WAEC Biology 2004 past questions and answers

Most plants are fixed in one place and cannot move their whole body away from a stimulus; they only grow towards or away from it. All plants respire, reproduce and adapt.

Hydra is an animal with no chlorophyll, so it cannot photosynthesise. It feeds, moves and egests through its mouth.

Euglena has a flexible protein pellicle instead of a cellulose cell wall, an animal-like feature. Nucleus and cytoplasm are found in all cells.

A palisade cell is a plant cell with a cellulose cell wall and chloroplasts. Both cells have a cell membrane and cytoplasm.

The DNA in the nucleus carries the instructions for making enzymes, and enzymes control every chemical reaction in the cell.

Ink particles move from where they are concentrated to where they are fewer until evenly spread: this is diffusion. Osmosis is movement of water across a membrane.

Excess amino acids from protein are broken down in the liver (deamination) to form urea, so a protein-rich meal raises urea in the urine.

In conjugation two Paramecia line up side by side and exchange nuclear material, so two conjugants take part.

The axial skeleton is the central axis of the body: skull, vertebral column, ribs and sternum. Limbs and girdles form the appendicular skeleton.

Xylem vessels have thick walls strengthened with lignin, which makes them rigid and able to hold the plant up.

Vitamin K is needed to make clotting factors in the liver; without it blood clots slowly and bleeding continues.

Digested food is absorbed into capillaries of the small intestine, which join to form the hepatic portal vein leading to the liver.

Aerobic respiration breaks down glucose with oxygen to give energy, carbon dioxide and water.

Transpiration is the loss of water vapour from plants, mainly through the stomata of leaves.

Body reactions are controlled by enzymes, which work best at an optimum temperature, so keeping the temperature steady keeps metabolism efficient.

An orange/brick-red precipitate shows a reducing sugar. The sugar found in urine, e.g. in diabetes, is glucose.

Insulin lowers blood glucose. Without enough insulin (diabetes mellitus) blood sugar rises and glucose spills into the urine.

The spinal cord runs through the neural canal of the vertebrae, which protect it. The other structures are in the skull.

Part I is at the very front of the brain, in front of the cerebral hemispheres; this is the olfactory lobe, concerned with smell.

Part VIII is the medulla oblongata at the back of the brain, which controls involuntary actions such as breathing and heartbeat.

In bright light the iris narrows the pupil. For a near object the ciliary muscles contract, the suspensory ligaments slacken and the lens becomes thicker.

A butterfly goes through egg, larva (caterpillar), pupa and adult, which is complete metamorphosis. Termites, cockroaches and locusts have nymphs instead.

Parthenocarpy is fruit formation without fertilization, giving seedless fruits such as some bananas and pineapples.

Calcium, magnesium and potassium are all needed in large amounts. Molybdenum, manganese, copper, zinc, boron and iron are micro-nutrients.

In water-culture experiments, the solution with every needed element in the right amounts is the complete culture solution; others leave one element out.

Manganese is needed for chlorophyll formation, so its lack causes yellowing of the leaves (chlorosis).

With no water the plant keeps losing water by transpiration, its cells become flaccid and it wilts. Its cells cannot be turgid.

Vitamin D and calcium are needed to make strong bones; their lack causes rickets, with soft bent bones.

A heterotroph cannot make its own food and depends on food already made by other organisms.

Digestion breaks large insoluble food molecules into small soluble ones that can be absorbed.

In carnivores such as the dog, the carnassial teeth are the last upper premolar and the first lower molar. Their sharp ridges slide past each other like scissors to slice flesh.

The biosphere is the whole part of the earth (land, water and air) where living things are found.

Wind, temperature and herbivores act on plants directly. Carnivores feed on animals, so they affect plants only indirectly.

Different crops have roots at different depths and need different nutrients, so rotating them uses soil nutrients at different levels and does not exhaust one layer.

Maize is the producer in all three chains. Every option except D includes maize, while humans, eagle and snakes are all consumers.

A food web shows how organisms are linked by feeding, so it shows that they depend on one another to survive.

Matter is recycled, but energy is not: producers get their energy only from sunlight. Decomposers pass nutrients back to plants, not energy.

The tapeworm's scolex has hooks and suckers that hold it firmly to the gut wall so it is not swept away by moving food.

Symbiosis (mutualism) is a close association in which both partners benefit, such as Rhizobium in legume roots.

Hydrophytes are water plants. Xerophytes live in dry places, halophytes in salty places and epiphytes on other plants.

Rain carries sprayed pesticides off the farm into streams, lakes and rivers, where they pollute the water and harm aquatic life.

A quadrat is placed at random several times and the plants inside counted, which gives the number per unit area of a plant like Tridax.

Ecological succession is the series of community changes in an area that ends in a stable (climax) community.

Antibiotics, such as penicillin, are drugs that kill or stop the growth of bacteria. Antibodies and antitoxins are made by the body.

Micro-organisms decompose the organic refuse, releasing mineral nutrients that make the soil fertile.

Cellophane is a manufactured material. Rubber, soil and water occur in nature.

Replanting forest trees restores the forest. The other practices destroy it.

Deforestation is the removal of forest, the opposite of conservation.

The gene for haemophilia is carried on the X chromosome, so it is sex-linked and mostly affects males.

Tasting PTC cannot be seen on the body; it is a difference in how the body works, so it is a physiological variation.

Females are XX and males are XY; the sex chromosome in the sperm decides the child's sex.

Rr × Rr gives RR, Rr, Rr and rr, a genotypic ratio of 1 : 2 : 1 (the phenotypic ratio is 3 : 1).

Skin colour can change with the environment, e.g. it darkens with exposure to sunlight. Eye colour and tongue-rolling are fixed by genes.

Tt × tt gives Tt and tt in equal numbers, so half the offspring are tall and half dwarf.

Crossing pure tall (TT) with pure short (tt) gives only Tt offspring, and since tall is dominant they are all long-stemmed.

During meiosis the pairs of chromosomes separate at random, so each haploid gamete gets a random mixture of chromosomes from the father and mother.

In a termite colony the queen lays eggs, workers find food and build, and soldiers defend: this is division of labour.

Loss of organs through disuse is Lamarck's idea (use and disuse). Darwin's theory is based on variation, struggle for existence and inheritance of useful features.

Charles Darwin (with Alfred Wallace) proposed natural selection; his book 'On the Origin of Species' appeared in 1859.

(a) A habitat is the natural place or area where an organism or a community of organisms lives.
(b) The sun is the source of energy; green plants and algae (phytoplankton, water weeds) trap light energy in photosynthesis and store it as food; zooplankton, tadpoles and small fish (primary consumers) eat the plants and get some of this energy; larger fish and water birds (secondary/tertiary consumers) eat them; at each step much energy is lost as heat in respiration, so less passes on; when organisms die, decomposers (bacteria, fungi) break them down, using the remaining energy; energy flows in one direction and is not recycled.
(c)(i) Any three: herbivores (grazing animals); parasites; decomposers/micro-organisms; competition with other plants; predators of pollinators/consumers; human activities.
(ii) Any five: light intensity; temperature; dissolved oxygen; dissolved carbon dioxide; pH; turbidity; water currents; salinity/mineral salts (nutrients); depth of water.

Energy flow must start with the sun and producers and show loss of energy at each level.

(a)(i) A joint is a place where two or more bones meet (articulate).
(ii) Any three: ball and socket joint – shoulder or hip; hinge joint – elbow or knee; gliding (sliding) joint – wrist, ankle or between vertebrae; pivot joint – between the atlas and axis in the neck.
(b)(i) Diagram of a synovial joint labelled: bone (e.g. humerus/femur), articular (hyaline) cartilage, synovial membrane, synovial fluid, synovial cavity, capsule (capsular ligament), ligaments, (tendon/muscle).
(ii) Smooth articular cartilage covers the bone ends, reducing friction and absorbing shock; synovial fluid lubricates the joint and nourishes the cartilage; the synovial membrane secretes the fluid; tough, slightly elastic ligaments hold the bones together but allow movement; the capsule encloses the joint and keeps the fluid in; tendons attach muscles to the bones so their contraction moves the joint; the shapes of the bone ends decide the direction of movement.

Link each structure in (b)(ii) to what it does for movement.

(a) Pollination is the transfer of pollen grains from the anther to the stigma; fertilization is the fusion of a male nucleus (gamete) from the pollen tube with the egg cell in the ovule to form a zygote. Pollination comes first; fertilization takes place inside the ovary.
(b) Any five with examples: dioecism – male and female flowers on separate plants (pawpaw); protandry – anthers ripen before the stigma (Hibiscus, sunflower); protogyny – stigma ripens before the anthers (Bryophyllum, grasses such as maize); self-sterility/self-incompatibility – pollen cannot fertilise the same flower (tobacco, Crotalaria); monoecism – separate male and female flowers on the same plant (maize); heterostyly – styles and stamens of different lengths (primrose); flower structure that keeps anthers and stigma apart (Hibiscus with stigma above anthers).
(c)(i) Insects; wind; water; birds; bats/other animals; man (any three).
(ii) Any three: light in weight; small in size; have wing-like outgrowths (e.g. Terminalia, Combretum); have hairs or parachutes (e.g. Tridax, cotton); produced in large numbers; dry fruits that may split open (capsules).

In (b) give the feature and a matching example for each.

(a) Destarch a potted plant by keeping it in the dark for 24–48 hours; cover part of one leaf on both sides with black paper or foil (or a stencil); place the plant in bright sunlight for some hours; remove the leaf and test it for starch with iodine; the uncovered part turns blue-black (starch present) while the covered part stays brown (no starch); conclusion: light is needed for photosynthesis. (A destarched plant left uncovered in light can act as the control.)
(b) Carbon dioxide; water; chlorophyll; suitable temperature (enzymes).
(c) The palisade mesophyll (layer). Reasons: its cells contain the most chloroplasts; they are just below the upper epidermis and receive the most light; they are long, closely packed and arranged at right angles to the surface to trap light; nearby air spaces in the spongy layer supply carbon dioxide.
(d) Glucose formed is changed into starch and stored temporarily in the leaf; it is converted to soluble sugar (sucrose) and translocated in the phloem to other parts; it is used in respiration to release energy; it is used to make cellulose, proteins, fats and oils; excess is stored in storage organs (seeds, fruits, tubers, roots).

Describe the destarching step and include a control and conclusion in the experiment.

(a)(i) Phenotype: the visible or measurable characteristics of an organism (e.g. tall, yellow), produced by its genotype and the environment.
(ii) Hybrid: an offspring of two parents that differ in one or more characters (genetically unlike), e.g. Yy.
(iii) Dominant character: a character that shows in the offspring even when only one allele for it is present, masking the other (recessive) character.
(b)(i) Parents: YY (yellow) × yy (purple); gametes: Y and y; F₁: all Yy – yellow grains. So the F₁ genotype is Yy.
(ii) F₁ × purple parent: Yy × yy; gametes: Y, y and y, y; offspring: Yy, Yy, yy, yy; phenotypes: 2 yellow : 2 purple, i.e. 1 : 1 (50% yellow, 50% purple). (Diagrams must label parents, gametes and offspring.)
(c) Any two: breeding high-yielding crops and animals; producing disease- and pest-resistant varieties; producing early-maturing varieties; producing drought-tolerant crops; improving quality, e.g. more protein or oil; producing hybrids with hybrid vigour.

Set out each cross in full: parents, gametes, offspring genotypes and phenotypes.

(a) Any six with examples: camouflage/cryptic colouration – body colour matches the surroundings (chameleon, grasshopper, stick insect); warning colouration – bright colours warn that the animal is poisonous or distasteful (some caterpillars, monarch butterfly); mimicry – a harmless animal looks like a harmful one (hoverfly resembling a wasp); poisonous stings or bites (bees, wasps, scorpions, snakes); protective shell or hard covering (snail, tortoise, pangolin scales); spines or quills (porcupine, hedgehog); playing dead/feigning death (some beetles, opossum); unpleasant smell or secretion (millipede, skunk); speed – running, swimming or flying away (antelope); flash colouration (some grasshoppers and moths); living in groups/herds (antelopes, fish shoals); electric shock (electric fish); ink ejection (squid, octopus).
(b)(i) Pollution is the release of harmful substances or energy (pollutants) into the environment (air, water, land) in amounts that harm living things.
(ii) Any six: burning fuels in vehicles and factories (smoke, exhaust fumes); bush burning; dumping refuse and sewage in water or on land; oil spillage from oil exploration; use of pesticides and fertilizers; mining and quarrying; noise from loud music, generators and machines; discharge of industrial wastes into rivers; smoking cigarettes; use of non-biodegradable materials such as plastics.

For (a), name each adaptation, say how it protects the animal and give an example.