Ecology and Environmental Biology
What you must understand
Know the levels: organism, population, community, ecosystem, biosphere. Understand biotic and abiotic factors, habitat vs niche, and producers, consumers, decomposers. Learn food chains and food webs, trophic levels, and that energy is lost at each level (roughly 10% transferred). Know population dynamics (birth rate, death rate, immigration, emigration, carrying capacity) and symbiosis types: mutualism, commensalism, parasitism, plus competition and predation. Understand biogeochemical cycles (carbon, nitrogen, water) and the causes/consequences of environmental problems: pollution, deforestation, greenhouse effect, loss of biodiversity, eutrophication. Know basic conservation ideas (protected areas, sustainable use).
Traps candidates fall into
- Drawing an arrow the wrong way in a food chain - the arrow points from the eaten to the eater (direction of energy flow).
- Calling decomposers "consumers" in a way that skips their role - they recycle nutrients back to producers.
- Confusing habitat (where it lives) with niche (its role and requirements).
- Assuming energy flows in a cycle - energy flows one way and is lost; matter cycles.
- Mixing eutrophication (nutrient overload → algal bloom → oxygen depletion) with ordinary pollution.
Worked example / rule of thumb
In the chain grass → grasshopper → frog → snake, the grass is the producer, the grasshopper a primary consumer, and the snake a tertiary consumer. If the grass stores 10 000 units of energy, roughly 1 000 reach the grasshopper and 10 reach the snake at 10% transfer. Rule of thumb: energy arrows point toward the eater; matter cycles, energy does not.