Ecology, Environment and Conservation
What this domain tests
Ecosystems, food chains and webs, energy flow, nutrient cycles, populations, competition, human impact and conservation.
Core rules
- Arrows in a food chain show the direction of energy flow, from producer to consumer.
- Only about 10% of energy passes to the next trophic level; the rest is lost mainly as heat from respiration, plus uneaten parts and excretion.
- Decomposers break down dead material and return mineral ions to the soil; they are not usually drawn in a food chain but are essential to nutrient cycling.
- Pyramids of numbers can be inverted (one tree, many insects); pyramids of energy cannot.
- Conservation means sustainable use and protection of habitats, not total exclusion of people.
Worked example
Producers in a habitat contain 50 000 kJ of energy. Assuming 10% transfer at each level: primary consumers receive 5 000 kJ, secondary consumers 500 kJ, tertiary consumers 50 kJ. If a question asks for energy “lost”, subtract: 4 500 kJ is lost between producers and primary consumers.
Traps that cost marks
- Drawing arrows from consumer to prey.
- Saying energy is “destroyed” - it is transferred and eventually lost as heat.
- Writing that decomposers are primary consumers.
- Ignoring the unit (kJ m⁻² yr⁻¹) when comparing productivity.