Biology Questions and Answers Form 3

KCSE Revision Questions and Answers

K.C.S.E Online Revision

1. a) i) What is meant by the term binomial nomenclature?scientific system of naming organisms using the generic(genus) and specific (species)

ii) State briefly the general principles of classification of living organismsscientific names must be in Latin or should be latinisedfamily names are formed by adding the suffix “idea” to the stem of the genus e.g the genus Rana become Ranaideageneric names should be a single unique name

b) State the main characteristics of the five kingdoms of organisms

i. Monerae.g. bacteriaunicellular (single celled)prokaryotic (genetic material not surrounded by membrane)cell Wall without celluloselack most organellessmall in size (microscopic)

ii. Protista(protoctista)single celled(unicellular)eukaryotic (most cell organelles present)when cell Walls are present have no cellulosee.g. protozoa and algaeusually microscopic

iii. Fungihave hyphae (which form mycelia)absence of chlorophyllhave rhizoids (lackroots, leaves, stem)have spore forming structures (sporangia)e.g. mucor, rhizopus

iv. Plantaemost are green/contain chlorophyllautotrophic/feed by photosynthesiscells have cellulose cell wallsrespond slowly to stimuli (tropism)lack locomotion (are stationary)indefinite growth (at meristems)lack specialized excretory structures

v. Animaliacells do not have cell wallsmost carry out locomotionheterotrophicfast response to stimuli (tactic)have specialized excretory structures

c) Describe the economic importance of:

i. Fungisome cause decay to our foodsome cause diseases to humans and animals e. g. ringwormsmay be used as food e. g. mushrooms, yeastsome are used in production of antibiotics e. g. penicillin, chloromycin, streptomycinyeast is used in brewing industry, baking and source of vitamin Bmany cause diseases to our crops e. g. late blightimportant in recycling nutrients in soil since they cause decay of organic mattermycorrhizal association in forest development may help in Water intake/absorptionhelp in nitrogen fixation

ii. Bacteriaare useful in the manufacture of antibioticssilage formation,fermentation of cheese, butter, milk yoghurtcuring of tea, tobacco and retting flaxformation of vitamin B12 and Kenzymes such as amylase and invertasehormones such as insulin ‘vinegar, acetic acid, lactic acid, citric acidin septic tanks and modern sewage Works make use of bacteriabiogas productionsaprophytic bacteria are used in compost decomposition or cause decaysymbiotic bacteria are used in compost decomposition or cause decaysymbiotic bacteria in herbivores/ruminants help in digestionsome diseases in animals/humans and plants are caused by bacteriamany bacteria cause‘ food spoilage/decaynitrifying and nitrogen fixing bacteria increase soil fertility/make nitrates availabledenitrifying bacteria reduce soil fertility/convert nitrates into nitrogen/reduce nitrates

d) State the main characteristics of the following division of kingdom plantae

i. Bryophytee.g. mosses and liverwortspresence of rhizoidslack of vascular tissues (lack phloem and xylem)body pans not differentiated into root, stem, leavescapsule or setagametophyte generation dominant.

ii. Pteridophytae.g. fernshas true roots, stems and leavesfond with sori on under-surfacevascular tissues presentsporophyte generation is dominant

iii. Spermatophytephotosyntheticwell differentiated into roots, stems and leaveswell developed vascular systemseed bearing plants

e) Name sub-divisions of spermatophyte and state the characteristics of each class

i. Gymnospermae (cornifers)naked seeds (exposedare all woody treesreproduce by means of conesshow xerophytic characteristicsxylem have tracheids but lack vesselsphloem lacks companion cells ~single fertilizationpollen lands directly on ovules

ii. Angiospermae (flowering plants)reproduce by flowersseeds enclosed (in fruits)flowers bisexual hence double fertilizationherbaceouspollen grains land on stigma of pistilxylem contains vesselsphloem contains companion cellsovules contained in ovary

iii. Name the classes and state characteristics of angiospermae

Dicotyledonaetwo seed leavesnetwork venation of leavesregularly arranged vascular bundlestap root systembroad leavessecondary growth occurs

Monocotyledonaeone seed leafparallel venation of leavesirregularly arranged vascular bundlesfibrous root systemnarrow leavessheath like leaf stalk (petiole)no secondary growth

iv)State the importance of plantsbalancing carbon IV oxide and oxygen in the atmosphere during photosynthesis and respiration influence water cyclereduce soil erosion by bind soil particles togetheruseful products e. g. food, medicine, timber, paper and clothinghabitat ( e. g. forests and grassland) for animals which may also be tourist attraction earn money from sales of productsaesthetic value/beauty e. g. flowers, shade/shelter, live fences, windbreaksSome are harmful e. g. poisons, weeds, injurious (stinging nettles, thorns), water hyacinth

f) i) Give the general characteristics of phylum arthropodajointed appendagespresence of exoskeletontriploblastic and coelomatesegmented bodybilateral symmetry (similar halves)

ii. State the characteristics of the following classes of arthropoda

Diplopodathe millipedestwo pairs of legs per segmentmany segmentsterrestrial habitatbody cylindrical and longherbivorousone pair of antennae

Chilopodathe centipedesone pair of legs per segmentmany segmentsterrestrial habitatbody long and ventro-dorsally flattenedcarnivorouslast pair of legs pointing backwards with poison claws called maxillipedesone pair of antennae

Insectathree body pans i.e. head thorax, abdomensix legs/three pairs of legsa pair of compound eyespresence of wingsa pair of antennae

Crustaceantwo body partssegmented bodyhave pincers (modified legs) to catch preyhave hard exoskeletona pair of compound eyes

Arachnidabody divided into two parts( abdomen and cephalothorax)simple eyeseight legs (four pairs of legs)

iii) State the economic importance of insects

Beneficial effectsfood supplyimportant in food chainspollinatorsbiological control of pests and other organismsaesthetic valuecontribute to decomposition e. g. litter feeders like beetles

Harmful effectspestsvectorsdirt and disease carriersinjurious e.g. stings and bites

g) i) State the general characteristics of chordatenotochorddorsal slits (pharyngeal cleft during development)bilateral symmetrytriploblastic (three layer body-ectoderm, mesoderm and endoderm)clear cut head formationmultilayered epidermispost anal tailclosed circulatory systemsegmented muscle blocks(myotomes)single pair of gonads

Give the characteristics of the following classes of chordate

Piscespresence of fins for locomotiontwo chambered heart *presence of overlapping scales ~presence of gills or operculum for gaseous exchangepresence of lateral line for protectionstreamlined bodypoikilothermic (body temperature varies with that of environment)

Amphibianpartially live in fresh Water and partially on landpoikilothermicpentadactylous with two pairs of limbswebbed feet for locomotion in waterbody streamlinedheart is three chamberedmoist skin for gaseous exchange

Reptiliascales on bodypoikilothermichomodont teeth except tortoise and turtleall have limbs except snakesskin is dryoviparous (lay eggs)no pinna (external ear)three chambered heart 9crocodile has four chambers)skin not glandularno mammary glands

Avesthe birdshomoeothermic (constant body temperature)four chambered heartstreamlined body for locomotion in airskin dry and covered by feathersscales on legshollow bonesoviparous (lay eggs)mouths modified into beaks

Mammalianhair on the bodyhomoeothermicviviparous (give birth to live young) eXcept a fewhave mammary glandsglandular skin e.g. sweat glands, sebaceous glandsfour chambered heartpinna (external ear)two pairs of pentadactyl limbspresence of diaphragmhave salivary glands

a) 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

i. State the necessity of using a dichotomous keyused to identify organisms quickly and accuratelyby 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

ii. List the rules followed in constructing a dichotomous keyuse observable characteristics onlystart with major characteristics, placing organisms into two groups at each stageuse a single characteristics at a timeuse contrasting characteristics at each stage e.g 1(a) short, 1(b) tallavoid repeating the same characteristics

iv) Describe the procedure of using a dichotomous key. Make a list of major features of the characteristics to be identifiedlook at the features of similaritieslook at the features of differences between the organismswe can then be able to identify the organisms by distinguishing one from anotherthe 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……. Go to 2

b) Leaf narrow……. Araicaria

2 a) Leaf parallel vein……. Cynodon

b) Leaf net veined……. Go to 3

3 a) Leaf with one lobe (simple Leaf)……. Go to 4

b) Leaf with many lobes (compound Leaf)……. Grevellea

4 a) Leaf Fleshy……. Kalanchoa

b) Leaf not fleshy……. Go to 5

5 a) Leaf petiole modified to form sheath……. Go to 6

b) Leaf petiole not modified to form sheath……. Brassica

6 a) Leaf purple……. Tradescantia

b) Leaf green……. commelina

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……. Go to 2

b) Animal without wings……. Go to 7

2 a) With two pairs of wings……. Go to 3

b) With one pair of wings……. Diptera

3 a) With membranous wings……. Go to 4

b) Hind pair of membranous wings……. Go to 6

4 a) With long abdomen ……. Odontata

b) Medium sized abdomen……. Go to 5

5 a) Wings with colored scales……. Lepidoptera

b) Wings without scales……. Hymenoptera

6 a) Forewings hard and shell-like……. Coleoptera

b) Forewings hard but not shell-like……. Orthoptera

7 a) Body horizontally flattened……. Isoptera

b) Body laterally flattened……. Symphonopteria

Identify the orders of the various specimen as per the table below

Specimen Order Step followed

K- housefly Diptera 1a, 2b

L- grasshopper Orthoptera 1a, 2a, 3b, 6b

M- beetle Coleoptera 1a, 2a, 3b, 6a

M- termite Isoptera 1b, 7a

2 a) Define the following ecological terms

i. Ecologystudy of the interrelationships between organisms and their environment

ii. Environmentsurrounding of the organism i.e. biotic or a biotic factors

iii. HabitatA specific locality (home) of a living organism with a set of factors (conditions) in which an organism lives.

iv. Ecological nicheRole of an organism in its habitat e. g. feeding relationship

v. PopulationNumber (group) of organisms of a species occupying a given habitat

vi. CommunityRefers 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

vii. EcosystemA community of organisms interacting with one another and the environment in which they live

vm. BiosphereThe earth and its atmosphere where living organisms are found

ix. AutecologyStudy of a single (individual) species of plants or animals within a community, ecosystem, habitat or environment.

x. SynecologyStudy of natural communities (plants and animals) or populations interacting within an ecosystem.

xi. Carrying capacitymaximum number of organisms an area can support without being depleted

xii. Biomegeographical area with particular climatic conditions and flora and faunait constitutes many ecosystems

xiii. Biomassdry weight (mass) of a living organism in a given areaunits of measurement are kg/m2/year

b) i) What are abiotic factors?non-living components of the ecosystem

ii) Explain how abiotic factors affect living organisms

Windthis influences rate of water evaporation from organismstherefore it affects distribution of organisms e. g. wind increases rate of transpiration and evaporation of water from the soilwind is an agent of soil erosion, may break and uproot treesmay aid in the formation of sand dunes which can form habitats for some desert plantswind disperses fruits, seeds, sporeswind forms waves in lakes and oceans which enhances aeration of water which replenishes oxygen concentration necessary for lifewind is an agent of pollination

Temperatureinfluences rate of enzyme action in photosynthesis and other metabolic reactions in plants and animalsorganisms function within a narrow range of temperatureit affects distribution of organismschanges in temperature affect rate of photosynthesis and biochemical reactions e.g. metabolism and enzyme reactiontemperature increases rate of transpiration

Lightneeded by green plants and photosynthetic bacteria which are primary producersanimals depend on plants directly or indirectly for foodmain source of light is the sunlight is necessary for synthesis of vitamin D in certain animalssome plants need light for floweringseeds like lettuce need light for germination

Humidityamount of water vapour held by the airaffects the rate at which water is lost from organisms body by evaporation and stomatal transpirationwhen humidity is low the rate of transpiration increaseshumidity influences distribution of organisms

pHeach plant requires a specific PH in which to grow (acidic, neutral or alkalinic)pH affects enzyme reaction in metabolism

Salinitysome ions are needed for plant and animal nutritionosmoregulation implants and animals is affected by salinity

Topographyaltitude affects light, atmospheric pressure and lightSlope influences surface runoff, wind erosion, etc.mountains affect distribution of organisms which differs in leeward side and windward sidemountains affect distribution of organisms which differ on lowlands and on highlandsmountains also form physical barriers to migration of organism and may cause isolation of speciesbackground may offer camouflage to some organisms hence protection from enemies

Rainfall (Water) or precipitationamount and distribution of rainfall affect vegetation typethis consequently affects distribution of animals e. g. polar region water frozen hence onlywell adapted organisms survivefewer organisms found in deserts where rainfall is lessWater is required for seed germination, raw material for photosynthesis, solvent for mineral salts. Provides turgidity for plant support, medium for transport, disperses fruits, seeds and spores

Pressurethe weight atmosphere exerts upon the earthvaries with altitude the higher the altitude the less the pressurethis variation implies change in density which directly means less oxygen for respiration and less carbon iv oxide for photosynthesis and this affects distribution of organisms

Mineral salts (trace elements)these affect distribution of plants in the soilplants thrive best where elements are availablePlants living in soil deficient in a particular element must have special methods of obtaining it.They harbor nitrogen fixing bacteria and others have carnivorous habitPlant distribution influences animal distribution

c) i) What are biotic factors?refers to living organisms in an areabiotic environment of an organism constitutes all organisms around it, which it relates or interacts with in various ways

ii) Give examples of biotic factors affecting ecosystemsfeeding relationshipspredationcompetitiondiseases and pestshuman activities

d) Discuss how the various biotic factors affect living organisms

i. Competitionorganisms compete with one another for food, light, water, mates and shelterorganisms must live together for competition for available resourcesthose which cannot cope either structurally or behaviorally will migrate or diethose remaining, due to better adaptations will increase in populationcompetition between members of the same species is called intra-specific competition e.g. for matesCompetition between members of different species is inter specific competition e. g. for food and space.

ii. Predationthis is predator-prey relationshippredator feeds on prey hence both control the other’s populationDistribution of predator and prey is important as predator cannot survive without preyIt there is no predator the prey will increase in population beyond carrying capacity hence die due to environment depletion

iii. Parasitisman association where an organism lives in or on another living organism obtaining food(and other benefits) from it, causing harm to it (without necessary killing it)parasites may kill hostthey deprive host of foodmake host weak by introducing diseasesmake reproductive ability of host low hence host becomes susceptible to predation

iv. Diseases and parasitesmake organisms weak and susceptible to predationkill organisms and reduce their population

v. Symbiotic

and association of organisms of different species where both benefit from the association i.e. there is mutual benefit

vi. Human activitiesthese are human factors which have an influence on the biosphereexamples are road construction, industrialization, deforestation, agriculture, pollution, poaching, fishing conservation, population controlaffect ecosystem and balance of nature

Saprophytismsaprophytes are organisms which obtain organic matter in solution from dead and decaying tissues of plants and animalsthey include saprophytic bacteria and fungithey make available carbon, nitrogen and other elements form dead to living organismsthey are useful in recycling nutrients in nature

e)i) What is nitrogen cycle?The process by which nitrogen in the air is made available plants and animals and eventually returns to the air.ii) Draw a simplified diagram representing the nitrogen cycle

iii) Describe the nitrogen cycleduring thunderstorms/lightning nitrogen gas combines with oxygen to form nitrogen oxidesnitrogen oxides dissolve in water to form nitric acidacid is deposited in the soil by rainnitric acid combines with chemical substances to form nitrates or nitric acid dissociates to form nitrates which are absorbed by plantssymbiotic bacteria (Rhizobium) which are found in root nodules of leguminous plants fix free nitrogen to nitratesfree living bacteria (clostridium and Azotobacter) fix nitrogen to nitratesnostoc algae (Anabaema chlorella) fix nitrogen to nitratesplants use nitrates to form plant proteinsanimals feed on plants and convert plant proteins into animal proteinsplants and animals die and are decomposed by putrefying bacteria, fungi(saprophytes)decomposing plants, animals and nitrogenous wastes release ammonia which is converted to nitrites by Nitrosomonas and nitrococcus bacterianitrites are converted to nitrates by nitrobacter bacterianitrates in the soil can be converted to free nitrogen (denitrification) by some fungi, pseudomonas and theobaccilus bacteria generally called denitrifying bacteria

iii. Nitrogen in the atmosphere cannot be directly utilized by plants. State two ways by which this nitrogen is made available for plant usefixation by microorganisms (Rhixobium, Axotobacter)fixation by electrical discharge in atmosphere i.e. conversion by thunderstorm or lightning

f) i) Describe how energy flows from the sun through the various trophic levels in an ecosystemenergy from the sun is trapped by green plants during photosynthesis, producing chemical energy9food or carbohydratesgreen plants are producers and occupy the first trophic levelgreen plants are eaten by herbivores called primary producers as they occupy the second trophic levelherbivores are eaten by carnivores, secondary consumers, which occupy the third trophic levelwhen organisms – plant and animals) die, fungi and bacteria which are saprophytic organisms feed on them thus causing them to decompose into simple substances e. g. mineral saltsthese organisms are called decomposers and detrivoresdecomposer feed on dead organic matter hence cause decomposition and decay which releases nutrients for plants, linking biotic and a biotic componentsat all levels energy is lost through respiration

Give the reasons for loss of energy from one trophic level to another in a food chaininsufficient utilization of food resources(wastage) e.g by defalcationthrough respirationthrough excretion e.g. urination and sweating

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 chaina 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 ecosystemif one consumer or the producer is removed the food chain is brokenarrow points to the direction of energy flow e. g. green plant herbivore carnivore decomposer

Food webcomplex feeding relationship Where a on more than one type of food while several herbivores feed on one type of plantit is an interrelationship of many consumers are usually fewer to ensure survival of both

Pyramid of numbers

this is a diagrammatic representation of numbers of organisms at each trophic level in a food chainusually there are more producers than consumershence producers herbivores carnivorethe reason for the pyramid is because herbivores feed on many plants (producers) as camivores feed on many herbivoressometimes this may not be true e. g. when many caterpillars feed on one tree or parasites on a herbivorethis gives an inverted pyramid of numbers

Pyramid of biomass

refers to diagrammatic representation total dry weight of organisms at different trophic levels in a food chainproducers have greater biomass than any level of consumers progressivelysize of organisms in successive e trophic levels increasesamount of individuals decreases in successive levels

Account for the decrease of biomass in the successive trophic levelsfixed 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

h) i) Describe the three characteristics of a population growthincrease in numbersdecrease in numbers growth ratechange in numbers

Dispersionspread or distribution of organisms in a habitat

Densitythe number of individuals per unit area

ii) Explain how the following methods are used to estimate population of organisms

quadrat methodidentify the study areathrow or mark out the quadrat in the area of study at randomidentify or label the various species of plants in the quadratcount plants of each speciesrecord the numbersrepeat the processwork out the average per quadrat for each speciescalculate the total number of different species in the area or calculate the population for the total area of habitat Q

Line transecta string is stretched along an identified areaall plants touching the string are counted

Belt transectpreliminary study of the study area to estimate siie or make a sketch maptwo parallel lines (strings or ropes) running for a determined distance and widthcount the number of organisms in the transectcalculate the area covered by the transectcalculate the number of organisms being investigated per unit arearepeat this process at least three times in other parts of the study areafind the mean number of organisms per unit area from all the belt transectsfrom this figure calculate the total population of the desired organisms in the study area

Capture-recapture methode.g. grasshoppers or fishcapture the grasshopperscount and mark using permanent inkrecordrelease and allow timerecapture and count the marked and unmarkedtotal population is equal to the number of marked and 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

2. a) Describe the adaptations of plants to various habitats

i. Xerophytesgrow in areas with scarcity of waterroots grow deeply and extensively (widely spread) to ensure access to waterthick succulent stems, roots and leaves for water storagephotosynthetic stems take place of leaves which would lose a lot of waterLeaves are needle-like (reduced to spines), scaly, have sunken stomata. Some have curled (rolled) leaves. Some have thick waxy cuticle, reduced number of stomata to reduce water loss by transpirationsome shed leaves during dry season to reduce water losspresence of thorns for protectionshort life cycle to ensure survivalreversed stomatal rhythm

ii. Hyrophytesgrow in places with plenty of water(waterlogged)aerenchyma a tissue (airspaces) and large intercellular spaces and long fibrous roots for buoyancy (floating in water)poorly developed support tissues (sclerenchyma) because water provides the necessary supportupper epidermis of leaves have more stomata than lower epidermis for gaseous exchange or for increased rate of transpirationpoorly developed conducting tissues (xylem and phloem) because plants obtain water by diffusion

iii. Mesophytesgrow in well watered soils ‘(common plants)no special adaptations, but depending on particular habitat, may have some adaptationsin forests they grow fast; tall to capture light. Have climbers while some are adapted to carry out photosynthesis in low light intensities (those that form undergrowth)in places with adequate water they form broad leaves, thin cuticle and many stomata on both leaf surfacesin direr regions they possess more stomata on the lower leaf surface and are deep rootedsome are shallow rooted and develop buttress and prop roots for supportsome have waxy or glossy surface to reflect sun rays and drip off rain water

iv. Halophytesplants that grow in very salty soil where the salt concentration is higher than that in the planthave root cells which concentrate a lot of salts in them and enable then to take in water by osmosissucculent roots to store waterhave pneumatophores (breathing roots) to take in oxygensome have buttress roots for supportsecrete excess salt by use of salt glandshave large airspaces in leaves and stems for buoyancy and to store aircapable of photosynthesis at low light intensities e.g. mangrove

b) 1) What is pollution?any process which leads to adverse or harmful changes in the environment

ii) Explain the various human activities that have caused pollution

Causes and effects of air pollutionsulphur 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 leavesaerosols, herbicides, insecticides (agrochemicals), paint spays, acaricides and CFC’s 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 layersmoke and fumes produced in areas withheavy industries, motor vehicles, fires which bum fuel, oil, wood and coal cause carbon ii oxide, poisoning affect respiratory systems and affect visibilityparticles in smoke and fumes settle on leaves and stop photosynthesiscarbon iv oxide causes green house effect which causes temperature inversion as a result of heating the lower layers of atmospheresound and noise produced incessantly by machines, aeroplanes and heavy vehicles affect hearing in animalsdust from cement factories, quarries, dust roads settles on leaves limiting photosynthesisremoval of vegetation interferes with carbon cycle radio-active emissions from nuclear reactors, mines and bombs cause cancer, mutations and death.

Control of air pollutionuse of lead free petrol in motor vehicles, air craft, aeroplanes and petroleum enginesuses of smokeless fuels and electricityfiltration, dissolution and use of chemicals to remove harmful gasesfactories should be erected far away from residential areasuse of tall chimneysreduce volume or intensity of sound e. g. by use of ear muffsconcords should fly at higher altitudes and aeroplanes to fly high up

State the causes, effects and methods of controlling and prop roots for support water pollution

Causes and effectsagrochemicals e.g. fertilizers cause eutrophication leading to increase in animal populationSilting makes water surfaces shallow and silt clogs stomata 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 populationindustrial 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 surfacesUntreated 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.Human feaces causes eutrophication, carbon IV oxide 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.Dumping of chemicals from industries with toxic pollutants which kill organismsSpillage of oil and chemicals block oxygen and kill organismsDischarge of water from industries into water body where high temperatures reduce amount of oxygen in the water causing organism to suffocate and dieUntreated sewage may lead to outbreak of epidemics

Control of water pollutionpollution caused by domestic effluents may be controlled by treating domestic waste, using biotechnology, banning the use ofphosphate-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 industriesOil spillage may be controlled by cleaning spilled oil biotechnology and penalizing the industryindividual or companies which cause oil spills/water pollutionPollution 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 agrochemicalssilting may be controlled by appropriate farming practices, contour farming, reafforestation, building gabions and terracing

iv) State the causes /effects and control methods of soil pollution

Causes and effectsAir pollutants e. g. sulphur IV oxide fumes form sulphuric acid with rain water. The acid rain alters soil pH therefore affecting plants that cannot tolerate acidic soilmost aerosols sprayed to control pests and diseases 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 thempetroleum products due to spillage by oil tankers making it impossible for plant roots to obtain oxygen in oil saturated soils, therefore plants are killedagrochemicals and inorganic fertilizers contain heavy metals that are not used up by plants and eventually soil microorganisms cannot inhabit the soilsorganic matter slows down, life ceases and soil becomes exhaustedcommunity, 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 pollutionuse of organic farming techniques _biological control of pests, diseases, parasitesrecycling of non-degradable containers or burying them safely after usecontrolled burning of garbagetreatment of human and industrial waste for safe disposalavoid spilling chemicals and oil when used

v) Define biological control give suitable examplesusing a living organism to regulate, control or reduce the population of another organism e.g beetles to feed on water hyacinth, fish to feed on mosquito larvae.

vi) What is eutrophication?enrichment of water bodies with nutrients due to discharge of sewage leading to rapid growth of surface plants

i) What are the effects of eutrophication?enrichment of water bodies with nutrients due to discharge of sewage leading to rapid growth of surface plants

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

Cholera

causative agentVibrio cholerae (bacterium)

TransmissionContaminated food or waterSpread by flies from faeces

SymptomsIntestinal painDiarrheaVomitingDehydration

ControlProper hygiene e.g boiling drinking watervaccination

Typhoid

Causative agentsalmonella typhi (bacterium)

TransmissionContaminated food or waterSpread by flies from faeces

SymptomsFeverRashesdiarrhea plus blood from bowels

ControlProper hygiene e.g boiling drinking watervaccination

Malaria

Causative agentPlasmodium (protozoa)

TransmissionBite by infected anopheles female mosquito

SymptomsFeverJoint painsVomitingHeadacheAnaemia

ControlKilling the mosquitoKilling the mosquito larvaeDraining stagnant waterClearing bushesTreatmentSleep under mosquito nets

Amoebic dysentery (amoebiasis)

Causative agentEntamoeba hystolytica (bacterium)

TransmissionContaminated food or water due to improper faeces disposal

SymptomsIntestinal painDiarrheaVomitingDehydration

ControlSanitationPersonal hygieneCook food wellTreatment using drugs

d) Discuss Ascaris lumbricoides under the following sub-headings

i. Mode of transmissionthrough ingestion of contaminated foodlive in intestines

ii. Effects of parasite on the hostinflammation of lungspneumoniaproduce toxic substancesintestinal obstruction

iii. Adaptationsthick cuticle which protects it against digestionlays many eggs to ensure survivalmouthparts for sucking partly digested foodlack of elaborate alimentary canaltolerant to low oxygen concentrationtwo hosts to ensure survivaleggs have protective cover to ensure survival in adverse environments

iv. Control and preventionproper sanitationwash hand after defaecation and before eating

e) Discuss schistosoma under the following sub-headings

i. Mode of transmissionthrough contaminated water in swamps, etc

ii. Effects on hostbleeding in lungsblood stained urineunthriftiness

iii. Adaptationshas two hosts to increase chances of survivaleggs have a hook like structure which raptures the walls of intestine or bladderlay large number of eggs to ensure survivallarvae have a sucker for attachment on human skin which it digestslarva has a tail which it swims with in search of host in waterprolonged association between male and female to ensure that fertilization takes placeadults can tolerate low oxygen concentration (in the animal tissues)adult worm secretes chemicals against antibodieslarvae and eggs (have glands that) secrete lytic enzymes to soften the tissues that ease penetrationlarvae are encysted so as to survive adverse conditions

Control and preventionproper use of toilet facilitiesboiling water before useavoid bathing/washing in infected waterUse of molluscicides (chemicals that kill snails/biological control/clearing water weeds on which snails feed.Drainage of stagnant waterWearing gum/rubber boots

3. a) i) What is reproduction?process by which living organisms give rise to new members of their own species which resemble the parents

ii) Why is reproduction important?for continuity of speciesl to ensure survival of speciesmaintaining life of speciesreplace dead individuals

iii) Name the types of reproductionsexual which involves fusion of male and female gametesasexual in which no gametes are involved but parts of a mature organism develops into new individuals

b) i) What is cell division?process by which cells are formed from pre-existing cells

ii) What are chromosomes?Threadlike structures found in nucleus of a cell.The units called genesGenes are factors that cause inheritance or determine characteristics of offspring

c) i) What is mitosis?A type of cell division that occurs during growth leading to increase in number of cellsall cells maintain the same chromosome constitution i.e. the diploid state

ii) Describe the five stages of mitosis

Interphase

replication of organellesduplication of DNAproduction of energy (ATP) for cell division

Prophase

stage of dehydrationchromosomes shorten and thickenchromosome replicates into two chromatidschromatids joined at centromereformation of spindle fibers

Metaphasechromosomes move to equator (early metaphase)chromosomes line up at the equatorhomologous chromosomes do not associate

AnaphaseChromatids separatemove to opposite ends (poles) of the cells

Telophase

chromatids reach the polesformation of two daughter cells occurs i.e. cytoplasmic division

ii) State the significance of mitosisensures each daughter cell has same number and kinds of chromosomes as daughter cellsgives rise to new cells (responsible for growth)

d) i) What is meiosis?division of diploid cells to form gametes which are haploid

ii) State the significance of meiosisgives rise to gametessource of variation

iii) Give a summary of the stages of meioeisFirst meiotic divisionInterphase Icell is in non-dividing conditionchromosomes appear threadlike

Prophase Ichromatic material shorten and thickendouble stranded chromosomes appear (bivalent)double stranded chromosomes pair and twist round each other (synapsis)point of contact of chromosomes is called chiasma

Metaphase Ipaired homologous chromosomes line up at the equator

Anaphase Ipaired homologous chromosomes move to the poles

Telophase Ipaired homologous chromosomes reach the porestwo new nuclei are formed

Second meiotic division

Prophase IIchromosomes shorten, thicken and become visible,stage of dehydration

Metaphase IImovement of chromosomes to equator

Anaphase IIchromatids of each chromosome separate to the poles

Telophase IIreach the polesfour haploid daughter cells are formed

iv) Give the similarities between mitosis and meiosisboth take part in cellsboth involve division (cell multiplication)

v) What are the differences between mitosis and meiosis?

Mitosismaintenance of chromosome number (diploid)take place in somatic cells/growthno crossing over/no variationresults in to two daughter cellsno pairing/no synapsis/no bivalent formeda one division process of four stages

meiosisreduction halving of chromosomes (haploid)occurs in reproductive cells/gonads/produces gametescrossing over takes place/variation occursresults in to 4 daughter cellsthere is pairing/synapsis/bivalenta two dicision process of four stages each

d) i) What is asexual reproductionformation of new individuals as a result of the fusion of two gametesfusion is called fertilization

ii) What is the significance of sexual reproduction in living organisms?leads to genetic variation e. g. cross breeding which gives rise to hybrids

iii) State the advantages of sexual reproductiongenetic variationgreater adaptability to environment by offspringfew bad or good traits inherited/retainedgreater amount of dispersal is possiblemay result in stronger offspring

iv) Give the disadvantages of sexual reproductionless certainty in egg and sperm meetinglow rate of survivalsex-linked diseases easily transmitted

e) i) What is asexual reproduction?formation of new organisms without fusion of gametesoccurs with only one parentparts of organism develop into new individual

ii) State the advantages of asexual reproductionretention of useful characteristics/genes/traitsoffspring establish faster/shorter life cyclebetter chances of survival because of suitable environment

iii) Give the disadvantages of asexual reproductionlack of genetic variationlowered resistance to disease ~loss of hybrid vigorcompetition for resources due to overcrowding

iv) Explain how reproduction occurs by the following methods of asexual reproduction

Sporulationformation of sporesspores are small haploid cells produced by plantsSpores give rise to new haploid organismsincludes moulds, ferns, bryophytes, pteridophytes

Buddingwhere an outgrowth arises from a parent and drops off to develop into a new organismshereditary material in the daughter cell and parent are exactly the sameoccurs in organisms such as hydra, jelly fish, sea anemones, yeast and some fungi

Binary fissiona cell splits into two new cells of equal sizeeach daughter cell grows into anew organismOccurs in organisms such as amoeba, euglena, paramecium, some fungi and bacteria.

f) i) What is a flower?this is the reproductive structure which bears the reproductive pans of a plantit produces seeds and fruits

ii) Draw a longitudinal section of a labeled diagram of a flower

iii) Give the functions of the parts of a flower

Receptacleexpanded end of stalk which bears floral parts

Calyxconsists of sepalsusually greenprotect flower in bud

Corollaconsist of petalsoften colored or scented to attract insects

Androeciummale part of flowerconsist of stamenseach stamen consists of an anther containing pollen sacsanther produces pollen grains which contain male gametes

Gynaeciumfemale part of flowerconsists of one or more carpelseach carpel contains one or more ovules in an ovarystyle bearing a stigma extends from ovaryovary contains female gametes which when fertilized become seeds

iv) What is inflorescence?a group of flowers borne on the same branch (main stalk)

v) Explain the meaning of the following terms which describe flowers

Hermaphroditeone with both stamen and carpelmost flowers are hermaphrodite/bisexual

Unisexualhave only one of carpel or stamen i.e. either male or female

Carpelatealso called pistilatecontains only carpels hence a female flower

Staminatealso called male flowercontains only stamens

Dioecious plantshave pistilate and staminate flowers on different plants e.g. pawpaw

Monoecius plantshave pistilate and staminate on one planthowever, pistilate and staminate occur at different plants e. g. maize

Complete flowerHas all four parts i.e. Calyx, corolla, androecium and gynoecium

Incomplete flowerdoes not have all four partsat least one is missing

vi) Explain the meaning of the following types of ovary

Superior Q ovary occurs above other floral parts on the receptacle Inferior (epigynous) Q other floral parts arise above ovary on the receptacle

g) i) What is pollination?transfer of pollen grains from anther of a stamen to stigma of a flower

ii) Explain the types of pollinationself pollination takes place when mature pollen grains of a flower fall on the stigma of the same flowercross pollination takes place when pollen grains of a flower fall on the stigma of another flower of the same species

iii) State the advantages of pollinationhealthy offspringleads to variationgreater chances of dispersal

iv) List the agents of pollinationwindwaterinsects

v) How are flowers adapted to wind and insect pollination?

Insect pollinated flowers (entomophilus)are scented to attract insectshave stick stigma for pollen grains to stick onare brightly coloured to attract insects ,presence of nectar to attract insectshave nectar guides to guide insects to the nectarineshave nectarines to secrete nectarstigmal anthers located inside the flower/tubal/funnel shaped corolla to increase chances of contact by insectssticky/spiny/spiky pollen grains which stick on the body of insects and on stigmalarge/conspicuous flowers easily seen by/attract insectsanthers firmly attached to the filament for insects to brush against themlanding platform to ensure contact with anthers and stigmamimicry to attract (male) insects

Wind pollinated flower (anemophilus)anthers/stigma hang outside the flower to increase chances of pollinationthe style/filament is long to expose stigma/anthersstigma is hairy/feathery/branched to increase surface area over which pollen grains land/to trap pollen grainspollen grains are smooth/dry/light/small to be easily carried by windlarge amount of pollen grains to increase chances of pollinationanthers loosely attached to filaments to enable them to sway to release pollen grainspollen grains may have structures which contain air to increase buoyancyflowers have long stalks holding them out in the wind

vi) State the Ways in which plants prevent self-pollinationprotandry(anthers/stamens mature first)protagyny (pistils mature first)monoecism (where male and female parts are on same plant but different parts)dioecism(where male and female parts are on different plants)incompatibility (self sterility)heterostyly (styles at different heights)

vii) Give the characteristics that ensure cross pollination takes place in flowering plantspresence of special structures that attract agents of pollinationprotandry/dichogamyprotagyny/dichogamymonoecismself sterilityheterostyly

viii) State the advantages of cross pollinationhybrid vigourless prone to diseasespromotes genetic variationgreater evolutionary potential

h) i) What is fertilization?Fusion of male and female gametes to form a zygote

ii) Describe how fertilization takes place in a flowerthis follows pollinationpollen grain is deposited on the stigmapollen grain sticks to the surface of the stigmathe surface of the stigma produces a chemical substance which stimulates the pollen grain to produce a pollen tube/to germinatethe pollen tube grows through the style tissues on which it feeds until it enters the ovarythe generative nucleus divides into two giving two male nucleiembryo sac contains eight nuclei i.e. two synergids, egg cell, two polar nuclei and three antipodal cellsthe pollen tube enters the embryo sac through the micropyle and one of the male nucleus fuses with the egg cell/ovum to form a zygotethe other male nucleus fuses with the two polar nuclei to form the triploid nuclei/endosperm)food storage used by developing embryo)the pollen tube nucleus in the pollen tube disintergrates soon afterwardsthis process is referred to as double fertilizationzygote grows into an embryo containing plumule, radicle and cotyledons

iii) What is double fertilization?there are two male nuclei entering embryo sacone fuses with the ovum to form a zygote, while the other fuses with the polar nuclei to form a triploid primary endosperm nucleustherefore there are two fusions at fertilization

iv) Name the changes that Occur in a flower after fertilizationpetals, stamen, calyx and style witherovary wall changes into pericarpintergument changes in to seed coat/testazygote changes into embryo ‘(by mitosis)primary endosperm nucleus changes into endospermwhole ovule changes in to seedovary develops and grows into fruit(under the influence of gibberrellic hormone)

b) i) Distinguish between a fruit and a seeda fruit is a fertilized ovary and has two scarsa seed is a fertilized ovule and has one scar

ii) How is a seed formed?after fertilization, zygote grows into an embryo, primary endosperm nucleus developed into endosperm, interguments harden to form testa, hence the whole ovule becomes the seedthe seed loses water to become drierthe seed has plumule, radicle, seed leaves called cotyledons, a microphyle and a scar

iii) Draw a labeled diagram of a seed

iv) Describe the main parts of a seed

Testaalso called seed coata tough outer covering which protects the seed from insects, bacteria etcsegment is the membrane inside the testa

Hiluma scarspot where the seed was attached to the fruit or pod

Micropylesmall hole through which water and air enter the seed

Radicleembryonic rootgrows into the shoot system

Cotyledonsembryonic leavesstore food for the germinating seed i.e. for plumule and radiclewhen plumule and radicle grow, they use food stored in the cotyledonin some seeds food is stored in the endosperm

v) Draw a labeled diagram of a fruit

vi) How is a fruit formed?one of the organs that remains on the plant after pollination and fertilization is the ovarywithin the ovary, the developing embryo produces special chemical substances that stimulate the young ovarythese substances also signal the start of the formation of the fruit, which is a mature ovarythe fruit may contain one or more seedsduring fruit formation the ovary increases in size while ripening or maturinga true fruit is formed from the ovary of a flower after fertilizationit has two scars(style scar and stalk scar) and contains seedssome seeds are not formed from the ovary of a flowersome other parts of a flower develop to form a fruitsuch fruits are called false fruits

vii) Explain the importance of fruits in the survival of plantsprotect the seed against dessication, predators and adverse conditionsaid in seed dispersal by attracting agents of dispersalstores food for the plant

vii. Distinguish between parthenogenesis and parthenocarpyparthenogenesis is development of new animals from unfertilized eggspaithenocarpy is development of a fruit without fertilization

iv) state the differences between a seed and a fruit

A Seedfertilized ovuleattached to the placenta through funicleone scar called hiliumhas seed coat/testaseed wall undifferentiated

fruitfertilized ovaryattached to branch through a stalktwo scars (style scar and stalk scar)has fruit wall/pericapfruit wall is differentiated

j. i) What is placentation?arrangement of ovules within the plant ovary

ii) Explain the following types of placentation

Marginal

placenta appears as one ridge on ovary wallovules are attached to placenta in rows e. g. peas in a pod

Basal

placenta formed at the base of the ovary With numerous ovules attached to it

Parietal

edges of carpels fuse togetherdividing Walls disappear, leaving onehave numerous seeds e. g. passion fruitplacenta of each carpel appears as ridge on ovary Wall

Axile

edges of carpels fuse together to form a single central placentanumerous ovules arranged on placentaovary divided into a number of loculi by walls of the carpel e. g.

Free central placentation

edges of carpels fuse togetherdividing was disappears leaving one loculusplacenta appears at base of ovaryhas numerous ovules

c) i) How are fruits grouped?

Simple fruitsformed from a single flower or one ovary e. g. mango

Aggregate fruitsconsists a group of ovaries that appear on a common receptacle e. g. strawberry

Multiple (compound) fruitsformed from several flowers whose ovaries fuse together after fertilizationform a bunch e. g. pineapple, figsare always false fruits

ii) What are succulent fruits?also called fleshy fruitsall or part of pericarp (fruit wall) becomes juicy

iii) Give types of juicy fruits

Berry

has many seedswhole pericarp is succulent e. g. orange, tomato, pawpaw

Drupeonly one seedpericarp divided into three layers i.e. epicarp, mesocarp(juicy) and endocarp(hard) eg mango and coconut

Pomejuicy part is swollen receptacleis usually a false fruitexample is a pear

iv) What are dry fruits?have a pericarp that is dry, hard and Woodyeither dehiscent or indehiscentcalled dry because they are not succulent

v) What are dehiscent fruits?split open when ripe to release seedscontain many seeds

vi) Give types of dehiscent fruits

Legumessplit along two edgesare usually pods e.g. beans, peas, crotolaria

Folliclesplit on one side only e. g. Sodom apple

Capsulehas several lines of Weakness/suturesopen in many places e.g. castor oil, cotton

vii) What are indehiscent fruits?non-splitting fruitsusually one seeded only

ii) Give main types of indehiscent fruits

Nutpericarp woody, hard and thick e.g. cashew

Achenehas thin, tough pericarp e.g. sunflower

d) 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

ii) Why is dispersal of seeds and fruits necessary?prevent overcrowdingreduces competition for space, nutrients and lightcolonization of new areas is made possibleto increase chances of survivalto prevent inbreedingto avoid extinction due to over competition for the necessities

iii) Explain how seeds and fruits are adapted to various methods of dispersal

Adaptations for wind dispersalthey have wings, feathers or hair-like structures to increase surface area for wind to carry them easily/buoyancyseeds/fruits are loosely attached on the stalks so that they can easily be released and carried away by wingseeds/fruits are generally light and small sized to be easily carried by windsome seeds/fruits have parachute-like structures to be easily carried b windsome have censor mechanism where seeds and fruits are borne on long stalks that are loosely attached which allows swaying so that movements of capsule by wind releases the seeds

Water dispersal seedsseed mesocarp has air spaces thus light/buoyant to float hence carried by waterthey have waterproof cover and tough pericarp protects seeds from getting soakedfibrous and spongy mesocarp to easily float

Animal dispersal seedspresence of hooks for attachment to animals thus carried to other partsfruits are brightly coloured, succulent and scented to attract animalsseed coats are hard and resistant to digestive enzymes hence seeds are dropped away from mother plantlarge in size or borne on clusters to be easily seen

Self dispersal/explosiveself opening seedsthey have lines of weakness called sutures for violent opening thus scattering seeds away from parent plant

5. a) i) Distinguish between external and internal fertilization in animalsin external fertilization fusion of the male and female gametes takes place outside the body of the female e. g. amphibians and fishin internal fertilization union of gametes occurs inside the body of the female

ii) State the advantages and disadvantages of external fertilization

Advantageslarge numbers produced therefore many offspring per breeding seasonfemale does not suffer gestation stressmother does not need to care for the young except in a few speciesthe surviving individuals are highly selected for better survival

Disadvantagesmany predators surround the eggs before and after fertilizationfewer chances of fertilization/a lot of gametes wastedembryo development at mercy of environmentlarge numbers of female gametes are required therefore female gets much exhausted

iii) State the advantages and disadvantages of internal fertilization

Disadvantagesnumber of gametes fewer hence less number of offspringless adapted for sudden change of environment after birthin mammals females suffer gestation stress

Advantagesmore chances of fertilizationfewer predators of oval/fertilized egg protected in females bodyStable internal environmentfewer gametes required

iii) Give a reason why it is necessary for frogs to lay many eggsto increase chances of survival/fertilization

iv) Compare external and internal fertilization

b) i) Draw and label the human male reproductive system

ii) Describe how the mammalian male reproductive system is adapted to perform its functions

Penisis highly vascularised/spongyhas a sensitive glandsbecomes erect to allow entry into the vagina

Scrotumcontains the testes outside the body on whose walls the process of spermatogenesis takes placethe process is favored by lower temperatureit contains sertoli cells which nourish sperms until they are mature

Epididymislong and coiled for the purpose of sperm storage

Vas deferensmuscularupon contraction pushes sperms out and allows ejaculation

Gametesproduced in large numbers to increase chances of fertilizationthe sperms have a tail for swimming/large number of mitochondria to provide energy/allow swimming to reach the egg

Accessory glandsare seminal vesicle, Cowper’s gland and prostate glandthey produce seminal fluid to provide a medium/nutrients for sperms to swim

iii) How is the sperm adapted to perform its function?acrosomes contain enzymes to digest egg membranenucleus contains genetic materialmitochondria produce energy to move the tail back and forth the lashing movement of the tail enables the sperm to move/propulsion in fluid medium towards the eggit is streamlined for faster/easier movement/swimming to meet the egg

c) i) Draw and label the human female reproductive system

ii) Describe how the various structures of the human female reproductive system are adapted to their function

Ovarieshave several graafian follicles that develop and burst open to release/produce mature ovasecretes sex hormones(oestrogen) which initiate/control development of secondary sexual characteristicsproduce hormones oestrogen and progesterone which prepare the uterus for implantation and subsequent nourishment of the embryo

Oviducts (Fallopian tube)are thin narrow and tubular to increase flowing speed of semen containing spermsare funnel shaped on the end next to ovary which enables them to receive the ovumtheir lining contains cilia which propel the ovum towards the uterushas peristaltic muscles that enable movement of zygote/ovum to the uterus for implantationis fairly long to increase surface area for fertilization

Uterusis muscular for protection of developing embryohas elastic wall that allows growth and development of foetus/embryohas a highly vascularised endometrium that provides nutrients/gaseous exchange to developing embryo

Cervixhas valves that close the lower end of the uterus to ensure continued pregnancy during gestation periodis capable of dilating ~has narrow entrance/neck-like entrance to uterus that enables quick swimming of sperms to uterushas suction mechanism that draws up/pulls sperms into uterushas a “W” shape that fits well with the glands of the penis to ensure sperms are deposited at the right point

Vaginais elastic and muscular to enable good accommodation or penetration of the penis thus proper deposition of sperms and for easy parturitionallows menstrual flowhas sensitive labial walls which secrete/produce lubricating substances thatensure/enable/facilitate good coitioncapable of considerable enlargement, due to elastic muscles, to accommodate baby during parturition

Clitorishas sensitive cells for orgasm

iii) Explain how the ovum is adapted to its functionnucleus contains genetic materialventelline membrane encloses plasma membrane which encloses yolky cytoplasmyolky cytoplasm provides nourishmentjelly coat protects ovum against dehydration

iv) Explain the differences between sperm and ovum

d) i) Explain the process of fertilizationa process whereby the egg and sperm are brought together and fuse to form a zygoteoccurs in the fallopian tube after copulationsperm head penetrates the outer coat of the ovum While the tail remains outsidepenetration is due to reaction of acrosomeacrosome digests the vitelline membranethereafter a zygote is formedzygote which is diploid undergoes rapid cell division to form a mass of cells called blastocystafter fertilization a membrane forms around the ovum to prevent further entry of spermsblastocyst eventually develops into an embryo

i) Explain the process of implantationthis is the embedding and attaching of the embryo in the uterine wall/endometiiumimplantation marks the beginning of pregnancysometimes implantation occurs in the oviduct Wall which is abnormal and results in ectopic pregnancy which is fatalthe outer wall of the blastocyst develops finger like projections which project into the uterine wall for attachmentthe projections are called villithe villi and endometrium develop into an organ that is called the placentathe embryo is attached to the placenta through a cord called the umbilical cord

State the functions of umbilical cordit contains blood vessels umbilical artery, iliac arteries and umbilical veins)it joins the placenta to the embryopassage for nutrients otherpassage of excretory substancess from foetus to mother for final dischargegaseous exchangepassage of antibodies from mother to foetus, for protection of foetus against diseases

State the role of placentaexchange of gases between mother and foetusexchange of nutrients and nitrogenous wastesanchorage/attachment of foetusproduces hormones (oestrogen and progesterone)

e) i) What is gestation period?time taken from fertilization to birth/pregnancy

ii) Explain the functions of the membranes associated with placenta

Chorionsurrounds the embryohas fingerlike projections that attach embryo to the uterus

Amnioncontains amniotic fluidfluid surrounds embryoprotects embryo from mechanical injury by acting as shock absorbersfluid also protects embryo from dehydrationdistributes pressure equally over embryo

Yolk sacsurround the yolkproduces blood cells for embryo until its own liver is able to perform the task

Allantoispresent only for a short timeremoves and store waste materialit eventually becomes the umbilical cord

iii) Explain the events that take place to facilitate parturitionnear birth the placenta produces less progesteroneoxytocin hormone is produced by posterior lobe of pituitary glandbecause progesterone level has decreased the uterus becomes sensitive to oxytocinoxytocin causes the contraction of the uterus (myometrium)these contractions are called labour painsjust before parturition the head turns downwardsthe contractions eventually push the baby through the vaginaamnion breaks and amniotic fluid is releasedoxytocin dilates the cervixfoetus is expelled through cervix with head coming out firstfinally the whole infant comes outthe umbilical cord is cut and the placenta is expelled as afterbirth

iv) State the reasons why later in pregnancy the ovary will b e removed without disturbing the pregnancycorpus luteum in the ovary secretes progesterone which maintains pregnancy and development of foetus after conceptionafter four months pregnancy is maintained by progesterone from the placenta

f) i) What are secondary sexual characteristicsCharacteristics (physiological and anatomical) that start developing at puberty due to the influence of male and female hormones

ii) State the main secondary changes in

Boysdeepening of the voicegrowth of hair on face, pubic part, chest, legspenis and testes become biggermuscular developmentsperm production begins at puberty and may continue throughout life

Girlsgrowth of hair on pubic part and armpitswidening/enlargement of hipsdevelopment of breastsmenstrual cycle starts as ovaries maturebody acquires extra fat

iii) Describe the role of hormones in secondary sexual characteristics in

Boys

Follicle stimulation hormone (FSH)from pituitarystimulates production of androgens(male hormones) mainly testosterone by testis

Testosteronesecondary sexual characteristics

Girls

FHSfrom pituitarydevelopment of folliclesstimulates oestrogen production by ovary

LHfrom pituitaryovulationstimulates release of progesterone by ovary

Oestrogenstimulates release of LHsecondary sexual characteristics

Progesteronealso from placentasustains pregnancy as it inhibits prolactin and oxytocin during pregnancy

Prolactinmilk formation

Oxytocinparturitionmilk ejection

g) i) What is menstruation?vaginal discharge due to disintegration of endometrium

ii) Describe the role of hormones in the human menstrual cycleit is controlled by sex hormones which are responsible for the onset of secondary sexual characteristics and also control of the menstrual cyclethe onset is signaled by discharge of blood/menses 14 days following the start of menstruationanterior lobe of pituitary gland secretes follicle stimulating honnone(FSH)Follicle stimulating hormone causes graafian follicle to develop in the ovary. It also stimulates tissues of the ovary/wall (theca) to secrete oestrogenoestrogen causes repair/healing of uterine walloestrogen stimulates anterior lobe of pituitary to produce luteinising hormonge (LH)LH causes ovulation. It also causes graafian follicle to change into corpus luteum. LH stimulates corpus luteum to secrete progesteroneProgesterone causes proliferation/thickening of uterine wallOesterogen/progesterone inhibits, the production of FSH by anterior lobe of pituitary, thus no more follicles develop and oestrogen production reducesIn the next two weeks progesterone level rises and inhibits production of LH from anterior lobe of pituitary“The corpus lutetium stopssecreting progesterone and menstruation occurs when the level of progesterone dropsAnterior lobe of pituitary starts secreting FSH again.

iii) What is menopause?end of ovulation in womenoccurs after age of 45 yearsdoes not occur in males

h) Explain the symptoms, methods of transmitting and prevention (control) of the following sexually transmitted diseases

i) Gonorrheacaused by a bacterium called neisseria gonorrheatransmitted 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 arthritisTreatment by antibioticsControl and prevention by proper sexual conduct

ii) Herpesnotably Herpes simplex and H. genitaliscaused by virus which attacks genitaliasymptoms are painful sores in genitalia, skin lesionstransmitted in saliva, sexual intercourse and injection by drug addictsno treatment

iii) Syphiliscaused by bacterium called Treponema palladiumsymptoms are painless wounds in genitaliaattack genitalia, nervous system, lipstreated by antibiotics

iv) Trichomoniasiscaused by plasmodium called trichomonasattacks reproductive tractsymptoms are itching and discharge of pus from the genitalstreated by antibiotics

v) HepatitisViral diseaseAffects the liverTransmitted through sexual intercourseNo known treatment

vi) Candidiasiscaused by fungus called candida albicanstransmitted through sexual intercoursesymptoms include itching urethra, and vaginal discharge (odourless)controlled by personal hygiene, early treatment and responsible sexual behavior

vii) HIV/AIDScaused by HIV virustransmitted by sexual intercourse, blood transfusion, sharing piercing instruments from infected mother to foetus, infant and babysymptoms include fever, swollen lymph nodes, night sweating, cough, weight loss, fatigue, loss of appetite, diarrhea, headache, a opportunistic infections and tumorsControl by responsible sexual behaviour, education, screening blood for transfusion and using sterile piercing instruments.

6. a) Define the terms

i) Growthan irreversible change in size of a cell, organ or whole organismgrowth is due to synthesis of protoplasm or extracellular substances

ii) Developmentrefers to a series of changes which an organism goes through in its lie cycleduring development both qualitative and quantitative changes take place(involves differentiation)

iii) Differentiationrefers to changes in which the cells of the body undergo and become specialised to perform specific functions

b) i) Differentiate growth in plants and animals

More differences between Plant Growth and Animal Growth

Plant Growth:

1. Growth continues throughout the life of the plant.
2. Here the growth involves increases in the number of parts.
3. Growth take place during definite seasons.
4. Growing pattern is distinct each species.
5. Plant possess well-defined growing regions.
6. A seedling does not resemble an adult plant.
7. A juvenile stage with distinct may be present in the life-history of a plant.
8. Growth is by addition of new parts ahead or around the older ones.

Animal Growth:

1. Growth takes place for definite periods before maturity.
2. Here it does not involve increase in the number of parts.
3. Each species has a distinct season for growth.
4. Growing pattern is absent.
5. They have no such defined growing regions.
6. The young one are identical to adults except in the body size and sexual maturity.
7. A juvenile stage with different morphology does not occur in higher animal.
8. Growth is diffused by all round increases in different organs of the body.

ii) List the processes involved in growthassimilationcell enlargementcell division(by mitosis)

iv) List the parameters used to measure growthheight/lengthdry Weightnumber of individualsvolumeleaf area of plant

iv) Name the patterns of growth in organismsallometric and isometriclimited and unlimiteddiscontinuous growth

c) i) Name the different types of growth curvessigmoid curve(normal growth curve)intermittent growth curve

ii) Draw a sigmoid growth curve and explain its different phases/stages

A-lag phase

– Slow growth rate at first

Organism adapting to the environment

B-exponential phase

– organisms already adapted

– first growth due to birth rate that is higher than death rate

C- Stationery phase (plateau)

– Birth rate equals death rate (equilibrium)

Lack of nutrients, accumulation of toxic waste products

D-phase of decline

– due to depletion of nutrients, accumulation of toxic wastes, lack of space

– some individuals old hence not reproducing

– death rate higher than birth rate

iii) Draw an intermittent curve and explain the various stages

A-growth

B-no growth

C- moulting/ecdysis

– 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

– the cuticle must be shed off first to allow further growth

– the shedding is called ecdysis or moulting

– when moulting has taken place animal grows but growth stops when the exoskeleton hardens again

d) i) What is seed dormancy?

– A state where a viable seed is incapable of germinating when all conditions are favorable.

ii) State the biological importance of seed dormancy

– 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

– presence of abscisic acid/ABA/ presence of germination inhibitors

– embryo not fully developed

– absence of hormones/enzymes/inactivity of hormones/enzymes/gibberellins/cytokinins

– impermeability of seed coat

External factors

– unsuitable temperature

– absence of light

– lack of oxygen

– lack of oxygen

– lack of water

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?

– process by which a seed develops in a seedling

ii) What is viability

– ability of a seed to germinate

iii) Discuss the various conditions necessary for the germination of seeds

Water

– medium for enzymatic activity

– hydrolysis of food into simpler substances

– medium of transport

– softens the seed

– acts as a solvent

Air

– in form of oxygen

– oxygen is used for respiration/oxidation of food to release energy

Suitable (optimum) temperature

– activates enzymes involved in mobilization of food reserves

Enzymes

-breakdown and subsequent oxidation of food

– conservation of hydrolyzed food products in to new plant tissues

Viability

– only viable seed are able to germinate and grow

iv) Name and describe the types of germination

Epigeal

cotyledons are brought above the ground level during germination due to elongation of the bean seed that elongates to bring about epigeal germination

Hypogeal

– the cotyledons remain below the surface during germination due to elongation of epicotyl e.g maize

vi) Account for the loss in dry weight of cotyledons in a germinating bean seedfood stored is mobilized/used up for respiration and growth

vii) Describe the physiological changes that occur in a seed during germinationin presence of oxygen, optimum temperature and water, food reserves in the seed are hydrolysed or broken down into soluble diffusible form by enzymessoluble food diffuses to the growing embryooils and carbohydrates provide energysimple sugars converted to cellulose to form cell wallamino acids make protoplasmseed develops plumule and radicle hence germinates

viii) Explain the biological significance of cotyledons being brought above the ground in epigeal germinationcotyledons have inadequate foodthey are brought above the ground to acquire chloroplasts to carry out photosynthesisbefore the formation of foliage leaves to supplement food supply required for growth during germination

f) i) Distinguish between primary and secondary growth

Primary growthoccurs at the apical (shoot and tip) apices regions where meristematic cells occurcauses plant elongation since cells divide by mitosis

Secondary growthoccurs at the cambium meristemsIncreases width (girth) of the stem

ii) What are meristemsdividing cellsmeristem means they are dividing

iii) State the characteristics of meristematic cellsdense cytoplasmthin cell wallsabsence of vacuoles/cell sap

iv) State the location and function of the following meristematic tissues

Apical meristemlocated at tips of roots and shootsincrease length of stem and roots/primary growth

Intercalary meristemfound at bases of internodesresponsible for elongation of internodes and increase in leaf sheath in grasses

Lateral meristemsfound near the periphery of stem and rootresponsible for secondary growth/growth in girth of stem and root/lateral growthcalled cambium and constitute vascular and cork cambium

v) Describe primary growthoccurs at tips of shoots and roots in the meristematic tissues of apical meristemat the apex there is a zone of cell division/mitosiscells elongate at elongation zonethe elongated cells differentiate at the region of differentiation resulting in increase in sizein the stems meristems give rise to leaf premodia which envelop the apex to form a budthe bud protects the delicate inner cellsin roots the meristem is protected by root capafter cells differentiate the form permanent tissues

vi) Describe secondary growth in plantsalso called secondary thickening ‘only occurs in dicotyledonous plants that have cambiummonocotyledonous plants do not undergo secondary growth because they lack intervascular cambiumcambium cells divide to produce more cells on either side of the cambiumcells produced to the inside become secondary cambiumcells produced to the outside become secondary phloemdivision of cambium cells occurs yearly producing new rings of secondary phloem and secondary xylem each yearintervascular cambium(cambium between vascular bundles) divide to form secondary parenchyma, thereby increasing growth of medullary raysmuch more xylem is formed than phloem, thus pushing phloem and cambium ring outwardthe rate of secondary growth is depended on seasons(rains) resulting in annual ringscork cambium is located beneath epidermis ad is responsible for secondary thickening of the bark of perennial plantscork cambium divides to form new cork(bark) tissues to accommodate increased growth on outside and secondary cortex on the insideCork cells (cells of the bark) are loosely parked at some points to form lenticels for gaseous exchange.

vii) State the significance of secondary growthincrease girth or circumference of treesannual rings which show seasonal growth can be used to tell the age of trees

g) i) Describe one method which can be used to measure the average growth rate of a single leaf of a plant

Either

– chose/identify a young leaf (just unfolded)

– use the same leaf throughout

– measure (total) length of (whole) leaf

– record

– repeat at regular intervals until no more change occurs/constant length

– average rate of growth is equal to total increase in length divided by the period taken to achieve full length

Average rate of growth = total increase in length divide by period taken to achieve full length

OR

– 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

Average rate of growth = total increase in area divide by period of time taken to achieve final area

i) Describe how the growth of a root can be determined

Materials

– fine thread, marking ink, germinating bean seedlings, blotting paper, ruler marked in millimeters, pins, cork, a boiling tube and moist cotton wool

Procedure

– 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

– 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

iii) A boy hammered a nail in the bark of a tree at a height of 1.5 metres 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 plantsindole acetic acid/IAA/ auxinsCell division/increase in cell divisionTropic responsesCell elongation/increases in ell elongationDevelopment of abscision layerGrowth of ovaries into fruits/parthenocarpy/initiates flowersInhibits growth of lateral buds/produces apical dominanceStimulates adventitious/lateral roots ‘Gibberellins (Gibberellic acid/GA3Promote cell elongation/rapid cell division/increase in length of the internodesPromote fruit formation without fertilization/parthenocarpyReduces root growthBreaks seed dormancy/promotes germination

Cytokinnins (Kinnins/Kinnetin/Zeatin)

– 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

Ethylene (ethynel C2H4)

– 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

Abscisic acid (ABA) abscisin hormone/dormin)

– causes bud dormancy

– encourages fruit/leaf fall

– high concentration causes closing of stomata

– causes seed dormancy

– inhibits cell elongation

Traumatin

– heals wounds by callous formation

Florigen

– promotes flowering

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

iii) Explain apical dominance

– a phenomenon whereby production of auxins by a growing apical bud of a shoot inhibits growth of lateral buds

– this inhibition is due to high concentration of auxins (indoleacetic acid/IAA) in apical bud

– removal of terminal/apical bud causes development and sprouting of several buds which later develop into branches

– applied in pruning coffee, tea and hedges

– this leads to more yield

iv) Describe the role of hormones in the growth and development of animal

somatotrophin (growth hormones)

– from anterior pituitary

– promotes cell division

– overproduction causes gigantism

– underproduction causes dwarfism

Thyroxine

– promotes growth and metamorphosis

– underproduction leads to a child becoming a cretin (mentally retarted)

Androgens

– in males

– growth of male reproductive organs

Oestrogen

– in females

– growth of female reproductive organs

Ecdysone

– in arthropods

– moulting (ecdysis)

t) i) What is metamorphosis?

– change in form during which there are changes in structure and function in body of organism

– prepares organism for life in a different habitat

ii) Explain complete metamorphosis

radical changes in the body during the life cycle of an organism

called holometabolous development

example is egg larva pupa adult (imago)

occurs in animals such as butterfly and bee

iii) What is the significance of each of the four stages in complete metamorphosis?

Larval stage

– feeding takes place

– larva is quite different from adult

– larva sheds its cuticle (exoskeleton) several times to emerge as pupa

– dispersal stage avoids overcrowding

Pupa

– enclosed in a case called puparium (cocoon)

– no feeding

– organ formation takes place

Adult

– 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 it becomes an adult

– stage of development between one moult and another is called instar

– occurs in insects such as locust and cockroach

v) Name the hormones that control metamorphosis in insects

– brain hormone responsible for moulting because it simulates production of ecdyson (moulting hormone)

– ecdysone(moulting hormone) causes moulting

– juvenile hormone causes moulting in larvae

vi) State the advantages of metamorphosis in the life of insects

– the adult and larvae exploit different niches

– do not compete for food

– pupa cam survive adverse pupa can survive adverse conditions eg-feeding stage

– dispersal prevents overcrowding