In an ecosystem generally sun is the only source of energy. The autotrophs like plants etc. fix the sun radiant energy, to make food from simple inorganic materials and convert it into chemical energy. All organisms are dependent for their food on plants directly or indirectly. So animals i.e. herbivores feed on plants and these herbivores are eaten by the carnivores form a food chain.
The energy trapped by the producer hence is passed on to the primary consumer and then to the secondary consumer. Ultimately this energy goes to the decomposers. The food chain or web formed is due to this interdependency of organisms. There are mainly two basic types of food chains Grazing Food Chain.
(i) Grazing Food Chain (GFC): This type of food chain starts at the producer level and completes at the decomposer level. This type of food chains have so many levels like- producer, herbivore, carnivore and at last the decomposers. Here in each level 90 percent of the total energy is consumed. For example: Grass – Deer- Tiger.
(ii) Detritus Food Chain (DFC): It begins with dead organic matter. It is made up of decomposers which are heterotrophic like fungi and bacteria. They meet their energy requirements by degrading detritus, with the help of some digestive enzymes secreted by them, into simple inorganic materials which are subsequently absorbed by them.