Nutrition is the process to obtain and utilize food or nutrients. It is mainly divided into two categories autotrophic (organisms prepare their own food) and heterotrophic (organisms obtain food from other organisms). Autotrophic mode of nutrition is further divided into two categories such as:
1. Phototrophic: Organisms prepare their own food in the presence of sunlight, water and carbon dioxide e.g., green plants.
2. Chemotrophic: Organisms prepare their own food in the presence of chemicals such as nitrate, hydrogen sulphate, iron etc, e.g., sulphur bacteria
Heterotrophic mode of nutrition is further divided into three categories such as:
1. Holozoic: Animals eat their whole food. It includes five stages of digestion such as ingestion, digestion, absorption, assimilation and egestion e.g., humans.
2. saprophytic: Organisms feed on dead and decaying organic matters. In this mode, organisms first convert the complex food into the simple form and then ingests them e.g., decomposers.
3. Parasitic: Organisms obtain food from other living organisms. In this mode, one organism (parasite) lives inside the other organism (host organism) and derive nutrients from that e.g., tapeworm.