The process of changing complex food into simple, absorbable form by the action of certain enzymes is called digestion. Many organs are associated with digestion. Digestion is of two types mechanical and chemical digestion, hi mechanical digestion, food is broken down in the mouth when we chew it with our teeth. In chemical digestion, the food is digested by the actions of certain enzymes.
Digestion is necessary because the food which is obtained is in complex form and our body is not able to absorb nutrients from it. So it is converted in to simple absorbable form. Nutrition is the process of obtaining and using food by the organisms. It is different in different organisms. Ingestion, digestion, absorption, Assimilation and egestion are the various steps involved in nutrition.