Nutrition is the procurement of substances necessary for growth, maintenance and activities of a living body. The substances used for nutrition are called nutrients.
  1. There are two types of nutrition, autotrophic and heterotrophic.
  2. Depending upon the source of energy, organsims can be classified as phototrophs and chemotrophs.
I. Autotrophs
Autotrophs (self feeders) are organisms whose sole source of carbon is CO2. These organisms use different source of energy to fix (reduce) CO2 to various organic compounds. Autotrophs include photosynthetic as well as chemosynthetic organisms.
a. Photosynthetic nutrition:
Nutrients are synthesized with the trapping of solar energy by help of chlorophyll. This nutrition is exhibited by plants having chlorophyll.
b. Chemosynthetic nutrition:
The breakdown of complex inorganic or organic molecules provides energy for synthesis of nutrients.
1. Nitrifying bacteria: Ammonia to nitrite, Nitrite to nitrate
2. Sulphur oxidizing bacteria: Hydrogen sulphide to sulphur
3. Iron bacteria: Ferrous ion to ferric ion.
II. Heterotrophs
All animals are heterotrophs. Animal which preys on is called predator. A predator eats on prey.
i. Holozoic: Animal like nutrition, ingests solid food.
ii. Holophytic: Plant like nutrition, synthesizes food.
iii. Parasite obtains nourishment from the body of the host.
iv. Detritus: Animal which feeds upon organic matter mixed with the soil, eg., Earthworm.
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