Ecology and Environmental Science
What you must understand
Ecology studies relationships between organisms and their environment. Know the levels of organisation (organism, population, community, ecosystem, biosphere). Understand food chains and webs, trophic levels, producers, consumers, decomposers, and energy flow (about 10% transferred between trophic levels). Know the carbon and nitrogen cycles and the roles of photosynthesis, respiration and decomposition. Understand population dynamics (birth rate, death rate, carrying capacity) and ecological relationships (predation, competition, mutualism, parasitism). Know environmental issues: deforestation, pollution, greenhouse effect, and biodiversity loss, and conservation strategies.
Traps that appear in questions
- Forgetting that energy is lost as heat at each trophic level - food chains rarely exceed 4–5 levels.
- Confusing a food chain (linear) with a food web (interconnected).
- Saying decomposers are not part of food chains - they recycle nutrients.
- Mixing up the greenhouse effect (natural) with global warming (enhanced by human activity).
- Confusing mutualism (both benefit) with parasitism (one benefits, one is harmed).
Worked example
If producers contain 10 000 kJ of energy, the primary consumers receive about 1 000 kJ, and secondary consumers about 100 kJ. Rule of thumb: multiply by 0.1 at each step.