Photosynthesis is a process by which plant prepare their food from carbon dioxide and water with the help of sunlight in the presence of chlorophyll. About 90% of photosynthesis is carried out by aquatic plants.
Word ‘Photosynthesis’ comprises of two words ‘photo’ & ‘synthesis. Photo means light and synthesis means preparation.
Thus photosynthesis is a process of preparation of food with the help of light.
Photosynthesis is carried out in 3 steps:
Absorption of light energy by chlorophyll.
Conversion of light energy into chemical energy and splitting of water molecules into Hydrogen and Oxygen
Reduction of by hydrogen to form carbohydrates like glucose by utilizing chemical energy.
The process of photosynthesis is carried out in leaf as well as green stems of the plant.
CONDITIONS NECESSARY FOR PHOTOSYNTHESIS ARE:
Water and Carbon dioxide are the raw material for photosynthesis.
HOW DO PLANTS OBTAIN CARBONDIOXIDE?
Plants obtain carbon dioxide from atmosphere for photosynthesis. The CO2 gas enters the leaves of the plant through the stomata.
Opening and closing of stomatal pore is controlled by guard cells. Guard cells are the specialized cell present in the epidermis of leaves. When water flows into the guard cells, it swells and becomes curved causing the stomatal pore to open for gaseous exchange. On the other hand, when the guard cells loose water, it shrinks, becomes straight and close the stomatal pore.
A large amount of water is also lost during this process so, when plants don’t need CO2, stomatal pores are closed.
Oxygen produced in the process of photosynthesis is also released out through the stomatal pores. In most broad-leaved plants, stomata are present on the lower surface of the leaf only. But in narrow-leaved plants stomata are equally distributed on both sides of the leaf.
HOW DO PLANTS OBTAIN WATER?
Plants obtain water from the soil. The water required by the plant to carry out photosynthesis is absorbed by the roots from the soils through the process of osmosis. Water is transported upward through the xylem vessel to the leaves where it reaches the photosynthetic cells and utilized in photosynthesis.
Along with the carbon dioxide and water plants also require Nitrogen. Phosphorus, Fe, Mg, etc., for building their body, these nutrients are absorbed from the soil. For e.g.: Nitrogen is an essential element used by the plant for the synthesis of protein.
SITE OF PHOTOSYNTHESIS: CHLOROPLASTS
Chloroplasts are enclosed by 2 membranes. Chloroplasts contains an aqueous fluid in it called stroma. Stroma contains grana of thylakoids which are the site of photosynthesis. Thylakoids are the flattened discs consists of a thylakoid lumen within it. Chlorophylls are arranged in and around thylakoid. Chlorophyll is a green pigment present in chloroplasts and absorbs sunlight to carry out photosynthesis. CO2 needed for photosynthesis enters from the air into the photosynthetic cells (mesophyll cell) and reaches chloroplast. Water needed is carried to the leaf by xylem vessels and passes into the mesophyll cells by diffusion and reaches the chloroplast.