Green plants form the initial and vital link within the food chain. As the energy transformers and reservoirs for an ecosystem, green plants are known as primary producers. They store the chemical power they create as high-energy carbohydrates – such as glucose, starch and sucrose. A certain quantity of this power is utilized through the plants themselves in growth and respiration. This ability to create high-energy molecules means plants aren’t dependent on any other organisms for power, and so are recognized as autotrophs. Other organisms in subsequent trophic levels are recognized as heterotrophs, and rely on autotrophs to bring chemical energy into the food chain.

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Plants are eaten by animals known as herbivores – such as cows, gazelles and horses. Herbivores are recognized as primary consumers, and they form the next stage (trophic degree) within the food chain. There is much less chemical power overall passed to this degree than was originally yielded by the green plants. Some is used up by the plants in growth and respiration, and not all green plants are eaten by herbivores. Power is also lost simply because some of the plants die and are decomposed before they’re eaten, and so the power within them cannot be passed on to the next level. Herbivores tend to be far fewer in number than plants due towards the reduction in power between trophic levels – there’s merely not sufficient power to support more animals. Only a little amount of the power that herbivores gain from plants is utilized for new growth within their bodies. Nevertheless, a staggering 96% of the power herbivores obtain from plants is lost as heat power through urination, faeces and respiration.