Cycling of materials in ecosystem:

Living organisms require four nutrients in relatively large amounts, these are carbon. oxygen, nitrogen and hydrogen. They also require phosphorus and sulphur. These elements are present in our environment in a fixed quantity,  therefore they must be  recycled  in order to sustain life. Also these'elements must move efficiently,  from the living  to nonliving components and vice versa. Let us understand this with the help of  an example. Plants take in  carbon as carbon dioxide to produce food. As the herbivores eat plants, carbon is on  to them, which  in  turn is passed on to carnivores,  and so on. Carbon is eventually returned to the nonliving pool  in  the ecosystem,  through the excretory processes of  the producers, the herbivores. the carnivores,  and also through the activity of the decomposers. Through such cyclic processe~these  nutrients are used over and over again by  the organisms. 

This aspect of  the ecosystem function is called the cycling of materials. In contrast to energy flow which Is  a one way process, mineral nutrients move more or less  in a  cyclic way. In  the following sub-sections,  you would study the cycles of nitrogen, carbon and water. This would give you an  idea of  the complex involvement of  the various living and nonliving components.