Ecology, ecosystems and human influence
Ecology and human influence
This domain tests ecosystems, food chains and webs, pyramids, nutrient cycles, biodiversity and human impact.
Core rules
- Habitat is where an organism lives; population is one species in an area; community is all populations; ecosystem includes biotic and abiotic factors.
- Food chains show energy flow. Producers make food by photosynthesis; consumers feed; decomposers break down dead material and recycle nutrients.
- Energy is lost between trophic levels through respiration, heat, movement, excretion and uneaten parts. Only about 10% is transferred, so food chains are short and top consumers are fewer.
- Carbon cycle: photosynthesis removes CO2; respiration, combustion and decomposition release it. Nitrogen cycle: nitrogen fixation, nitrification, assimilation, decomposition, denitrification.
- Human impacts: deforestation, burning fossil fuels, eutrophication, overfishing, plastic pollution and introduced species reduce biodiversity. Conservation includes protected areas, recycling and sustainable use.
Worked example
A food chain has 10,000 kJ of energy in producers. If 10% transfers to the next level, primary consumers receive 1,000 kJ, secondary consumers 100 kJ and tertiary consumers 10 kJ. Reasoning: the loss is not a single 10% rule caused by one process; it is the net result of respiration, heat loss, movement, excretion and material not eaten. This explains why large top predators need large territories.
Traps
- Adding decomposers at the start of a food chain.
- Confusing pyramid of numbers with pyramid of biomass.
- Saying energy is recycled; nutrients are recycled, energy flows.
- Blaming eutrophication on toxic algae rather than nutrient enrichment.
- Treating biodiversity as simply number of individuals.