WAEC Biology 2003 past questions and answers

Cells in a many-celled organism are specialised and differ in shape and function (e.g. nerve, muscle and blood cells), so they are not all the same.

Ribosomes make proteins and are rich in RNA; many sit on the endoplasmic reticulum. Releasing digestive enzymes is the job of lysosomes.

Protoplasm is all the living material of the cell: the nucleus plus the cytoplasm. The cell wall and cell sap are non-living.

Bacteria are prokaryotes: their DNA lies free in the cytoplasm without a nuclear membrane around it. They do have a cell wall and a cell membrane.

Transpiration is fastest when it is hot and the air is dry. The strong transpiration pull draws the dye solution up the xylem quickly.

Rhizopus and Mucor are fungi with no chlorophyll, so they cannot make their own food; they feed saprophytically.

Egg shells are porous, so gases from rotten eggs can diffuse into fresh eggs and spoil them.

Growth is a permanent increase in dry weight (new living material), not just extra water taken in.

Growth from a zygote happens by mitosis, which makes identical body cells. Meiosis only makes gametes.

Both plants and animals respire and give off carbon dioxide as waste. Oxygen is a waste only of photosynthesis in plants, and urine only of animals.

Meristem cells are thin-walled dividing cells for growth. Sclerenchyma, collenchyma and xylem have thickened walls that support the plant.

Red blood cells contain haemoglobin, which carries oxygen. Making antibodies and destroying bacteria are jobs of white blood cells.

Alveoli are very many, thin-walled, moist and surrounded by capillaries, giving a huge surface for gases to diffuse.

The cells (and cell fragments) of blood are red cells (erythrocytes), white cells (leucocytes) and platelets. Haemoglobin is a pigment inside red cells, not a cell.

Water evaporating from the leaves pulls more water up from the roots, giving a continuous stream of water (the transpiration stream) through the plant.

The kidneys filter the blood all the time and pass out excess water as urine, more than the lungs or skin lose.

In the cold, skin blood vessels narrow to keep heat in. Dilation of skin capillaries happens in hot conditions to lose heat.

Blood cells (and large proteins) are too big to pass through the glomerulus into Bowman's capsule, so they stay in the blood.

The pituitary gland makes hormones that control many other endocrine glands, so it is called the master gland.

Blinking is a reflex controlled by the brainstem in the hind brain, not by the thinking part (cerebrum).

The pituitary gland secretes thyroid-stimulating hormone (TSH), which makes the thyroid release thyroxine.

The retina contains rods and cones, the light-sensitive cells that send impulses to the brain.

The iris changes the size of the pupil, controlling how much light gets into the eye. Focusing is done by the lens and cornea.

Placentation is the way the ovules are attached and arranged inside the ovary (e.g. marginal, axile, parietal).

Monoecious means 'one house': separate male and female flowers on the same plant, as in maize. Dioecious plants have them on different plants.

The amniotic fluid cushions the foetus against shocks and knocks. Food, oxygen and wastes pass through the placenta.

The light stage splits water, giving oxygen, and makes ATP and NADPH₂. RuBP belongs to the dark stage, where it picks up carbon dioxide.

Boiling kills the cells, stops their reactions and makes the membranes permeable so alcohol and iodine can get in. Chlorophyll is removed later by alcohol.

Vitamin D is made in the skin by the action of sunlight, not by water. Water does help cool the body, dissolves substances and is needed for many reactions.

Moulds (fungi) release enzymes onto their food, digest it outside their bodies and then absorb the products.

Vegetables are an important source of mineral salts (and vitamins) in our diet.

Good food gives energy, growth and health, but it cannot protect a person from malaria, which is caused by Plasmodium carried by mosquitoes.

Spirogyra is a green alga that makes its own food by photosynthesis, which is holophytic nutrition.

An ecosystem is the community of living things together with the non-living (physical) environment they interact with.

Ecology studies how organisms relate to one another and to their environment.

Turbidity is the cloudiness of water, so it is measured only in aquatic habitats.

Biomass falls at each step up a food chain: producers 40,000, primary consumers 3,000, secondary consumers 20, tertiary consumers 1.

Bacteria breaking down proteins in dead matter release hydrogen sulphide, the gas that gives rotting matter its bad smell.

Fish breathe with gills, which collapse and dry out in air. Without lungs a fish cannot get oxygen on land.

Pneumatophores are breathing roots that grow up out of waterlogged mud so mangrove roots can get air.

Food supply, predators and disease change birth and death rates quickly. Mutations are rare and have little direct effect on numbers.

When individuals compete for limited food and space, the best adapted ones win and survive, so competition favours the fittest.

Without gills an animal cannot take dissolved oxygen from water, so a land mammal would drown.

Tuberculosis is caused by a bacterium (Mycobacterium tuberculosis). Measles, smallpox and polio are viral.

A renewable resource can replace itself naturally, as living things that keep regenerating do.

Cutting down many trees destroys the forest; conservation means protecting, replanting and harvesting carefully.

Rhizobium bacteria in legume root nodules fix nitrogen gas into compounds the plant uses to make protein. Azotobacter lives free in the soil.

Poor sewage disposal causes bad smells and spreads diseases such as cholera and typhoid. Lack of space for wastes is not a danger it causes.

Height shows a smooth range of values between short and tall. Blood groups, sex and haemoglobin types fall into distinct groups.

Sex is either male or female with nothing in between, so it is discontinuous. Height and weight ranges are continuous.

Karl Landsteiner, who also discovered the ABO groups, worked on the Rhesus factor, and Levine (printed 'Lavine') linked it to disease in newborns. Hooke studied cells and Darwin evolution.

The nucleus holds chromosomes made of DNA and protein, and the nucleolus contains RNA.

448 : 154 is about 3 : 1. Two red parents giving some white offspring must both carry the hidden r, so both are Rr.

448 ÷ 154 ≈ 2.9, so the ratio of red to white is about 3 : 1.

A sudden change in a characteristic is caused by a mutation; here, a change in the genes of the skin's pigment cells.

When all F₁ offspring show only one parent's trait, that trait is dominant and hides the other (recessive) one.

Carriers (HbAS) resist malaria better, so in malaria areas they survive and pass the sickle gene on to their children.

Cryptic colouring, mimicry and flash colouring are protective adaptations. 'Season' is not an adaptation at all.

Darwin argued that resources are limited, causing a struggle for existence. If food were abundant there would be no competition to drive selection.

(a) A balanced diet is a meal that contains all the classes of food (carbohydrates, proteins, fats and oils, vitamins, mineral salts and water, with roughage) in the right amounts for the person's needs.
(b)(i) and (ii) Any four with an example each: carbohydrates – rice, yam, bread, garri; fats and oils – groundnut oil, palm oil, butter; vitamins – fresh fruits such as oranges, vegetables, carrots; mineral salts – vegetables, milk, table salt; water – drinking water, fruit juice.
(c)(i) Any three: growth/building new cells; repair of worn-out tissues; making enzymes; making hormones; making antibodies; source of energy when carbohydrates and fats are short.
(ii) Kwashiorkor signs: stunted growth; swollen (pot) belly; swelling (oedema) of feet and legs; thin arms and legs; cracked, peeling skin with pale patches; thin hair that turns reddish-brown; tired, unhappy look.
(d)(i) Ribosome.
(ii) Any two: pepsin; trypsin; rennin; erepsin (peptidases).

Pair each food class with a correct named example.

(a) The pollen grain absorbs sugary fluid from the stigma and germinates; a pollen tube grows out through a pore; the tube grows down the style, digesting its way and taking food from the style tissues; it carries the tube nucleus (at the tip) and the generative nucleus; the generative nucleus divides to form two male nuclei; the tube enters the ovule through the micropyle and reaches the embryo sac; the tip bursts and the tube nucleus breaks down; one male nucleus fuses with the egg cell (ovum) to form the zygote; the other fuses with the polar/definitive nucleus to form the endosperm nucleus (double fertilization).
(b) The amniotic sac holds the amniotic fluid around the embryo; it protects the embryo from shocks and injury; keeps it moist and stops it drying out; keeps its temperature steady; lets the embryo move freely and develop normally; helps prevent infection.
(c) Viral: yellow fever, poliomyelitis, measles, common cold, small pox, influenza, chicken pox.
Bacterial: typhoid, tuberculosis, tetanus, leprosy, cholera, whooping cough.
Protozoan: malaria, amoeboid dysentery, trypanosomiasis.

Describe the steps in order, from germination of the pollen grain to fusion of the gametes.

(a)(i) Respiration is the breakdown of food (e.g. glucose) in living cells, with or without oxygen, to release energy, with carbon dioxide and water (or other products) given off.
(ii) Aerobic respiration and anaerobic respiration.
(iii) Glucose → lactic acid + (a little) energy.
(b)(i) Diagram labelled: nasal cavity/nostrils, pharynx, epiglottis, larynx, trachea with cartilage rings, bronchi, bronchioles, alveoli (air sacs), lungs, pleural membranes, ribs, intercostal muscles, diaphragm.
(ii) Any two: tuberculosis; pneumonia; bronchitis; asthma; whooping cough; lung cancer; common cold/influenza.
(c)(i) Amoeba: the cell (plasma) membrane/whole body surface.
(ii) Cockroach: tracheae (tracheal system opening by spiracles).
(iii) White mangrove: pneumatophores (breathing roots) with lenticels.
(iv) Hibiscus: stomata (in the leaves) and lenticels (in the stem).

In (a)(iii) the muscle during hard exercise respires anaerobically, so the product is lactic acid.

(a)(i) A cell is the basic structural and functional unit of life: a mass of protoplasm (nucleus and cytoplasm) enclosed by a cell membrane.
(b)(i) Nucleus – structure: a round or oval body bounded by a double nuclear membrane with pores, containing chromatin (chromosomes) and a nucleolus in nucleoplasm. Function: controls all activities of the cell; carries hereditary information (genes); controls cell division.
(ii) Mitochondrion – structure: a small rod-shaped or oval organelle with a double membrane, the inner membrane folded into cristae, filled with a matrix. Function: site of aerobic respiration, where energy (ATP) is released.
(c)(i) Diagram labelled: flagellum, gullet (reservoir), eyespot (stigma), contractile vacuole, chloroplasts, nucleus, nucleolus, paramylum (starch) granules, pellicle, cytoplasm.
(ii) Animal-like (any three): has a flagellum and moves about; has a flexible pellicle, not a cellulose wall; has an eyespot; has a contractile vacuole; can feed heterotrophically (saprophytically) in the dark; has a gullet.
Plant-like (any two): has chloroplasts with chlorophyll; makes its own food by photosynthesis (holophytic); stores food as paramylum, a starch-like carbohydrate.

For each organelle give both its structure and its function.

(a) Fore brain (cerebrum, thalamus, hypothalamus); mid brain; hind brain (cerebellum, medulla oblongata).
(b)(i) Cerebrum: controls thinking, intelligence, memory, learning, speech and voluntary actions; receives and interprets sensations (sight, hearing, touch).
(ii) Hypothalamus: controls body temperature, water balance, hunger and thirst; links the nervous system with the pituitary gland.
(iii) Medulla oblongata: controls involuntary actions such as breathing rate, heartbeat, blood pressure, swallowing, coughing and sneezing.
(c)(i) Any three: shoot/stem; root; leaf; tendril; flower (e.g. petals opening).
(ii) A tactic movement is the movement of a whole organism (or a free-moving cell) from one place to another in response to a directional stimulus, towards it or away from it.
(d)(i) Phototaxis: movement of a whole organism in response to light, e.g. Euglena or Chlamydomonas swimming towards light.
(ii) Hydrotaxis: movement in response to water or moisture, e.g. woodlice or earthworms moving to damp places.
(iii) Chemotaxis: movement in response to chemicals, e.g. sperm of mosses/ferns swimming towards chemicals from the archegonium; bacteria moving towards food.

Taxis is movement of the whole organism; do not confuse it with tropism (growth of part of a plant).

(a) Any four: sharp, curved claws for gripping bark; long prehensile tail for holding branches (e.g. monkeys); opposable thumbs/toes for grasping; adhesive pads or suckers on the feet (e.g. tree frogs, geckos); long, strong limbs for climbing and swinging; skin flaps for gliding (flying squirrel); light body; good eyesight to judge distances.
(b) Any five: raw material for photosynthesis; solvent for dissolving and transporting substances; medium for chemical reactions in cells; keeps plant cells turgid for support; cools the body by sweating and transpiration; habitat for aquatic organisms; medium for fertilization (e.g. mosses, ferns, frogs); helps in seed germination and dispersal; drinking water for animals.
(c) Use a thermometer: a maximum and minimum (Six's) thermometer is left in the habitat for 24 hours; the index in each arm is reset with a magnet first; next day the highest and lowest temperatures are read from the bottom of the indices; readings are taken at the same place over several days and averages worked out; soil or water temperature can be read by placing a thermometer in it for a few minutes.
(d)(i) Any two: Charles Darwin; Jean-Baptiste Lamarck; Alfred Russel Wallace; Gregor Mendel; Hugo de Vries.
(ii) Any five: fossil records; comparative anatomy (homologous and vestigial organs); comparative embryology; geographical distribution; comparative biochemistry/serology; classification/taxonomy; cell biology (cytology); genetic evidence and artificial selection (breeding).

In (c) name the instrument and describe how the reading is taken.