Triple Science Only - Transfer Of Biomass
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of trophic levels and biomass.
What is biomass?
Biomass is the total mass of living material in a specific area or at a specific trophic level.
What is a producer?
Photosynthesising plants - found at the first trophic level.
What are the products of aerobic respiration?
Carbon Dioxide and Water.
Topic Explainer Video
Check out this @JoeDoesGCSEBiology video that explains the transfer of biomass, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Transfer of Biomass
How Biomass Is Transferred
Biomass is transferred through food chains when organisms eat each other. However, only a small fraction of biomass and energy is passed on from one trophic level to the next.
Producers
- Mostly plants and algae (Trophic level 1 in food chains).
- They use photosynthesis to convert light energy into chemical energy (in glucose).
- Most light actually misses the leaves or the chloroplasts, or is the wrong wavelength to be absorbed by chlorophyll.
Biomass Transfer Between Trophic Levels
- Typically, only about 10% of the biomass is passed on to the next trophic level.
- The rest is lost due to several processes:
|
Reason for Biomass Loss |
Explanation |
|
Not all ingested material is absorbed |
Some material is egested as faeces. |
|
Respiration |
Glucose is used for energy and energy is lost as heat during respiration. Respiration also produces the waste gas CO2. |
|
Excretion |
Waste products like carbon dioxide and urea are lost. |
|
Uneaten material |
Some parts of organisms (bones, fur, etc.) are not eaten at all. |
Efficiency of Biomass Transfer
You need to know how to calculate the efficiency of biomass transfer:
Efficiency (%) = (Biomass of the trophic level / Biomass available at previous level) x 100
Example:
If the biomass of the primary consumers is 5000 kg, and secondary consumers biomass is 500 kg:
Efficiency = (500 / 5000) x 100 = 10%
Why Are Food Chains Short?
- Because only 10% of energy is transferred at each level, there's less biomass available higher up.
- This limits the number of trophic levels and the number of organisms that can survive at higher levels.
Key Terms & Definition
Biomass - The total mass of living organisms in a given area or trophic level.
Trophic level - A position an organism occupies in a food chain.
Egestion - The removal of undigested food as faeces.
Excretion - The removal of metabolic waste (e.g. CO₂, urea).
Efficiency - The percentage of biomass or energy transferred from one trophic level to the next.
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Exam Tip:
- Remember, biomass and energy are lost at each trophic level. Always give reasons for these losses, such as loss in faeces, loss in urine and loss of heat energy during respiration.
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Practice Question
Explain why biomass is lost between trophic levels in a food chain. (4 marks)
Model Answer:
- Not all the food eaten is digested; some is egested as faeces.
- Some of the absorbed food is used in respiration and lost as heat energy.
- Other materials are excreted as waste products like carbon dioxide and urea.
- Some parts of the organism, like bones or fur, are not eaten.
More Practice
Try to answer the practice question from the TikTok video on your own, then watch the video to see how well you did!