Ecology, Environment and Conservation
What this domain tests
Ecology, Environment and Conservation examines ecosystems, food chains and webs, energy flow, nutrient cycling, populations, adaptations, biodiversity and human impact.
Core rules
- A habitat is where an organism lives; a population is all organisms of one species in an area; a community is all populations; an ecosystem includes the community and its physical environment.
- Food chains show feeding relationships. Arrows point in the direction of energy transfer, from producer to consumer.
- Producers make food by photosynthesis; primary consumers eat producers; decomposers break down dead matter and recycle nutrients.
- Energy is lost at each trophic level through respiration, heat, movement and undigested material. Only about 10% is transferred to the next level, so food chains rarely have more than four or five links.
- Nutrient cycles such as the carbon cycle depend on photosynthesis, respiration, feeding, decomposition and combustion.
- Conservation protects biodiversity and habitats; pollution, deforestation, overfishing and introduced species reduce biodiversity.
Worked example
A grassland producer stores 20,000 kJ of energy. If 10% is transferred to primary consumers, they receive 2,000 kJ. Secondary consumers receive 10% of that, 200 kJ. Tertiary consumers receive 20 kJ. This explains why top carnivores are few and why eating lower down the food chain is more energy-efficient. The calculation uses the transfer ratio, not the total energy at the start.
Traps
Do not reverse the arrows in a food chain. A pyramid of numbers can be inverted, for example many insects on one tree; a pyramid of energy is always wider at the base. Decomposers are not usually shown at the end of a food chain but are essential for recycling. Environment is not the same as ecosystem.