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Plants obtain nutrition by a process called Photosynthesis.


  • The process by which green plants make their own food (like glucose) from carbon dioxide and water by using light energy (sunlight) in the presence of chlorophyll is called photosynthesis .


  • 'Photo' means ‘light’ and 'synthesis' means to ‘build’, thus 'photosynthesis' means 'building up by light'.


The process is chemically represented as:


Necessary conditions for Photosynthesis:



(1) Sunlight:

Sunlight provides energy required to carry out all the chemical reactions involved in the photosynthetic process.


(2) Carbon Dioxide:

  • The carbon dioxide gas enters the leaves of the plant through the stomata present on the surface. 
  • Stomata are tiny pores present on the surface of the leaf.
  • Each stomatal pore is controlled by guard cells
  • When water flows into guard cells, they swell up , become curved and cause the pore to open . On the other hand when guard cells lose water they shrink, become straight and close the stomatal pores.
  • The exchange of gases takes place due to the opening and closing of stomata.


(3) Chlorophyll:

  • Chlorophyll is a green colored pigment .
  • It is found in the chloroplast of cells.

Chlorophyll helps in the absorption of sunlight which provides energy for carrying out photosynthesis.


(4) Water and Minerals:

  • The water required by the plants for photosynthesis is absorbed by the roots of the plant from the soil. Water is transported to the leaves through the roots and stem.
  • The plants need other minerals such as nitrogen, phosphorus, potassium etc which are taken from the soil.


Stepwise Process of Photosynthesis:

Photosynthesis takes place inside Chloroplast .

The major steps involved in the process of photosynthesis are:


  1. Absorption of sunlight by chlorophyll
  2. Absorption of water , and obtaining carbon dioxide for conversion.
  3. Conversion of Chemical energy into light energy and splitting of water into hydrogen and oxygen by light energy.
  4. Reduction of carbon dioxide by hydrogen to form carbohydrates like glucose by utilizing the chemical energy (obtained by transformation of light energy)


The Reaction for Photosynthesis is as follows :


The oxygen released as a by-product is released into the air. 


Plants that do not have chlorophyll are heterotrophs .

  • Plants like the venus fly trap have chlorophyll, and photosynthesize, but they obtain their nutrients and minerals from the insects they trap.
  • C roton sp. Plants are plants with leaves that appear to be not green due to higher concentration of other colour pigments in the leaves. But since chlorophyll is also present , they carry out photosynthesis normally.  
  • Many plants are also parasitic/saprophytic in nature.
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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo