A farmer decides to rear cattle for beef rather than growing wheat to sell directly as food for humans. Explain why feeding the wheat to cattle before humans eat the beef is a less efficient use of biomass than humans eating the wheat directly.

Biomass is lost at each trophic level – only a small fraction of the energy in the wheat is transferred to the cattle. The rest is lost as heat during respiration, used for movement and to keep the cattle warm.

Adding the extra trophic level of cattle means that, before the biomass reaches humans, it has already been reduced by the cattle’s metabolic needs. Consequently, less biomass is available for human consumption.

If humans eat the wheat directly, they are at a lower trophic level and therefore receive a larger proportion of the original biomass, making the use of the wheat more efficient.