GCSE Biology · AQA 8461 · Topic 4.7.2
Organisation of an ecosystem
Key points
- Food chains start with a producer (photosynthesising organism). Consumers are primary, secondary and so on; predator–prey cycles rise and fall out of step.
- Sampling: quadrats estimate population size; transects show how distribution changes across a habitat. Mean number per quadrat × total area / quadrat area estimates population.
- The carbon cycle: photosynthesis removes CO; respiration, combustion and decay release it.
- The water cycle: evaporation, transpiration, condensation and precipitation provide fresh water.
- Decomposition by bacteria and fungi is faster when warm, moist and with oxygen. Compost and biogas are made this way.
- Environmental change (water, temperature, gas levels) can change where species are found.
Topic notesPremium
Ecosystems are organised by feeding relationships, and materials are constantly recycled through them. This sub-topic covers food chains, measuring populations in the field, the carbon and water cycles and decomposition.
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