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:
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.
- 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:
- Absorption of sunlight by chlorophyll
- Absorption of water , and obtaining carbon dioxide for conversion.
- Conversion of Chemical energy into light energy and splitting of water into hydrogen and oxygen by light energy.
- 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.