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Quiz yourself on Ecosystems CommunitiesGet your flashcardsBuild my revision planTrack my progress📊 Pyramids of Biomass
A pyramid of biomass shows the total mass of living material at each trophic level in a food chain. Each bar represents the biomass (dry mass) of all organisms at that level.
Figure: Pyramid of biomass — each level is ~10% of the one below.
Why Is It Pyramid-Shaped?
At each trophic level, energy is lost through:
- Respiration — organisms use energy for movement, growth, and keeping warm
- Waste products — not all food is digested (faeces, urine)
- Heat — energy transferred to the surroundings
Only about 10% of the biomass at one level is passed to the next. This means there is always less biomass at higher trophic levels — which is why the diagram forms a pyramid shape.
Pyramids of Biomass vs Pyramids of Numbers
Pyramids of numbers can sometimes look inverted (e.g. one oak tree → thousands of caterpillars), but pyramids of biomass are almost always pyramid-shaped because biomass accounts for the size of organisms, not just how many there are.
Exam tip: If asked why biomass decreases at each trophic level, always mention respiration and waste/egestion — these are the two mark points examiners look for.
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