DNA Formaldehyde iv State the characteristics of mutations arise suddenly are unpredictable random generally rare may breed true some are desirable while others are lethal br br Effects br br gene/chromosome alteration br br structural distortion of DNA br br Effect br br prevents spindle formation chromosome aberrations br br chromosomes aberrations adenine in DNA is deaminated so br br addition and removal of bases of br br v Explain chromosomal mutation - Change in nature, structure or number of chromosomes vi Explain how the following types of chromosomal mutations occur Duplication br br a section of a chromosome is repeated/replicates therefore genes are repeated br br Inversion br br occurs when chromatids break at 2 places and when br br rejoining the middle piece rotates and joins in an inverted position br br Deletion br br portion of a chromosome is left out after it breaks off alters number and sequence of genes br br Translocation br br occurs when a section of a chromatid breaks off and becomes attached to another chromatid of another chromosome br br increased yields/hybrid vigour//heterosis resistance to pests early maturity resistance to drought resistance to diseases br br vii What are gene mutations ? br br an alteration in the structure of a gene vii Explain how the following occur during gene br br mutation br br Deletio n br br some bases/nucleotides of a gene are removed br br Inversion br br the order of some bases/nucleotides of a gene is reversed br br Insertion br br addition of a base between two existing bases br br Substitution br br a portion of a gene is replaced by a new portion viii Name the disorders in humans caused by gene br br mutation br br albinism sickle cell anaemia achondroplasia/chondordystorphic dwarfism haemophilia colour blindness phenylketonuria I. State the practical applications of genetics i. Breeding programmes research br br high yielding/hybrid vigour/heterosis resistance to diseases resistance to drought/salinity early maturing br br ii. Genetic engineering br br genetic manipulation to produce desired characteristics iii. Law br br - legal questions of paternity knowledge of blood groups or blood transfusion iv Genetic counseling br br aimed at reducing harmful traits e.g. albinism, congenital br br idiots, colour blindness e.t.c br br v Others - Pre-sex determination Understanding human evolution and origin of other species. 2. a i Explain the meaning of evolution a gradual change in living organisms from simple life br br forms to more complex forms over a long period of time. ii Differentiate organic evolution from chemical evolution as theories of origin of life br br organic evolution refers to the emergence of present forms of organisms gradually from pre-existing forms some of which no longer exist br br chemical evolution explains the origin of life as having br br occurred when simple chemical compounds reacted to form the simplest life forms iii What is special creation? br br maintains that the whole universe and all living organisms came into being due to the act of a supernatural being br br b Discuss the various kinds of evidence for evolution br br i Fossils fossils are remains of organisms preserved in naturally br br occurring materials for many years br br they give evidence of types of plants/animals that existed at br br certain geological age/long ago/millions of years ago gives evidence of morphological/anatomical/structural br br changes that have taken place over a long period of time e.g. human skull, leg of horse ii Comparative anatomy gives evidence of relationship among organisms/gives br br evidence of a common ancestry of a group of organisms organisms have similar structures/organs performing the br br same function e.g. digestive system/ urinary system/nervous system/vestigial structures and vertebrate heart br br Divergence where the basic structural form is modified to serve different functions e.g. vertebrate forelimb/beak structure in birds/birds feet/parts of a flower. These are called homologous structures br br homologous structures have a common embryonic origin but are modified to perform different functions e.g. the pentadactyl limb br br adaptive radiation is a situation where organism have a homologous structure with common embryonic origin which is modified to perform different functions to adapt organisms to different ecological niches/habitats e.g. beaks of Darwinian finches birds Convergence is where different structures are modified to br br perform a similar function e.g. wings of birds and insects/eyes of humans and octopuses. These are called analogous structures br br Vestigial structures are greatly reduced in size and have ceased to function e.g. human appendix/caecium/coccix in humans, wings of kiwi flightless bird , presence of hind limb pad in python, halters in insects, human hair nictitating membrane in human eye, human ear muscle, pelvic girdle in whale and third digit of wing of bird. br br iii Comparative embryology some embryos of different animals appear very similar thus showing relationship and possibility of a common ancestry br br e.g. different classes of vertebrates larvae of annelida and br br mollusca are similar tocophere br br iv Comparative serology/physiology these show biochemical and immunological comparisons of br br blood groups/components to show immunological similarities of tissues therefore showing relatedness of different organisms br br e.g. antigen antibody reactions, human blood groups/Rh br br factor reveal some phylogenic relationship among organisms/common ancestry v Geographical distribution organisms differ in various geographical regions present continents are thought to have been a large land mass joined together/pangea/Eurasia/Gondwanaland present continents drifted apart from one land br br mass/continental drift br br as a result of continental drift isolation of organisms occurred bring about different patterns of evolution br br organisms in each continent evolved along different lines hence emergence of new species/divergence/convergence br br Examples br br marsupials in Australia illama, jaguar, panther in S. America lion, camel in Africa tiger in Asia vi Cell biology cytology structures and functioning of cells are similar occurrence of organelles e.g. mitochondria in all cells/both br br plant and animal cells these point at a common ancestry br br c i State the evolutionary characteristics that adopt human beings to the environment - Brain - Eyes - Upright posture/bipedal locomotion - prehensible arm/hand - Speech ii State the ways in which Homo sapiens differs from Homo habilis br br standing upright/erect posture intellectual capacity/higher thinking capacity/bigger br br brain/higher brain capacity br br communication through language/speech d i Explain Larmarcks theory of evolution br br - Inheritance of acquired characteristics/environment induces br br production of a favorable trait which is then inherited br br ii Explain why Lamarcks theory of evolution is not accepted by biologists today br br - evidence does not support Lamarcks theory - acquired characteristics are not inherited/inherited characteristics are found in reproductive cells only br br iii Explain Darwins theory of evolution br br - inheritance of genetically acquired characteristics - a character happens to appear spontaneously which gives br br advantage to an organism therefore adapted then inherited through natural selection e i What is natural selection? - Organisms with certain characteristics are favoured by the environment Such organisms tend to survive and produce viable offspring Others not favored are eliminated from subsequent generations ii With examples, explain how natural selection takes place - organism with certain characteristics are favored by their environment br br - such organisms tend to survive and produce viable br br offspring br br - others not favored are eliminated from subsequent br br generations br br - as the environmental conditions change the survival value of a character may alter with time so that characteristics which were favored may no longer have advantage and other characters may then become favorable br br - if a favorable character is inherited, then offspring produce br br generations which are better adapted to survive in a population br br - more offspring are produced than can survive which results br br in struggle for survival br br - the fittest survive br br iii State the advantages of natural selection to organisms br br - assist to eliminate disadvantageous br br characteristics/perpetuates advantageous characteristics - allows better adapted organisms to survive adverse changes in the environment/less adapted organisms are eliminated br br iv State the ways in which sexual reproduction is important in the evolution of plants and animals br br - brings about useful variations/desirable characters - variations make offspring better adapted for survival/more br br resistant to diseases br br - may lead to origin of new species br br v Explain the significance of mutation in evolution - Mutation bring about variation which can be inherited - Some of these variations are advantageous to the organism - Others are disadvantageous - The advantageous variations favour the organism to compete better in the struggle for survival - This results into a more adapted organism to its environment or new species/varieties - Those with disadvantageous characters will be discriminated against therefore eliminated from the population/death/perish vi Plain why it is only mutations in genes of gametes that influence evolution - gametes form the new offspring br br vii How would you prove that evolution is still taking place? - resistance of organism to antibiotics, pesticides and drugs - new varieties of bacteria are resistant to certain antibiotics br br such as penicillin br br - houseflies and mosquitoes are resistant to DDT vii Explain why some bacteria develop resistance to a br br drug after they have bee subjected to it for some time br br - bacteria mutates/develops a new strain/chemical composition is altered hence is able to produce enzymes/chemicals which degrade the drug rendering it non-susceptible to the drug br br - the new strain is favoured by selection pressure/ natural br br selection f How has industrial melaninism i.e. peppered moth contributed towards the mechanism of evolution - This is an example of natural selection - The peppered moth exists in two distinct forms, the speckled white form normal form and a melanic form the black/dark - They usually rest on leaves and barks of trees that offer camouflage for protection - Originally the speckled white form predominated the unpolluted area of England - This colouration offered protection against predatory birds - Due to industrial pollution tree barks have blackened with soot - The white form underwent mutation - A black variety/mutant emerged suddenly by mutation - It had selective advantage over the white forms that were predated upon in the industrial areas - The speckled white form is abundant in areas without soot/smoke 3. a i Define irritability, stimulus and response irritability -also called sensitivity - Responsiveness to change in environment Stimulus A change in the environment of organism which causes change in organisms activity Response br br - change in activity of an organism caused by a stimulus ii State importance of irritability to living organisms br br - Adjusting to environmental conditions. br br Sensitive/defect/responding br br iii List the examples of external stimuli to organisms - air/oxygen aero - light photo - osmotic pressure osmo - current Rheo - chemical concentration chemo - water/moisture hydro - Touch/contact hapto/thigmo - Gravity/soil geo - Temperature thermo br br b i What are tactic responses? br br - response in which whole organism or its motile parts move br br e.g. gamete br br ii What causes tactic responses? br br - caused by unidirectional stimulus br br - usually doesnt involve growth - response is either positive or negative - named according to source of stimulus - e.g phototaxis, aerotaxis, chemotaxis br br iii State the importance of tactic response to: Members of kingdom protista br br - move towards favorable environment/move away from br br unfavorable environment - move towards their prey/food br br Microscopic plants - escape injurious stimuli/seek favorable habitats br br iv Name the type of response exhibited by: Euglena when they swim towards the source of light br br - phototaxis - sperms when they swim towards the ovum - chemotaxis v State the advantages of tactic responses to organisms - to avoid unfavorable environment/injurious stimuli - escape from predators - to seek favorable environment - to seek for food/prey c i Define the term tropism br br - growth movement of plants in response to external br br unilateral/unidirectional stimuli br br ii Explain the various types of tropism in plants Phototropism br br - growth movements of plant shoots in response to unilateral br br sources of light br br - the tip of the shoots produce auxins down the shoot - light causes auxins to migrate to outer side/darker side causing growth on the side away from light hence growth curvature towards source of light roots are negatively phototrophic br br Geotropism br br - response of roots/parts of a plant to the direction of force of br br gravity br br - auxins grow towards the direction of force of gravity br br causing positive geotropism in roots while shoot grows away from force of gravity negatively geotrophic br br Thimotropism/Haptotropism br br - growth response of plant when in contact with an object br br - contact with support causes migration of auxins to outer side causing faster growth on the side away from contact surface br br - this causes tendrils/stem to twin around a support br br Hydrotropism br br - growth movement of roots in response to unilateral source br br of water/moisture br br - the root grows towards the source of water/ positively hydrotropic while leaves are negatively hydrotropic br br chemotropism br br - growth movement of parts of plant to unilateral source of br br chemicals br br - the chemicals form a gradient between two regions e.g. pollen tube growing towards the ovary through the style iii State the ways in which tropisms are important to plants - expose leaves/shoots in positions for maximum absorption br br of sunlight for photosynthesis br br - enables roots of plants to seek/look/search for water - enables plant stems/tendrils to obtain mechanical support br br especially those that lack woody stems br br - enables roots to grow deep into the soil for anchorage - enables pollen tube grow to embryo sac to facilitate br br fertilization br br iv Explain the differences between tropic and tactic responses Tropisms Taxes br br - growth curvature in br br - locomotory response - fast - external influence br br response br br - slow - influenced by hormones br br d The diagram below represents growing seedlings which were subjected to unilateral light at the beginning of an experiment br br br br R br br i - P will bend/grow towards light br br State the results of P, Q and R after 5 days br br 384 - Q will remain straight/have little or no growth - R will remain/grow straight/grow upwards ii Account for your results in i above br br P- Growth substance/growth hormone/IAA/auxin are produced by the stem tip br br - they move downwards and get distributed to the side br br away from light where they cause rapid/more growth/cell division/elongation that results in bending br br Q- Source of auxin has been removed R- The auxins cannot be affected by light because the tip has been covered br br iii If the tin foil were removed from the tip of seedling R, br br what results would be observed after two days br br - it will bend/grow towards light iv State the expected results after 3 day is if the box br br were removed br br - all seedlings will grow straight/upwards br br e In an experiment to investigate a certain aspect of plant response, a seedling was placed horizontally as shown in diagram I below. After seven days the appearance of the seedling was as shown in diagram 2 Account for the curvature of the shoot and root after the seven days br br Shoot i - auxins accumulate on the lower side of the seedling due to br br gravity br br - high concentration of auxins in shoot stimulates faster br br growth causing more elongation on the lower side than the upper side hence curvature occurs upwards br br ii Root - the high concentration of auxins inhibits growth hence the upper side with less auxins grows faster than the lower side therefore the curvature occurs downwards f What is etiolation? br br - phenomenon exhibited by plants when grown in darkness - such plants are pale yellow due to absence of chlorophyll, br br have small leaves, long stems/hypocotyle and slender stems br br - plants exhibit etiolation to reach light/obtain light - this is a survival response 3. a i What is coordination in animals ii Name the main systems for coordination in animals - Nervous system/sensory system - Endocrine hormonal system iii List the components of the mammalian sensory system - Central nervous system CNS , brain spinal cord - Peripheral nervous system PNS cranial and spinal nerves - Sense organs - Autonomic nervous system ANS nerve fibers and ganglia iv .Explain the terms receptors, conductors and effectors - Receptors are structures that detect stimuli i.e. sense organs - Conductors transmit impulses from receptors to effectors e.g. neurons - Effectors are the responding parts e.g. muscles, glands v What are the functions of the central nervous system? - provides a fast means of communication between receptors and effectors - coordinates the activities of the body vi State the differences between somatic and autonomic systems of peripheral nervous system - Somatic is concerned with controlling the conscious or voluntary actions of the body i.e. skin, bones, joints and skeletal muscles - the autonomic automatic nervous system controls involuntary actions of internal organs, digestive system, blood vessels, cardiac muscles and glandular products. b i What is a neurone? br br ii Name the parts of a typical neurone and state the functions of each part br br cell body/centron contains nucleus and cytoplasm axon transmits impulses away from cell body dendrites relays impulses across adjacent neurons myelin sheath insulates axon and speeds up transmission of br br impulses br br schwan cells forms myelin sheath and aid in nutrition and br br regeneration of axon br br node of ranvier occur between schwan cells, where axon is br br not covered, speeds up impulse transmission br br nissils granules contain mitochondria that provide cell body br br with energy for metabolic process br br i Describe the structure and function of a motor br br neurone br br motor neurone relays impulses from CNS brain/spinal br br cord to effectors muscles/glands br br ii Describe the structure and function of sensory br br neurone br br sensory neurone relays impulses from receptors sense br br organs to CNS br br 387 br br iii State structural differences between motor and br br sensory neurons br br Cell body in motor neurone is terminal at the end and br br inside central nervous system. br br Cell body in sensory neurone is terminal but has axon at br br both ends bipolar br br iv Describe the structure and function of a relay br br neurone br br also called br br intermediate/internuncial/associate/connector/interneurone br br locate inside central nervous system and spinal cord usually lack myelin sheath br br c State the functions of the major parts of the human brain br br 388 br br i Cerebrum br br called forebrain occupies most of the brain consists of four lobes each with specific function temporal lobe controls taste smell hearing learning and br br memory br br partial lobe controls sensory output and touch occipital lobe controls vision, motor output and speech frontal lobe controls personality, learning thought and br br speech br br also has parts called thalamus and hypothalamus thalamus helps to sort sensory information hypothalamus controls hunger, heartbeat body temperature br br and aggression br br ii Mid brain br br quite small in humans relay centre for audio and visual information also involves in some sight, hearing and orientation br br responses i Hind brain consists of cellebral and medulla oblongata cerebellum is responsible for coordinating impulses, br br posture and balance, motor coordination and muscle tone br br 389 medulla oblongata controls heartbeat, blood pressure br br breathing rate, coughing and sneezing br br a i What is reflex action? an automatic response to an external stimulus e.g. sneezing br br or withdrawing hand from a hot object br br ii Describe a reflex action that will lead to the withdrawal of a hand from a hot object br br Receptors in the skin respond to stimuli. Are stimulated an impulse is transmitted through the sensory neurone, across a synapse to the central nervous system white matter , through the relay neurone into grey matter, then to the motor neurone and finally to the effect muscle which contracts br br the hand is then withdrawn br br br br iii Explain how an impulse is transmitted across the synapse gap br br impulse initiates release of transmitter substance acetylcholine at the end of the sensory neurone br br acetylcholine diffuses across the synapse and generates an br br impulse in the next neurone br br ii Briefly describe the transmission of a nervous impulse across a neuro-muscular junction impulse arrives at synoptic knob and causes vesicle to br br move to the pre-synaptic membrane br br vesicle discharges transmitter substance into synaptic cleft transmitter substance/acetylcholine diffuses across the cleft br br and attaches to post-synaptic membrane br br the membrane is depolarized, generating the action br br potential br br iii What are the functions of a synapse? allows transmission of nerve impulses from neurone to br br neurone br br ensures nerve impulses travel in only one direction br br 390 in the brain they store information/memory b i What is a conditioned reflex? A response caused by a unilateral stimulus associated br br stimulus which substitutes the normal stimulus br br ii Explain a conditioned reflex br br it is automatic it involves the spinal cord it is usually learned e.g. writing, cycling, dancing it involves the interaction of highly specialized centers of the brain with a large number of neurone necessary to bring about conditioning br br example is experiments carried out by Pavlov using dogs iii Compare a simple reflex action with a conditioned reflex Simple reflex br br Conditioned reflex dependent on experience independent of experience br br one stimulus to evoke both substitute and br br response br br original reflex evoke response some sensory and br br sensory component replaced but motor remains unchanged br br motor neurons used br br reflex is simple br br reflex is modified br br c i What are endocrine glands? ductless glands that produce hormones in animals hormones are chemical substances which help to coordinate br br the functions of the body br br ii State the functions of hormones in animals br br regulate growth and development control behavior during breeding proper functioning of cells regulate metabolic activities iii Name the main endocrine glands, their secretions and functions in the human body Gland Thyroid Hormone Thyroxine br br Functions Increases rate of metabolism Regulates calcium and phosphate levels Regulate growth of br br Parathyroid Parathyroid hormone br br Pituitary Hormone growth body br br Gonadotrophic hormone Stimulates the br br development of male and female sex organs Stimulates secretion of milk after child birth - proper functioning of thyroid gland/thyroxine production - stimulates release of adrenal cortex hormone br br Lactogenic hormone prolactin br br Thyrotropic hormone TSH br br Oxytocin regulates br br blood pressure br br stimulates smooth muscles stimulates br br contraction of uterus during childbirth aids in flow of milk from mammary glands causes br br Follicle stimulating hormone FSH br br maturation of egg in females br br stimulates sperm production in males - regulates water balance by kidneys for emergency prepares body to cope up with stress - maintains balance Aldosterone br br supplements br br sex hormones produced by gonads promotes br br development of sexual characteristics regulates level of sugar in blood br br enables liver to store sugar regulates level of sugar in blood br br causes sexual secondary characteristics in females br br prepares uterus for pregnancy growth of br br mucus lining of uterus maintains br br uterus during pregnancy br br Testes causes br br secondary sexual characteristics in males stimulates release of gastric juice br br Stomach cells br br stimulate release of pancreatic juice br br iv Give the differences between nervous and endocrine hormonal communication br br Nervous Response confined to effector organs localized targets Response less rapid Speed of response is rapid Hormones transferred Nervous impulse thro ugh nerves/nerve cell/neurons through blood Duration of response is short Persist for long Speed of transmission is rapid Transmission is electrical br br Hormonal endocrine Response more widespread various targets br br Speed of transmission is slower Transmission is chemical v State the effects of over secretion and under secretion of adrenaline and thyroxine in humans br br Hormone Adrenaline br br Over secretion Under secretion br br thin toneless muscles high blood pressure weak bones obesity early onset of br br low blood pressure inability to br br withstand stress br br fatigue muscular weakness muscle wasting increased dark br br sexual development br br pigmentation of skin br br Thyroxine increased cretinism retarded g i Define the following terms Drug a substance that causes a change in body function br br Drug abuse br br indiscriminate use of drugs without minding their side br br effects br br misuse or wrong use of drugs br br ii State the types of drugs, examples and side effects Sedatives br br also called depressant a drug that decreases the action of the central nervous br br system br br reduce anxiety, and tension, induce sleep and act as muscle br br relaxants br br when abused they cause withdrawal effects such as anxiety, br br delirium and death br br includes barbiturates, other sedatives, tranquilizers and br br alcohol Pain-killers br br suppress centers of pain in the brain br br Hallucinogens br br given to people with hallucination or mentally ill patients to br br calm then down br br when abused they lead to a feeling of confusion, agitation, depression and violent behavior that can lead to murder or suicide br br examples include valium, LSD, bhang, narcotics and br br cannabis Stimulants br br drugs that temporarily increase the action of the central br br nervous system br br they create a feeling of alertness, wakefulness, a sense of br br self confidence and well being br br used to decrease fatigue and mild depression when abused they cause feelings of persecution, br br hallucination and addiction br br include amphetamines, cocaine, caffeine, miraa and br br nicotine br br iii State the general effects of drug abuse on human health br br damage to body organs e.g. liver cirrhosis drug addiction impaired judgment resulting in clumsiness socio-economic problems e.g. crime, loss of jobs, divorce, br br prostitution, HIV/AIDS br br may cause poor health br br h i List the special sense organs in mammals and the major function of each - Eye for sight - Ear for hearing and balance - Nose for smell - Skin for touch, temperature detection, pain detection br br iii How is the human eye adapted to its function? br br br br conjunctiva is thin/transparent/tough to allow light to pass br br through/to protect the eye br br 396 Sclerotic layer is made up of collagen fibers/fibrous. It br br maintains shape of the eyeball/protects the eye br br cornea is transparent/curved thus refracts light rays/allows br br light to pass through br br Choroid is a layer of tissue with black pigment/dark pigment. Prevents internal reflection of light in the eye/contains blood vessels that supply oxygen/nutrients/remove metabolic wastes from the eye br br retina has cones/rods for bright colour vision/low light br br vision br br yellow spot has a high concentration of cones for accurate br br vision/visual acuity br br Blind spot has no cones and rods. Place where optic nerve br br leaves/enters the eye br br optic nerve has sensory nerve fibers for transmission of br br impulses to the brain for interpretation br br Lens is biconvex/made up of elastic material/transparent. Adjust focus on far or near objects allow light to pass through/for refraction of light rays br br ciliary body is made up of muscle fibers/glandular which br br contract/relax to change shape br br suspensory ligaments are inelastic to hold lens in position/attach it to ciliary body br br iris is the coloured part of the eye it has radial and circular br br muscles which control size of pupil br br pupil is the small hole at the centre of iris through which br br light passes into the eye br br aqueous humor is a fluid through which oxygen/nutrients br br pass to the cornea/lens/maintains shape of the eyeball/refracts light rays br br vitreous humor is a fluid which maintains shape of br br eye/refracts light rays br br iii What is accommodation of the eye? br br ability of the eye to adjust to bring an image from a near or br br far object into sharp focus on the retina br br iv Explain how an eye viewing a near object adjusts to viewing a far object br br ciliary muscles relax suspensory ligaments become taut/tight lens decreases curvature/becomes thinner radial muscles relax circular muscles contract br br size of pupil decreases to reduce amount of light v What changes occur in the eye if it changes from observing an object at a distance to one at a closer range? - ciliary muscles contract - Tension in suspensory ligaments reduces/relax/ slackens - Lens bulges/thickens/increases curvature - Radial muscles contract - Circular muscles relax - Size of pupil becomes large to allow in more light. br br viii State the changes which would take place in the eye if a person in a dark room had lights switched on br br circular muscles contract and radial muscles relax pupil becomes small to allow less light into the eye ix Explain how the eye forms an image the mammalian eye works like a camera light rays enter the cornea pass through the pupil, aqueous br br humor, lens and vireous humor br br light rays are refracted by the aqueous and humor and br br lenses br br finally light falls on the retina to form an image the image is real and inverted and smaller than object, back br br to front/reversed br br Retina forms a fine image when light rays reach it. x Name the defects of the eye and state how they can be corrected br br Short sight Myopia br br eye cannot focus on far objects image is formed in front of the retina because light rays br br converge in front of retina br br the lens is too thick, curve and eyeball too long corrected by wearing concave/biconcave/lenses these lenses diverge light rays onto retina br br Long sight Hypermetropia br br eye lenses are unable to focus because they are flat, thin and weak hence unable to focus image on the retina they are unable to accommodate/change the focal length near image is formed behind the retina but a distant one is br br correctly focused on the retina br br corrected by wearing convex/biconvex/converging lenses br br Presbyopia br br occurs in old age hence called old sight caused due to loss of elasticity of lenses, weakness of br br ciliary muscles hence lack of focus of light rays br br 399 this causes long sight corrected by wearing biconvex/convex/converging lenses br br Squinting br br eyeballs are uncoordinated/do not turn at the same time eye muscles move in different directions this makes accommodation and focusing difficult corrected through surgery br br Astigmatism br br surface of cornea is uneven leads to weak focus of light raise on retina corrected by using cylindrical lenses/lenses with combined br br curvature br br xi State the advantages of having two eyes in human br br beings br br stereoscopic vision gives a wider angle of binocular vision if one is damaged human is not blinded I i What are the functions of the human ear? br br hearing balancing iv How are the structures of the human ear suited to br br perform the function of hearing? br br br br 400 shape of the external ear/pinna allows collection of sound br br waves and channels them down the auditory canal/auditory mateus br br auditory canal is a tube that concentrates and directs sound br br waves to tympanic membrane/ tympanum/eardrum br br Eardrum is thin and tight. It sets into br br vibration/vibrates/converts sound waves into vibrations the vibrations are transmitted to the ear ossicles/malleus, br br incus and stapes that amplify the sound vibrations the vibrations are then transmitted to the fennestra br br ovalis/oval window br br Oval window is a membrane which amplifies/transmits br br vibrations to the fluids perilymph and endolymph then to cochlea. br br The cochlea is coiled to occupy a small space and accommodate a large number of sensory cells The sensory cells/hairs in the cochlea are set into br br vibrations/stimulated producing nerve impulses in the auditory nerve br br Impulses in the auditory nerve are transmitted to the brain br br for interpretation for hearing br br Eustachian tube connects the inner ear to the throat. It br br equalizes air pressure in the middle ear with the atmospheric air pressure in outer ear Fennestra rotundus/round window br br dissipates/discharges/discards vibrations from inner ear to middle ear br br iii Explain how the structure of the human ear performs the function of balancing br br there are three semi-circular br br canals/utriculus/succulus/vestibular apparatus arranged in planes at right angles to each other br br at the end of each canal is a swelling called ampulla which br br contains receptors br br the movement of the head causes movement of the br br fluid/endolymph in at least one canal br br the fluid movement causes stimulation of the br br receptors/sensory hairs br br sensory impulses are generated the auditory nerve transmits the impulses to the brain for interpretation for the position of body/posture/balance iv State what would happen if the auditory nerve was completely damaged br br deafness loss of body balance impulse not transmitted to the brain 7. a i What is support? br br to support is to carry part of the weight/mass of an br br organism br br ii What is locomotion? br br progressive change in the position of an organism iii State the importance of support systems in living organisms br br they provide a framework for the body of organisms and br br help to determine their shape br br provide land animals with means for support to their br br weights against gravity br br organs are attached to the skeleton for support and stability br br to avoid entanglement and crushing each other br br they protect very important and delicate organs whether br br inside or outside the body e.g. eyes, heart br br in large plants the rigid trunks of trees support the greater br br mass of leaves and fruits br br iv State the importance of locomotion in animals br br in search of food search for mates escaping predators br br b i Name the tissues in higher plants that provide mechanical support sclerenchyma collenchyma not lignified xylem/tracheids and vessels ii State the importance of support in plants br br exposing the surface area of leaf to sunlight for br br photosynthesis br br ensure flowers are exposed to pollination agents expose fruits and seeds to agents of dispersal to resist breakages due to their own weight and that of other br br organisms br br for proper transport and translocation of materials br br iii Name the types of plant stems br br herbaceous e.g. shrubs woody e.g. trees br br weak stems in creepers, twining plants and plants bearing br br tendrils br br iv Name the tissues in plants that are strengthened with lignin br br sclerenchyma xylem vessels/tracheids/xylem br br v What makes young herbaceous plants remain upright? br br turgidity presence of collenchyma br br vi State the ways by which plants compensate for lack of ability to move from one place to another br br ability to pollinate response to nastic and tropic movement ability to exploit localized nutrients ability to disperse seed or fruit propagation br br c i Explain the ways in which erect posture is maintained in a weak herbaceous stem - This is the function of turgidity and presence of collencyma Cells take in water and become turgid ii Explain how support in plants is achieved br br Turgor pressure due to absorption of water keeps cells firm br br hence hold herbaceous plants upright br br collenchyma and clerenchyma tissues are closely packed in br br stem and roots to provide support br br inelastic cuticle on epidermis is covered by a waxy layer hence keeping shape of plant and setting inward pressure against turgid cells and this causes a force to hold plant upright br br xylem vessels and tracheids are lignified to provide support br br to stems, roots and leaves br br climbing plants obtain mechanical support from other br br plants and objects br br they have climbing structures like tendrils which hold on to br br other objects br br d i Give the reasons why support is necessary in animals br br for attachment of muscles For attachment of other body organs to protect delicate body organs to maintain body shape/form to enable movement/locomotion br br ii Why is movement necessary in animals? br br enables animals to search for food br br enables animals to search for shelter enables animals to escape predators/harmful conditions enables animals to search for water enables animals to search for mates enables animals to search for breeding sites e i Name the organ used for support by animals - Skeleton ii Name the different types of skeletons in animals, giving an example of an animal for each type of skeleton named br br exoskeleton e.g. arthropoda crab, insect endoskeleton e.g. chordata cat, fish br br iii State the difference between exoskeleton and endoskeleton br br endoskeleton is a rigid framework covered by body tissues br br of an animal br br exoskeleton is a rigid framework found on the surface of an br br animal br br iv State the advantages of having an exoskeleton br br supports/protects delicate inner parts water proof/prevents drying up of body provided surface for muscle attachment br br v Explain the importance of having an endoskeleton br br support the body give body its shape protect delicate organs e.g. skull, brain, ribs used in locomotion e.g. bones serve as levers red blood cells are formed in bone marrow minerals are stored in bones e.g. calcium and phosphorus f i Explain how a fish is adapted to living in water streamlined body for easy movement in water swim bladder controls depth of swimming fins for movement, balance, direction and stability gills for gaseous exchange in water presence of lateral line to sense vibrations scales provide protection colour which offers camouflage against predators ii Explain how a finned fish is adapted to locomotion in water br br streamlined body to reduce resistance/friction to swim br br smoothly br br the vertebral column consists of a series of vertebrae held br br together loosely so that it is flexible myotomes/muscles associated with vertebral column br br produce movement br br the sideways and backwards thrust of the tail and body br br against water results in resistance of water pushing the fish sideways and forwards in a direction opposed to thrust br br heat not flexible so as to maintain forward thrust presence of fins help in propulsion/balance/paired fins br br pectoral and pelvic for controlling pitch and slow down movement/unpaired fins dorsal, ventral, anal for yawing and rolling caudal for swimming/propulsion and steering/change of direction br br presence of swim bladder to make fish buoyant scales tip towards the back to provide smooth surface body covered with mucus to reduce friction flattened surface for easy floating br br g i Name the main parts of the vertebral column giving the types of bones found in each part Axial skeleton br br forms the main axis of the body formed by the skull, sternum, ribs and vertebrae br br Appendicular skeleton br br composed of limbs and girdles the forelimbs are connected to the trunk by the pectoral br br girdles shoulder bones hind limbs are connected to the pelvic girdle hips bones are scapular, clavicle, humerus, ulna, femur, tibia, br br fibula, metacarpals, carpals, tarsals, metatarsals, phalanges, ilium, ischium and pubis ii What are the vertebrae? br br bones of the vertebral column br br iii State the functions of the vertebral column br br gives flexibility absorbs shock protects spinal cord supports weight of body provide surface for muscle attachment between the vertebrae are soft discs which offer cushioning br br called interverterbral discs br br iv State the general characteristics of vertebrae br br have solid structure called centrum to support weight of br br body has transverse process lateral to centrum for muscle br br attachment br br neural spine is dorsal to centrum and provides surface area br br for muscle attachment br br neural canal a passage for spinal cord and offers protection br br to it br br has facets for articulation with other vertebrae neural arch encloses neural canal br br br br 406 br br v Name the bones of the vertebral column - Cervical vertebra - Thoracic vertebra - Lumbar vertebra - Sacral vertebra - Caudal vertebra br br 407 br br vi Describe how the various vertebrae are adapted to their functions Bone Skull br br Structure Function br br cranium and jaw bones attachmen t of jaws br br made of several bones joined together large box called cranium and smaller paired boxes for eyes, ears, nose, jaws has large br br protect br br brain and other delicate parts br br hole called foramen magnum for the passage of spinal br br 408 cord br br ring shaped no Centrum broad, flat transverse processes vertebrateria l canal for passage of vertebral artery facet for br br articulation of condyles of skull br br adontoid peg br br projects from Centrum br br large br br flattened neural spine vertebrasteri al canal br br small br br transverse process short neural br br spine branched transverse process for neck muscles vertebrateria l canals wide neural br br canal long br br backward pointing neural spine transverse br br process that points sideways facets for br br articulation of ribs notch for br br spinal nerves to pass through short neural br br spine long br br transverse process pointing towards abdomen br br large br br Centrum br br extra br br processes e.g. prezygapoph ysis, hypapophysi s, anapophysis, metapophysi s br br fused bones to form sacrum br br well br br developed transverse process of first vertebra vertebrateria l canals short neural br br spine vii Describe the bones that form the appendicular skeleton Structure Bone Pectoral girdle scapular shoulder bone br br Function Support Muscle attachment Articulates with humerus br br Broad i.e. br br Flattened blade glenoid cavity to articulate with humerus br br metacromion/acro mion for muscle attachment hard to provide br br support socket with br br cartilage/smooth surface to reduce friction br br Humerus long shaft for moveme br br muscle attachment nt br br round head to articulate with glenoid cavity muscle attachm ent br br trochlea for br br articulation with ulna br br olecranon fosa to br br prevent arm bending the other way Ulna and radius br br ulna longer and on side of little finger has sigmoid notch and olecranon process to form hinge joint with humerus br br moveme br br nt br br muscle attachm ents br br radius is smaller and lies along thumb side and does not join ulna allows articulation with wrist bones br br Pelvic girdle hip bone composed of three moveme br br fused bones ilium, ischium, pubis br br nt br br muscle attachm ent support absorbs pressure exerted by ground when animal moves br br upper end fused to br br sacrum br br lower end has acetabalum for articulation with femur br br has abturator foramen for passage of nerves and blood vessels br br 412 rounded head to fit in acetabulum of pelvis br br projections called trochanter for attachment of thigh muscles condyles at lower br br end for articulation with tibi br br patella that covers knee and prevents leg from bending backwards br br Tibia and fibula tibia is longer than moveme br br fibula nt br br tibia is outer bone and fibula is inner bone muscle attachm ent br br tibia lies on side of large toe br br fibula is fused to tibia on outer side br br 8. a What is a joint? the point where bones meet ii State the functions of joints br br provide a point of articulation between bones br br iii Name the main types of joints br br immovable joints e.g. skull, pelvic girdles and sacrum slightly movable joints e.g. between vertebrae Freely movable joints e.g. knee, elbow br br iv Give the features of movable joints br br ends of bones covered with articular cartilage ends bound by capsules of ligaments have joint cavity filled with lubricating fluid called synovial fluid secreted by synovial membrane br br they are called synovial joints br br b Describe the synovial joints br br iv Ball and socket allow movement in all planes /directions i.e. 360o rounded end of bone fits into a rounded cavity in another br br bone br br e.g. shoulder joint and hip joint br br br br v Hinge joint convex surface of one bone fits into the concave surface of br br another bone br br this allows movement in only one plane/direction 180o e.g. elbow joint and knee joint br br vi Pivot joint allows rotation e.g. where atlas pivots on olecranon process br br of axis br br c i What is synovial fluid? br br lubricating fluid produced by synovial membrane at br br movable joints br br ii State the functions of synovial fluid br br absorbs shock reduces friction/gives lubrication nourishment distributes pressure d Explain the following terms v Ligament connective tissue joining one bone to another vi Cartilage supporting soft tissue found at joints they cushion the bones and absorb shock vii Tendon tissue that connects muscle to bones br br 9. Muscles br br 414 e i What is a muscle? fleshy part of body composed of long cells enclosed in a sheath specialized cells capable of contracting br br ii State the functions of muscles br br cover the skeleton provide shape contract and relax to enable body to move f Describe the structure and function of various types of br br muscles br br i also called voluntary/striated/stripped muscles they are attached to skeleton they consist of striated, multinucleated, ling fibers and are br br skeletal muscles br br cylindrical shaped br br found on legs, arms, eyes, neck where they cause br br movement br br ii also called smooth/visceral/unstriated/unstripped their movement is not controlled by the will they are unstriated, nucleated, short fibred and spindle br br Involuntary muscles br br shaped br br are found in alimentary canal, blood vessels, secretory glands, other tubular visceral organs, bladder, uterus, urinary tract, reproductive system, respiratory tract, ciliary body, iris br br iii Cardiac muscles also called myocardium found in the walls of the heart are not under control of the will composed of long cylindrical cells with special junctions myogenic i.e. generate their own contraction they are not fatigued their function is contraction of the heart to pump blood g Explain how muscles cause movement of the human arm br br the muscles which bring about these movements are called br br biceps and triceps br br biceps are attached to scapula and radius for bending triceps are attached to scapula, humerus and ulna for br br stretching when the biceps contracts, it pulls the radius forearm and br br the hand bends br br the triceps relaxes at the same time when the triceps contracts and biceps relaxes extends the br br arm is stretched br br biceps flexes the arm flexor and triceps extend extensor br br muscle the arm br br h i State the structural differences between skeletal br br muscles e.g. biceps and smooth muscles e.g. gut muscle br br Skeletal biceps br br Smooth gut muscle uninucleated unstriated short muscle fibers spindle shaped multinucleated striated/stripped long muscle fibers block/cylindrical br br ii Name the cartilage found between the bones of the vertebral column br br intervertebral disc iv What are the functions of the cartilage named in d br br ii above br br acts as a cushion/absorbs shock reduces friction flexibility of vertebral column