Ecology and conservation
Biology · WAEC and JAMB · SS2 and SS3
Heavy on definitions and on applying ideas to Nigerian examples. Examiners reward candidates who name a real local case.
What you need to know
- An ecosystem is a community of organisms together with its non-living environment.
- Energy flows one way through a food chain and is lost as heat at each level, which is why chains are short.
- Only about 10 per cent of energy passes from one trophic level to the next.
- Producers are green plants; primary consumers are herbivores; secondary and tertiary consumers are carnivores.
- Decomposers return nutrients to the soil, which is why nutrient cycles continue but energy does not.
- Nitrogen cycle: fixation, nitrification, assimilation, ammonification, denitrification.
- Pollution in Nigeria: oil spillage in the Niger Delta, gas flaring, urban refuse, industrial effluent.
- Conservation methods: afforestation, controlled grazing, game reserves, laws against poaching, waste recycling.
Key terms
- Habitat
- The place where an organism lives.
- Niche
- The role an organism plays in its habitat, including what it eats and when it is active.
- Biome
- A large region with a characteristic climate and community, such as savanna or rainforest.
- Food web
- Interconnected food chains showing the real feeding relationships in a community.
Worked example
Explain why a food chain rarely has more than five trophic levels.
- Energy enters at the producers and passes along the chain.
- At each transfer about 90 per cent is lost as heat, in respiration and in uneaten parts.
- After four or five levels too little energy remains to support another population.
Answer: Because energy is lost at each trophic level, leaving too little to sustain further levels.
The mistake to avoid
Energy cycles and nutrient cycles are different. Nutrients cycle; energy does not — it flows through and is lost. Saying "energy is recycled" is marked wrong.
In the exam
Name a Nigerian example wherever you can: Niger Delta oil spillage, Lake Chad shrinkage, Yankari Game Reserve. Specific examples separate a good answer from an average one.