Biomass Transfer and Efficiency of Food Production — AQA GCSE Biology (Separate)

Energy and biomass are lost at each stage of a food chain, which has important consequences for food production.

Trophic levels

Each stage in a food chain is a trophic level:

Level 1: producers (plants/algae that photosynthesise).
Level 2: primary consumers (herbivores).
Level 3: secondary consumers (carnivores).
Level 4: tertiary consumers (apex predators).
Decomposers break down dead material at all levels.

Biomass transfer

Biomass is the mass of living material. Producers convert only about 1% of the light energy that reaches them into biomass. At each consumer level, only about 10% of the biomass is transferred to the next level.

Why is so much lost?

Not all of an organism is eaten or digested (some is lost in faeces).
Energy is used for respiration (movement and keeping warm), and lost as heat and in waste (urine).

Calculating efficiency

$$\text{efficiency} = \frac{\text{biomass transferred to the next level}}{\text{biomass available at the previous level}} \times 100$$

Because so much is lost, food chains rarely have more than about four or five trophic levels.

Implications for food production

Eating plants (lower trophic levels) is more efficient than eating meat, because less biomass has been lost along the chain. This is relevant to feeding a growing population.

Exam tips

Learn that ~10% of biomass passes to the next trophic level.
Explain the losses: faeces, respiration, heat, urine.
Use the efficiency calculation.
Eating lower trophic levels (plants) is more efficient — link to food security.

Biomass transfer and efficiency of food production