AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Only approximately 10 % of the biomass from each trophic level is…
Full specification wording
Transfer of biomass: Only approximately 10 % of the biomass from each trophic level is transferred to the level above it.
When a consumer eats a producer or another consumer, only about 10 % of the biomass of the eaten organism becomes biomass of the eater.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 7
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When a consumer eats a producer or another consumer, only about 10 % of the biomass of the eaten organism becomes biomass of the eater. The remaining biomass is accounted for by material that is not eaten, material that is ingested but not absorbed and is egested as faeces, and absorbed material that is used in respiration and lost as carbon dioxide, water and heat, or excreted as urea. Because each transfer is so inefficient, the biomass available at each successive trophic level falls sharply, producing a pyramid with much smaller upper bars. This also limits food chains to about four or five trophic levels, since too little biomass remains to support another level. The figure is an approximation and varies with the organisms and environment.
What earns the marks
- States that approximately 10 % of biomass is transferred from one trophic level to the next.
- Applies the 10 % figure to calculate the biomass available at a higher trophic level from a given starting biomass.
- Explains that the remaining biomass is lost through uneaten material, egestion as faeces, respiration and excretion.
- Links the low transfer efficiency to the narrowing shape of a pyramid of biomass.
- Uses the 10 % figure to explain why food chains rarely contain more than four or five trophic levels.
- Recognises that 10 % is an approximation that varies between ecosystems and organisms.
Common mistakes and how to put them right
Treating 10 % as an exact value in every ecosystem.
Put it right: Describe it as approximate and note that it varies.
Calculating 10 % of the energy at the previous level but labelling the answer as energy at the current level without units.
Put it right: Keep the unit consistent, such as kJ m⁻² year⁻¹ or g m⁻².
Assuming the missing 90 % is destroyed.
Put it right: It is transferred to the environment or remains in uneaten and egested material.
Exam tips
- Show each multiplication step when calculating biomass at successive trophic levels.
- Use the phrase approximately 10 % to signal that the value is not exact.
- When explaining food chain length, refer both to the small proportion transferred and to losses by respiration and egestion.
Try the lesson
The start of the Transfer of biomass: Only approximately 10 % of the biomass from each trophic level is transferred to the level above it. lesson, made from checked teaching notes for this specification point.
Have a go first
In a food chain, what percentage of biomass is typically transferred from one trophic level to the next?
Listen
When a consumer eats a producer or another consumer, only about 10 % of the biomass of the eaten organism becomes biomass of the eater. The remaining biomass is accounted for by material that is not eaten, material that is ingested but not absorbed and is egested as faeces, and absorbed material that is used in respiration and lost as carbon dioxide, water and heat, or excreted as urea. Because each transfer is so inefficient, the biomass available at each successive trophic level falls sharply, producing a pyramid with much smaller upper bars. This also limits food chains to about four or five trophic levels, since too little biomass remains to support another level. The figure is an approximation and varies with the organisms and environment. A strong answer earns marks for these points. States that approximately 10 % of biomass is transferred from one trophic level to the next. Applies the 10 % figure to calculate the biomass available at a higher trophic level from a given starting biomass. Explains that the remaining biomass is lost through uneaten material, egestion as faeces, respiration and excretion. Links the low transfer efficiency to the narrowing shape of a pyramid of biomass. A common slip: Treating 10 % as an exact value in every ecosystem. Instead, describe it as approximate and note that it varies. Exam tip: Show each multiplication step when calculating biomass at successive trophic levels.
Key words
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Efficiency of biomass transfer
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Limits on food chain length
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See every definition
- Efficiency of biomass transfer
- Only approximately 10 % of the biomass from each trophic level is transferred to the level above it, and this figure is an approximation that varies with the organisms and environment.
- Limits on food chain length
- Too little biomass remains to support another level, which limits food chains to about four or five trophic levels.
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