Feeding RelationshipsEdexcel GCSE Biology: Revision notes
Section 1
Trophic Levels and Energy Loss
Energy lost at each trophic level via respiration (heat), egestion, excretion — not fully passed on.
Key termstrophic levelproducerbiomass
Common mistake
Energy is transferred to less useful forms (mainly heat), not 'lost' entirely.
Section 2
Effect on Numbers and Food Chain Length
Fewer organisms at higher trophic levels; food chains limited to ~4-5 levels since energy runs out.
Key termsenergy transfer
Example
Grass supports many rabbits but only few foxes.
Section 3
Pyramids of Biomass
Almost always a true pyramid shape (wide base, narrows up) since biomass decreases at each level.
Key termspyramid of biomass
Section 4
Calculating Efficiency of Energy Transfer
efficiency(%) = (energy transferred ÷ energy available) × 100.
Key termsefficiency of energy transfer
Example
Producers=8000kJ, consumers=800kJ: efficiency=(800/8000)×100=10%.
Must Know
- Energy lost via respiration/egestion/excretion, mainly as heat.
- Fewer organisms at higher trophic levels; chains limited to 4-5 levels.
- Pyramids of biomass: true pyramid shape.
- Efficiency(%) = (transferred÷available)×100, typically ~10%.
That's the notes covered.
Carry on to the next subtopic.