WAEC SSCE - Biology - 2021 (Essay)

Answer Details

(a)

Fungi

(b) (i) Products of decomposition:

1. Carbon dioxide
2. Water
3. Organic matter
4. Nutrients

(ii) Roles of decomposers on a refuse dump:

1. Breaking down organic matter into smaller components that can be reabsorbed by the ecosystem
2. Returning nutrients to the soil, thereby supporting plant growth
3. Reducing the volume of waste in the refuse dump.

(c) Three materials found in a refuse dump which would not be affected by the action of decomposers:

1. Glass
2. Metals (such as aluminum, iron, or steel)
3. Plastic

Answer Details

(a) Five West African wildlife animals and the body part that makes them endangered by human activity

(b) Effects of the following factors on conservation of natural resources

(i) Poor economy of a nation

• There is insufficient funding to establish and maintain game reserves and national parks.
• Poverty pushes citizens into illegal hunting, logging and over-exploitation of resources for survival.
• Enforcement of conservation laws is weak because there is little money to pay and equip game wardens.

(ii) Poaching

• It reduces the population of wildlife and can drive some species to extinction.
• It disrupts the food chain and upsets the balance of the ecosystem.
• It reduces the genetic diversity (loss of some genes) of the affected species.

(c) Four roles played by the Government in conservation of natural resources

1. Establishing and maintaining game reserves, national parks and forest reserves.
2. Making and enforcing laws that prohibit poaching, indiscriminate felling of trees and bush burning.
3. Educating the public and creating awareness on the need to conserve natural resources.
4. Providing funds and trained personnel (game wardens) for the protection of wildlife and forests.

Answer Details

(a) Nutrient cycle for each process

(b)(i) What is irritability?

Irritability (sensitivity) is the ability of a living organism to detect and respond to changes (stimuli) in its internal or external environment.

(b)(ii) Type of response elicited by each action

(c) Three animals that exhibit each behaviour

(i) Territoriality: male Agama lizard; male Tilapia (fish); dog.

(ii) Seasonal migration: swallow; wildebeest; salmon.

(iii) Display: peacock; domestic fowl (cock); pigeon.

Answer Details

(a) Dentition in animals

Dentition is the type, number, arrangement and pattern of the teeth in the jaws of an animal. The kind of dentition an animal has (for example the presence and development of incisors, canines, premolars and molars) is related to its mode of feeding.

(b) Generalised structure of a tooth

A tooth has two main regions: the crown, which projects above the gum, and the root, which is embedded in the socket of the jaw bone; the slightly narrowed part where they meet, at gum level, is the neck.

• Enamel - the hard, white, non-living outer covering of the crown; it is the hardest substance in the body and resists wear.
• Dentine - a bone-like living layer beneath the enamel that makes up the bulk of the tooth.
• Pulp cavity - the central space containing the pulp, which is made of blood vessels (supplying food and oxygen) and nerve fibres (sensitive to pain and temperature).
• Cement - a layer that covers the dentine of the root and, together with the periodontal fibres, fixes the tooth firmly in its socket.

(c) Three food substances plants manufacture from glucose

• Starch (for storage).
• Cellulose (for building cell walls).
• Sucrose (for transport); also fats/oils and, with nitrogen, proteins.

(d) Diagram of an experimental set-up to show that oxygen is produced during photosynthesis

Make a labelled drawing 6 - 8 cm long of the classic aquatic-plant set-up: a beaker of water containing sprigs of a water plant such as Elodea (or Hydrilla), the plant covered by an inverted glass funnel, and an inverted test tube full of water placed over the funnel stem to collect the gas. Label the water plant, the funnel, the test tube and the gas bubbles (oxygen) collecting at the top of the test tube. When placed in sunlight, bubbles of gas rise and collect in the tube; the collected gas relights a glowing splint, showing it is oxygen.

Answer Details

(a) Four main components of blood

• Plasma
• Red blood cells (erythrocytes)
• White blood cells (leucocytes)
• Platelets (thrombocytes)

(b) Naming the component described

• (i) Forms the top layer in the test tube - plasma (it is the lightest and stays on top after spinning).
• (ii) Destroys pathogens - white blood cells.
• (iii) Is biconcave in shape - red blood cells.
• (iv) Would be relatively low in a haemophilic condition - platelets.
• (v) Is produced in the bone marrow - red blood cells.
• (vi) Is a thrombocyte - platelets.
• (vii) Is nucleated - white blood cells.

(c) Three chemical substances transported by plasma (the component in b(i))

• Digested food substances such as glucose and amino acids.
• Excretory waste such as urea (and carbon dioxide as hydrogencarbonate).
• Hormones (also dissolved mineral salts and antibodies).

(d) Four diseases associated with blood

• Anaemia
• Leukaemia
• Sickle-cell anaemia
• Haemophilia (also thrombosis)

(e) Why a disease of the blood could be dangerous

Blood circulates throughout the whole body and performs vital functions such as transporting oxygen, food, hormones and waste, defending the body against disease, and clotting to prevent excessive bleeding. A disease of the blood therefore affects the entire body at once: it can reduce the supply of oxygen and nutrients to the tissues, weaken the body's defence against infection, prevent proper clotting so that a person may bleed to death, and, because the affected blood reaches every organ, the disorder spreads quickly and can be fatal.