WAEC Biology 1998 past questions and answers

Euglena has chloroplasts and makes its own food like a plant, but it also moves with a flagellum and can feed like an animal.

An organ is made of several tissues working together. A hair is just a dead outgrowth of the skin, not an organ.

Osmosis is the movement of water through a semipermeable membrane, while diffusion can happen with or without any membrane.

Homologous chromosomes pair up only in meiosis (prophase I); the other events happen in both kinds of division.

Ginger is grown from pieces of its underground stem (rhizome), which carry buds that sprout into new plants.

Layering is done by people: a branch is bent and covered with soil until it roots. The others are natural organs of propagation.

The xylem forms a star in the centre with phloem between its arms, and root hairs grow from the outer layer: this is a cross section of a root.

II is the wide region of packing cells between the outer layer and the central stele, which is the cortex.

IV points to the star-shaped arms in the centre of the root, which are the xylem.

Bile is made in the liver and carried to the duodenum by the bile duct, not by the blood.

The pulmonary vein carries oxygenated blood from the lungs to the heart; blood enters the lungs (deoxygenated) through the pulmonary artery.

Ventricles pump blood out to the lungs and the whole body, so their walls are thicker and more muscular than the auricles'.

Amoeba is a single cell with a large surface compared with its volume, so oxygen simply diffuses in through its cell membrane.

Stomata and spiracles are both small openings through which gases pass in and out of the organism.

During inspiration the diaphragm contracts and flattens; it relaxes during expiration.

Sweat is made by the sweat glands of mammals; plants do not sweat.

Bile is produced by the liver, not by the kidney.

Blood under high pressure in the glomerulus is filtered into the Bowman's capsule; this is ultrafiltration.

The liver breaks down or changes poisons such as alcohol and drugs into harmless substances.

Oestrogen from the ovaries causes female features such as breast growth and widening of the hips.

I points to the rounded part containing the nucleus, from which the dendrites branch: the cell body.

II is the myelin sheath, the fatty covering that insulates and protects the axon and speeds up impulses.

The Eustachian tube joins the middle ear to the throat, so air pressure on both sides of the eardrum stays equal.

Chlamydomonas is a single-celled alga; the whole cell divides or acts as a gamete, so it has no reproductive organ.

The embryo floats in amniotic fluid, which cushions it against knocks and jolts.

The gynoecium (pistil) is all the carpels together: stigma, style and ovary. The androecium is the male part.

Bright petals attract insects that carry pollen, so without them pollination suffers.

II lies just inside the fused fruit wall and fills most of the maize grain: the endosperm, the food store.

IV is the lower end of the embryo axis, which grows into the first root: the radicle.

V is the coleorhiza, a sheath that covers and protects the radicle as it pushes out of the grain.

Wind-pollinated flowers make many small, light, smooth pollen grains that are easily blown about; the other features attract insects.

Hot alcohol dissolves the green chlorophyll out of the leaf so the blue-black iodine colour can be seen clearly.

Green plants take in carbon dioxide and use it to make sugar in photosynthesis; respiration and combustion release it.

Breaking carbohydrates down to carbon dioxide belongs to the carbon cycle; the other processes move nitrogen compounds.

Holozoic nutrition means taking in solid food and digesting it inside the body, as most animals do.

Homodont means all the teeth are alike, as in reptiles such as the lizard; mammals have different kinds of teeth (heterodont).

Pancreatic juice enters the duodenum, the first part of the small intestine, through the pancreatic duct.

Rennin, made in the stomach of young mammals, curdles milk protein (caseinogen).

The sundew traps insects on sticky hairs and digests them to get nitrogen.

Hydra catches small animals with its tentacles and starts digesting them with enzymes released into its body cavity, outside the cells.

A hygrometer measures how much water vapour is in the air (relative humidity).

Each feeding step in a food chain (producer, primary consumer and so on) is called a trophic level.

The diagram stacks the organisms by who eats whom, from phytoplankton up to the king fisher, which shows a food chain.

Phytoplankton are the 1st level, tadpoles the 2nd and small fish the 3rd.

The tadpole feeds directly on the phytoplankton (plants), so it is the herbivore.

Mangroves grow in soft, airless mud, so they have stilt roots for support and breathing roots (pneumatophores) for air.

The waxy, waterproof cuticle covering the leaf cuts down water loss.

Simple green algae are the first (pioneer) organisms to grow on fresh moist soil; ferns come later when there is humus.

Earthworms burrow through the soil, letting air and water in and mixing in humus.

The banana 'stem' is a pseudostem made of rolled leaf bases; it does not store food like the others.

Polio is caused by a virus, not a bacterium.

Larvae and pupae hang from the water surface to breathe; the oil film stops them attaching, so they suffocate.

Epithelial tissue covers the body surface (skin) and lines its organs, protecting the tissues beneath.

Gametes are made by meiosis, which halves the chromosome number: 8 ÷ 2 = 4.

The two alleles separate into different gametes, so half the gametes carry T and half carry t.

Rr × rr gives Rr, Rr, rr, rr, so 2 out of 4 offspring (1/2) are Rr.

Social insects live together in organised colonies where different castes share the work.

A honeybee colony has a queen, drones (males) and workers; bees have no soldier caste.

Camouflage is colouring that blends with the surroundings, like a green snake hidden in green grass.

(a)(i) Light stage (light-dependent stage/photolysis); dark stage (light-independent stage/carbon dioxide fixation).
(ii) Light stage: water is split by light energy absorbed by chlorophyll: 2H₂O → 4H⁺ + 4e⁻ + O₂ (or 4H₂O → 4H⁺ + 4OH⁻).
(b)(i) Any six: autotrophic/holophytic (photosynthetic), chemosynthetic, holozoic, saprophytic, parasitic, symbiotic; also herbivorous, carnivorous, omnivorous.
(ii) Paramecium: cilia/oral groove/food vacuole. Spirogyra: chloroplast (chlorophyll). Rhizopus: hyphae/rhizoids that secrete enzymes and absorb. Tapeworm: thin flat body surface that absorbs digested food (suckers/hooks for attachment).
(c) A balanced diet contains all the food classes (carbohydrate, protein, fats and oils, vitamins, mineral salts, water and roughage) in the right amounts and proportions for the body's needs.
(d)(i) Any three: they are proteins; they speed up reactions (catalysts); they are specific; they are not used up; they work best at an optimum temperature and are destroyed by high heat; they work best at an optimum pH; small amounts work on large amounts of substrate; many reactions they catalyse are reversible.
(ii) Ptyalin: source mouth/salivary glands; substrate cooked starch; product maltose. Pepsin: source stomach/gastric glands; substrate proteins; product peptones/polypeptides.

Learn each enzyme as a set: where it is made, what it acts on and what it makes.

(a) Any four: calyx (sepals); corolla (petals); androecium (stamens); gynoecium (pistil/carpels); also receptacle, pedicel, epicalyx.
(b)(i) Wind-pollinated vs insect-pollinated: small, dull flowers vs large, brightly coloured; no scent vs scented; no nectar vs nectar present; large amounts of pollen vs less pollen; light, smooth, dry pollen vs heavy, rough/sticky pollen; large feathery stigmas hanging outside vs small, sticky stigmas inside the flower; long filaments with loosely attached anthers vs short, firm stamens.
(ii) Wind: maize/grass/rice. Insect: pride of Barbados/hibiscus/Delonix.
(c)(i)–(ii) Any three agents with an example: wind – Tridax/cotton/Aspilia; animals – mango/pawpaw/Desmodium (hooks); water – coconut/water lily; explosive (self) mechanism – pride of Barbados/okra/balsam; man – cocoa/oil palm.
(d)(i) Hormones are organic chemical substances made in small amounts in one part of an organism and carried to another part where they bring about a specific effect.
(ii) Auxin (IAA), gibberellin, cytokinin, abscisic acid or ethylene.
(iii) Any two: promote cell elongation/growth; cause tropisms (bending towards light); promote fruit ripening (ethylene); cause seedless fruit (parthenocarpy); cause dormancy or abscission of leaves (abscisic acid); maintain apical dominance; promote rooting of cuttings.

Put the wind/insect differences in matching pairs across a two-column table.

(a) Queen; king; workers; soldiers (also winged reproductives/alates).
(b)(i) Roles: queen – lays eggs; king – mates with/fertilises the queen; workers – build and repair the nest, find and store food, feed the queen, king, soldiers and young, care for eggs; soldiers – defend the colony; winged reproductives – fly out to start new colonies.
Two types of courtship behaviour: e.g. display (dancing/colour or body display) and calling (croaking/singing); also pairing and nest building.
(ii) Any two: brings male and female of the same species together; makes the female ready to mate (synchronises readiness); helps choose a fit mate; ensures fertilisation and so continuity of the species; reduces aggression between partners.
(d) The adult male develops bright colours (orange-red head, blue body); he nods/bobs his head up and down and does push-ups on his fore limbs in front of the female; he chases her and, if she accepts, he grips her neck with his jaws and mates with her.

Termite castes: queen and king reproduce, workers work, soldiers defend.

(a) Organic evolution is the gradual change in living organisms over a very long time, by which complex forms developed from simpler ancestors.
(b)(i) Lamarck: use and disuse – organs that are used a lot develop, unused ones waste away; inheritance of acquired characters – such changes are passed to offspring (e.g. the long neck of the giraffe).
(ii) Darwin: theory of natural selection – organisms produce more young than can survive; there is a struggle for existence; offspring vary; those with useful variations survive (survival of the fittest) and pass them on; over many generations this produces new species.
(c) Any three: fossil records; comparative anatomy (homologous organs, e.g. pentadactyl limb); comparative embryology; vestigial organs; geographical distribution; molecular/biochemical similarities; observed changes such as industrial melanism.
(d)(i) Mutation: a sudden change in genes or chromosomes that produces new heritable variation, the raw material on which natural selection acts.
(ii) Isolation: when groups of a species are separated (geographically, by season or by behaviour), they cannot interbreed; each group changes in its own way until they can no longer interbreed and become separate species.

Lamarck = use and disuse; Darwin = natural selection.