The land mass, water bodies and atmosphere are the three endowments of nature on which the living beings have to depend for their nourishment and sustenance. The inter-dependence of various living species to derive their food materials has resulted in the transfer of energy and nutrients from one to another, thus setting up a process of ‘Food chain’.

Biological Recycling Solar energy is the primary energy on which the entire living system on the earth depends. The plants conserve and build up nutrients and energy, while the animals degrade and utilize them. Microbes form side links in the food chain. Soil microorganisms involved in the decaying process of organic matter in the soil help the release of nutrients in utilizable forms to assist their uptake by the plants. Rhizobial organisms in the root nodules of leguminous plants fix the atmospheric nitrogen in the soil for the utilization of plants. Micro-organisms inhabiting the complex stomach of ruminants help in the digestion of fibrous feed materials and synthesize high quality microbial proteins and B-complex vitamins to be utilized by the host animal. Materials shed and voided by plants and animals are food materials for a wide variety of lower forms of life. It is noteworthy that the skill of micro-organisms like yeasts and fungi for utilizing even petroleum products is exploited biotechnologically to produce edible food material like single cell proteins.