Biology Questions and Answers Form 3 - Biology Form Three Notes

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 name

b) 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 microscopic

iii. Fungi

have hyphae (which form mycelia)

absence of chlorophyll

have rhizoids (lackroots, leaves, stem)

have spore forming structures (sporangia)

e.g. mucor, rhizopus

iv. Plantae

most are green/contain chlorophyll

autotrophic/feed by photosynthesis

cells have cellulose cell walls

respond slowly to stimuli (tropism)

lack locomotion (are stationary)

indefinite growth (at meristems)

lack specialized excretory structures

v. Animalia

cells do not have cell walls

most carry out locomotion

heterotrophic

fast response to stimuli (tactic)

have specialized excretory structures

c) Describe the economic importance of:

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 fixation

ii. 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 nitrates

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

i. Bryophyte

e.g. mosses and liverworts

presence of rhizoids

lack of vascular tissues (lack phloem and xylem)

body 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 dominant

iii. Spermatophyte

photosynthetic

well differentiated into roots, stems and leaves

well developed vascular system

seed bearing plants

e) 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 ovules

ii. Angiospermae (ﬂowering plants)

reproduce by ﬂowers

seeds enclosed (in fruits)

flowers bisexual hence double fertilization

herbaceous

pollen grains land on stigma of pistil

xylem contains vessels

phloem contains companion cells

ovules contained in ovary

iii. Name the classes and state characteristics of angiospermae

Dicotyledonae

two seed leaves

network venation of leaves

regularly arranged vascular bundles

tap root system

broad leaves

secondary growth occurs

Monocotyledonae

one seed leaf

parallel venation of leaves

irregularly arranged vascular bundles

fibrous root system

narrow leaves

sheath like leaf stalk (petiole)

no secondary growth

iv)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 hyacinth

f) 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

Diplopoda

the millipedes

two pairs of legs per segment

many segments

terrestrial habitat

body cylindrical and long

herbivorous

one pair of antennae

Chilopoda

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 antennae

Insecta

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 antennae

Crustacean

two body parts

segmented body

have pincers (modified legs) to catch prey

have hard exoskeleton

a pair of compound eyes

Arachnida

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 beetles

Harmful effects

pests

vectors

dirt and disease carriers

injurious e.g. stings and bites

g) 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 gonads

Give the characteristics of the following classes of chordate

Pisces

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 exchange

Reptilia

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 glands

Aves

the birds

homoeothermic (constant body temperature)

four chambered heart

streamlined body for locomotion in air

skin dry and covered by feathers

scales on legs

hollow bones

oviparous (lay eggs)

mouths modified into beaks

Mammalian

hair on the body

homoeothermic

viviparous (give birth to live young) eXcept a few

have mammary glands

glandular skin e.g. sweat glands, sebaceous glands

four chambered heart

pinna (external ear)

two pairs of pentadactyl limbs

presence of diaphragm

have salivary glands

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 key

used to identify organisms quickly and accurately

by following the statements in the key we are able to identify each organism on the basis of a characteristic which is not to be found in other specimens

ii. 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 characteristics

iv) 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 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. Ecology

study of the interrelationships between organisms and their environment

ii. Environment

surrounding of the organism i.e. biotic or a biotic factors

iii. 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 relationship

v. Population

Number (group) of organisms of a species occupying a given habitat

vi. 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 live

vii. Ecosystem

A community of organisms interacting with one another and the environment in which they live

vm. Biosphere

The earth and its atmosphere where living organisms are found

ix. 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 depleted

xii. Biome

geographical area with particular climatic conditions and ﬂora and fauna

it constitutes many ecosystems

xiii. Biomass

dry weight (mass) of a living organism in a given area

units 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

Wind

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 pollination

Temperature

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 transpiration

Light

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 germination

Humidity

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 organisms

each plant requires a specific PH in which to grow (acidic, neutral or alkalinic)

pH affects enzyme reaction in metabolism

Salinity

some ions are needed for plant and animal nutrition

osmoregulation implants and animals is affected by salinity

Topography

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 enemies

Rainfall (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 spores

Pressure

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 organisms

Mineral 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 distribution

c) 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 ways

ii) Give examples of biotic factors affecting ecosystems

feeding relationships

predation

competition

diseases and pests

human activities

d) 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 depletion

iii. 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 predation

iv. Diseases and parasites

make organisms weak and susceptible to predation

kill organisms and reduce their population

v. Symbiotic

and association of organisms of different species where 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 nature

Saprophytism

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 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 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 bacteria

iii. 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

f) i) Describe how energy ﬂows from the sun through the various trophic levels in an ecosystem

energy from the sun is trapped by green plants during photosynthesis, producing chemical energy9food or carbohydrates

green plants are producers and occupy the first trophic level

green plants are eaten by herbivores called primary producers as they occupy the second trophic level

herbivores are eaten by carnivores, secondary consumers, which occupy the third trophic level

when 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 salts

these organisms are called decomposers and detrivores

decomposer feed on dead organic matter hence cause decomposition and decay which releases nutrients for plants, linking biotic and a biotic components

at all levels energy is lost through respiration

Give the reasons for loss of energy from one trophic level to another in a food chain

insufficient utilization of food resources(wastage) e.g by defalcation

through respiration

through 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 chain

a nutritional sequence between producers and consumers through which energy ﬂows in a straight line i.e. linear representation of feeding relationship between different organisms in an ecosystem

if one consumer or the producer is removed the food chain is broken

arrow points to the direction of energy ﬂow e. g. green plant herbivore carnivore decomposer

Food web

complex feeding relationship Where a on more than one type of food while several herbivores feed on one type of plant

it 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 chain

usually there are more producers than consumers

hence producers herbivores carnivore

the reason for the pyramid is because herbivores feed on many plants (producers) as camivores feed on many herbivores

sometimes this may not be true e. g. when many caterpillars feed on one tree or parasites on a herbivore

this 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 chain

producers have greater biomass than any level of consumers progressively

size of organisms in successive e trophic levels increases

amount of individuals decreases in successive levels

Account for the decrease of biomass in the successive trophic levels

fixed energy which supports living matter decreases at each successive trophic level since energy is lost by respiration and indigested (unconverted) materials hence less biomass supported at each level

h) i) Describe the three characteristics of a population growth

increase in numbers

decrease in numbers growth rate

change in numbers

Dispersion

spread or distribution of organisms in a habitat

Density

the number of individuals per unit area

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

quadrat method

identify the study area

throw or mark out the quadrat in the area of study at random

identify or label the various species of plants in the quadrat

count plants of each species

record the numbers

repeat the process

work out the average per quadrat for each species

calculate the total number of different species in the area or calculate the population for the total area of habitat Q

Line transect

a string is stretched along an identified area

all plants touching the string are counted

Belt transect

preliminary study of the study area to estimate siie or make a sketch map

two parallel lines (strings or ropes) running for a determined distance and width

count the number of organisms in the transect

calculate the area covered by the transect

calculate the number of organisms being investigated per unit area

repeat this process at least three times in other parts of the study area

find the mean number of organisms per unit area from all the belt transects

from this figure calculate the total population of the desired organisms in the study area

Capture-recapture method

e.g. grasshoppers or fish

capture the grasshoppers

count and mark using permanent ink

record

release and allow time

recapture and count the marked and unmarked

total population is equal to the number of marked and 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. Xerophytes

grow in areas with scarcity of water

roots grow deeply and extensively (widely spread) to ensure access to water

thick succulent stems, roots and leaves for water storage

photosynthetic stems take place of leaves which would lose a lot of water

Leaves 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 transpiration

some shed leaves during dry season to reduce water loss

presence of thorns for protection

short life cycle to ensure survival

reversed stomatal rhythm

ii. Hyrophytes

grow in places with plenty of water(waterlogged)

aerenchyma a tissue (airspaces) and large intercellular spaces and long fibrous roots for buoyancy (ﬂoating in water)

poorly developed support tissues (sclerenchyma) because water provides the necessary support

upper epidermis of leaves have more stomata than lower epidermis for gaseous exchange or for increased rate of transpiration

poorly developed conducting tissues (xylem and phloem) because plants obtain water by diffusion

iii. Mesophytes

grow in well watered soils ‘(common plants)

no special adaptations, but depending on particular habitat, may have some adaptations

in 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 surfaces

in direr regions they possess more stomata on the lower leaf surface and are deep rooted

some are shallow rooted and develop buttress and prop roots for support

some have waxy or glossy surface to reﬂect sun rays and drip off rain water

iv. Halophytes

plants that grow in very salty soil where the salt concentration is higher than that in the plant

have root cells which concentrate a lot of salts in them and enable then to take in water by osmosis

succulent roots to store water

have pneumatophores (breathing roots) to take in oxygen

some have buttress roots for support

secrete excess salt by use of salt glands

have large airspaces in leaves and stems for buoyancy and to store air

capable 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 pollution

sulphur iv oxide, hydrogen sulphide, chlorine, oxides of nitrogen produced by industries, sewage, decomposing organic matter and fumes affect gaseous exchange, makes acid rain and damage plant leaves

aerosols, 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 layer

smoke 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 visibility

particles in smoke and fumes settle on leaves and stop photosynthesis

carbon iv oxide causes green house effect which causes temperature inversion as a result of heating the lower layers of atmosphere

sound and noise produced incessantly by machines, aeroplanes and heavy vehicles affect hearing in animals

dust from cement factories, quarries, dust roads settles on leaves limiting photosynthesis

removal of vegetation interferes with carbon cycle radio-active emissions from nuclear reactors, mines and bombs cause cancer, mutations and death.

Control of air pollution

use of lead free petrol in motor vehicles, air craft, aeroplanes and petroleum engines

uses of smokeless fuels and electricity

filtration, dissolution and use of chemicals to remove harmful gases

factories should be erected far away from residential areas

use of tall chimneys

reduce volume or intensity of sound e. g. by use of ear muffs

concords 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 effects

agrochemicals e.g. fertilizers cause eutrophication leading to increase in animal population

Silting 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 population

industrial and domestic wastes contain toxic materials which kill producers and other organism while oily substances in wastes may clog gills of fish and may change pH of water oxygen solubility is also reduced by oily surfaces

Untreated sewage and effluents where decomposition or organic matter in sewage reduces oxygen supply and sewage provides food for bacteria increasing their population and demand for oxygen thus depriving fish of oxygen.

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 organisms

Spillage of oil and chemicals block oxygen and kill organisms

Discharge of water from industries into water body where high temperatures reduce amount of oxygen in the water causing organism to suffocate and die

Untreated sewage may lead to outbreak of epidemics

Control of water pollution

pollution 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 industries

Oil spillage may be controlled by cleaning spilled oil biotechnology and penalizing the industry

individual or companies which cause oil spills/water pollution

Pollution caused by agrochemicals may be controlled by using mechanical control of weeds, biological control of weeds and pests, biodegradable organic fertilizer herbicides, insecticides pesticides, organic farming educate farmers on the use of correct amount of agrochemicals

silting may be controlled by appropriate farming practices, contour farming, reafforestation, building gabions and terracing

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

Causes and effects

Air 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 soil

most 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 them

petroleum products due to spillage by oil tankers making it impossible for plant roots to obtain oxygen in oil saturated soils, therefore plants are killed

agrochemicals and inorganic fertilizers contain heavy metals that are not used up by plants and eventually soil microorganisms cannot inhabit the soils

organic matter slows down, life ceases and soil becomes exhausted

community, household wastes and industrial wastes disposal is a major problem in big towns and cities. commodities packaged in metal tins, rubber, plastic containers, scrap metal, glass bottles, different types of paper are nuisance to the environment, rendering it useless for agricultural purposes

Control of soil pollution

use of organic farming techniques _

biological control of pests, diseases, parasites

recycling of non-degradable containers or burying them safely after use

controlled burning of garbage

treatment of human and industrial waste for safe disposal

avoid spilling chemicals and oil when used

v) Define biological control give suitable examples

using 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 agent

Vibrio cholerae (bacterium)

Transmission

Contaminated food or water

Spread by flies from faeces

Symptoms

Intestinal pain

Diarrhea

Vomiting

Dehydration

Control

Proper hygiene e.g boiling drinking water

vaccination

Typhoid

Causative agent

salmonella typhi (bacterium)

Transmission

Contaminated food or water

Spread by flies from faeces

Symptoms

Fever

Rashes

diarrhea plus blood from bowels

Control

Proper hygiene e.g boiling drinking water

vaccination

Malaria

Causative agent

Plasmodium (protozoa)

Transmission

Bite by infected anopheles female mosquito

Symptoms

Fever

Joint pains

Vomiting

Headache

Anaemia

Control

Killing the mosquito

Killing the mosquito larvae

Draining stagnant water

Clearing bushes

Treatment

Sleep under mosquito nets

Amoebic dysentery (amoebiasis)

Causative agent

Entamoeba hystolytica (bacterium)

Transmission

Contaminated food or water due to improper faeces disposal

Symptoms

Intestinal pain

Diarrhea

Vomiting

Dehydration

Control

Sanitation

Personal hygiene

Cook food well

Treatment using drugs

d) Discuss Ascaris lumbricoides under the following sub-headings

i. Mode of transmission

through ingestion of contaminated food

live in intestines

ii. Effects of parasite on the host

inﬂammation of lungs

pneumonia

produce toxic substances

intestinal obstruction

iii. Adaptations

thick cuticle which protects it against digestion

lays many eggs to ensure survival

mouthparts for sucking partly digested food

lack of elaborate alimentary canal

tolerant to low oxygen concentration

two hosts to ensure survival

eggs have protective cover to ensure survival in adverse environments

iv. Control and prevention

proper sanitation

wash hand after defaecation and before eating

e) Discuss schistosoma under the following sub-headings

i. Mode of transmission

through contaminated water in swamps, etc

ii. Effects on host

bleeding in lungs

blood stained urine

unthriftiness

iii. Adaptations

has two hosts to increase chances of survival

eggs have a hook like structure which raptures the walls of intestine or bladder

lay large number of eggs to ensure survival

larvae have a sucker for attachment on human skin which it digests

larva has a tail which it swims with in search of host in water

prolonged association between male and female to ensure that fertilization takes place

adults can tolerate low oxygen concentration (in the animal tissues)

adult worm secretes chemicals against antibodies

larvae and eggs (have glands that) secrete lytic enzymes to soften the tissues that ease penetration

larvae are encysted so as to survive adverse conditions

Control and prevention

proper use of toilet facilities

boiling water before use

avoid bathing/washing in infected water

Use of molluscicides (chemicals that kill snails/biological control/clearing water weeds on which snails feed.

Drainage of stagnant water

Wearing 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 species

maintaining life of species

replace dead individuals

iii) Name the types of reproduction

sexual which involves fusion of male and female gametes

asexual in which no gametes are involved but parts of a 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 genes

Genes 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 cells

all cells maintain the same chromosome constitution i.e. the diploid state

ii) Describe the five stages of mitosis

Interphase

replication of organelles

duplication of DNA

production of energy (ATP) for cell division

Prophase

stage of dehydration

chromosomes shorten and thicken

chromosome replicates into two chromatids

chromatids joined at centromere

formation of spindle fibers

Metaphase

chromosomes move to equator (early metaphase)

chromosomes line up at the equator

homologous chromosomes do not associate

Anaphase

Chromatids separate

move to opposite ends (poles) of the cells

Telophase

chromatids reach the poles

formation of two daughter cells occurs i.e. cytoplasmic division

ii) State the signiﬁcance of mitosis

ensures each daughter cell has same number and kinds of chromosomes as daughter cells

gives 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 meiosis

gives rise to gametes

source of variation

iii) Give a summary of the stages of meioeis

First meiotic division

Interphase I

cell is in non-dividing condition

chromosomes appear threadlike

Prophase I

chromatic material shorten and thicken

double stranded chromosomes appear (bivalent)

double stranded chromosomes pair and twist round each other (synapsis)

point of contact of chromosomes is called chiasma

Metaphase I

paired homologous chromosomes line up at the equator

Anaphase I

paired homologous chromosomes move to the poles

Telophase I

paired homologous chromosomes reach the pores

two new nuclei are formed

Second meiotic division

Prophase II

chromosomes shorten, thicken and become visible,

stage of dehydration

Metaphase II

movement of chromosomes to equator

Anaphase II

chromatids of each chromosome separate to the poles

Telophase II

reach the poles

four haploid daughter cells are formed

iv) Give the similarities between mitosis and meiosis

both take part in cells

both involve division (cell multiplication)

v) What are the differences between mitosis and meiosis?

Mitosis

maintenance of chromosome number (diploid)

take place in somatic cells/growth

no crossing over/no variation

results in to two daughter cells

no pairing/no synapsis/no bivalent formed

a one division process of four stages

meiosis

reduction halving of chromosomes (haploid)

occurs in reproductive cells/gonads/produces gametes

crossing over takes place/variation occurs

results in to 4 daughter cells

there is pairing/synapsis/bivalent

a two dicision process of four stages each

d) i) What is asexual reproduction

formation of new individuals as a result of the fusion of two gametes

fusion 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 reproduction

genetic variation

greater adaptability to environment by offspring

few bad or good traits inherited/retained

greater amount of dispersal is possible

may result in stronger offspring

iv) Give the disadvantages of sexual reproduction

less certainty in egg and sperm meeting

low rate of survival

sex-linked diseases easily transmitted

e) i) What is asexual reproduction?

formation of new organisms without fusion of gametes

occurs with only one parent

parts of organism develop into new individual

ii) State the advantages of asexual reproduction

retention of useful characteristics/genes/traits

offspring establish faster/shorter life cycle

better chances of survival because of suitable environment

iii) Give the disadvantages of asexual reproduction

lack of genetic variation

lowered resistance to disease ~

loss of hybrid vigor

competition for resources due to overcrowding

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

Sporulation

formation of spores

spores are small haploid cells produced by plants

Spores give rise to new haploid organisms

includes moulds, ferns, bryophytes, pteridophytes

Budding

where an outgrowth arises from a parent and drops off to develop into a new organisms

hereditary material in the daughter cell and parent are exactly the same

occurs in organisms such as hydra, jelly fish, sea anemones, yeast and some fungi

Binary fission

a cell splits into two new cells of equal size

each daughter cell grows into anew organism

Occurs in organisms such as amoeba, euglena, paramecium, some fungi and bacteria.

f) i) What is a ﬂower?

this is the reproductive structure which bears the reproductive pans of a plant

it 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

Receptacle

expanded end of stalk which bears ﬂoral parts

Calyx

consists of sepals

usually green

protect ﬂower in bud

Corolla

consist of petals

often colored or scented to attract insects

Androecium

male part of ﬂower

consist of stamens

each stamen consists of an anther containing pollen sacs

anther produces pollen grains which contain male gametes

Gynaecium

female part of ﬂower

consists of one or more carpels

each carpel contains one or more ovules in an ovary

style bearing a stigma extends from ovary

ovary contains female gametes which when fertilized 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

Hermaphrodite

one with both stamen and carpel

most ﬂowers are hermaphrodite/bisexual

Unisexual

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

Carpelate

also called pistilate

contains only carpels hence a female ﬂower

Staminate

also called male ﬂower

contains only stamens

Dioecious plants

have pistilate and staminate ﬂowers on different plants e.g. pawpaw

Monoecius plants

have pistilate and staminate on one plant

however, pistilate and staminate occur at different plants e. g. maize

Complete ﬂower

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

Incomplete ﬂower

does not have all four parts

at 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 pollination

self pollination takes place when mature pollen grains of a flower fall on the stigma of the same ﬂower

cross 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 pollination

healthy offspring

leads to variation

greater chances of dispersal

iv) List the agents of pollination

wind

water

insects

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

Insect pollinated ﬂowers (entomophilus)

are scented to attract insects

have stick stigma for pollen grains to stick on

are brightly coloured to attract insects ,

presence of nectar to attract insects

have nectar guides to guide insects to the nectarines

have nectarines to secrete nectar

stigmal anthers located inside the ﬂower/tubal/funnel shaped corolla to increase chances of contact by insects

sticky/spiny/spiky pollen grains which stick on the body of insects and on stigma

large/conspicuous ﬂowers easily seen by/attract insects

anthers firmly attached to the filament for insects to brush against them

landing platform to ensure contact with anthers and stigma

mimicry to attract (male) insects

Wind pollinated ﬂower (anemophilus)

anthers/stigma hang outside the ﬂower to increase chances of pollination

the style/filament is long to expose stigma/anthers

stigma is hairy/feathery/branched to increase surface area over which pollen grains land/to trap pollen grains

pollen grains are smooth/dry/light/small to be easily carried by wind

large amount of pollen grains to increase chances of pollination

anthers loosely attached to filaments to enable them to sway to release pollen grains

pollen grains may have structures which contain air to increase buoyancy

ﬂowers have long stalks holding them out in the wind

vi) State the Ways in which plants prevent self-pollination

protandry(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 plants

presence of special structures that attract agents of pollination

protandry/dichogamy

protagyny/dichogamy

monoecism

self sterility

heterostyly

viii) State the advantages of cross pollination

hybrid vigour

less prone to diseases

promotes genetic variation

greater evolutionary potential

h) i) What is fertilization?

Fusion of male and female gametes to form a zygote

ii) Describe how fertilization takes place in a flower

this follows pollination

pollen grain is deposited on the stigma

pollen grain sticks to the surface of the stigma

the surface of the stigma produces a chemical substance which stimulates the pollen grain to produce a pollen tube/to germinate

the pollen tube grows through the style tissues on which it feeds until it enters the ovary

the generative nucleus divides into two giving two male nuclei

embryo sac contains eight nuclei i.e. two synergids, egg cell, two polar nuclei and three antipodal cells

the pollen tube enters the embryo sac through the micropyle and one of the male nucleus fuses with the egg cell/ovum to form a zygote

the 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 afterwards

this process is referred to as double fertilization

zygote grows into an embryo containing plumule, radicle and cotyledons

iii) What is double fertilization?

there are two male nuclei entering embryo sac

one fuses with the ovum to form a zygote, while the other fuses with the polar nuclei to form a triploid primary endosperm nucleus

therefore there are two fusions at fertilization

iv) Name the changes that Occur in a ﬂower after fertilization

petals, stamen, calyx and style wither

ovary wall changes into pericarp

intergument changes in to seed coat/testa

zygote changes into embryo ‘(by mitosis)

primary endosperm nucleus changes into endosperm

whole ovule changes in to seed

ovary develops and grows into fruit(under the inﬂuence of gibberrellic hormone)

b) i) Distinguish between a fruit and a seed

a fruit is a fertilized ovary and has two scars

a seed is a fertilized ovule and has one scar

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 seed

the seed loses water to become drier

the 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

Testa

also called seed coat

a tough outer covering which protects the seed from insects, bacteria etc

segment is the membrane inside the testa

Hilum

a scar

spot where the seed was attached to the fruit or pod

Micropyle

small hole through which water and air enter the seed

Radicle

embryonic root

grows into the shoot system

Cotyledons

embryonic leaves

store food for the germinating seed i.e. for plumule and radicle

when plumule and radicle grow, they use food stored in the cotyledon

in 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 ovary

within the ovary, the developing embryo produces special chemical substances that stimulate the young ovary

these substances also signal the start of the formation of the fruit, which is a mature ovary

the fruit may contain one or more seeds

during fruit formation the ovary increases in size while ripening or maturing

a true fruit is formed from the ovary of a ﬂower after fertilization

it has two scars(style scar and stalk scar) and contains seeds

some seeds are not formed from the ovary of a ﬂower

some other parts of a ﬂower develop to form a fruit

such fruits are called false fruits

vii) Explain the importance of fruits in the survival of plants

protect the seed against dessication, predators and adverse conditions

aid in seed dispersal by attracting agents of dispersal

stores food for the plant

vii. Distinguish between parthenogenesis and parthenocarpy

parthenogenesis is development of new animals from unfertilized eggs

paithenocarpy is development of a fruit without fertilization

iv) state the differences between a seed and a fruit

A Seed

fertilized ovule

attached to the placenta through funicle

one scar called hilium

has seed coat/testa

seed wall undifferentiated

fruit

fertilized ovary

attached to branch through a stalk

two scars (style scar and stalk scar)

has fruit wall/pericap

fruit 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 wall

ovules 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 together

dividing Walls disappear, leaving one

have numerous seeds e. g. passion fruit

placenta of each carpel appears as ridge on ovary Wall

Axile

edges of carpels fuse together to form a single central placenta

numerous ovules arranged on placenta

ovary divided into a number of loculi by walls of the carpel e. g.

Free central placentation

edges of carpels fuse together

dividing was disappears leaving one loculus

placenta appears at base of ovary

has numerous ovules

c) i) How are fruits grouped?

Simple fruits

formed from a single ﬂower or one ovary e. g. mango

Aggregate fruits

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

Multiple (compound) fruits

formed from several ﬂowers whose ovaries fuse together after fertilization

form a bunch e. g. pineapple, figs

are always false fruits

ii) What are succulent fruits?

also called ﬂeshy fruits

all or part of pericarp (fruit wall) becomes juicy

iii) Give types of juicy fruits

Berry

has many seeds

whole pericarp is succulent e. g. orange, tomato, pawpaw

Drupe

only one seed

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

Pome

juicy part is swollen receptacle

is usually a false fruit

example is a pear

iv) What are dry fruits?

have a pericarp that is dry, hard and Woody

either dehiscent or indehiscent

called dry because they are not succulent

v) What are dehiscent fruits?

split open when ripe to release seeds

contain many seeds

vi) Give types of dehiscent fruits

Legumes

split along two edges

are usually pods e.g. beans, peas, crotolaria

Follicle

split on one side only e. g. Sodom apple

Capsule

has several lines of Weakness/sutures

open in many places e.g. castor oil, cotton

vii) What are indehiscent fruits?

non-splitting fruits

usually one seeded only

ii) Give main types of indehiscent fruits

Nut

pericarp woody, hard and thick e.g. cashew

Achene

has 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 overcrowding

reduces competition for space, nutrients and light

colonization of new areas is made possible

to increase chances of survival

to prevent inbreeding

to avoid extinction due to over competition for the necessities

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

Adaptations for wind dispersal

they have wings, feathers or hair-like structures to increase surface area for wind to carry them easily/buoyancy

seeds/fruits are loosely attached on the stalks so that they can easily be released and carried away by wing

seeds/fruits are generally light and small sized to be easily carried by wind

some seeds/fruits have parachute-like structures to be easily carried b wind

some 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 seeds

seed mesocarp has air spaces thus light/buoyant to ﬂoat hence carried by water

they have waterproof cover and tough pericarp protects seeds from getting soaked

fibrous and spongy mesocarp to easily ﬂoat

Animal dispersal seeds

presence of hooks for attachment to animals thus carried to other parts

fruits are brightly coloured, succulent and scented to attract animals

seed coats are hard and resistant to digestive enzymes hence seeds are dropped away from mother plant

large in size or borne on clusters to be easily seen

Self dispersal/explosive

self opening seeds

they 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 animals

in external fertilization fusion of the male and female gametes takes place outside the body of the female e. g. amphibians and fish

in internal fertilization union of gametes occurs inside the body of the female

ii) State the advantages and disadvantages of external fertilization

Advantages

large numbers produced therefore many offspring per breeding season

female does not suffer gestation stress

mother does not need to care for the young except in a few species

the surviving individuals are highly selected for better survival

Disadvantages

many predators surround the eggs before and after fertilization

fewer chances of fertilization/a lot of gametes wasted

embryo development at mercy of environment

large numbers of female gametes are required therefore female gets much exhausted

iii) State the advantages and disadvantages of internal fertilization

Disadvantages

number of gametes fewer hence less number of offspring

less adapted for sudden change of environment after birth

in mammals females suffer gestation stress

Advantages

more chances of fertilization

fewer predators of oval/fertilized egg protected in females body

Stable internal environment

fewer gametes required

iii) Give a reason why it is necessary for frogs to lay many eggs

to 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

Penis

is highly vascularised/spongy

has a sensitive glands

becomes erect to allow entry into the vagina

Scrotum

contains the testes outside the body on whose walls the process of spermatogenesis takes place

the process is favored by lower temperature

it contains sertoli cells which nourish sperms until they are mature

Epididymis

long and coiled for the purpose of sperm storage

Vas deferens

muscular

upon contraction pushes sperms out and allows ejaculation

Gametes

produced in large numbers to increase chances of fertilization

the sperms have a tail for swimming/large number of mitochondria to provide energy/allow swimming to reach the egg

Accessory glands

are seminal vesicle, Cowper’s gland and prostate gland

they 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 membrane

nucleus contains genetic material

mitochondria 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 egg

it 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

Ovaries

have several graafian follicles that develop and burst open to release/produce mature ova

secretes sex hormones(oestrogen) which initiate/control development of secondary sexual characteristics

produce 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 sperms

are funnel shaped on the end next to ovary which enables them to receive the ovum

their lining contains cilia which propel the ovum towards the uterus

has peristaltic muscles that enable movement of zygote/ovum to the uterus for implantation

is fairly long to increase surface area for fertilization

Uterus

is muscular for protection of developing embryo

has elastic wall that allows growth and development of foetus/embryo

has a highly vascularised endometrium that provides nutrients/gaseous exchange to developing embryo

Cervix

has valves that close the lower end of the uterus to ensure continued pregnancy during gestation period

is capable of dilating ~

has narrow entrance/neck-like entrance to uterus that enables quick swimming of sperms to uterus

has suction mechanism that draws up/pulls sperms into uterus

has a “W” shape that ﬁts well with the glands of the penis to ensure sperms are deposited at the right point

Vagina

is elastic and muscular to enable good accommodation or penetration of the penis thus proper deposition of sperms and for easy parturition

allows menstrual ﬂow

has sensitive labial walls which secrete/produce lubricating substances that

ensure/enable/facilitate good coition

capable of considerable enlargement, due to elastic muscles, to accommodate baby during parturition

Clitoris

has sensitive cells for orgasm

iii) Explain how the ovum is adapted to its function

nucleus contains genetic material

ventelline membrane encloses plasma membrane which encloses yolky cytoplasm

yolky cytoplasm provides nourishment

jelly coat protects ovum against dehydration

iv) Explain the differences between sperm and ovum

d) i) Explain the process of fertilization

a process whereby the egg and sperm are brought together and fuse to form a zygote

occurs in the fallopian tube after copulation

sperm head penetrates the outer coat of the ovum While the tail remains outside

penetration is due to reaction of acrosome

acrosome digests the vitelline membrane

thereafter a zygote is formed

zygote which is diploid undergoes rapid cell division to form a mass of cells called blastocyst

after fertilization a membrane forms around the ovum to prevent further entry of sperms

blastocyst eventually develops into an embryo

i) Explain the process of implantation

this is the embedding and attaching of the embryo in the uterine wall/endometiium

implantation marks the beginning of pregnancy

sometimes implantation occurs in the oviduct Wall which is abnormal and results in ectopic pregnancy which is fatal

the outer wall of the blastocyst develops ﬁnger like projections which project into the uterine wall for attachment

the projections are called villi

the villi and endometrium develop into an organ that is called the placenta

the embryo is attached to the placenta through a cord called the umbilical cord

State the functions of umbilical cord

it contains blood vessels umbilical artery, iliac arteries and umbilical veins)

it joins the placenta to the embryo

passage for nutrients other

passage of excretory substancess from foetus to mother for final discharge

gaseous exchange

passage of antibodies from mother to foetus, for protection of foetus against diseases

State the role of placenta

exchange of gases between mother and foetus

exchange of nutrients and nitrogenous wastes

anchorage/attachment of foetus

produces 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

Chorion

surrounds the embryo

has fingerlike projections that attach embryo to the uterus

Amnion

contains amniotic ﬂuid

ﬂuid surrounds embryo

protects embryo from mechanical injury by acting as shock absorbers

ﬂuid also protects embryo from dehydration

distributes pressure equally over embryo

Yolk sac

surround the yolk

produces blood cells for embryo until its own liver is able to perform the task

Allantois

present only for a short time

removes and store waste material

it eventually becomes the umbilical cord

iii) Explain the events that take place to facilitate parturition

near birth the placenta produces less progesterone

oxytocin hormone is produced by posterior lobe of pituitary gland

because progesterone level has decreased the uterus becomes sensitive to oxytocin

oxytocin causes the contraction of the uterus (myometrium)

these contractions are called labour pains

just before parturition the head turns downwards

the contractions eventually push the baby through the vagina

amnion breaks and amniotic ﬂuid is released

oxytocin dilates the cervix

foetus is expelled through cervix with head coming out first

finally the whole infant comes out

the umbilical cord is cut and the placenta is expelled as afterbirth

iv) State the reasons why later in pregnancy the ovary will b e removed without disturbing the pregnancy

corpus luteum in the ovary secretes progesterone which maintains pregnancy and development of foetus after conception

after four months pregnancy is maintained by progesterone from the placenta

f) i) What are secondary sexual characteristics

Characteristics (physiological and anatomical) that start developing at puberty due to the inﬂuence of male and female hormones

ii) State the main secondary changes in

Boys

deepening of the voice

growth of hair on face, pubic part, chest, legs

penis and testes become bigger

muscular development

sperm production begins at puberty and may continue throughout life

Girls

growth of hair on pubic part and armpits

widening/enlargement of hips

development of breasts

menstrual cycle starts as ovaries mature

body acquires extra fat

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

Boys

Follicle stimulation hormone (FSH)

from pituitary

stimulates production of androgens(male hormones) mainly testosterone by testis

Testosterone

secondary sexual characteristics

Girls

FHS

from pituitary

development of follicles

stimulates oestrogen production by ovary

from pituitary

ovulation

stimulates release of progesterone by ovary

Oestrogen

stimulates release of LH

secondary sexual characteristics

Progesterone

also from placenta

sustains pregnancy as it inhibits prolactin and oxytocin during pregnancy

Prolactin

milk formation

Oxytocin

parturition

milk ejection

g) i) What is menstruation?

vaginal discharge due to disintegration of endometrium

ii) Describe the role of hormones in the human menstrual cycle

it is controlled by sex hormones which are responsible for the onset of secondary sexual characteristics and also control of the menstrual cycle

the onset is signaled by discharge of blood/menses 14 days following the start of menstruation

anterior 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 oestrogen

oestrogen causes repair/healing of uterine wall

oestrogen 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 progesterone

Progesterone causes proliferation/thickening of uterine wall

Oesterogen/progesterone inhibits, the production of FSH by anterior lobe of pituitary, thus no more follicles develop and oestrogen production reduces

In 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 drops

Anterior lobe of pituitary starts secreting FSH again.

iii) What is menopause?

end of ovulation in women

occurs after age of 45 years

does not occur in males

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

i) Gonorrhea

caused by a bacterium called neisseria gonorrhea

transmitted through sexual intercourse,

infects urethra and vaginal tract (epithelia)

Symptoms include pain, discharge of mucus and bad smell (females)

Effects include sterility, heart diseases, blindness of foetus and arthritis

Treatment by antibiotics

Control and prevention by proper sexual conduct

ii) Herpes

notably Herpes simplex and H. genitalis

caused by virus which attacks genitalia

symptoms are painful sores in genitalia, skin lesions

transmitted in saliva, sexual intercourse and injection by drug addicts

no treatment

iii) Syphilis

caused by bacterium called Treponema palladium

symptoms are painless wounds in genitalia

attack genitalia, nervous system, lips

treated by antibiotics

iv) Trichomoniasis

caused by plasmodium called trichomonas

attacks reproductive tract

symptoms are itching and discharge of pus from the genitals

treated by antibiotics

v) Hepatitis

Viral disease

Affects the liver

Transmitted through sexual intercourse

No known treatment

vi) Candidiasis

caused by fungus called candida albicans

transmitted through sexual intercourse

symptoms include itching urethra, and vaginal discharge (odourless)

controlled by personal hygiene, early treatment and responsible sexual behavior

vii) HIV/AIDS

caused by HIV virus

transmitted by sexual intercourse, blood transfusion, sharing piercing instruments from infected mother to foetus, infant and baby

symptoms include fever, swollen lymph nodes, night sweating, cough, weight loss, fatigue, loss of appetite, diarrhea, headache, a opportunistic infections and tumors

Control by responsible sexual behaviour, education, screening blood for transfusion and using sterile piercing instruments.

6. a) Deﬁne the terms

i) Growth

an irreversible change in size of a cell, organ or whole organism

growth is due to synthesis of protoplasm or extracellular substances

ii) Development

refers to a series of changes which an organism goes through in its lie cycle

during development both qualitative and quantitative changes take place(involves differentiation)

iii) Differentiation

refers 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 growth

assimilation

cell enlargement

cell division(by mitosis)

iv) List the parameters used to measure growth

height/length

dry Weight

number of individuals

volume

leaf area of plant

iv) Name the patterns of growth in organisms

allometric and isometric

limited and unlimited

discontinuous growth

c) i) Name the different types of growth curves

sigmoid 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 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 seed

food stored is mobilized/used up for respiration and growth

vii) Describe the physiological changes that occur in a seed during germination

in presence of oxygen, optimum temperature and water, food reserves in the seed are hydrolysed or broken down into soluble diffusible form by enzymes

soluble food diffuses to the growing embryo

oils and carbohydrates provide energy

simple sugars converted to cellulose to form cell wall

amino acids make protoplasm

seed develops plumule and radicle hence germinates

viii) Explain the biological signiﬁcance of cotyledons being brought above the ground in epigeal germination

cotyledons have inadequate food

they are brought above the ground to acquire chloroplasts to carry out photosynthesis

before the formation of foliage leaves to supplement food supply required for growth during germination

f) i) Distinguish between primary and secondary growth

Primary growth

occurs at the apical (shoot and tip) apices regions where meristematic cells occur

causes plant elongation since cells divide by mitosis

Secondary growth

occurs at the cambium meristems

Increases width (girth) of the stem

ii) What are meristems

dividing cells

meristem means they are dividing

iii) State the characteristics of meristematic cells

dense cytoplasm

thin cell walls

absence of vacuoles/cell sap

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

Apical meristem

located at tips of roots and shoots

increase length of stem and roots/primary growth

Intercalary meristem

found at bases of internodes

responsible for elongation of internodes and increase in leaf sheath in grasses

Lateral meristems

found near the periphery of stem and root

responsible for secondary growth/growth in girth of stem and root/lateral growth

called cambium and constitute vascular and cork cambium

v) Describe primary growth

occurs at tips of shoots and roots in the meristematic tissues of apical meristem

at the apex there is a zone of cell division/mitosis

cells elongate at elongation zone

the elongated cells differentiate at the region of differentiation resulting in increase in size

in the stems meristems give rise to leaf premodia which envelop the apex to form a bud

the bud protects the delicate inner cells

in roots the meristem is protected by root cap

after cells differentiate the form permanent tissues

vi) Describe secondary growth in plants

also called secondary thickening '

only occurs in dicotyledonous plants that have cambium

monocotyledonous plants do not undergo secondary growth because they lack intervascular cambium

cambium cells divide to produce more cells on either side of the cambium

cells produced to the inside become secondary cambium

cells produced to the outside become secondary phloem

division of cambium cells occurs yearly producing new rings of secondary phloem and secondary xylem each year

intervascular cambium(cambium between vascular bundles) divide to form secondary parenchyma, thereby increasing growth of medullary rays

much more xylem is formed than phloem, thus pushing phloem and cambium ring outward

the rate of secondary growth is depended on seasons(rains) resulting in annual rings

cork cambium is located beneath epidermis ad is responsible for secondary thickening of the bark of perennial plants

cork cambium divides to form new cork(bark) tissues to accommodate increased growth on outside and secondary cortex on the inside

Cork cells (cells of the bark) are loosely parked at some points to form lenticels for gaseous exchange.

vii) State the signiﬁcance of secondary growth

increase girth or circumference of trees

annual 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

- 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 plants

indole acetic acid/IAA/ auxins

Cell division/increase in cell division

Tropic responses

Cell elongation/increases in ell elongation

Development of abscision layer

Growth of ovaries into fruits/parthenocarpy/initiates ﬂowers

Inhibits growth of lateral buds/produces apical dominance

Stimulates adventitious/lateral roots ‘

Gibberellins (Gibberellic acid/GA3

Promote cell elongation/rapid cell division/increase in length of the internodes

Promote fruit formation without fertilization/parthenocarpy

Reduces root growth

Breaks seed dormancy/promotes germinationCytokinnins (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

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KCSE PIVOT BIOLOGY

Biology Questions and Answers Form 3 - Biology Form Three Notes

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