Plants, as being themselves capable enough to synthesize organic compounds, “are called autotrophs. They nourish themselves independently on existing organic compounds, therefore, this mode of feeding is known as autotrophic or holophytic nutrition.
This type of nutrition is not only restricted to plants but it is also found in some animals, particularly which contain chlorophyll in their body, such as Euglena, Volvox. It is also found in some bacteria which contain bacterio-chlorin in their body.
There are two kinds of autotrophs:
(i) Chemosynthetic autotrophs:
These use the energy from oxidation of substances already present on earth to ‘fix’ carbon to organic compounds, such as sulphur bacteria.
(ii) Photosynthetic autotrophs:
These use the energy of light to fix carbon to organic compounds, such as green plants.
2. Heterotrophic nutrition:
This type of nutrition is characteristic of animals and some non-green plants. Here the animals unable to use free energy to synthesize organic compounds necessary for life but depend upon organic source of carbon, they are, thus, dependent upon plants and are called heterotrophs.
There are three kinds of heterotrophs:
(i) Holozoic heterotrophs:
These are those which, like animals, feed exclusively on solid material which they take in through mouth.
(ii) Saprophytic heterotrophs:
These include organisms such as the fungi which take in dissolved organic material often all over the body.
(iii) Parasitic heterotrophs:
These (“parasitic” means also a way of life as well as a method of nutrition) are those which feed in or on another organism, the host and cause it harm, e.g., tapeworm, and potato blight.