Trophic Efficiency
The fraction of energy transferred from one trophic level to the next (typically approximately 10%), explaining why food chains have limited length.
Formula
Trophic Efficiency (%) = (Energy at level N+1 ÷ Energy at level N) × 100
Real World
In the North Sea, roughly 1,000 kg of phytoplankton supports only ~10 kg of cod — the 10% rule explains why it takes vast amounts of fish feed to raise 1 kg of farmed salmon.
Exam Focus
Show your working in calculations; state the 10% figure and multiply step-by-step — don't skip trophic levels.
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