Pyramids of biomass and energy transfer

Energy passes along food chains, but most of it is lost at each step. This explains the shape of pyramids of biomass and why food chains are short.

Practise this lesson free (6 questions)

Trophic levels and pyramids

Producers (plants and algae) make food by photosynthesis. Primary consumers eat producers; secondary consumers eat primary consumers, and so on. Each feeding level is a trophic level.
A pyramid of biomass shows the dry mass of living material at each level. It is usually pyramid-shaped, because there is less biomass at each higher level.

Where the energy goes

Only a small fraction of energy (often about 10%) is passed to the next level. The rest is lost because:
some of the organism is not eaten (roots, bones);
some is not digested and leaves as faeces;
some is lost as urine and other waste;
most is used in respiration and transferred to the surroundings as heat, and used for movement.

Calculating efficiency

efficiency = (energy transferred to next level ÷ energy at the previous level) × 100
Example: grass has 12 000 kJ; rabbits get 1200 kJ. Efficiency = 1200 ÷ 12 000 × 100 = 10%.
Because so much is lost at each step, there is rarely enough energy for more than about four or five trophic levels.
Worked example

Producers contain 20 000 kJ. Primary consumers receive 1600 kJ. Calculate the efficiency of the transfer.

  1. Efficiency = 1600 ÷ 20 000 × 100
  2. = 8%

Answer: 8%

Key idea

A pyramid of biomass shows dry mass at each trophic level. Energy is lost through parts not eaten, faeces, urine and respiration (heat). Efficiency = energy passed on ÷ energy available × 100. Food chains are short because so much is lost.

Key words
Trophic level
The position of an organism in a food chain, such as producer or primary consumer.
Respiration
An exothermic reaction in all living cells that releases energy from glucose.
Photosynthesis
The process in which plants use light energy to make glucose and oxygen from carbon dioxide and water.

All GCSE and International GCSE Biology key terms and definitions →

Quick check

Try two quick questions

See if it has sunk in. Answers are marked straight away.

Extra practice

2 more questions

Try each one, then tap to check.

  1. A trophic level contains 3600 kJ. The next level receives 360 kJ. Calculate the efficiency of transfer.

    Show the answer

    Answer: 10 %

    360 ÷ 3600 × 100 = 10%

  2. A producer level contains 20 000 kJ. If 10% is passed on, how much energy reaches the primary consumers?

    Show the answer

    Answer: 2000 kJ

    20 000 × 0.1 = 2000 kJ

Check you have got it

Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (6 questions)All GCSE and International GCSE Biology lessons

Video for this lesson coming soon. Subscribe on YouTube

Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

What do exam command words like explain and evaluate mean? →

Related lessons