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How is energy transferred through trophic levels, and how can food production be made sustainable?

Trophic levels and the transfer of biomass, the calculation of efficiency of biomass transfer, pyramids of biomass, the impact of food security, and methods of sustainable food production including fish stocks and biotechnology.

A focused answer to AQA GCSE Biology 4.7.4 to 4.7.5, covering trophic levels, the transfer and efficiency of biomass, pyramids of biomass, food security, and sustainable methods of food production.

Generated by Claude Opus 4.810 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. Trophic levels
  3. Transfer of biomass
  4. Food security and sustainable production
  5. Try this

What this dot point is asking

This higher-tier-heavy dot point asks you to describe trophic levels, explain why only a small proportion of biomass is transferred between them, calculate the efficiency of transfer, and discuss food security and sustainable food production.

Trophic levels

Transfer of biomass

Not all the biomass at one level passes to the next. Energy and biomass are lost at each step because:

  • Not all of an organism is eaten (roots, bones), and not all of what is eaten is digested, so material is lost in faeces.
  • Energy is used for respiration, which powers movement and, in mammals and birds, keeping warm. This energy is eventually lost to the surroundings as heat.
  • Some nitrogen-containing compounds are lost in waste products such as urine.

This loss explains why food chains are usually short (rarely more than four or five levels): after several transfers there is too little biomass left to support another level. It also means there is more biomass at the bottom than the top, shown in a pyramid of biomass, which is always widest at the producer level.

Food security and sustainable production

Methods to make food production more efficient or sustainable include:

  • Limiting animal movement and keeping them warm so less energy is lost in respiration (intensive farming), which increases efficiency but raises ethical and animal-welfare concerns.
  • Managing fish stocks by setting quotas (catch limits) and controlling net mesh size so young fish escape and breed, allowing populations to recover and keeping fishing sustainable.
  • Using biotechnology, for example growing the fungus Fusarium in fermenters to make mycoprotein (a high-protein meat substitute), and genetically modified crops with higher yields or pest resistance.

Eating lower down the food chain (more plants, less meat) is also more efficient because less biomass is lost between levels.

Try this

Q1. A trophic level contains 20 000 kJ20\ 000\ kJ of biomass and the next level contains 2000 kJ2000\ kJ. Calculate the efficiency of transfer. [2 marks]

  • Cue. (2000/20 000)×100=10%(2000 / 20\ 000) \times 100 = 10\%.

Q2. Give two reasons biomass is lost between trophic levels. [2 marks]

  • Cue. Any two of: respiration, movement, keeping warm, parts not eaten or not digested, waste.

Exam-style practice questions

Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AQA 20204 marksA producer in a food chain has a biomass of 80 000 kJ per square metre per year. The primary consumers contain 6400 kJ per square metre per year. Calculate the percentage efficiency of biomass transfer between these levels, and explain why so much biomass is lost. Show your working.
Show worked answer →

A 4-mark calculation-and-explain question rewards the correct working plus reasons.

Efficiency equals biomass transferred divided by biomass available, multiplied by 100. Efficiency equals 640080 000×100=8%\dfrac{6400}{80\ 000} \times 100 = 8\%.

Biomass is lost between levels because not all of the producer is eaten or digested (some passes out as faeces), and the primary consumers use energy in respiration for movement and, in mammals and birds, for keeping warm, with some lost in waste such as urine.

Markers reward the correct efficiency (8 percent) with working, and at least two reasons for the loss of biomass.

AQA 20224 marksExplain why managing fish stocks and using biotechnology can make food production more sustainable for a growing human population.
Show worked answer →

A 4-mark explain question rewards reasoning for each method.

Fish stocks are managed using fishing quotas (limits on how much can be caught) and controlling net mesh size so that young fish escape and can breed. This lets fish populations recover and reproduce, so fishing can continue in the future without the stock collapsing, which makes it sustainable.

Biotechnology can increase food supply efficiently, for example growing the fungus Fusarium to make mycoprotein, a high-protein meat substitute produced in fermenters, or genetically engineering crops to give higher yields or pest resistance. This produces more food using less land and fewer animals.

Markers reward quotas or mesh size linked to stock recovery, and a named biotechnology example linked to feeding more people sustainably.

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