Environment, Ecology, and Natural Resources
This domain tests ecosystem structure, energy flow and nutrient cycling, the effects of pollution, and the management of natural resources.
Core rules
- An ecosystem has biotic components such as producers, consumers, and decomposers, and abiotic components such as light, water, temperature, and soil.
- A food chain starts with a producer. Energy passes to herbivores and then to carnivores. At each trophic level, only about 10% of energy is transferred; the rest is lost mainly as heat.
- Biogeochemical cycles such as the carbon, nitrogen, and water cycles recycle matter. Decomposers return nutrients to the soil.
- Pollution includes air pollution from burning fossil fuels, water pollution from sewage and fertilisers, and soil pollution from pesticides. Resource management includes reducing, reusing, recycling, and conserving water and forests.
Worked example
A food chain has producers with 10,000 J of energy. Using the ten-percent law, herbivores receive about 1,000 J, small carnivores about 100 J, and top carnivores about 10 J. The sharp decrease explains why food chains rarely have more than four or five trophic levels: too little energy remains to support another level.
Traps that cost marks
Do not start a food chain with a decomposer or a carnivore. Do not confuse the greenhouse effect with ozone depletion; they involve different gases and mechanisms. Decomposers are essential recyclers but are not usually counted as a trophic level. Remember that energy flows one way, while nutrients cycle.
Key points
- Ecosystems combine biotic and abiotic components.
- Food chains begin with producers.
- About 10% of energy passes to the next trophic level.
- Energy flows; nutrients cycle through biogeochemical cycles.