Ecology and Environmental Science
Core concepts
Understand levels of organization (organism, population, community, ecosystem, biosphere) and the factors that regulate populations (biotic potential, carrying capacity, density-dependent vs. density-independent factors). Know energy flow through trophic levels (10% rule), food webs, and biogeochemical cycles (carbon, nitrogen, water). Be able to explain primary and secondary succession, biodiversity, and human impacts (pollution, habitat loss, climate change).
Traps in questions
- Energy decreases up trophic levels (~10% transferred); biomass pyramids can invert in aquatic systems.
- Decomposers recycle nutrients, not energy.
- Density-dependent factors (disease, competition) intensify with crowding; density-independent factors (fire, drought) do not.
- Primary succession starts on bare substrate; secondary succession follows disturbance where soil remains.
Worked example / rule of thumb
If producers fix 10,000 kcal, primary consumers receive ~1,000 kcal, secondary ~100 kcal. Rule of thumb: energy flows one way and is lost as heat; matter cycles. Always identify the trophic level and the direction of transfer before computing.