Nutrition is the mode of consumption of food. According to nutrition, the living beings are classified into two categories.
I. Autotrophs :
They are organisms, which can synthesize their own food. They use an external energy source to synthesize carbohydrate source. Based on the energy source, autotrophs are further classified into two groups.
a. Phototrophs: They use sunlight to synthesize carbohydrates (Example: all green plants, green bacteria, Euglena, blue green algae etc.).
b. Chemotrophs: They use chemical energy by the oxidation or reduction of metals or minerals (Example: Ferro Bacillus, Hydrogenomonas, Sulphur bacteria).
II. Heterotrophs :
They cannot synthesize their own food but can obtain it from autotrophs. Bashttp://www.blogger.com/img/blank.gifed on the method of consumption, they are further classified as follows
a. Holozoic: They eat or engulf large particles of food (Example: Amoeba, all animals).
b. Saprozoic: They absorb nutrients from dead and decaying matter (Example: Paramecium, decomposing bacteria).
c. Parasitic: They obtain food from others and cause damage to the host (Example: Taenia Solium, Ascaris, Fasciola)
d. Symbiotic: Two organisms co-operate each other and share the food (Example: Lichen)
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