Ecology
What the exam tests
This domain tests organism-environment interactions, population growth, community interactions, ecosystem productivity, energy flow, nutrient cycling, ecological pyramids, biodiversity, and conservation.
Core rules and concepts
- Population growth can be exponential (J-shaped) or logistic (S-shaped, limited by carrying capacity).
- Community interactions include competition, predation, parasitism, mutualism, and commensalism.
- Gross primary productivity (GPP) is total organic matter fixed; net primary productivity (NPP) = GPP − respiration.
- Energy flow is unidirectional; the 10% law describes transfer between trophic levels.
- Ecological pyramids can be of numbers, biomass, or energy; energy pyramids are always upright.
- Nutrient cycles include gaseous cycles (carbon, nitrogen) and sedimentary cycles (phosphorus).
- Biodiversity hotspots are regions with high species richness and high endemism under threat.
Worked example
If producers fix 10,000 kcal of energy, how much reaches secondary consumers under the 10% law? Primary consumers receive 10% = 1,000 kcal; secondary consumers receive 10% of that = 100 kcal. The reasoning applies the transfer efficiency at each trophic step, not once overall.
Traps that cost marks
Do not confuse GPP with NPP. A pyramid of numbers can be inverted, but an energy pyramid cannot. Standing crop is not the same as productivity. Do not treat habitat and niche as synonyms: habitat is where an organism lives; niche is its functional role.