Efficiency and biomass calculationsSpec 9.8B
In short
Efficiency of transfer is the percentage of the energy or biomass at one trophic level that passes to the next. Efficiency (%) = energy or biomass transferred to the next level ÷ energy or biomass available at the previous level × 100. For example, 4 000 kJ ÷ 40 000 kJ × 100 = 10 %.
You may be asked to work out how efficiently energy or biomass is transferred from one trophic level to the next.
Energy transfer efficiency
The grass in a field contains 40 000 kJ of energy. The cattle that eat the grass gain 4 000 kJ in their biomass. Calculate the efficiency of energy transfer from grass to cattle.
- Efficiency = energy transferred ÷ energy available × 100
- = 4 000 ÷ 40 000 × 100
- = 10 %
Answer: 10 %
Percentage of biomass
A caterpillar eats 40 g of leaf (dry mass) and its own dry mass increases by 6 g. Calculate the percentage of the leaf biomass that became caterpillar biomass.
- Percentage = mass gained ÷ mass eaten × 100
- = 6 ÷ 40 × 100
- = 15 %
Answer: 15 %
The numbers are always less than 100 %, because energy and biomass are lost at every stage. The remainder is the part lost as heat, waste or uneaten material.
Divide by the amount at the lower trophic level (the one that came first), not the higher one. Give your answer as a percentage with a % sign.
Quick check
Give two ways energy is lost between trophic levels.
Show answer
Any two of: respiration (heat), movement, waste (faeces, urine), parts not eaten.
Why are food chains short?
Show answer
Energy is lost at each level, so too little remains to support more trophic levels.
What shape is a pyramid of biomass?
Show answer
Wide at the bottom, narrower at each higher trophic level.
State the equation for efficiency of transfer.
Show answer
Energy transferred to next level ÷ energy available at previous level × 100.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026