(i) Photosynthesis: The biochemical process by which green plants produce sugary food by chemically combining water and carbon dioxide with the help of chlorophyll in the presence of sunlight and releasing oxygen as a by-product is called photosynthesis. Carbon dioxide needed for photosynthesis enters the cell through the stomata. Carbon dioxide reacts with water to form sugars and release oxygen as a byproduct. Oxygen is released out of the cell through the stomata. Therefore, stomata play an important role in carrying out the process of photosynthesis.
(ii) Respiration : The biochemical process in which respired matter is completely oxidized in the presence of free oxygen to produce water, CO2 and energy is called respiration. Oxygen required for plant growth enters the cells through the stomata. Oxygen reacts with oxygen to produce water, CO2 and energy. The carbon dioxide produced is released out of the cell through the stomata. Therefore, stomata play an important role in carrying out the reproductive process.
(iii) Transpiration: The process by which the excess water absorbed by the roots of the plant evaporates through the stomata is called transpiration. Green plants use only 1-2% of the water absorbed by their roots. The remaining 98-99% of water is useless. Excess water is released by evaporation through the stomata. Therefore, stomata play an important role in carrying out the process of respiration.
(iv) Temperature regulation: A lot of heat is generated as a result of various biological processes in the plant body. During respiration, heat is released through the stomata. If the heat wasn’t released outside, the plant would burn to death.
(v) Gaseous exchange: It involves the exchange of gaseous substances or O2 and CO2.
(vi) Opening and closing of stomata : Guard cells control the opening and closing of stomata.
(vii) Synthesis and storage of organic food: Glucose is synthesized in the guard cells and temporarily stored as glucose.