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The arrows in a food chain show the transfer of biomass from one trophic level to another. An example of a food chain is:

maize → locust → lizard → snake

Some of the energy from the Sun absorbed by maize when it photosynthesises is transferred to the locusts when they eat the plant. So biomass is transferred. Then some of the biomass in the locust is transferred to the lizards when they are eaten and so on.

Not all of the biomass is passed from the maize plants to the locusts. In fact, only about ten per cent of the biomass is transferred from each trophic level to the next. The remaining 90 per cent is used by the trophic level to complete life processes. Biomass can be lost between trophic levels because not all of the matter eaten by an organism is digested. Some of it is excreted as waste such as solid faeces, carbon dioxide and water in respiration and water and urea in urine.

Because only around ten per cent of the biomass at each trophic level is passed to the next, the total amount becomes very small after only a few levels. So food chains are rarely longer than six trophic levels.

In fact, only about one per cent of the energy from the Sun that reaches the plant's leaves is used by the plant during photosynthesis. This sounds small but is still enough to power almost all food chains on our planet.