Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems.

Many animals also need large quantities of this element to make shells, bones and teeth.

The natural reservoir of phosphorus is rock which contains phosphorus in the form of phosphates.

When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants.

Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate solubilizing bacteria releasing phosphorus.

Unlike carbon cycle, there is no respiratory release of phosphorus into atmosphere.

The other two major and important differences between carbon and phosphorus cycle are firstly atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs and secondly, gaseous exchanges of phosphorus between organisms and environment are negligible.