WAEC SSCE - Biology - 1988 (Essay)
Question 1 Report
(i) Make a labelled drawing of a typical plant cell to show its essential features.
(ii) Give the functions of two labelled organelles
(b) Describe briefly two levels of cell organization in living organisms giving an example of each type.
(c) What role do the following processes play in the activities of a living cell (i) osmosis; (ii) diffusion.
(a)(i) Labelled drawing of a typical plant cell
(a)(ii) Functions of two labelled organelles
- Mitochondrion: it is the site of aerobic respiration, where energy is released from food and trapped in ATP for the activities of the cell.
- Chloroplast: it contains chlorophyll, which absorbs light energy for the manufacture of food during photosynthesis.
(b) Two levels of cell organisation
- Tissue level: a tissue is a group of similar cells working together to perform a particular function. For example, xylem tissue in a plant conducts water and mineral salts; muscle tissue in an animal brings about movement.
- Organ level: an organ is made up of different tissues working together to carry out one or more functions. For example, a leaf is a plant organ for photosynthesis and gaseous exchange, while the heart is an animal organ that pumps blood.
(c) Roles of processes in a living cell
- Osmosis: this is the movement of water molecules through a selectively permeable membrane from a region of higher water potential, or more dilute solution, to a region of lower water potential, or more concentrated solution. It enables root-hair cells to absorb water from the soil and keeps plant cells turgid for support. It also helps to maintain the water balance of cells.
- Diffusion: this is the movement of particles from a region of higher concentration to a region of lower concentration. It enables cells to take in oxygen and soluble food substances and to remove wastes such as carbon dioxide. Thus, it is important in gaseous exchange and in movement of nutrients from tissue fluid into cells.
Answer Details
(a)(i) Labelled drawing of a typical plant cell
(a)(ii) Functions of two labelled organelles
- Mitochondrion: it is the site of aerobic respiration, where energy is released from food and trapped in ATP for the activities of the cell.
- Chloroplast: it contains chlorophyll, which absorbs light energy for the manufacture of food during photosynthesis.
(b) Two levels of cell organisation
- Tissue level: a tissue is a group of similar cells working together to perform a particular function. For example, xylem tissue in a plant conducts water and mineral salts; muscle tissue in an animal brings about movement.
- Organ level: an organ is made up of different tissues working together to carry out one or more functions. For example, a leaf is a plant organ for photosynthesis and gaseous exchange, while the heart is an animal organ that pumps blood.
(c) Roles of processes in a living cell
- Osmosis: this is the movement of water molecules through a selectively permeable membrane from a region of higher water potential, or more dilute solution, to a region of lower water potential, or more concentrated solution. It enables root-hair cells to absorb water from the soil and keeps plant cells turgid for support. It also helps to maintain the water balance of cells.
- Diffusion: this is the movement of particles from a region of higher concentration to a region of lower concentration. It enables cells to take in oxygen and soluble food substances and to remove wastes such as carbon dioxide. Thus, it is important in gaseous exchange and in movement of nutrients from tissue fluid into cells.
Question 2 Report
(a) What is conservation of natural resources?
(b) List various natural resources that need to be conserved. State briefly the benefits of conservation in each case.
(c) List the problems often encountered in ensuring conservation of natural resources.
(d) What are the efforts being employed in your country to ensure conservation of natural resources?
(a) Conservation of natural resources
Conservation of natural resources is the careful and wise management, protection and use of the earth's natural resources so that they are not wasted, destroyed or exhausted, and so that they remain available for the benefit of both present and future generations.
(b) Natural resources to be conserved and the benefits
| Natural resource | Benefit of conserving it |
|---|---|
| Forests (vegetation) | Provide timber, fuel and food, act as habitat for wildlife, prevent soil erosion, and release oxygen while absorbing carbon dioxide. |
| Wildlife (animals) | Maintains the balance of nature and food chains, provides meat, and preserves species for research, tourism and future use. |
| Soil | Supports crop and pasture growth for food; conserving it prevents erosion and keeps land fertile for farming. |
| Water | Needed for drinking, domestic use, irrigation, fisheries and industry; conservation ensures a steady, clean supply. |
| Minerals and fossil fuels | Provide raw materials and energy for industry; wise use makes these non-renewable resources last longer. |
| Air | Clean air is needed for respiration; conservation reduces pollution and disease. |
(c) Problems often encountered in ensuring conservation
- Rapid population growth increases demand for land, food, timber and fuel, causing over-exploitation.
- Poverty and unemployment force people to exploit resources such as forests and wildlife for survival.
- Ignorance and lack of public awareness about the importance and methods of conservation.
- Poor enforcement of conservation laws and inadequate funding of enforcement agencies.
- Bush burning, illegal logging, poaching and over-grazing that destroy resources faster than they can be replaced.
- Industrialisation and urbanisation leading to pollution and destruction of natural habitats.
- Corruption and conflict of interest between economic development and conservation.
(d) Efforts employed in my country to ensure conservation
- Establishment of national parks, game reserves and forest reserves to protect wildlife and vegetation.
- Enactment and enforcement of conservation and anti-poaching laws, and a ban on indiscriminate bush burning and illegal logging.
- Afforestation and reforestation programmes (tree-planting campaigns) to replace felled trees.
- Setting up agencies such as environmental protection and forestry commissions to regulate resource use.
- Public enlightenment and environmental education in schools and the media to create awareness.
- Encouraging controlled or selective harvesting, crop rotation and use of alternative energy to reduce pressure on resources.
- Control of pollution through laws on waste disposal and treatment of industrial effluents.
Answer Details
(a) Conservation of natural resources
Conservation of natural resources is the careful and wise management, protection and use of the earth's natural resources so that they are not wasted, destroyed or exhausted, and so that they remain available for the benefit of both present and future generations.
(b) Natural resources to be conserved and the benefits
| Natural resource | Benefit of conserving it |
|---|---|
| Forests (vegetation) | Provide timber, fuel and food, act as habitat for wildlife, prevent soil erosion, and release oxygen while absorbing carbon dioxide. |
| Wildlife (animals) | Maintains the balance of nature and food chains, provides meat, and preserves species for research, tourism and future use. |
| Soil | Supports crop and pasture growth for food; conserving it prevents erosion and keeps land fertile for farming. |
| Water | Needed for drinking, domestic use, irrigation, fisheries and industry; conservation ensures a steady, clean supply. |
| Minerals and fossil fuels | Provide raw materials and energy for industry; wise use makes these non-renewable resources last longer. |
| Air | Clean air is needed for respiration; conservation reduces pollution and disease. |
(c) Problems often encountered in ensuring conservation
- Rapid population growth increases demand for land, food, timber and fuel, causing over-exploitation.
- Poverty and unemployment force people to exploit resources such as forests and wildlife for survival.
- Ignorance and lack of public awareness about the importance and methods of conservation.
- Poor enforcement of conservation laws and inadequate funding of enforcement agencies.
- Bush burning, illegal logging, poaching and over-grazing that destroy resources faster than they can be replaced.
- Industrialisation and urbanisation leading to pollution and destruction of natural habitats.
- Corruption and conflict of interest between economic development and conservation.
(d) Efforts employed in my country to ensure conservation
- Establishment of national parks, game reserves and forest reserves to protect wildlife and vegetation.
- Enactment and enforcement of conservation and anti-poaching laws, and a ban on indiscriminate bush burning and illegal logging.
- Afforestation and reforestation programmes (tree-planting campaigns) to replace felled trees.
- Setting up agencies such as environmental protection and forestry commissions to regulate resource use.
- Public enlightenment and environmental education in schools and the media to create awareness.
- Encouraging controlled or selective harvesting, crop rotation and use of alternative energy to reduce pressure on resources.
- Control of pollution through laws on waste disposal and treatment of industrial effluents.
Question 3 Report
(a) (i) Define the term population. (ii) List two biotic and abiotic factors each that affect population growth.
(b) What are the effects of food shortage on a population?
(c) Describe two methods each for:
(i) improving crop yield (ii) preserving and storing food. Explain the principle involved in each of the methods described.
(a)(i) Definition of population
A population is a group of organisms of the same species living together in the same habitat at a particular time, and which are able to interbreed to produce fertile offspring.
(a)(ii) Factors affecting population growth
Biotic factors (living factors):
- Availability of food - abundant food supports growth while scarcity limits it.
- Predation, competition, parasitism and disease - these reduce numbers by increasing the death rate.
Abiotic factors (non-living factors):
- Temperature - extreme heat or cold slows reproduction and raises mortality.
- Availability of water, light and space - shortage of any of these restricts survival and reproduction.
(b) Effects of food shortage on a population
- Increased competition among members for the limited food, both intraspecific and interspecific.
- Increased death rate (higher mortality) as the weaker individuals starve.
- Reduced reproductive rate (lower natality) because underfed organisms produce fewer offspring.
- Migration or emigration of some members in search of food, reducing the local population.
- Stunted growth and poor health, making individuals more prone to disease.
- Overall the population size falls until it matches the available food (the carrying capacity).
(c) Methods and their principles
(i) Improving crop yield
- Application of fertilizers (manuring) - Principle: fertilizers add essential mineral nutrients such as nitrogen, phosphorus and potassium to the soil, which the crops need for the manufacture of proteins and healthy growth, thereby raising yield.
- Use of improved (high-yielding) varieties through selective breeding - Principle: plants with desirable genes (fast growth, disease resistance, large produce) are selected and bred so that these favourable characteristics are passed on, giving heavier harvests.
Other acceptable methods: irrigation (supplies water for photosynthesis and transport of nutrients) and pest and weed control (removes organisms that compete with or destroy the crop).
(ii) Preserving and storing food
- Refrigeration or freezing (low temperature) - Principle: low temperatures slow down the activity of enzymes and inhibit the growth and multiplication of decay-causing micro-organisms (bacteria and fungi), so the food does not spoil quickly.
- Drying (dehydration) - Principle: removing moisture from the food deprives micro-organisms of the water they need to grow and reproduce, thereby preventing decay.
Other acceptable methods: salting or sugaring (high salt/sugar concentration draws water out of microbial cells by osmosis, killing or inhibiting them) and canning/pasteurisation (heat kills micro-organisms and sealing prevents re-entry of air and microbes).
Answer Details
(a)(i) Definition of population
A population is a group of organisms of the same species living together in the same habitat at a particular time, and which are able to interbreed to produce fertile offspring.
(a)(ii) Factors affecting population growth
Biotic factors (living factors):
- Availability of food - abundant food supports growth while scarcity limits it.
- Predation, competition, parasitism and disease - these reduce numbers by increasing the death rate.
Abiotic factors (non-living factors):
- Temperature - extreme heat or cold slows reproduction and raises mortality.
- Availability of water, light and space - shortage of any of these restricts survival and reproduction.
(b) Effects of food shortage on a population
- Increased competition among members for the limited food, both intraspecific and interspecific.
- Increased death rate (higher mortality) as the weaker individuals starve.
- Reduced reproductive rate (lower natality) because underfed organisms produce fewer offspring.
- Migration or emigration of some members in search of food, reducing the local population.
- Stunted growth and poor health, making individuals more prone to disease.
- Overall the population size falls until it matches the available food (the carrying capacity).
(c) Methods and their principles
(i) Improving crop yield
- Application of fertilizers (manuring) - Principle: fertilizers add essential mineral nutrients such as nitrogen, phosphorus and potassium to the soil, which the crops need for the manufacture of proteins and healthy growth, thereby raising yield.
- Use of improved (high-yielding) varieties through selective breeding - Principle: plants with desirable genes (fast growth, disease resistance, large produce) are selected and bred so that these favourable characteristics are passed on, giving heavier harvests.
Other acceptable methods: irrigation (supplies water for photosynthesis and transport of nutrients) and pest and weed control (removes organisms that compete with or destroy the crop).
(ii) Preserving and storing food
- Refrigeration or freezing (low temperature) - Principle: low temperatures slow down the activity of enzymes and inhibit the growth and multiplication of decay-causing micro-organisms (bacteria and fungi), so the food does not spoil quickly.
- Drying (dehydration) - Principle: removing moisture from the food deprives micro-organisms of the water they need to grow and reproduce, thereby preventing decay.
Other acceptable methods: salting or sugaring (high salt/sugar concentration draws water out of microbial cells by osmosis, killing or inhibiting them) and canning/pasteurisation (heat kills micro-organisms and sealing prevents re-entry of air and microbes).
Question 4 Report
(a) State four modes of nutrition in plants.
(b) Outline the process involved in the light and dark reactions of photosynthesis.
(c) Describe briefly the modifications and the mechanisms associated with the following feeding habits:
(i) filter feeding in mosquito larva; (ii) parasitic feeding in tapeworm.
(a) Four modes of nutrition in plants
- Autotrophic (holophytic) nutrition: green plants manufacture their own food by photosynthesis, e.g. most green plants.
- Saprophytic nutrition: feeding on dead organic matter, e.g. Mucor, Rhizopus, mushroom.
- Parasitic nutrition: feeding on a living host, e.g. Cuscuta (dodder), mistletoe.
- Carnivorous (insectivorous) nutrition: trapping and digesting insects, e.g. sundew, pitcher plant, bladderwort.
(Symbiotic nutrition, e.g. lichen, is also acceptable.)
(b) Light and dark reactions of photosynthesis
Light reaction (light-dependent stage):
- Takes place in the grana of the chloroplast and requires light.
- Chlorophyll absorbs (traps) light energy.
- The trapped energy splits water molecules into hydrogen and oxygen (photolysis of water); the oxygen is released as a by-product.
- The light energy is used to form energy-rich ATP, and hydrogen is picked up by a carrier (NADP) to form reduced NADP (NADPH2).
Dark reaction (light-independent stage / Calvin cycle):
- Takes place in the stroma of the chloroplast and does not need light directly.
- Carbon dioxide is fixed (combined) using the hydrogen (from reduced NADP) and the energy (from ATP) produced in the light stage.
- This reduces carbon dioxide to form simple sugar (glucose), which may then be built up into starch.
Overall: \[ 6CO_2 + 6H_2O \xrightarrow{\text{light, chlorophyll}} C_6H_{12}O_6 + 6O_2 \]
(c) Modifications and mechanisms of feeding habits
- (i) Filter feeding in mosquito larva: the larva lives in water and hangs just below the surface. It has a pair of brushes of fine hairs (mouth brushes) around the mouth. These hairs beat rapidly and set up water currents that sweep small floating food particles (plankton, tiny organisms and organic matter) in the water towards the mouth, where they are filtered out and swallowed. In this way the larva strains (filters) food from the water.
- (ii) Parasitic feeding in tapeworm: the tapeworm lives in the small intestine of its host (man), where digested food is abundant. It has a head (scolex) bearing hooks and suckers for firm attachment to the intestinal wall, so that it is not swept away. It has no mouth and no gut; instead it has a thin, flat, ribbon-like body with a very large surface area covered by a resistant cuticle that protects it from the host's digestive enzymes. It simply absorbs already-digested, soluble food from the host through its whole body surface (osmosis and diffusion). Its long, segmented body also allows it to produce large numbers of eggs for reproduction.
Answer Details
(a) Four modes of nutrition in plants
- Autotrophic (holophytic) nutrition: green plants manufacture their own food by photosynthesis, e.g. most green plants.
- Saprophytic nutrition: feeding on dead organic matter, e.g. Mucor, Rhizopus, mushroom.
- Parasitic nutrition: feeding on a living host, e.g. Cuscuta (dodder), mistletoe.
- Carnivorous (insectivorous) nutrition: trapping and digesting insects, e.g. sundew, pitcher plant, bladderwort.
(Symbiotic nutrition, e.g. lichen, is also acceptable.)
(b) Light and dark reactions of photosynthesis
Light reaction (light-dependent stage):
- Takes place in the grana of the chloroplast and requires light.
- Chlorophyll absorbs (traps) light energy.
- The trapped energy splits water molecules into hydrogen and oxygen (photolysis of water); the oxygen is released as a by-product.
- The light energy is used to form energy-rich ATP, and hydrogen is picked up by a carrier (NADP) to form reduced NADP (NADPH2).
Dark reaction (light-independent stage / Calvin cycle):
- Takes place in the stroma of the chloroplast and does not need light directly.
- Carbon dioxide is fixed (combined) using the hydrogen (from reduced NADP) and the energy (from ATP) produced in the light stage.
- This reduces carbon dioxide to form simple sugar (glucose), which may then be built up into starch.
Overall: \[ 6CO_2 + 6H_2O \xrightarrow{\text{light, chlorophyll}} C_6H_{12}O_6 + 6O_2 \]
(c) Modifications and mechanisms of feeding habits
- (i) Filter feeding in mosquito larva: the larva lives in water and hangs just below the surface. It has a pair of brushes of fine hairs (mouth brushes) around the mouth. These hairs beat rapidly and set up water currents that sweep small floating food particles (plankton, tiny organisms and organic matter) in the water towards the mouth, where they are filtered out and swallowed. In this way the larva strains (filters) food from the water.
- (ii) Parasitic feeding in tapeworm: the tapeworm lives in the small intestine of its host (man), where digested food is abundant. It has a head (scolex) bearing hooks and suckers for firm attachment to the intestinal wall, so that it is not swept away. It has no mouth and no gut; instead it has a thin, flat, ribbon-like body with a very large surface area covered by a resistant cuticle that protects it from the host's digestive enzymes. It simply absorbs already-digested, soluble food from the host through its whole body surface (osmosis and diffusion). Its long, segmented body also allows it to produce large numbers of eggs for reproduction.
