WAEC Biology 2012 past questions and answers

Biology comes from 'bios' (life) and 'logos' (study): the study of living things.

A tissue is a group of similar cells doing the same job, which is what the epidermal cells are.

Euglena and Spirogyra are at the cell level; a ginger rhizome is a storage organ, the usual example of the organ level.

In a large, complex body most cells are far from the surface, so oxygen cannot reach them fast enough by diffusion alone; transport systems are needed.

In Volvox the cells are joined by protoplasmic strands and some are specialised for reproduction, so the cells depend on one another.

In a sprint the muscles need energy faster than oxygen can arrive, so they respire anaerobically and lactic acid builds up.

The step-like graph shows growth only in bursts after each moult, because the hard exoskeleton stops growth in between; this is typical of insects.

'Pulmonary' refers to the lungs; this circuit takes blood from the heart to the lungs and back.

Haemophilia is a failure of blood clotting; platelets help blood clot, and only individual IV has a low platelet count.

HIV destroys white blood cells (lymphocytes), so an infected person has a low white cell count, like individual III.

Amphibians have a three-chambered heart with two auricles and one ventricle; fish have two chambers and birds four.

Z is a cluster of alveoli at the end of a bronchiole, which is found inside the lung tissue labelled IV.

Adrenaline prepares the body for action: it sends more blood to the heart, lungs and muscles and less to organs not needed at once, such as the gut and liver.

Walking is a voluntary (or learned) action controlled by the brain; swallowing, sneezing and blinking are automatic reflexes.

Dendrons (dendrites) carry impulses towards the cell body; axons carry them away.

A convex lens converges light rays so that the image falls exactly on the retina, correcting long sight.

The retina contains the rods and cones, which respond to light.

In the cold, erector muscles raise the hairs to trap a layer of air that reduces heat loss.

Fertilisation is the fusion of the sperm nucleus with the egg nucleus; the tail is left outside.

After fertilisation the ovule becomes the seed and the ovary becomes the fruit.

II is the sperm duct (vas deferens); cutting and tying it (vasectomy) stops sperm leaving the testes.

Bright petals attract insects, which carry pollen from flower to flower.

Removing a ring of bark destroys the phloem, so food cannot reach the roots and the tree dies.

Accessory pigments widen the range of light a plant can use: they absorb light chlorophyll misses and pass the energy to chlorophyll a.

Plants combine carbon dioxide and water, using light energy, to make glucose; oxygen is a product.

Lightning makes nitrogen and oxygen combine; the oxides dissolve in rain and reach the soil as nitrates.

Magnesium is part of the chlorophyll molecule and must be absorbed from the soil; carbon comes from the air.

Proteins are body-building foods used for growth and repair of tissues.

Animals store carbohydrate as glycogen in the liver and muscles.

Bones are hardened by calcium phosphate; lack of calcium and phosphorus causes soft, bent bones (rickets).

Yeast fermenting sugar gives off carbon dioxide, which turns lime water milky.

Bile emulsifies fats into tiny droplets so lipase can work on them; without bile, fat digestion suffers.

The child shows signs of kwashiorkor (swollen belly), caused by lack of protein; beans are rich in protein.

Water supplies no energy; proteins, carbohydrates and lipids all release energy when oxidised.

A community is all the populations of different species living and interacting in one area.

The biosphere is the part of the earth (land, water and air) where living things are found.

Bacteria are living (biotic); topography, water and wind are non-living.

A barometer measures atmospheric pressure; a hygrometer measures humidity and a photometer light.

The organisms live on land and the feeding links are interconnected chains, which make a food web.

Grass→grasshopper→toad→snake→hawk→man; grass→field mouse→snake→hawk→man; grass→field mouse→hawk→man; grass→goat→lion→man; grass→grasscutter→man: five chains.

Mangroves in salt-water swamps grow in waterlogged mud with little oxygen, so they have breathing roots (pneumatophores).

Zone IV is the deep sea; there is no light for photosynthesis and it is cold, so very few organisms live there.

Light decreases with depth; it controls where producers can photosynthesise and so where other organisms can live.

Flushed faeces go straight into a closed tank, so flies cannot touch them and spread germs to food.

Vibrio cholerae comes from human faeces; finding it in drinking water shows the water is polluted with sewage.

Density-dependent factors grow stronger as a population gets crowded (waste, predators, parasites). Weather affects the population the same way however many mice there are, so it is density independent.

Destruction of habitats by farming, logging and building is the biggest threat to most endangered species.

Eye colour falls into distinct groups and body weight varies continuously, so this pair is in the wrong order.

In the ABO system the antigens are on red blood cells and the antibodies (anti-A, anti-B) are in the plasma.

Fingerprints are classed as arch, loop, whorl and compound (composite).

Sickle cell anaemia is caused by an inherited faulty gene for haemoglobin.

Crossing two heterozygous red plants (Rr × Rr) gives 3 red : 1 white, i.e. 75% red and 25% white; white offspring prove both parents carry r.

The base pairs in DNA are A–T and G–C, held by hydrogen bonds; DNA sugar is deoxyribose, not ribose.

Bb × Bb gives BB, Bb, Bb, bb; with complete dominance the first three are black, so 3 black : 1 white.

Yy × Yy gives YY, Yy, Yy, yy; only yy (1 in 4) has green flowers.

A mutation is a sudden, inheritable change in a gene or chromosome.

By pollinating crop flowers, bees allow fruits and seeds to form, which matters most for crop yield.

Plants evolved from simple water-living algae to liverworts and mosses, then to ferns with vascular tissue.

(a) Any four, each explained: concentration gradient — the steeper the gradient, the faster the diffusion; temperature — higher temperature makes molecules move faster; size of molecules — small molecules diffuse faster; surface area — a larger area allows more diffusion; distance/thickness of membrane — thinner surface, faster diffusion; medium — faster in gases than in liquids.
(b)(i) Active transport: movement of substances across a living membrane from a region of low concentration to high concentration (against the gradient), using energy (ATP) from respiration.
(ii) Transpiration: loss of water as vapour from the aerial parts of a plant, mainly through the stomata of leaves.
(c) Any four: thick waxy cuticle; sunken stomata; few or small stomata; leaves reduced to spines/needles or small leaves; hairy leaves; rolling of leaves; shedding of leaves in the dry season; closing stomata during the hottest part of the day.
(d) Biconcave disc shape — large surface area for absorbing oxygen; no nucleus — more room for haemoglobin; contains haemoglobin — combines with oxygen to carry it; thin membrane — short diffusion distance for gases; small and flexible — can squeeze through capillaries.

In (d) pair each feature with how it helps the cell carry oxygen.

(a) Stores food for a few hours; muscular walls contract to churn and mix food with gastric juice; gastric glands secrete hydrochloric acid, pepsinogen, rennin and mucus; HCl kills germs, stops salivary amylase and gives an acid pH; HCl activates pepsinogen to pepsin, which breaks proteins into polypeptides/peptides; rennin curdles milk protein (caseinogen) in young mammals; mucus protects the stomach wall from acid and enzymes; food leaves as chyme through the pyloric sphincter.
(b) Any three, each with an example: root — cassava/carrot/sweet potato; stem — yam/ginger/sugar cane/Irish potato; leaf — onion/cabbage; fruit — mango/orange; seed — maize/groundnut/beans.
(c) When blood sugar rises (after a meal), the pancreas secretes insulin, which makes the liver and muscles change glucose into glycogen and cells take up more glucose, so the level falls. When blood sugar falls, the pancreas secretes glucagon, which makes the liver change glycogen back into glucose, so the level rises. (Adrenaline also raises blood sugar in emergencies.)

For (c) name both hormones and say what each makes the liver do.

(a)(i) Conservation is the protection, preservation and wise, planned use of natural resources so that they are not wasted or destroyed and remain available for the future.
(ii) Endangered species are species whose numbers have fallen so low (through habitat loss, hunting, pollution etc.) that they are in danger of becoming extinct.
(b)(i) Any five: provide timber and fuel wood; provide food and medicine; habitat for wildlife; prevent soil erosion and protect water catchments; help regulate climate and rainfall; absorb carbon dioxide and release oxygen; source of income and tourism; act as windbreaks.
(ii) Any four: afforestation and reafforestation; laws against illegal felling; selective logging; forest reserves guarded by forest guards; prevention of bush burning; public education; use of alternative fuels.
(c)(i) Decomposers break down dead organisms and wastes; they release minerals back into the soil for plants (recycling of nutrients); they clean up the environment and form humus.
(ii) Plant decomposer: a fungus such as mushroom/Rhizopus/Mucor (or bacteria). Animal decomposer: earthworm/millipede/termite/maggot.

Give a clear definition before listing reasons.

(a)(i) A gene is a unit of inheritance, a section of DNA on a chromosome that controls a particular characteristic.
(ii) Genotype is the genetic make-up (set of alleles) of an organism; phenotype is its observable features, produced by the genotype together with the environment.
(b)(i) Hybrid: offspring of a cross between two genetically different parents (e.g. heterozygous Tt).
(ii) Pure breeding: an organism that is homozygous for a trait and always produces offspring like itself when bred with a similar one.
(iii) Nucleotide: the unit of a nucleic acid, made of a pentose sugar, a phosphate group and a nitrogenous base.
(c) Let S = smooth, s = rough. The smooth plant had rough (ss) parents, so it must be Ss. Cross: ss × Ss; gametes s and S, s; offspring Ss and ss; result: 1 smooth : 1 rough (50% smooth, 50% rough).

First work out the smooth parent's genotype from its rough parents.

(a)(i) Disease: a condition in which the normal functioning of the body or part of it is disturbed, so the organism is unwell.
(ii) Symptoms: the signs or changes (e.g. fever, pain, rash, diarrhoea) felt or seen that show a person has a particular disease.
(b)(i) Physical: intact skin; mucus in the nose/airways; cilia; hairs in the nose; blood clotting; tears washing the eye. Chemical: hydrochloric acid in the stomach; lysozyme in tears and saliva; sebum/sweat; acidic vaginal secretions.
(ii) A vaccine contains dead or weakened germs or their toxoids; when introduced it stimulates the body to make antibodies and memory cells without causing the disease; if the real germ later enters, memory cells quickly produce large amounts of antibodies that destroy it before illness develops.
(c) An antigen is a foreign substance (usually protein on a germ's surface) that stimulates the body to make antibodies; an antibody is a protein made by white blood cells (lymphocytes) that combines with and neutralises a specific antigen.
(d)(i) Plasmodium (a protozoan, carried by female Anopheles mosquito); (ii) Vibrio cholerae (a bacterium); (iii) HIV (human immunodeficiency virus).

Antigen = the trigger; antibody = the body's response.

(a)(i) The seed absorbs water through the micropyle and swells; enzymes become active and food in the cotyledons is broken down; the radicle emerges first and grows down to form the root; the hypocotyl grows rapidly, forming a hook that pulls the cotyledons above the soil; the hypocotyl straightens, the cotyledons open, turn green and photosynthesise for a while; the plumule grows up to form the first foliage leaves; e.g. bean.
(ii) Table — Epigeal: cotyledons brought above the soil / Hypogeal: cotyledons remain below the soil; Epigeal: hypocotyl elongates / Hypogeal: epicotyl elongates; Epigeal: cotyledons become green and photosynthesise / Hypogeal: cotyledons do not; e.g. bean / e.g. maize.
(b)(i) Seed dormancy is the state in which a viable seed does not germinate even when conditions (water, oxygen, warmth) are suitable.
(ii) Any three: scarification (scratching/cracking the testa); soaking in water to leach out inhibitors; treatment with gibberellin; exposure to light or to low temperature (stratification); heat/fire; passage through an animal's gut; ageing/after-ripening.
(c) Any six: prevents unwanted pregnancy; allows spacing of births; helps control population growth; improves health of mother and child; some (condoms) prevent sexually transmitted infections including HIV; allows parents to plan family size they can support; reduces unsafe abortions; lets women continue education/careers.

Use a ruled table in (a)(ii).