The process of intake of food and its utilization by the body is called as nutrition. Depending on the mode of obtaining nutrients all the organisms, broadly classified into two groups:
(1) Autotrophic (2) Heterotrophic
Auto – self; troph – nutrition. The mode of nutrition in which organisms prepare their own food from inorganic raw materials. These organisms are independent of external organic sources and are called as autotrophs. Eg: green plants. Green plants prepare their food by the process photosynthesis.
The mode of nutrition in which organisms derive their food from other living organisms is known as Heterotrophic nutrition. It is of different types:
(a) Saprotrophic nutrition (b) Parasitic nutrition (c) Holozoic nutrition
(a) Saprotrophic nutrition:
The mode of nutrition in which organisms obtain food from the dead and decaying organic matter by releasing digestive juices on them.
Eg. Fungi, yeast and bacteria.
(b) Parasitic Nutrition:
In this mode of nutrition organisms depend on the food that is synthesised by other organisms. Organism that depends on another organism is called ‘parasite’ and organism that provides food for parasite is called ‘host’.
Eg. Ticks, lice, leeches, fungi, bacteria, few plants like cuscuta.
(c) Holozoic Nutrition:
The mode of nutrition in which complex food is taken in the solid form and then digested and absorbed into the cells.
Eg. Amoeba, Frog, Human beings.