We will discuss here about the different functions of leaf.
(i) Synthesis of food: We treat leaves as the kitchen of a plant because leaves provide a suitable site for the synthesis of food. Leaves have many minute pores on its surface. Those are called stomata (singular stoma). During day time the stomata remain open. Leaves take in atmospheric carbon dioxide through stomata. Roots transport water and minerals from soil to leaves through stem. Leaf cells have a green pigment called chlorophyll. In presence of sunlight, chlorophyll helps carbon dioxide and water to combine to form glucose, which is the food of green plants. The energy, necessary for this process comes from sunlight. This process of synthesis of glucose in green plants in presence of sunlight is called photosynthesis.
(ii) Removal of excess water: Generally, roots absorb more water than it is required by a plant. Excess water is liberated through stomata of leaves. The process to get rid of excess water by a plant in the form of water vapour is called transpiration.
(iii) Storage of food: Some plants store excess food within the leaves. In plants like onion, garlic, bryophyllum food is stored in the fleshy leaves.
(iv) Respiration: Plants require oxygen for its respiration. Here the leaves act as the breathing organ. The stomata of leaves help plants to intake oxygen and liberate carbon dioxide. It is the reverse process of photosynthesis.
(v) Reproduction: Young plants may grow from leaves of some plants. In case of bryophyllum, baby plants grow from the edge of its leaves if these are placed in moist soil.