The whole process by which an organism obtain its food. 

  • Some organisms use simple food material obtained from inorganic sources in the form of carbon
    dioxide and water. These organisms, the autotrophs, include green plants and some bacteria.
  • Other organisms utilise complex substances. These complex substances have to be broken down into simpler ones before they can be used for the upkeep and growth of the body.These organisms are called heterotrophs. The heterotrophs survival depends directly or indirectly on autotrophs which includes animals and fungi.


Modes of Nutrition 

Autrotrophic Hetrotrophic
Kind of nutrition in which
inorganic materials like CO2, water etc. are utilized to prepare organic food by the process of photosynthesis.

Kind of nutrition in which organisms do not possess the ability to synthesize their own food. They depend on autotropha for their food supply directly or indirectly. 


E.g. Green plants E.g. Animals, fungi.


Autotrophic Nutrition 

The organisms which carry out autotrophic nutrition are called autotrophs (green plants). Autotrophs use simple inorganic material to convert it in to comples high energy molecules (carbohydrates). Autotrophic nutrition is fulfilled by the process by which autotrophs take in CO2 and H2O and convert these into carbohydrates in the presence of chlorophyll, sunlight is
called Photosynthesis.


Raw Materials for Photosynthesis :

  • Sunlight
  • Chlorophyll → Sunlight absorbed by chlorophyll
  • CO2 → Enters through stomata and oxygen (O2) is released as by-product through stomata on leaf.
  • Water → Water + dissolved minerals like nitrogen, phosphorus etc. are taken up by the 
    roots of the soil.

Site of Photosynthesis :
Chloroplast in the leaf, chloroplast contain chlorophyll (green pigment).

Main Events of Photosynthesis :

  • Absorption of light energy by chlorophyll
  • Conversion of light energy into chemical energy + splitting (breaking) of water into hydrogen and oxygen
  • Reduction of CO2 to carbohydrates,

Stomata : Tiny pores present on the surface of the leaves. The opening and closing of the stomatal  pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore
closes if the guard cells shrink.
Functions :
(a) Exchange of gases O2/CO2.
(b) Loses large amount of water (water vapour) during transpiration.


Heterotrophis Nutrition

Holozoic Saprophytic Parasitic
Animals take in solid food and breakdown inside the body. Organisms feed on dead, decaying matter.

Parasites live inside or outside other organism (host) and derive nutrition from it.

E.g. Amoeba, animals E.g.Fungi. E.g., Cuscuta (plant parasites), Ticks etc.

How do organisms obtain their food
Unicellular/Single celled organisms : Food is taken up through entire surface.
Example :

(i) Amoeba
(ii) Paramaecium


In Paramoecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell.

Nutrition in Human Beings


Different organisms utilize different nutritional processes as it depends upon the source of carbon from where the food is taken.