Explain how energy is transferred in a food web.

Energy is transferred through the separate trophic levels of a food chain or web by feeding. The first trophic level (producers) is that of plants which are examples of autotrophs - they make their own food. Photosynthesis occurs when the plants use solar energy and convert it into chemical energy so it can be stored in a carbon compound. Once this has happened the energy can be taken up by the primary consumers - these are in the second trophic level (herbivores and omnivores). Secondary consumers also need to gain energy in some way, and this is by eating the primary consumers that have gained energy from the producers, this means that the second trophic level has successfully transferred energy into the third level containing omnivores and carnivores. A succession in energy transferral means that a food web or food chain has a tertiary and/or quaternary trophic level which can contain carnivores and omnivores which are plant and animal eaters (this includes humans). This transfer in energy is fairly efficient for the organisms involved as around 10% of light energy that is converted into chemical energy through photosynthesis is transferred through the trophic levels, the rest is lost in respiration, as heat, faeces and urine. Not all of the energy can be passed along a food web or chain as it must be used in other things too, so it cannot be 100% efficient.

Sunlight is energy, and plants use this energy to turn water and carbon dioxide into plant food. This process is called "photosynthesis". Plants also need minerals and nutrients. Then animals consume the plants and their energy.