★ The process by which plant prepare food (carbohydrates) from inorganic raw materials like carbon dioxide (CO2) and water in (H2O) in presence of sunlight and chlorophyll is called photosynthesis.The photosynthesis occurs in 2 phases:●Light Reaction: It needs light that is absorbed by chlorophyll molecules to split water (H2O) molecules into hydrogen and oxygen. The ATP is produced during it. ●Dark reaction: This does not need light energy. It takes place in stroma of the chloroplasts. The ATP and NADPH2 formed during light reaction are utilised and CO2 is reduced to synthesize carbohydrates.◆Four factors affect the rate of Photosynthesis, they are: ●Sunlight: It provides energy needed for preparation of food by plants. In absence of sunlight, the photosynthesis does not occur.●Carbon dioxide: C09 acts as substrate for photosynthesis , carbon dioxide and water are converted into carbohydrates.●Water: During photosynthesis, the water is photolysed into oxygen and hydrogen. This provides energy for photosynthesis.●Chlorophyll: The chlorophyll is green pigment. It occurs in leaves that absorbs sunlight.
For ex :- Desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the choloryphyll during the day.
3 events occur during this process :–(1) Absorption of light energy by chlorophyll. (2) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. (3) Reduction of carbon dioxide to carbohydrates .