WAEC Biology 2020 past questions and answers

Every living cell, plant or animal, has cytoplasm and a nucleus (protoplasm). Cell walls and large vacuoles are found only in plant cells.

Crustaceans (crabs, prawns, shrimps, water fleas) mostly live in water and breathe with gills. Insects, spiders and centipedes are mainly land animals.

Crustaceans have two pairs of antennae. Insects and centipedes have one pair, and arachnids have none.

Each Spirogyra cell has ribbon-shaped chloroplasts coiled in a spiral, and its nucleus hangs in the middle of the vacuole on cytoplasmic strands.

The organ is an onion bulb. Food is stored in the thick, fleshy scale leaves (II) inside it.

It has a short flat stem at the base, layers of fleshy leaves and adventitious roots below: an onion bulb.

Part I is the thin, dry outer covering of the bulb. It is a scale leaf that protects the fleshy leaves inside.

Cellophane is a man-made (non-living) membrane. Pig's bladder, pawpaw and yam tissue come from living organisms.

Yeast can respire anaerobically (fermentation), so it gets energy even without oxygen. The mould needs oxygen and died.

Collenchyma and lignified xylem give mechanical support, and parenchyma supports herbaceous plants when its cells are turgid. Phloem carries food and is not a supporting tissue.

This is a potometer. The air bubble moves as the cut shoot draws water from the tube, so what is measured directly is the rate of water uptake. Transpiration is estimated from it.

By timing the bubble with the same shoot in still air, wind, light or heat, one can compare how fast the shoot transpires under each condition.

Insects such as the cockroach breathe through a system of air tubes, the tracheae, which open at spiracles.

Reptiles, birds and insects excrete nitrogen as uric acid, a nearly dry paste that saves water.

Endocrine glands are ductless: they release hormones straight into the blood. Glands that pour secretions into ducts are exocrine glands.

The cerebellum controls balance, posture and the smooth coordination of muscles without our thinking about it. The cerebrum controls conscious, voluntary actions.

Contraction of the ciliary muscles slackens the suspensory ligaments, so the elastic lens becomes rounder (more convex). This is how the eye focuses on near objects.

Part I is the long style. The pollen tube grows down through it, carrying the male gametes to the ovary.

Part II is the swollen base of the pistil, the ovary, formed here by fused carpels. The feathery branches at the top are the stigmas.

Carbon (IV) oxide turns clear lime water milky.

Oxygen is more concentrated inside the leaf than outside, so it moves out through the stomata by diffusion.

Photosynthesis first produces simple sugar (glucose). The glucose is later changed into starch for storage or sucrose for transport.

Trace elements (micronutrients) are needed in tiny amounts; copper is one. Potassium, calcium and magnesium are macronutrients needed in larger amounts.

Enzymes are specific: a protease acts only on proteins, so it leaves the starch unchanged.

In mutualism both partners gain, while in parasitism the parasite gains and the host is harmed.

Habitat W has plankton, water fleas, tilapia and frogs, which are freshwater organisms. It is a pond.

Plankton, water fleas and tilapia live only in water, so the organisms show that habitat W is aquatic.

There are many more antelopes (51) than lions (6). Predators are usually fewer than their prey, so the lion is the predator.

The instrument is a rain gauge, which measures rainfall. Too much rain causes flooding, which is harmful.

A rain gauge is set in open ground with its funnel a little above the soil, so it catches rain but not water splashing up from the ground.

Clay particles are the smallest of all soil particles, smaller than silt, sand or gravel, so clay soil has the finest texture.

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

The ozone layer absorbs most of the sun's ultraviolet rays. When it thins, more ultraviolet reaches the ground.

Honeybees give honey and pollinate crops but can sting. Termites recycle dead plant matter and aerate soil but damage wood and crops.

Weevils bore into stored grains such as maize and beans and eat them.

Conservation protects species from dying out; it does not threaten their survival.

Banning products made from leopard skin protects leopards, which are wild animals. This conserves wildlife.

Group AB blood has no anti-A or anti-B antibodies, so it accepts blood of any group: AB is the universal recipient.

In continuous variation, such as height, there is a smooth range of values from the smallest to the largest with many in-between.

Height and weight change gradually from one person to the next, with no clear groups, so they show continuous variation.

Sickle cell anaemia is caused by a faulty gene passed from parents to children. The other diseases are caused by germs.

Plant A (YYrr) makes only Yr gametes and plant B (yyRR) makes only yR gametes. Every F₁ plant is therefore YyRr: high yield and high resistance.

Pollen from one plant fertilised the ovules of a different plant (A × B). This is cross fertilisation.

DNA polymerase joins nucleotides to build the new DNA strands. Ptyalin, pepsin and amylase are digestive enzymes.

Charles Darwin (with Alfred Wallace) proposed evolution by natural selection. Lamarck proposed use and disuse.

Swarming termites are soft, slow fliers and easy food. Flying at night protects them from birds and other daytime predators.

(a) Balance is controlled by the inner ear: the three semicircular canals (at right angles to each other, one for each plane) and the utriculus and sacculus are filled with endolymph. When the head moves, the endolymph moves and bends the sensory hair cells in the ampullae (or the otoliths in the utriculus/sacculus shift with gravity). The hair cells send impulses along the auditory (vestibular) nerve to the cerebellum, which interprets them and sends impulses to muscles to keep the body balanced.
(b)(i) Drawing 8–10 cm with title and labels: pinna, external auditory meatus, tympanum (eardrum), malleus, incus, stapes, oval window, round window, Eustachian tube, semicircular canals with ampullae, utriculus, sacculus, cochlea, auditory nerve; outer, middle and inner ear marked.
(ii) The middle ear is an air-filled cavity in the skull bone between the eardrum and the inner ear; it contains three small bones (ossicles): malleus (hammer) attached to the eardrum, incus (anvil) and stapes (stirrup) fitting into the oval window; they are linked to one another and pass and amplify vibrations; the Eustachian tube connects the middle ear to the throat (pharynx) and keeps air pressure equal on both sides of the eardrum; the round window is also on its inner wall.

Name the semicircular canals, endolymph and hair cells and say how they detect movement.

(a)(i) A deficiency disease is a disease caused by lack of (or too little of) a particular nutrient, such as a vitamin, mineral or protein, in the diet.
(ii) Any five, each with its remedy: kwashiorkor – eat protein-rich food (beans, eggs, fish, meat); marasmus – enough protein and energy foods; rickets – vitamin D and calcium (milk, eggs, sunshine); scurvy – vitamin C (oranges, fresh fruit and vegetables); beriberi – vitamin B₁ (unpolished rice, whole grains); night blindness – vitamin A (carrots, palm oil, liver); anaemia – iron (liver, green vegetables); goitre – iodine (iodised salt, sea food); pellagra – niacin (vitamin B₃).
(b)(i) Peel and cut a slice of yam (or mash some in water); add a few drops of iodine solution; a blue-black colour shows starch is present.
(ii) Squeeze some orange juice into a test tube; add an equal volume of Benedict's solution (or Fehling's A and B); heat in a water bath; a colour change from blue to green, yellow and finally brick-red (orange-red precipitate) shows glucose (reducing sugar) is present.

For each test say what is added, what is done, what is seen and what it shows.

(a) Cholera – causative organism: Vibrio cholerae (bacterium); vector: none (spread by contaminated water/food, houseflies can carry it); control: boil or treat drinking water, good sanitation, wash hands, cover food, vaccination.
Sleeping sickness (trypanosomiasis) – Trypanosoma; vector: tsetse fly; control: clear bushes where tsetse flies breed, use insecticides and traps, treat patients.
Malaria – Plasmodium; vector: female Anopheles mosquito; control: sleep under treated nets, clear stagnant water and bushes, spray insecticides, take antimalarial drugs.
Ringworm – a fungus (e.g. Tinea/Trichophyton); vector: none (spread by contact and shared items); control: personal hygiene, avoid sharing combs, towels and clothes, antifungal creams.
(b)(i) Salting: salt draws water out of the food and out of microorganisms by osmosis; without water, bacteria and fungi cannot grow, so the food does not rot.
(ii) Irradiation: exposing food to radiation (e.g. gamma rays) kills microorganisms and insects in it, and slows ripening or sprouting.
(iii) Smoking: heat dries the food (removes water) and the chemicals in smoke kill or stop the growth of microorganisms.

In the table fill each blank cell; give the scientific name of each organism.

(a)(i) Independent assortment (Mendel's second law): when gametes form, the alleles of one gene separate into the gametes independently of the alleles of another gene (on a different chromosome), so all combinations of the alleles are equally likely in the gametes.
(ii) The allele for O is recessive to both A and B. A person shows group O only when both alleles are O (OO). The A and B alleles are dominant over O, so group A can be AA or AO and group B can be BB or BO.
(b) In evolutionary order, each with one example: Pisces (fish) – tilapia; Amphibia – toad/frog; Reptilia – lizard/snake/crocodile; Aves (birds) – domestic fowl/pigeon; Mammalia – human/goat/rat.

List the five classes from the oldest (fish) to the most recent (mammals).

(a)(i) External fertilisation: the male and female gametes are released into water and fuse outside the female's body.
(ii) Internal fertilisation: the male places sperm inside the female's body and the gametes fuse inside her reproductive tract.
(b)(i) External, any two: fishes (bony fish such as tilapia), amphibians (toads, frogs).
(ii) Internal, any two: mammals, birds, reptiles, insects.
(c)(i) Any three: the foetus will not get oxygen; it will not get food (nutrients); its wastes (CO₂, urea) will not be removed; it will lose protection by maternal antibodies; it may die (miscarriage/stillbirth); bleeding.
(ii) Any three: umbilical cord; amnion (amniotic sac) with amniotic fluid; chorion; thick, blood-rich uterine wall (endometrium); muscular uterine wall.
(d) Producers make food, consumers eat producers and other consumers, and decomposers return nutrients to the soil; predators keep prey numbers in check and prey numbers limit predators; materials such as carbon, nitrogen and water are cycled. These feeding relationships and cycles keep population sizes and materials fairly steady over time, which is dynamic equilibrium.
(e) Any four: drying out (desiccation) when the tide goes out; changes in temperature; changes in salinity; strong wave action that can wash them away; predators from land and sea at different tides; changes in oxygen supply; strong sunlight.
(f)(i) Moisture: water activates the enzymes in the seed, softens the seed coat and dissolves stored food so it can move to the growing embryo.
(ii) Viable seed: only a seed with a living embryo can respire and grow; a dead (non-viable) seed cannot germinate whatever the conditions.
(g) Light supplies the energy for photosynthesis. When light is weak (or absent), the rate of photosynthesis is held back even if CO₂, water and temperature are favourable, so the factor in shortest supply (light) limits how much food autotrophs can make.

Section C (candidates in Nigeria only). Answer every lettered part briefly.