Biology Questions and Answers Form 3

Biology Questions and Answers Form 3

Biology Questions and Answers Form 3

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 organisms


  • 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
  • generic names should be a single unique nameb) State the main characteristics of the five kingdoms of organisms

    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)ii. Protista(protoctista)


  • single celled(unicellular)
  • eukaryotic (most cell organelles present)
  • when cell Walls are present have no cellulose
  • e.g. protozoa and algae
  • usually microscopiciii. Fungi


  • have hyphae (which form mycelia)
  • absence of chlorophyll
  • have rhizoids (lackroots, leaves, stem)
  • have spore forming structures (sporangia)
  • e.g. mucor, rhizopusiv. 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 structuresv. Animalia


  • cells do not have cell walls
  • most carry out locomotion
  • heterotrophic
  • fast response to stimuli (tactic)
  • have specialized excretory structuresc) Describe the economic importance of:

    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, chloromycin, streptomycin
  • yeast is used in brewing industry, baking and source of vitamin B
  • many cause diseases to our crops e. g. late blight
  • important in recycling nutrients in soil since they cause decay of organic matter
  • mycorrhizal association in forest development may help in Water intake/absorption
  • help in nitrogen fixationii. 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
  • biogas production
  • saprophytic bacteria are used in compost decomposition or cause decay
  • symbiotic bacteria are used in compost decomposition or cause decay
  • symbiotic bacteria in herbivores/ruminants help in digestion
  • some diseases in animals/humans and plants are caused by bacteria
  • many bacteria cause‘ food spoilage/decay
  • nitrifying and nitrogen fixing bacteria increase soil fertility/make nitrates available
  • denitrifying bacteria reduce soil fertility/convert nitrates into nitrogen/reduce nitratesd) 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 pans 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 dominantiii. Spermatophyte


  • photosynthetic
  • well differentiated into roots, stems and leaves
  • well developed vascular system
  • seed bearing plantse) Name sub-divisions of spermatophyte and state the characteristics of each class

    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 ovulesii. 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 ovaryiii. Name the classes and state characteristics of angiospermae



  • two seed leaves
  • network venation of leaves
  • regularly arranged vascular bundles
  • tap root system
  • broad leaves
  • secondary growth occursMonocotyledonae


  • one seed leaf
  • parallel venation of leaves
  • irregularly arranged vascular bundles
  • fibrous root system
  • narrow leaves
  • sheath like leaf stalk (petiole)
  • no secondary growthiv)State the importance of plants


  • balancing carbon IV oxide and oxygen in the atmosphere during photosynthesis and respiration influence water cycle
  • reduce soil erosion by bind soil particles together
  • useful products e. g. food, medicine, timber, paper and clothing
  • habitat ( e. g. forests and grassland) for animals which may also be tourist attraction earn money from sales of products
  • aesthetic value/beauty e. g. flowers, shade/shelter, live fences, windbreaks
  • Some are harmful e. g. poisons, weeds, injurious (stinging nettles, thorns), water hyacinthf) i) Give the general characteristics of phylum arthropoda


  • jointed appendages
  • presence of exoskeleton
  • triploblastic and coelomate
  • segmented body
  • bilateral symmetry (similar halves)ii. State the characteristics of the following classes of arthropoda



  • the millipedes
  • two pairs of legs per segment
  • many segments
  • terrestrial habitat
  • body cylindrical and long
  • herbivorous
  • one pair of antennaeChilopoda


  • 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 called maxillipedes
  • one pair of antennaeInsecta


  • three body pans i.e. head thorax, abdomen
  • six legs/three pairs of legs
  • a pair of compound eyes
  • presence of wings
  • a pair of antennaeCrustacean


  • two body parts
  • segmented body
  • have pincers (modified legs) to catch prey
  • have hard exoskeleton
  • a pair of compound eyesArachnida


  • body divided into two parts( abdomen and cephalothorax)
  • simple eyes
  • eight legs (four pairs of legs)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 beetlesHarmful effects


  • pests
  • vectors
  • dirt and disease carriers
  • injurious e.g. stings and bitesg) i) State the general characteristics of chordate


  • notochord
  • dorsal slits (pharyngeal cleft during development)
  • bilateral symmetry
  • triploblastic (three layer body-ectoderm, mesoderm and endoderm)
  • clear cut head formation
  • multilayered epidermis
  • post anal tail
  • closed circulatory system
  • segmented muscle blocks(myotomes)
  • single pair of gonadsGive the characteristics of the following classes of chordate



  • 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 environment)Amphibian


  • 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 exchangeReptilia


  • scales on body
  • poikilothermic
  • homodont teeth except tortoise and turtle
  • all have limbs except snakes
  • skin is dry
  • oviparous (lay eggs)
  • no pinna (external ear)
  • three chambered heart 9crocodile has four chambers)
  • skin not glandular
  • no mammary glandsAves


  • 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 beaksMammalian


  • 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 glandsa) i) What is a dichotomous key?


  • A biological device (tool) which enables one to identify an organism by progressively opting between two alternative observable characteristicsi. 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 specimensii. List the rules followed in constructing a dichotomous key


  • use observable characteristics only
  • start with major characteristics, placing organisms into two groups at each stage
  • use a single characteristics at a time
  • use contrasting characteristics at each stage e.g 1(a) short, 1(b) tall
  • avoid repeating the same characteristicsiv) Describe the procedure of using a dichotomous key. Make a list of major features of the characteristics to be identified


  • 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 distinguishing one from another
  • the key uses a method of elimination by following statements that are correct only for the organismiv 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. Ecology


  • study of the interrelationships between organisms and their environmentii. Environment


  • surrounding of the organism i.e. biotic or a biotic factorsiii. Habitat


  • A specific locality (home) of a living organism with a set of factors (conditions) in which an organism lives.iv. Ecological niche


  • Role of an organism in its habitat e. g. feeding relationshipv. Population


  • Number (group) of organisms of a species occupying a given habitatvi. Community


  • 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 livevii. Ecosystem


  • A community of organisms interacting with one another and the environment in which they livevm. Biosphere


  • The earth and its atmosphere where living organisms are foundix. Autecology


  • Study of a single (individual) species of plants or animals within a community, ecosystem, habitat or environment.x. Synecology


  • Study of natural communities (plants and animals) or populations interacting within an ecosystem.xi. Carrying capacity


  • maximum number of organisms an area can support without being depletedxii. Biome


  • geographical area with particular climatic conditions and flora and fauna
  • it constitutes many ecosystemsxiii. Biomass


  • dry weight (mass) of a living organism in a given area
  • units of measurement are kg/m2/yearb) i) What are abiotic factors?


  • non-living components of the ecosystemii) Explain how abiotic factors affect living organisms



  • 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
  • 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 aeration of water which replenishes oxygen concentration necessary for life
  • wind is an agent of pollinationTemperature


  • influences rate of enzyme action in photosynthesis and other metabolic reactions in plants and animals
  • organisms function within a narrow range of temperature
  • it affects distribution of organisms
  • changes in temperature affect rate of photosynthesis and biochemical reactions e.g. metabolism and enzyme reaction
  • temperature increases rate of transpirationLight


  • needed by green plants and photosynthetic bacteria which are primary producers
  • 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 animals
  • some plants need light for flowering
  • seeds like lettuce need light for germinationHumidity


  • amount of water vapour held by the air
  • affects the rate at which water is lost from organisms body by evaporation and stomatal transpiration
  • when humidity is low the rate of transpiration increases
  • humidity influences distribution of organismspH


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


  • some ions are needed for plant and animal nutrition
  • osmoregulation implants and animals is affected by salinityTopography


  • altitude affects light, atmospheric pressure and light
  • Slope influences surface runoff, wind erosion, etc.
  • mountains affect distribution of organisms which differs in leeward side and windward side
  • mountains affect distribution of organisms which differ on lowlands and on highlands
  • mountains also form physical barriers to migration of organism and may cause isolation of species
  • background may offer camouflage to some organisms hence protection from enemiesRainfall (Water) or precipitation


  • 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
  • fewer organisms found in deserts where rainfall is less
  • Water 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 sporesPressure


  • the weight atmosphere exerts upon the earth
  • varies with altitude the higher the altitude the less the pressure
  • this variation implies change in density which directly means less oxygen for respiration and less carbon iv oxide for photosynthesis and this affects distribution of organismsMineral salts (trace elements)


  • 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 have special methods of obtaining it.
  • They harbor nitrogen fixing bacteria and others have carnivorous habit
  • Plant distribution influences animal distributionc) i) What are biotic factors?


  • 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 waysii) Give examples of biotic factors affecting ecosystems


  • feeding relationships
  • predation
  • competition
  • diseases and pests
  • human activitiesd) Discuss how the various biotic factors affect living organisms

    i. Competition


  • organisms compete with one another for food, light, water, mates and shelter
  • organisms must live together for competition for available resources
  • those which cannot cope either structurally or behaviorally will migrate or die
  • those remaining, due to better adaptations will increase in population
  • competition between members of the same species is called intra-specific competition e.g. for mates
  • Competition between members of different species is inter specific competition e. g. for food and space.ii. Predation


  • this is predator-prey relationship
  • predator feeds on prey hence both control the other’s population
  • Distribution of predator and prey is important as predator cannot survive without prey
  • It there is no predator the prey will increase in population beyond carrying capacity hence die due to environment depletioniii. Parasitism


  • an 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 host
  • they deprive host of food
  • make host weak by introducing diseases
  • make reproductive ability of host low hence host becomes susceptible to predationiv. Diseases and parasites


  • make organisms weak and susceptible to predation
  • kill organisms and reduce their populationv. Symbiotic

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

    vi. Human activities


  • these are human factors which have an influence on the biosphere
  • examples are road construction, industrialization, deforestation, agriculture, pollution, poaching, fishing conservation, population control
  • affect ecosystem and balance of natureSaprophytism


  • saprophytes are organisms which obtain organic matter in solution from dead and decaying tissues of plants and animals
  • they include saprophytic bacteria and fungi
  • they make available carbon, nitrogen and other elements form dead to living organisms
  • they are useful in recycling nutrients in naturee)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 cycle


  • during thunderstorms/lightning nitrogen gas combines with oxygen to form nitrogen oxides
  • 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 nitrates or nitric acid dissociates to form nitrates which are absorbed by plants
  • symbiotic bacteria (Rhizobium) which are found in root nodules of leguminous plants fix free nitrogen to nitrates
  • free living bacteria (clostridium and Azotobacter) fix nitrogen to nitrates
  • nostoc algae (Anabaema chlorella) fix nitrogen to nitrates
  • plants use nitrates to form plant proteins
  • animals feed on plants and convert plant proteins into animal proteins
  • plants 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 bacteria
  • 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 bacteriaiii. Nitrogen in the atmosphere cannot be directly utilized by plants. State two ways by which this nitrogen is made available for plant use


  • fixation by microorganisms (Rhixobium, Axotobacter)
  • fixation by electrical discharge in atmosphere i.e. conversion by thunderstorm or lightning


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