Ecology and the Environment
What you must understand
Learn the levels of organisation - organism, population, community, ecosystem - and the terms habitat, niche, producer, consumer, decomposer. Understand food chains and webs, energy transfer, pyramids of number and biomass, and why energy is lost at each trophic level (respiration, heat, excretion, uneaten parts).
Know the carbon and nitrogen cycles in outline, the factors affecting population size, and the effects of human activity: pollution, deforestation, greenhouse gases, eutrophication and conservation. Understand sampling with quadrats and transects.
Traps examiners set
- Drawing arrows in food chains the wrong way - arrows show energy flow to the consumer.
- Confusing a pyramid of numbers with a pyramid of biomass.
- Saying energy is "lost" as if destroyed - it is transferred to the environment as heat.
- Forgetting that decomposers recycle nutrients, not energy.
Worked rule of thumb
When asked why a food chain is short, calculate: only about 10% of energy passes to the next level, so after four levels little remains to support another trophic level. Use "10% rule" to justify answers.