WAEC SSCE - Biology - 1999 (Essay)

(a)(i) Hydrosphere

The hydrosphere is the part of the earth that is made up of all the water bodies; that is, the total mass of water that covers the surface of the earth in liquid, solid or vapour form.

(a)(ii) Three examples of the hydrosphere

Oceans and seas, rivers and streams, and lakes (also ponds, springs, ground water, and ice caps/glaciers).

(b) The two laws of thermodynamics

• First law (law of conservation of energy): energy can neither be created nor destroyed but can only be transformed (changed) from one form to another. In a food chain, light energy is converted into chemical energy and then into other forms.
• Second law: whenever energy is transformed from one form to another, some of the energy is lost (usually as heat) to the surroundings, so no energy transfer is 100 per cent efficient. This is why the amount of usable energy decreases from one trophic level to the next.

(c)(i) Two local biotic communities in Nigeria (with a State)

• Mangrove swamp / rainforest community – Rivers or Delta State (Niger Delta area).
• Guinea/Sudan savanna (grassland) community – Kano or Sokoto State (northern Nigeria).

(Other acceptable pairs: freshwater swamp – Bayelsa; derived savanna – Oyo.)

(c)(ii) Three factors affecting organisms in the marine habitat

• Salinity (high salt concentration of the water).
• Light penetration (which decreases with depth).
• Temperature of the water.
• Water pressure and wave/tidal action (also acceptable).

(c)(iii) Three adaptive features of seaweeds

• They have holdfasts (root-like structures) for firm attachment to rocks against wave action.
• They have flexible, slippery (mucilage-covered) bodies that bend with the waves and resist drying.
• They possess air bladders that keep the fronds afloat near the surface for adequate light for photosynthesis.
• Their whole surface can absorb water and dissolved mineral salts.

(a)(i) Law of independent assortment

Mendel's law of independent assortment states that when two or more pairs of contrasting characters (alleles) are considered together, each pair separates and is inherited independently of the other during the formation of gametes.

(a)(ii) Findings from the red-flowered and white-flowered pea cross

When a pure-breeding red-flowered pea plant was crossed with a pure-breeding white-flowered pea plant, all the offspring of the first filial generation (F₁) were red-flowered. When these F₁ plants were self-crossed, the second generation (F₂) contained both red-flowered and white-flowered plants in the ratio of about 3 red : 1 white. This showed that red is dominant to white, and that the white character had only been hidden (masked) in the F₁, reappearing in the F₂.

(a)(iii) Illustration by diagrams

Let R = allele for red flower (dominant), r = allele for white flower (recessive).

Parents: RR (red) × rr (white)

Gametes: R and r

F₁: all Rr (red-flowered)

F₁ cross: Rr × Rr

F₂ ratio: 3 red : 1 white.

(b) Why A and B can be heterozygous or homozygous but O only homozygous

Blood groups in man are controlled by three alleles: IA and Ib, which are both dominant, and io, which is recessive. Because IA and Ib are dominant over io, group A can be produced by either IAIA (homozygous) or IAio (heterozygous), and group B can be produced by either IbIb (homozygous) or Ibio (heterozygous); in the heterozygous forms the dominant allele still expresses A or B and masks the recessive io. Group O, on the other hand, is caused only by the recessive allele io, which is expressed only when no dominant allele is present. Therefore group O can arise only from the homozygous recessive genotype ioio and cannot exist in a heterozygous state.

(a)(i) Pollution

Pollution is the release of harmful or unwanted substances (pollutants) into the environment (air, water or soil), which makes it unclean, unsafe or unfit for living things.

(a)(ii) Two pollutants each

• Air pollutants: carbon monoxide and sulphur dioxide (also carbon dioxide, smoke/soot, oxides of nitrogen).
• Water pollutants: crude oil (petroleum) and sewage (also industrial chemicals, detergents, fertilisers, refuse).

(b)(i) Four effects of water pollution

• It kills fish and other aquatic organisms.
• It causes water-borne diseases such as cholera and typhoid in humans.
• It makes water unfit for drinking, domestic and industrial use.
• It reduces the dissolved oxygen in water (leading to death of aquatic life).
• It destroys the beauty of water bodies and can cause the growth of harmful algae (eutrophication).

(b)(ii) Four ways of preventing water pollution

• Treating sewage and industrial waste before discharging it into water bodies.
• Preventing the dumping of refuse and chemicals into rivers, streams and drains.
• Preventing oil spillage and cleaning up spills promptly.
• Enforcing laws (legislation) against polluting water bodies and educating the public.

(c)(i) Three sources of noise pollution

Vehicles and aeroplanes (traffic), industries and factory machines, and loud music/loudspeakers (also generators, blasting/explosions, market noise).

(c)(ii) Three effects of noise pollution on man

• It causes deafness or partial loss of hearing.
• It causes headache, high blood pressure and stress.
• It disturbs sleep, concentration and communication, and can cause nervousness or irritability.

(a) Principles of food preservation methods

• (i) Salting: salt draws water out of the food and out of any microorganisms by osmosis, creating a dry, high-salt condition in which bacteria and fungi cannot grow or multiply.
• (ii) Refrigeration: low temperature slows down (inactivates) the enzymes and the growth and multiplication of the microorganisms that cause food to spoil, so decay is delayed.
• (iii) Drying: removal of water (moisture) from the food deprives spoilage microorganisms of the water they need to grow and reproduce, and slows enzyme activity, so the food does not decay.
• (iv) Smoking: heat and smoke dry the food and coat it with chemicals (such as creosote and other antiseptic substances in wood smoke) that kill or check the growth of microorganisms.
• (v) Chemicals (chemical preservatives): added chemicals such as sodium benzoate, sugar or vinegar kill microorganisms or create conditions (acidity, high sugar concentration) in which they cannot grow.

(b) Four problems caused by human overpopulation

• Shortage of food, leading to malnutrition and hunger.
• Shortage of housing / overcrowding and growth of slums.
• Unemployment and poverty.
• Pressure on and inadequacy of social amenities (schools, hospitals, water, roads).
• Increased pollution and destruction of the environment.
• Increased spread of diseases and rise in crime rate.

(c) Three ways the Government may increase food production

• Providing loans, subsidies and farm inputs (improved seeds, fertilisers, pesticides) to farmers at cheaper rates.
• Encouraging mechanised farming and providing modern farm machinery and irrigation facilities so that larger areas can be cultivated all year round.
• Establishing agricultural research institutes to produce improved (high-yielding, disease-resistant) crop varieties and livestock breeds, and training farmers through extension services.
• Building good storage and processing facilities and good roads to reduce post-harvest losses and encourage farmers.

(a)(i) Four similarities in plant and animal cells

• Both possess a cell membrane (plasma membrane).
• Both have cytoplasm.
• Both have a nucleus.
• Both have mitochondria.
• Both have ribosomes and an endoplasmic reticulum.

(Any four.)

(a)(ii) Four cells found in man and their functions

(Any four.)

(b)(i) Two types of cell division

Mitosis and meiosis.

(b)(ii) Two examples of life processes involving each

• Mitosis: growth (increase in body size); repair of damaged tissues / healing of wounds; asexual reproduction.
• Meiosis: formation of gametes (sperms and eggs / pollen grains and ovules); sexual reproduction (ensuring the constant chromosome number is restored at fertilization).

(c) Two types of reproduction in organisms

Asexual reproduction and sexual reproduction.

(a)(i) Metamorphosis

Metamorphosis is the series of changes in body form and structure that an animal undergoes from the egg (or young stage) to the adult stage.

(a)(ii) Two types of metamorphosis with organisms

• Complete metamorphosis (egg → larva → pupa → adult): butterfly and housefly (also mosquito, beetle, moth).
• Incomplete (partial) metamorphosis (egg → nymph → adult): cockroach and grasshopper (also termite, locust, dragonfly).

(b)(i) Four economic importances of insects (with examples)

• Pollination of flowers: honey bee – helps in fertilisation and fruit/seed formation.
• Production of useful products: honey bee – produces honey and wax; silkworm (moth larva) – produces silk.
• Serve as food: termites and locusts – eaten by humans and animals (source of protein).
• Destruction of crops (pests): grasshopper/locust – destroys farm crops, causing loss.
• Transmission of diseases (vectors): mosquito – transmits malaria; housefly – transmits typhoid and cholera; tsetse fly – transmits sleeping sickness.
• Decomposition: some beetles help to break down dung and dead matter.

(Any four, each with an example.)

(b)(ii) Four peculiar features of social insects

• They live together in large numbers in a colony (community).
• There is division of labour, with different castes performing different duties.
• They show polymorphism, that is, different body forms for different castes (queen, workers, soldiers, drones).
• They cooperate and communicate to build and defend the nest and to care for the young.
• Only certain members (the queen/king) are fertile and carry out reproduction.