WAEC Biology 2015 past questions and answers

Ascaris is a roundworm (a nematode), a many-celled animal. Amoeba, Plasmodium and Paramecium are all single-celled protozoans.

The cell membrane is built on a double layer of phospholipid molecules. Proteins sit on and in this lipid bilayer, so the lipid is in the middle and protein is on either surface.

A guard cell has a special shape and job: it opens and closes the stoma. Meristematic cells are unspecialised dividing cells, and Amoeba and Plasmodium are whole single-celled organisms.

Spirogyra is a filamentous alga with no flagella, cilia or pseudopodia. Amoeba uses pseudopodia, Volvox flagella and Paramecium cilia.

Protoplasm is all the living material of the cell: cytoplasm plus nucleus. The liquid part of the nucleus is the nucleoplasm, not the protoplasm.

The salt solution is more concentrated than the cell sap, so water leaves the cells by osmosis. The cytoplasm shrinks away from the cell wall: the cells are plasmolysed.

The transparent eyelid (I) protects the eyes under water, eyes on top of the head (II) let it see above water while hidden, and a nostril at the tip of the nose (V) lets it breathe with only the snout out.

Crocodiles are reptiles. Reptiles have a dry skin covered in scales (III) and teeth that are all alike, homodont teeth (IV).

Exhaled air carries water vapour and carbon dioxide but no salts. Sweat and urine both contain water with dissolved salts.

Growth is a permanent increase in size, usually measured as length. A young seedling has no flowers, and the length of its radicle (young root) increases steadily as it grows.

The diagrams show homologous chromosomes pairing up and separating, which happens in meiosis. Meiosis takes place only when gametes such as sperm cells are formed.

Bryophyllum produces small buds along the edges of its leaves; each bud can grow into a new plant.

The vertebra has small holes on each side of the neural canal (vertebrarterial canals) and short transverse processes, which are features of a cervical (neck) vertebra.

Part I is the neural canal, the large central hole of the vertebra. The spinal cord runs through it and is protected by it.

Each contraction of the ventricles forces blood into the arteries under high pressure, and the arteries' elastic walls recoil as the heart relaxes. This is why arterial pressure is high.

Abscisic acid (abscisin) is a growth inhibitor that keeps seeds dormant. Auxins, gibberellins and cytokinins all promote growth or germination.

Smell is sensed in the nose but interpreted in the olfactory lobes of the brain. If the nose is fine but smell is lost, the olfactory lobes must have been damaged.

Accommodation is the changing of the lens shape by the ciliary muscles so that both near and far objects are focused sharply on the retina.

In monocots the sepals and petals usually look alike (a perianth of tepals). Fibrous roots, narrow leaves and floral parts in threes are typical monocot features.

A fruit develops from the ovary, so it has two scars: one from the stalk and one from the style. A seed develops from an ovule and has only one scar, the hilum.

Green plants take in carbon (IV) oxide and use it to make sugar during photosynthesis. Burning, decay and respiration all release carbon (IV) oxide.

Boiling with dilute acid hydrolyses (breaks down) a non-reducing sugar such as sucrose into reducing sugars (glucose and fructose), which can then react with Benedict's solution.

Sodium hydroxide neutralises the acid added in step II. Benedict's solution works only in a neutral or slightly alkaline solution.

After hydrolysis there are reducing sugars, so boiling with Benedict's solution gives a brick-red (orange-red) precipitate.

The human appendix is a small blind tube with no digestive role; it does not release enzymes. The other pairs are correct.

A climax community is the final, stable stage of succession, where the kinds and numbers of organisms stay about the same for a long time.

An ecosystem is all the living things (plants, animals, decomposers) in an area together with the non-living factors around them. Only option B covers everything.

Small water bodies such as ponds and puddles can dry up in the dry season, leaving their organisms without a habitat.

Capillarity is the rising of water from below through the tiny pore spaces between soil particles. How easily water drains through soil is a different property, permeability.

Every food chain starts with a producer (a green plant), which traps the sun's energy and passes it on. The sun is the energy source but not an organism.

This is a pitcher plant. Its green leaves photosynthesise, and its pitchers trap and digest insects, so it is also carnivorous.

Part I is the jug-shaped pitcher, a modified leaf that holds digestive fluid and traps insects.

Insect-eating plants grow where the soil is poor in nitrogen. Digesting insects gives them the nitrogen they need to make proteins.

An endoparasite lives inside its host. The tapeworm lives in the intestine; fleas, ticks and aphids feed from the outside (ectoparasites).

Mosquito larvae breathe air through a siphon at the water surface. An oil film blocks the siphon, so the larvae suffocate.

Cover crops spread over the ground, shield the soil from rain splash and bind it with their roots, which reduces erosion.

The alleles for A and B are co-dominant: a person with both has blood group AB. So 'A is dominant over B' is false, while O is recessive to both A and B.

Tasting PTC, tongue rolling and ear moving are inherited traits used in genetics studies. Everyone can roll the eyeball, so it is not an inherited variation.

A group O child (OO) must get an O allele from each parent. A father with group AB has no O allele, so he cannot be the father.

All the F₁ are spotted and black reappears in the F₂ (3 spotted : 1 black), so spotted is dominant and black is recessive.

The black parent shows the recessive trait, so it is hh. All F₁ are spotted (Hh), which means the spotted parent gave H every time: it is HH.

Mendel's first law came from crossing pure tall with pure short pea plants: the pair of factors for height separate (segregate) into different gametes, so short plants reappear in the F₂.

Sex-linked genes are on the X chromosome. A male has only one X, so he cannot hide a recessive allele: he is never a carrier. Carriers are females.

Q is covered in spots like the spotted water plants, so it blends in (camouflage) and predators find it hardest to see.

Camouflage works because the animal's markings match its surroundings, so predators fail to notice it.

(a) Sexual reproduction is by conjugation between hyphae of two different mating strains (+ and −).
The two hyphae touch and each grows a short side branch (progametangium) towards the other.
A cross wall cuts off a gametangium at each tip, leaving a suspensor behind.
The walls between the gametangia dissolve and their nuclei fuse to form a zygote.
The zygote forms a thick, dark, resistant wall: the zygospore, which can survive bad conditions.
In favourable (damp) conditions the zygospore germinates into a hypha bearing a sporangium.
(b)(i) Adrenaline.
(ii) Adrenal glands (adrenal medulla), above the kidneys.
(iii) Any five: faster heartbeat; faster, deeper breathing; rise in blood pressure; liver changes glycogen to glucose, so blood sugar rises; more blood sent to skeletal muscles and less to skin and gut; pupils dilate; hair stands on end; muscles become tense; faster release of energy in respiration.
(c)(i) Any three, in a table: plants have no special excretory organs / humans have kidneys, skin, lungs and liver; plants make small amounts of waste / humans make large amounts; plants excrete slowly / humans excrete fast; plants store many wastes (tannins, resins, gums, alkaloids) in their tissues / humans remove wastes from the body; plants reuse some products (CO₂, O₂, water) / humans cannot reuse urea; plant wastes include resins, gums, latex, tannins / human wastes include urea, sweat, salts.
(ii) Any two: vacuole; mitochondrion; chloroplast.

For (c)(i) set out a two-column table and keep each row on the same point of comparison.

(a) Broad, flat lamina gives a large surface to trap light.
Thin lamina lets light and gases reach all cells quickly.
Palisade cells packed with chloroplasts lie just under the upper epidermis, at right angles to it.
Spongy mesophyll has large air spaces for gaseous exchange.
Many stomata (controlled by guard cells) let CO₂ in and O₂ out.
Transparent epidermis lets light through.
Network of veins: xylem brings water, phloem carries away sugar.
Leaf arrangement (mosaic) reduces shading.
(b) The tapeworm is a parasite in the host's intestine. It has no mouth or gut. It holds on with hooks and suckers on the scolex and absorbs already digested food through its whole body surface; its body is protected from the host's enzymes by a thick cuticle and anti-enzymes.
(c)(i) Calcium (or phosphorus). (ii) Iron. (iii) Iodine.
(d)(i) Any three: adds bulk to food; helps peristalsis; prevents constipation; helps remove waste; may reduce risk of bowel disease.
(ii) Any three: growth; repair of worn-out tissues; making enzymes and hormones; making antibodies; source of energy when carbohydrate and fat run short; forming haemoglobin.

Link each leaf feature to the job it does in photosynthesis.

(a)(i) Sewage is liquid and solid waste (faeces, urine, waste water) from homes, industries and farms carried in drains and sewers.
(ii) Any five: oxygen in the water is used up by decomposing bacteria; fish and other aquatic animals die; bad smell; water becomes dirty and unfit to drink; spreads water-borne diseases such as cholera and typhoid; nutrients cause algal bloom (eutrophication); breeding of mosquitoes and other pests; toxic chemicals poison organisms.
(b) Surface terracing: a slope is cut into a series of flat steps (terraces) across the slope. Water flows slowly from step to step instead of rushing down, so less soil is washed away and more water soaks in.
(c) Adaptation (printed 'adoption'): a feature of structure, function or behaviour that helps an organism survive and reproduce in its habitat.
(d)(i) Hydrophytes, any two: large air spaces (aerenchyma) for buoyancy and gas storage; thin or no cuticle; stomata on the upper surface of floating leaves; finely divided submerged leaves resist currents; poorly developed roots and xylem.
(ii) Xerophytes, any two: thick waxy cuticle reduces water loss; sunken stomata or few stomata; leaves reduced to spines or rolled; deep or wide-spreading roots to find water; water-storage tissue in fleshy stems or leaves.

For (d), give the feature and say how it helps the plant.

(a)(i) A test cross is a cross between an organism showing the dominant trait (unknown genotype) and a homozygous recessive organism, to find out whether the first is homozygous or heterozygous.
(ii) A monohybrid cross is a cross between parents that differ in one pair of contrasting characters (one gene), e.g. round × bean-shaped seed.
(b)(i) Parents: rr × RR; gametes: r, r and R, R; offspring: Rr, Rr, Rr, Rr. All offspring are Rr (heterozygous, round-seeded).
(ii) Bean-shaped is recessive, so a bean-shaped parent can only be rr; a heterozygous parent (Rr) is round. Treated as Rr × Rr: gametes R, r and R, r; offspring RR, Rr, Rr, rr, i.e. genotypes 1 RR : 2 Rr : 1 rr (3 round : 1 bean-shaped).
(If treated as rr × Rr: offspring 1 Rr : 1 rr.)
Each diagram must show parents, gametes, fusion (lines or a Punnett square) and offspring genotypes.

Always show parent genotypes, gametes and offspring in a genetic diagram.

(a) Kidney stone – effect: severe pain in the back/abdomen, blocked urine flow or blood in urine; remedy: drink plenty of water, drugs to dissolve the stone, or surgery/laser removal.
Nephritis – effect: kidneys fail to filter properly, protein/blood in urine, swelling (oedema), high blood pressure; remedy: antibiotics, low-salt and low-protein diet, dialysis or kidney transplant.
Diuresis – effect: passing large amounts of urine, leading to dehydration and loss of salts; remedy: drink fluids and replace salts, treat the cause (e.g. control diabetes), antidiuretic drugs.
(b) Diagram with arrows: CO₂ in the air → photosynthesis by green plants → carbon compounds in plants → feeding → animals; respiration of plants and animals → CO₂; death → decomposers (decay, respiration) → CO₂; fossil fuels → burning (combustion) → CO₂. Title and labels needed.
(c)(i) An estuary is where a river meets the sea; the water is brackish (salinity changes with the tide) and the bottom is muddy.
(ii) e.g. Phytoplankton → shrimps → tilapia/mudskipper → kingfisher (any correct chain of three or more estuarine organisms).
(d)(i) Pests, any two: locusts, aphids, weevils, stem borers, rodents, birds, nematodes. Diseases, any two: maize rust, cassava mosaic, rice blast, cocoa black pod, groundnut rosette, maize smut.
(ii) Any three: use resistant varieties; spray fungicides or other chemicals; crop rotation; remove and burn infected plants; plant clean, disease-free seeds; control insect vectors; good spacing and weeding.
(e) Any four: provide safe water; proper disposal of refuse and sewage; inspect food, markets and abattoirs; vaccination and immunisation; control of disease vectors; health education; quarantine and isolation of infectious cases; inspect houses and premises.
(f) Any four: wash hands before handling food; cover food from flies and dust; cook food well; wash fruits and vegetables; store food in clean containers or refrigerate; keep kitchens and utensils clean; food handlers should be medically checked; dispose of waste properly.

Section C (candidates in Nigeria only). Keep each table answer short: one effect and one remedy per disease.