Candidates performed fairly on the (a) part of question four as they were able to correctly define pollution as well as state pollutants of water.
In describing the effects of the named pollutants on aquatic organisms some candidates wrote on general effects of pollution on the environment. A few candidates who wrote on effect of the pollutants on aquatic organisms did not separate the effects of each pollutant. They lumped the effect of all the pollutants which led to loss of marks. Expected answers include:
Effect of pollutants on aquatic organisms:
Domestic wastes
- Bacterial breakdown of sewage reduces dissolved oxygen in water/eutrophication;
- aquatic animals suffocate and die;
- rapid growth of aquatic plants due to mineral rich sewage;
- reduces light penetration and photosynthesis;
- contaminated sewage spread disease-causing organisms.
Industrial wastes
- are poisonous to aquatic organisms;
- detergents form foam on the water surface reducing light penetration;
- and photosynthesis; '
- reduces surface tension, causing floating animals to sink;
- phosphates cause rapid plant growth;
- dyes from textile factories reduce light penetration/photosynthesis.
Agricultural wastes
These may accumulate to toxic levels; thereby poisoning aquatic organisms;
Fertilizer residues stimulate growth of aquatic plants which form a dense mat on the surface of the water; leading to depletion of oxygen/eutrophication; reduction of light penetration; resulting in decrease in the rate of photosynthesis; and causing death of aquatic organisms.
Oil Spillage
- Oil reduces surface tension of water;
- causing floating animals to sink;
- animals die from lack of oxygen;
- coats feathers/fur of animals;
- making them unable to fly/causing affected animals to freeze/starve to death;
- coats gills/filters of aquatic organisms;
- reduces light penetration;
- and decreases rate of photosynthesis;
- toxic to aquatic organisms.
Hot Water
- kills living organisms;
- upsets the balance of the ecosystem;
- hot water increases the water temperature;
- thereby reducing the oxygen content;
- and leading to death.
Bacteria breakdown of sewage reduces dissolved oxygen in water/eutrophication;
Aquatic animals suffocate and die; rapid growth of aquatic plants due to mineral rich sewage reduces light penetration and photosynthesis; contaminated sewage spread disease-causing 
