WAEC Biology 2013 past questions and answers

The lower the level, the more alike the members; species is the lowest of these levels.

Spirogyra cells are joined end to end in a thread called a filament; the diagram shows a cell in the filament with its neighbours.

In Spirogyra the pyrenoids are small round bodies that store starch along the spiral, ribbon-shaped chloroplast.

Its cells are connected to one another, so they work together as one organism rather than as separate single cells.

Scales on the skin plus a backbone point to a reptile such as the lizard; toads have bare skin and rats and bats have fur.

Water enters the guard cells by osmosis, they become turgid and curve apart, opening the stoma.

The shoot tip makes auxin, which causes cells below it to elongate. Auxin from the agar block replaces it, so growth continues as normal.

Without oxygen glucose is only partly broken down, giving 2 ATP instead of about 38.

Plasma is the liquid part of blood; chitin, cartilage and bone form skeletons.

The right ventricle pumps blood to the lungs through the pulmonary artery; the aorta leaves the left ventricle.

An adult toad has no gills; it exchanges gases through its moist skin, the lining of its mouth and its lungs.

Air enters an insect's tracheal system through small openings along its body called spiracles.

The diaphragm is a sheet of muscle (with tendon), not epithelium; it separates the thorax from the abdomen and helps breathing.

Small molecules like glucose pass into the filtrate; large proteins (fibrinogen, albumin) and cells stay in the blood.

The loop of Henle pumps salt into the medulla, making the tissue around the collecting ducts very salty. Water is then drawn out of the urine, so the urine passed is hypertonic.

Homeostasis is keeping conditions inside the body, such as temperature and water content, steady.

Blood is filtered under pressure from the glomerulus into the Bowman's capsule.

ADH makes the kidney keep water. After drinking a lot of water the blood is dilute, so ADH output falls and a large volume of dilute urine is passed.

Petals attract insects; a wind-pollinated flower does not need them and they are often small or absent.

After a pollen grain lands on the stigma, it germinates and grows a pollen tube down through the style to the ovule.

III is the tube running down the middle (pollen tube) and IV is the stalk tissue around it (style).

I points to the integument around the ovule, which becomes the seed coat (testa); stigma, style and ovary wall do not become part of the seed.

Magnification makes things look bigger; resolution decides how much detail you see, i.e. whether two close objects appear separate.

Photosynthesis uses light energy to make glucose from carbon dioxide and water.

Xylem vessels are long, narrow, hollow tubes joined end to end with no cross walls, so water flows up easily.

A larger exposed surface relative to volume means more surface from which water can evaporate.

Hexokinase adds a phosphate from ATP to glucose, forming glucose-6-phosphate.

Fats give about twice as much energy per gram as carbohydrates and proteins; water gives none.

Glucose is a simple sugar (monosaccharide); glycogen, cellulose and starch are polysaccharides.

An epiphyte grows on another plant only for support, making its own food; a fern on a palm tree does this. Mistletoe is a parasite.

Bird I has a long, thin, curved beak for reaching into flowers to suck nectar, like a sunbird.

Bird II has a short, thick, strong beak for cracking seeds.

Carrying capacity is the largest population the food, water and space of an area can support for a long time.

Phytoplankton are tiny floating plants and algae that photosynthesise; they start aquatic food chains.

The frog's hind feet are more fully webbed, giving a larger paddle to push against the water.

Denitrifying bacteria (common in waterlogged soil) break nitrates down to nitrogen gas, which escapes to the air.

You count (take a census of) the organisms at each trophic level and draw bars in proportion.

A vaccine makes the body produce antibodies and memory cells, so it can fight the real germ quickly later.

Both benefit: the bacteria get food and shelter, and the plant gets fixed nitrogen.

Ascaris is a nematode, the human intestinal roundworm.

Pests are animals that damage crops (birds, nematodes, rodents); bacteria cause plant diseases and are called pathogens.

A tapeworm lives in already-digested food in the host's gut and absorbs it through its body surface, so it needs no gut.

Wild animals bring tourists, food and income, but they do not increase rainfall.

Keeping and breeding endangered animals in zoos protects them until numbers recover.

Genes that lie close together on the same chromosome are usually passed on together; this is called linkage.

A group O child needs an O allele from each parent; an AB father has no O allele, so the chance is 0%.

If the baby is Rh-positive, the mother can make anti-Rh antibodies that destroy the red cells of later babies, which can cause stillbirth.

Mendel's law of segregation says the two alleles separate into different gametes, giving 1 AA : 2 Aa : 1 aa when hybrids are crossed.

Genes carried on the sex (X) chromosome are called sex-linked genes.

The boy is OO, so the father must carry an O allele; of the choices only AO has one.

X^hY × X^HX^h gives X^HX^h, X^hX^h, X^HY and X^hY; two of the four (50%) are haemophilic.

The Rhesus factor matters for the health of future babies, so it is checked before marriage (with genotype and blood group).

The centrosome (with its centrioles) organises the spindle during animal cell division; the other structures are present all the time.

Drones are the male bees; their only job is to mate with the queen.

A chameleon changes colour to match its surroundings, so predators do not notice it.

Lamarck proposed an early theory of evolution (use and disuse); Mendel and Morgan worked on genetics and Pasteur on microbes.

Unrelated organisms facing similar conditions evolve similar features; this is convergent evolution.

(a)(i) Respiration is the breakdown (oxidation) of food, mainly glucose, in living cells to release energy as ATP, with or without oxygen.
(ii) Table — Gaseous exchange: physical process / Aerobic respiration: chemical process; takes place at respiratory surfaces (outside cells) / inside cells (mitochondria); no energy released / energy released; no enzymes needed / enzymes needed; O₂ taken in and CO₂ given out / O₂ used to oxidise glucose and CO₂ and water produced.
(b)(i) Residual air is the volume of air (about 1.5 litres) that remains in the lungs even after the deepest possible breathing out.
(ii) It keeps the alveoli from collapsing; allows gaseous exchange to continue between breaths; mixes with fresh air.
(c) Any four: large surface area; thin walls (short diffusion distance); moist surface; rich blood supply (capillaries); well ventilated.
(d)(i) Oxygen debt is the extra oxygen needed after vigorous exercise to oxidise the lactic acid built up in muscles during anaerobic respiration.
(ii) Any three: sprinting/running a race; lifting heavy weights; climbing stairs or hills quickly; swimming fast; prolonged strenuous work or games.

Use a ruled table with matching rows in (a)(ii).

(a) Photosynthesis is the process by which green plants make glucose from carbon dioxide and water using light energy trapped by chlorophyll, releasing oxygen.
(b)(i) External (any four): light intensity; carbon dioxide concentration; temperature; water supply; mineral salts (e.g. Mg). (ii) Internal (any two): amount of chlorophyll; number/structure of stomata; enzymes; leaf structure/thickness; accumulation of end products.
(c)(i) ATP; NADPH₂ (reduced NADP/hydrogen); oxygen.
(ii) ATP supplies energy for the dark (light-independent) stage; NADPH₂ supplies hydrogen to reduce CO₂ to carbohydrate; oxygen is released for respiration (by-product).
(d)(i) Light does not reach the deep water, so plants there cannot photosynthesise and cannot survive.
(ii) Decomposers break down dead matter and release mineral salts (e.g. nitrates) into the soil, which plants absorb for growth.

Light-stage products power the dark stage.

(a)(i) Ecological succession is the gradual, orderly change in the species making up a community over time, until a stable climax community is reached.
(ii) Pioneer organisms such as lichens, algae and mosses colonise the bare ground; they break down rock and add humus, forming thin soil; grasses and herbs then grow, followed by small animals (insects, worms); shrubs replace them and shade out the grasses; larger animals (lizards, rats, birds) arrive; finally trees grow and a stable climax community (e.g. forest) is reached.
(b)(i) Biosphere: the part of the earth (land, water, air) where life exists.
(ii) Population: all the organisms of one species living in an area at a given time.
(iii) Community: all the populations of different species living and interacting in one area.
(iv) Ecosystem: a community of organisms together with its non-living environment, interacting as a unit.
(c)(i) Hygrometer (wet-and-dry bulb thermometer); (ii) anemometer.

Name the stages of succession in order, from pioneers to climax.

(a)(i) Conservation is the protection, preservation and wise management of natural resources so they last and remain available for the future.
(ii) Any six: uncontrolled hunting/poaching; deforestation and destruction of habitats; bush burning; pollution of land and water; urbanisation and road building; overgrazing; drought and desertification; introduction of alien species; diseases.
(b) Any six: establish game reserves and national parks; pass and enforce laws against poaching; ban or control bush burning; afforestation; licensing and closed seasons for hunting; public education on wildlife; zoos and captive breeding; control of pollution; employ game wardens.
(c)(i) Eutrophication is the over-enrichment of a water body with nutrients (nitrates, phosphates), causing rapid growth of algae (algal bloom); when they die, decomposers use up the oxygen and fish and other organisms die.
(ii) Any two: run-off of fertilisers from farms; discharge of sewage; detergents (phosphates) in waste water; animal wastes.

For (c) describe the chain: nutrients → algal bloom → decay → oxygen loss.

(a) Carbon dioxide in the air is taken in by green plants and made into carbohydrates by photosynthesis; animals obtain carbon compounds by eating plants or other animals; plants and animals release CO₂ back to the air by respiration; when they die, decomposers (bacteria and fungi) break them down, releasing CO₂; some remains form fossil fuels (coal, oil), which release CO₂ when burnt; volcanic eruption also releases CO₂; carbon dioxide dissolves in water and forms carbonates (limestone).
(b)(i) Nitrogen-fixing bacteria (Rhizobium, Azotobacter) convert atmospheric nitrogen into nitrogen compounds that plants can use.
(ii) Nitrifying bacteria convert ammonium compounds to nitrites (Nitrosomonas) and nitrites to nitrates (Nitrobacter), which plants absorb.
(iii) Denitrifying bacteria (e.g. Pseudomonas) convert nitrates back to free nitrogen gas, returning it to the atmosphere.

A labelled cycle diagram can support the description in (a).

(a)(i) Excretion is the removal from the body of waste products of metabolism (e.g. urea, CO₂, excess water and salts) that would be harmful if they built up.
(ii) Kidney — urea/urine; skin — sweat (water and salts); lungs — carbon dioxide and water vapour; liver — bile pigments.
(b) Blood enters the kidney through the renal artery; in the glomerulus it is filtered under high pressure (ultrafiltration) into the Bowman's capsule, giving a filtrate of water, glucose, salts and urea; in the tubules, useful substances (all glucose, amino acids, much water and salts) are selectively reabsorbed into the blood; more water is reabsorbed in the loop of Henle, distal tubule and collecting duct (controlled by ADH); the remaining fluid (urine: water, urea, salts) passes down the ureter to the bladder; purified blood leaves through the renal vein.
(c)(i) Malpighian tubules; (ii) nephridia.

Describe the kidney's work in three steps: filtration, reabsorption, then urine leaving.