GCSE Biology · AQA 8461 · Topic 4.7.4
Trophic levels in an ecosystem
Key points
- Trophic level 1: producers; 2: primary consumers (herbivores); 3 and 4: secondary and tertiary consumers. Apex predators have no predators.
- Decomposers break down dead material and waste by secreting enzymes.
- Pyramids of biomass show the mass of living material at each level and are drawn to scale.
- Only about 10% of biomass passes to the next level. Losses: not all is eaten, some is egested, lost as urea, or used in respiration.
- Efficiency of transfer .
- Because of these losses food chains rarely have more than four or five levels.
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Each step in a food chain is a trophic level, and only a small fraction of the biomass at one level ends up in the next. This explains why food chains are short and why predators at the top are relatively few.
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