Ecology and Environmental Biology
Ecology and Environmental Biology
This domain tests ecosystems, energy flow, nutrient cycling, population growth, succession, biodiversity and human impacts. Questions often use a food web or a population graph and ask for an explanation, not just a label.
Core rules
- Producers capture light energy. Consumers feed at successive trophic levels; decomposers break down dead matter and recycle nutrients.
- Energy flows one way and is lost as heat and through excretion and respiration. Only about 10% is transferred to the next trophic level, so food chains are short.
- Nutrients such as carbon, nitrogen and phosphorus cycle through biotic and abiotic reservoirs.
- Populations show exponential growth when resources are unlimited and logistic growth when carrying capacity is reached. Primary succession starts on bare rock; secondary succession follows disturbance where soil remains.
Worked example
A producer level contains 100,000 kcal. At 10% transfer, primary consumers receive 10,000 kcal, secondary consumers 1,000 kcal, and tertiary consumers 100 kcal. Reasoning: multiply by 0.1 at each step. The tertiary consumer therefore needs a large area of producers to support it.
Traps
An energy pyramid is never inverted. A pyramid of numbers can be inverted, for example many insects on one tree. Decomposers are not the same as producers. Eutrophication is caused by excess nutrients, not by toxic waste alone. Energy is not recycled in an ecosystem; nutrients are.