A farmer grows wheat in a large field. The wheat is eaten by mice, which are eaten by owls. The farmer wants to produce as much food as possible for humans. Explain why humans eating wheat directly is more efficient than humans eating meat from animals that have been fed on wheat.

In a food chain only about 10 % of the energy in one trophic level is transferred to the next. When wheat is eaten by mice, only 10 % of the wheat’s energy reaches the mice; when the owls eat the mice, only 10 % of that energy reaches the owls. Thus only 1 % of the original wheat energy reaches the owls.

Energy is lost as heat during respiration and as waste (faeces, urine, indigestible parts) at each trophic transfer. These losses mean that the energy available to the next level is far less than the energy stored in the previous level.

If humans eat wheat directly, only one trophic transfer occurs. The 10 % loss at that single step is far less than the cumulative 99 % loss that would occur if humans ate meat from animals that have fed on wheat. Therefore a greater proportion of the original energy in the wheat reaches humans, making direct consumption more efficient.