The mode of taking food by an organism and its utilisation by the body is called as nutrition. The nutrients are required by living organisms for growth, repair and to obtain energy for performing life processes. There are two modes of obtaining nutrition- autotrophic mode of nutrition and heterotrophic mode of nutrition.

Some organisms can not prepare their own food, and they depend on others for their food, they are called heterotroph. Heterotrophic plants can be either saprotroph, parasitic or symbiont. Saprotrophs are those organisms which take their nutrition from the dead and decaying organism. They absorb their nutrition in liquid forms. Example: Fungi and certain bacteria.

Organisms that prepare their own food from simple inorganic compounds present in their environment are called autotrophs and the mode of nutrition is called as an autotrophic mode of nutrition. For example- green plants. There are two types of autotrophs- photoautotrophs and chemoautotrophs.

The green pigment present in plants is known as chlorophyll. During photosynthesis, it captures energy from the sunlight and uses it to prepare food from carbon dioxide and water. This pigment is also present in algae which makes them perform photosynthesis.