Every living organism requires food to fulfill the requirement of energy for their various activities. Green plants are autotrophic in nature. So, they synthesize their food by a very important process called photosynthesis. The term ‘photosynthesis’ consists of two words ‘photo’ means ‘light’ and ‘synthesis’ means ‘to make’. Thus, photosynthesis is the process of making food with the help of sunlight.

It may be defined as the process of making food by green plants from carbon dioxide andwater by chlorophyll in the presence of sunlight. In the process of photosynthesis oxygen gas is liberated.  The process of photosynthesis takes place in leaves of a plant, because these contain the green colouring pigment chlorophyll which is necessary for synthesis of food in plants. Thus, leaves are the site of preparation of food in plants. That is why; leaves are also called food factories of a plant.

The carbon dioxide required for photosynthesis is obtained from the air which enters the leaves through very minute pores called stomata. But, aquatic plants use carbon dioxide dissolved inwater. The water is absorbed from the soil by the roots of plants and transported to leaves by a network of tiny veins called xylem vessels. The sunlight energy is absorbed by chlorophyll. A chemical reaction using the trapped sunlight energy takes place in the chloroplasts (chlorophyll containing organelles of cells) to prepare food. The food prepared by the leaves of a plant is usually in the form of carbohydrates.