WAEC Biology 2007 past questions and answers

A stimulus is any change in the surroundings that an organism can detect; its reaction to it is the response.

A species is a group of organisms that can breed together and produce fertile young.

Pollination within the same flower (or another flower on the same plant) is self pollination.

Chromosomes, which carry the genes (DNA), are found in the nucleus.

Respiration breaks down food in cells to release the energy the cell needs for its activities.

The endoplasmic reticulum is a network of channels that carries materials such as proteins through the cytoplasm.

Water enters by osmosis, but the strong cell wall stops the plant cell from bursting, so it becomes firm (turgid).

Yeast ferments the sugar in the dough and gives off carbon dioxide gas, which makes the dough rise.

Growth comes from mitosis, cell enlargement and differentiation; meiosis only produces gametes or spores.

In conjugation the contents of two Spirogyra cells (gametes) fuse to form a zygospore, which is sexual reproduction.

The coarse adjustment focuses at low power; the fine adjustment makes the small, careful changes needed under high power.

White blood cells are larger than red cells and have a nucleus; red cells carry oxygen and platelets help clotting.

Blood in veins is under low pressure, so veins have valves to stop it flowing backwards.

The malpighian body (renal corpuscle) is the glomerulus, a knot of capillaries, together with the Bowman's capsule around it.

Glucose in urine is a sign of diabetes, caused when the pancreas does not make enough insulin.

The pituitary, the 'master gland', is joined to the hypothalamus of the brain and makes hormones that control other glands.

Insulin is made by the islets of Langerhans in the pancreas.

The cell body is not always at the end: in a sensory neurone it lies to one side, part way along the fibre.

Fine branches from the cell body are dendrites; the larger branch they come from is a dendron.

Afferent (sensory) neurones carry impulses from receptors towards the central nervous system.

Melanin, the dark pigment in the skin, absorbs ultra-violet rays and shields deeper cells.

Tilapia guards its young and even shelters eggs and fry in its mouth; toads, cockroaches and snails abandon their eggs.

Most ATP is made during aerobic respiration in the mitochondria, the 'powerhouse' of the cell.

Hot alcohol dissolves out the chlorophyll so that the blue-black iodine colour can be seen clearly.

Green plants make their own food by photosynthesis, which is autotrophic nutrition.

Magnesium is part of the chlorophyll molecule and iron is needed to make it; lack of either causes yellow leaves (chlorosis).

Biuret reagent turns purple or violet when protein is present.

Boiling with acid breaks sucrose into glucose and fructose, which are reducing sugars that then react with Fehling's or Benedict's solution.

Iodine solution turns blue-black when starch is present.

Inhibitors are substances that slow down or stop enzyme action.

Amylases, proteases and lipases are whole classes of digestive enzymes; sucrase is one particular enzyme.

Boiling destroys the amylase in saliva, so the starch stays unchanged (X); fresh saliva digests starch to maltose (Y).

Sucrase digests the sugar sucrose; pepsin, trypsin and erepsin all digest proteins or peptides.

Plasmodium, the malaria parasite, lives and feeds inside human liver and red blood cells.

Plant food is hard to digest, so herbivores like tadpoles have a long, coiled intestine.

A community is all the populations of plants and animals living in one area and interacting with one another.

Phytoplankton are tiny floating green plants and algae that photosynthesise, so they are the producers.

An anemometer has spinning cups whose rate of turning shows the wind speed.

At each level much energy is lost: some parts are not eaten or digested, and much is used in respiration and lost as heat.

Producers are at the base of the energy pyramid and hold far more energy than any consumer level, so the largest value fits.

Aircraft taking off and landing make very loud noise, so noise pollution is the main problem near airports.

CFCs from old fridges and aerosol sprays break down ozone in the upper atmosphere, thinning the ozone layer.

On dry bare ground, hardy xerophytes come first, then shrubs as soil builds up, and finally mesophytic trees form the climax.

The numbers rise sharply, overshoot what the environment can support and then crash, so the graph rises and falls like a bell.

Measles is caused by a virus, and antibiotics act only on bacteria.

The tsetse fly carries Trypanosoma, the parasite of sleeping sickness, from person to person when it bites.

Rhizobium lives in the root nodules of legumes and fixes nitrogen; Azotobacter is free-living.

Endangered species are at risk of extinction, so they must be protected.

Air is present everywhere and cannot be stored or managed like minerals, soil and water, so it is the one not normally listed as conservable.

Conservation aims to protect all species; deliberately wiping some out goes against it.

Body weight shows continuous variation; most people are near the average, giving a bell-shaped normal curve.

Short offspring (tt) need a t allele from each parent, so both tall parents must be heterozygous, Tt.

A dominant character shows itself even when the contrasting (recessive) allele is present.

An O child is possible only if the man is AO; then AO × OO gives AO and OO in equal numbers, so the chance is 50%.

The woman (AA) gives only the normal allele, so every child is Aa: a carrier but normally pigmented.

Only the red colour shows in the offspring, so red is dominant over white.

A sickle cell carrier (HbAS) shows a mild form of the condition (sickle cell trait), so neither allele fully hides the other.

Survival of the fittest is part of Darwin's theory of natural selection.

Soldier termites have big heads and strong mandibles for defending the colony.

(a) Tropic vs nastic: growth movement vs not a growth movement (turgor change); response to a one-sided (directional) stimulus vs response to a diffuse (non-directional) stimulus; direction depends on the stimulus (positive or negative) vs direction does not; slow vs fast; not reversible vs reversible; e.g. shoot bending to light vs closing of Mimosa leaves.
(b) Auxin (IAA) is made at the shoot and root tips.
One-sided light causes auxin to move to the shaded side.
In the stem, the high auxin makes cells on the shaded side grow faster, so the stem bends towards light (positive phototropism).
In the root, high auxin slows growth, so the shaded side grows less and the root bends away from light (negative phototropism).
(c) Auxin collects on the lower side of root and shoot due to gravity; the shoot tip curves upwards (negative geotropism) and the root tip curves downwards (positive geotropism).
(d) Any five: produces growth hormone; stimulates the thyroid (TSH); stimulates the adrenal cortex (ACTH); FSH and LH control the ovaries and testes; prolactin starts milk production; oxytocin causes contraction of the uterus during birth; ADH controls water reabsorption in the kidney; controls other endocrine glands (master gland).
(e) Any two: plants grow at meristems (tips) only, animals grow all over; plant growth is indefinite (throughout life), animal growth stops at maturity; plants can grow by secondary thickening, animals cannot; plant growth is towards stimuli (tropic) in parts.

Mention auxin redistribution in (b) and (c).

(a) A balanced diet is one that contains all the classes of food in the right amounts and proportions for the body's needs.
(b) Classes: carbohydrates, proteins, fats and oils, vitamins, mineral salts, water (and roughage).
Any two: carbohydrates – main source of energy; proteins – growth and repair of tissues, making enzymes and hormones; fats – energy store, insulation; vitamins – prevent deficiency diseases, help body processes; minerals – build bones and teeth (calcium), make haemoglobin (iron); water – solvent, transport, temperature control; roughage – prevents constipation.
(c) Ptyalin: source – salivary glands (saliva); substrate – starch; product – maltose.
Pepsin: source – gastric glands of stomach; substrate – proteins; product – peptones/polypeptides.
Lipase: source – pancreas (pancreatic juice) and intestinal glands; substrate – fats and oils; product – fatty acids and glycerol.

Use a table with source, substrate, product columns.

(a)(i) A gene is a unit of inheritance, a section of DNA on a chromosome that controls a particular characteristic and is passed from parents to offspring.
(ii) A gene mutation is a sudden, permanent change in the structure of a gene (its DNA), which may be inherited.
(b)(i) Mitosis – plants: root tip, shoot tip (apical meristem), cambium; animals: skin (Malpighian layer), bone marrow, wounded tissue, embryo.
(ii) Meiosis – plants: anthers, ovules (ovary); animals: testes, ovaries.
(c) Any four: higher milk yield; more and better meat; faster growth/early maturity; resistance to disease; tolerance of heat or poor feed; increased fertility; hybrid vigour.
(d) Any three: genetic counselling of couples (e.g. sickle cell); prevention of hereditary diseases; blood transfusion matching (blood groups); settling disputed paternity (blood groups, DNA tests); organ transplant matching; gene therapy; production of drugs such as insulin by genetic engineering.

Name actual organs for (b).

(a)(i) Pollution is the release of harmful substances or energy into the environment in amounts that damage living things or make the environment unpleasant or unsafe.
(ii) Any four: crude oil; sewage; industrial wastes/chemicals (heavy metals such as lead, mercury); fertilizers; pesticides/herbicides; hot water (thermal pollution); detergents; refuse/plastics.
(b) Effects (to match the pollutants named): oil – forms a film that stops oxygen dissolving, clogs gills and feathers, poisons organisms; sewage – decomposers use up oxygen so fish suffocate, spreads disease germs; fertilizers – cause eutrophication: algal bloom, then lack of oxygen and death of organisms; pesticides and heavy metals – poison organisms and build up along the food chain; hot water – lowers dissolved oxygen and kills sensitive organisms; detergents – froth reduces oxygen and harms gills; refuse/plastics – organisms get trapped or swallow them.

Give an effect for each pollutant you list.

(a)(i) Any five: condom; diaphragm/cap; contraceptive pills; injection/implants; intra-uterine device (IUD/loop); spermicides; rhythm (safe period) method; withdrawal; abstinence; tubal ligation; vasectomy.
(ii) Any five: controls population growth; allows parents to provide food, education and health care for their children; improves the health of mothers (spacing births); reduces strain on social amenities (schools, hospitals, housing); reduces unemployment and crime; helps economic development and better standard of living; reduces infant and maternal deaths.
(b) Front view, 8–10 cm, title, labels on ruled guidelines: ovaries, oviducts (Fallopian tubes), funnel with fimbriae, uterus, endometrium/uterine wall, cervix, vagina (and vulva).

Drawing: front view, both ovaries and tubes.

(a) Dense, evergreen vegetation with many plant species; tall trees in three or more layers (strata) with emergents up to 40 m or more; closed canopy, so little light reaches the floor and there is little undergrowth; trees have buttress roots and straight trunks with smooth, thin bark; broad leaves with drip tips; many climbers (lianas) and epiphytes; hardwoods such as mahogany, iroko, obeche.
(b) Any two with a town: Guinea savanna – Ilorin, Oyo, Makurdi, Minna, Abuja; Sudan savanna – Kano, Sokoto, Katsina, Zaria; Sahel savanna – Maiduguri, Nguru; derived savanna – Ogbomosho, Enugu; montane – Jos plateau, Obudu.
(c)(i) Drought: produce dry faeces and very concentrated urine (uric acid); get water from food and from respiration (metabolic water); store fat/water (camel's hump); impermeable skin or scales reduce water loss; few sweat glands; some aestivate in the dry season.
(ii) High temperatures: burrow underground or hide in shade during the day; active at night (nocturnal); large ears or thin body parts radiate heat (e.g. fennec fox); light-coloured body reflects heat; tolerate a rise in body temperature; long legs keep the body away from the hot sand.

Each savanna type needs one correct town.