WAEC Biology 2000 past questions and answers

Amoeba has no breathing organs; oxygen dissolved in the water diffuses straight in through its cell membrane.

The cells of a Volvox colony are joined by strands of cytoplasm and work together, so they depend on one another.

Hydra's body wall has an outer ectoderm and an inner endoderm, with jelly (mesogloea) between them.

The cell wall is a non-living layer of cellulose, not a membrane; the nucleus and vacuole are bounded by membranes, and the cell membrane is itself a membrane.

The heart is an organ made of several tissues working together; Hydra is organised only at tissue level, Euglena is a single cell and a virus is not even a cell.

Genes on the chromosomes carry the instructions that decide an organism's features such as form and shape.

Plants store carbohydrate as starch; animals store it as glycogen.

Mitochondria release energy by respiration, so cells that need much energy, like muscle cells, have many of them.

In diffusion molecules move from where they are more concentrated to where they are less concentrated, not the other way round.

Amoeba lives in water, so it can get rid of very soluble, toxic ammonia by diffusion; man excretes urea and birds uric acid.

Supporting tissues (collenchyma, sclerenchyma, xylem) give strength, rigidity and flexibility; they do not secrete.

The smaller the organism, the larger its surface compared with its volume; the tiny single-celled Amoeba has the largest ratio.

The epidermis is a protective covering, not a supporting tissue, so B is the group that includes a non-supporting part.

Decay of meat spoils food, which is harmful; the other activities are useful to man.

Each vascular bundle contains xylem, phloem and the intra-fascicular cambium between them; inter-fascicular cambium lies between the bundles, outside them.

Without enough oxygen, pyruvic acid is turned into lactic acid, which builds up in the muscles and causes fatigue and cramp.

Carbon dioxide enters through the stoma, which is controlled by the two guard cells; the labels on the guard cells and pore are I, II, V and VI.

I is a guard cell; in a strong solution it loses water, and its contents shrink away from the wall.

The guard cells are swollen with water (turgid), which bends them apart and opens the stoma.

In a hypotonic (weaker) solution the guard cells take in water by osmosis, become turgid and open the stoma.

When the erector muscles relax, hairs lie flat and trap less air, so more heat is lost; the other options keep heat in or make heat.

Fear makes the adrenal glands release adrenaline, the 'fight or flight' hormone that speeds up the heart.

Nerves that come straight from the brain are cranial nerves; spinal nerves come from the spinal cord.

Efferent (motor) neurones carry impulses from the central nervous system to effectors such as muscles and glands.

White matter is a region of the brain and spinal cord made of many axons; it is not part of a single neurone.

A reflex arc is the shortest pathway: receptor, sensory neurone, relay neurone, motor neurone, effector.

The retina contains the light-sensitive rods and cones.

After fertilisation the ovule develops into a seed, while the ovary becomes the fruit.

A legume (pod) splits open along two sides to release its seeds, so it is dehiscent.

Manganese, molybdenum and zinc are needed only in tiny amounts; sulphur, calcium, magnesium and phosphorus are macro-nutrients.

Glucose (a simple sugar) is the first carbohydrate formed in photosynthesis; it is later changed to starch for storage.

Nitrogen is built into proteins and chlorophyll and so promotes leafy growth; activating enzymes is a role of elements such as magnesium and potassium.

Magnesium is part of chlorophyll; without it leaves turn yellow (chlorosis) and growth is poor.

The chemical name of vitamin C is ascorbic acid.

Lack of vitamin C causes scurvy, with bleeding gums and slow healing of wounds.

The B vitamins, like vitamin C, dissolve in water; vitamins A, D, E and K are fat-soluble.

Vitamin E is known as the anti-sterility vitamin; lack of it affects fertility in experimental animals.

Option C has carbohydrate (yam), protein (beef, milk), fat and oil (stew) and vitamins (oranges) in sensible amounts; A and D are mostly protein and B lacks protein.

Sudan III is a red dye that dissolves in fats and oils, staining them red.

Carbohydrates are the body's main source of energy for daily activities.

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

Turbidity is the cloudiness of water; the more suspended particles, the less deep light reaches.

Spirogyra is a green alga that makes food by photosynthesis; the others are fungi.

Man and fungi such as Mucor and mushrooms cannot make their own food; the other groups include green organisms.

Spirogyra is a green alga that makes its own food; bacteria, moulds and earthworms break down dead matter.

Decomposers use up oxygen as they respire and release carbon dioxide, ammonia and heat.

In commensalism one partner benefits and the other is neither helped nor harmed.

A parasite benefits by feeding on its host, which is harmed.

The earthworm breathes through a moist skin, so it stays in its burrow by day to avoid drying out.

Trypanosomiasis (sleeping sickness) is spread by the bite of the tsetse fly.

Covering food keeps out germs, dust and flies that carry disease.

Bush burning destroys plants, animals and soil organic matter; the others protect or manage resources.

Mineral deposits took millions of years to form and cannot be replaced once used up.

A recessive character is hidden by the dominant one in the F1 and reappears in a quarter of the F2.

Lamarck's theory said organs that are used develop and unused ones waste away.

Mendel's second law (independent assortment) says each pair of factors is passed on independently of the other pair.

Fingerprints are classed as arches, loops and whorls (and compound); 'contour' is not a fingerprint type.

Group O plasma has both anti-A and anti-B antibodies, so a group O person can safely receive only group O blood.

(a) A sense organ is an organ with receptor cells that detect a particular stimulus (e.g. light, sound) and send impulses to the brain.
(b)(i) Hearing; balance (maintaining posture).
(ii) Hearing: sound waves enter the outer ear and make the eardrum vibrate; the ossicles (malleus, incus, stapes) pass and amplify the vibrations to the oval window; this sets the fluid in the cochlea vibrating, which stimulates sensory hair cells; impulses travel along the auditory nerve to the brain, which interprets the sound.
OR Balance: movement of the head moves the fluid (endolymph) in the semicircular canals, utriculus and sacculus; this bends sensory hairs in the ampullae, which send impulses through the auditory nerve to the cerebellum, which keeps the body balanced.
(c) Diagram 1: light rays from a distant object focused in front of the retina because the eyeball is too long (or the lens too thick/curved). Diagram 2: a concave (diverging) lens placed in front of the eye spreads the rays so they focus on the retina. Labels: eye lens, retina, point of focus, concave lens, light rays; title and neat labelling.

Short sight: image in front of the retina, corrected with a concave lens.

(a) Any five with example: stem cuttings – cassava, sugarcane; grafting – citrus, mango; budding – citrus, rubber; layering (marcotting) – hibiscus, cocoa; suckers – banana, plantain; tubers – yam (stem tuber), sweet potato (root tuber); rhizomes – ginger; corms – cocoyam; bulbs – onion; runners/stolons – grass; leaves – Bryophyllum.
(b)(i) Advantages (any five): offspring are exactly like the parent, so good qualities are kept; plants mature and yield faster; no need for pollination or seeds; useful for plants that produce few or no viable seeds; the food store in the organ helps young plants survive; a quick way to get many plants.
(ii) Disadvantages (any five): no variation, so no new better varieties; diseases of the parent are passed on; overcrowding near the parent and competition; propagating materials are bulky to store and carry; they may not keep long (rot); poor adaptation to changing environments.

Pair each method with a crop example.

(a) Proteins; fats and oils (lipids); vitamins; mineral salts; water; (roughage).
(b) Glucose is a simple sugar that needs no digestion; it is absorbed directly into the blood and quickly respired to release energy. Corn meal contains starch, which must first be digested to glucose, so its energy is released slowly.
(c) Put a little of the food (or a few cm³ of its solution) in a test tube or on a tile; add a few drops of iodine solution; a blue-black colour shows that starch is present (the iodine stays brown if starch is absent).

Glucose = quick energy because no digestion is needed.

(a)(i) Cell; tissue; organ; system (organ system). (Organism may also be named.)
(ii) Any two: cell – the basic unit of life that can carry out all life processes, e.g. Amoeba; tissue – a group of similar cells doing the same job, e.g. xylem, epithelium; organ – several tissues working together for a function, e.g. heart, leaf; system – several organs working together, e.g. digestive system.
(iii) Euglena – cell level; onion bulb – organ level; blood – tissue level.
(b) Any four: division of labour – each part specialises and works more efficiently; organisms can grow larger; better adaptation to many environments; cells can specialise (e.g. nerve, muscle); body is less affected by small changes outside (internal environment controlled); injury to some cells is not fatal; longer life span.
(c)(i) Amoeba can live on its own and carry out all life processes, while a lizard's cell cannot survive alone (it is specialised).
(ii) Any two: Amoeba is a complete organism; it has a large surface area to volume ratio for diffusion of food, gases and wastes; it is not specialised, so it feeds, respires, excretes and reproduces by itself; a lizard cell depends on other cells/tissues for food and removal of waste.

Cell → tissue → organ → system → organism.

(a) Annotated diagram showing: water evaporates from seas, rivers and soil (sun's heat); transpiration from plants and respiration/sweating of animals add water vapour; vapour rises, cools and condenses into clouds; precipitation as rain, snow or hail; water runs off into rivers and seas, or soaks into the soil (infiltration) to form ground water, which is absorbed by roots; arrows linking each step in a cycle.
(b) Any: main part of protoplasm; solvent in which reactions take place; raw material for photosynthesis; medium of transport (blood, sap); keeps body temperature steady (sweating, transpiration); keeps plant cells turgid for support; habitat for aquatic organisms; needed for germination; medium for fertilisation in some organisms; removes wastes (urine); lubrication (synovial fluid, mucus).

In (a) use labelled arrows only, as the question asks for a diagram.

(a) Osmosis is the movement of water molecules from a dilute solution (high water concentration) to a more concentrated solution (low water concentration) through a semi-permeable membrane.
(b) Place a leafy shoot (e.g. Balsam) or uprooted seedling with its roots in water coloured with eosin (red dye) for a few hours. Cut transverse sections of the stem/root and look at them under a microscope (or hand lens). Only the xylem vessels are stained red, showing that water moves up through the xylem. (A control in plain water shows no stain.)
(c)(i) Water enters the red blood cell by osmosis because the solution outside is more dilute than its cytoplasm; the cell swells and, having no cell wall, bursts (haemolysis), releasing haemoglobin.
(ii) Any three: placing red cells in a hypotonic solution or distilled water; some snake venoms; malaria parasites; incompatible blood transfusion; some bacterial toxins/chemicals; sickle-cell crisis.

Red cells have no wall, so in a weak solution they burst.