Pyramids of Biomass and Biomass Transfer
Build confidence in Pyramids of Biomass and Biomass Transfer for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) biology topic on drawing pyramids of biomass and calculating the roughly 10% efficiency of biomass transfer between levels.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Pyramids of biomass show the relative amount of biomass at each trophic level, with producers always at the bottom. This is a Triple-only topic.
Producers convert only about one per cent of the light energy falling on them into glucose for photosynthesis. Then only about ten per cent of the biomass at each trophic level is transferred to the level above.
The losses occur because not all the ingested material is absorbed — some is egested as faeces — and large amounts of glucose are used in respiration, with energy lost as heat. Losses also occur through excretion of urea in urine. This is why pyramids of biomass are always pyramid-shaped and why food chains are short.
Revision notes
Efficiency of transfer
Producers convert about 1 per cent of the light energy falling on them into glucose.
Approximately 10 per cent of the biomass from each trophic level is transferred to the level above. The efficiency calculation is biomass transferred ÷ biomass available × 100.
Where biomass is lost
Not all the ingested material is absorbed — some is egested as faeces.
Some absorbed material is lost as waste, such as carbon dioxide and water in respiration and urea in urine. Large amounts of glucose are used in respiration, releasing energy for movement and to maintain body temperature, which is lost as heat.
Why food chains are short
Because only about 10 per cent transfers at each stage, the biomass available falls rapidly.
After four or five levels there is too little biomass remaining to support another trophic level, which is why food chains rarely extend further.
Key points
- Producers convert about 1 per cent of light energy into glucose.
- About 10 per cent of biomass transfers between trophic levels.
- Biomass is lost as faeces in egestion.
- Biomass is lost as urea in urine.
- Respiration releases energy lost as heat.
- Efficiency = biomass transferred ÷ biomass available × 100.
Worked examples
Example 1
A trophic level contains 8000 kJ of biomass and transfers 800 kJ to the next level. Calculate the percentage efficiency. [2 marks]
Model answer
Efficiency = 800 ÷ 8000 × 100 (1 mark) = 10 per cent (1 mark).
Example 2
Give three ways biomass is lost between trophic levels. [3 marks]
Model answer
Not all ingested material is absorbed, so some is egested as faeces (1 mark). Some absorbed material is lost as waste such as urea in urine (1 mark). Large amounts of glucose are used in respiration, with energy transferred to the surroundings as heat (1 mark).
Example 3
Explain why food chains rarely have more than five trophic levels. [2 marks]
Model answer
Only about 10 per cent of the biomass is transferred at each level (1 mark), so after several levels there is too little biomass remaining to support another trophic level (1 mark).
Common mistakes
Saying 10 per cent of energy is lost.
About 10 per cent is TRANSFERRED; about 90 per cent is lost.
Confusing egestion with excretion.
Egestion is faeces, material never absorbed; excretion is waste made by the body, such as urea.
Forgetting respiration as a loss.
It is the largest single route, with energy lost as heat.
Dividing the wrong way in the efficiency calculation.
It is transferred ÷ available, not the reverse.
Exam tips
- Remember 10 per cent is transferred, not lost.
- Learn the three loss routes: egestion, excretion and respiration.
- Keep egestion and excretion clearly distinct.
- Remember this is a Triple-only topic.
Key terms
- Biomass
- The mass of living material.
- Egestion
- The removal of material never absorbed, as faeces.
- Excretion
- The removal of waste produced by the body.
- Trophic level
- The position of an organism in a food chain.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.