The method of obtaining nutrition from organic matter sources is called Heterotrophic Nutrition. There are three types of it as follows :
(1) Saprophytic Nutrition : Organisms obtain nutrition from other dead organisms or decayed organic substance. They produce enzymes. Its releases enzymes outside the body and also digest the food outside the body. Digestion absorbs simple substance from it and takes it insides the body for eg. Mushroom, fungi, bacteria, yeast, bread mould.
(2) Parasitic Nutrition : In this type of nutrition organism obtain nutrition from other organism. Some organisms obtain nutrition by living in the body of other organisms called endoparasites. Some organisms obtain nutrition by living outside the body of other organisms. It is called ectoparasite for eg. Tapeworms, mosquitoes, round worms, cuscutta, lice, leeches, termites etc.
(3) Holozoic Nutrition : Normally this method of nutrition is found in all animals. It has several stages.
1. Food ingestion : The process of taking in food.
2. Digestion : The process of converting complex organic substance into simple organic substance with the help of enzymes.
3. Absorption : The act of absorbing digested simple organic substance in the body.
4. Assimilation : Storage of simple substances in the cell in various forms or the process of using the substance is known as Assimilation.
5. Excretion : The process of removing undigested food out of the body.