Transfer of biomass — AQA GCSE Biology
Test yourself on Transfer of biomass with AQA GCSE practice questions.
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Transfer of biomass explained
A pyramid of biomass is a quantitative diagram in which each trophic level is drawn as a horizontal bar whose area is proportional to the dry mass of living material present, usually measured in g m⁻² or kg m⁻².
Read the full explanation
Producers form the wide base, primary consumers the next bar, and so on, so the shape shows how much energy-containing material is available at each stage. Biomass is lost between levels because much ingested material is not absorbed and is egested as faeces, absorbed material is used in respiration and lost as carbon dioxide and water, and some is excreted as urea or other waste. Energy also leaves as heat, and dead organisms and waste become detritus for decomposers. Because only about 10 % of biomass passes to the next level, pyramids usually narrow sharply, and food chains rarely have more than four or five trophic levels.
Your focus
- Draw and interpret a pyramid of biomass with correctly scaled bars for named trophic levels.
- Identify and sequence the processes by which biomass is lost between trophic levels.
- Use the approximate 10 % transfer figure to explain the shape of pyramids and the length of food chains.
Transfer of biomass exam tips
Marking Points
- Defines a pyramid of biomass as a diagram whose bar areas represent the dry mass of organisms at each trophic level, with producers at the base.
- States that biomass is measured as dry mass per unit area, for example g m⁻², and that the bars are drawn to scale.
- Explains that not all ingested material is absorbed, so some is egested as faeces and is not available to the next trophic level.
- Explains that absorbed material is used in respiration, releasing carbon dioxide and water, so biomass is lost as these waste products.
- Explains that some absorbed material is excreted as waste such as urea, and that heat from respiration is also lost to the environment.
- Uses the idea that only about 10 % of biomass is transferred to the next trophic level to explain why pyramids narrow and food chains are short.
Examiner Tips
- 💡Label each bar with the trophic level and the organism, and state the unit of biomass on the axis.
- 💡When explaining losses, work through the sequence ingestion, absorption, egestion, respiration and excretion so no stage is omitted.
- 💡Use the 10 % figure as a quantitative anchor when asked why a food chain has few trophic levels.
Common Mistakes
- Drawing bars of equal width or using numbers of organisms instead of biomass; correction: make each bar's area proportional to the dry mass at that trophic level.
- Claiming that energy is destroyed or simply disappears between levels; correction: state that energy is transferred to the environment by respiration, heat and waste, and is not destroyed.
- Confusing biomass with the total mass of water-containing tissue; correction: use dry mass, since water content varies and is not useful for comparing trophic levels.