Photosynthesis is the process of formation of organic compounds from carbon dioxide and hydrogen donor like water using radiation or light energy trapped by chlorophyll. Oxygen is evolved where water is used as hydrogen donor. Duringphotosynthesis, light energy is changed into chemical or bond energy present inside the organic compounds.
The overall equation for photosynthesis is
6CO2 + 12H20 --> C6H12O6 + 6O2 + 6H20
Water is the hydrogen donor. A molecule of water can donate only one hydrogen. As photosynthesis
converts inorganic carbon into organic state, it is also called carbon assimilation.
CO2 is obtained from air. Concentration of CO2 in the atmosphere is only 0.03%.However the total amount is quite large, sufficient to last for several years even without replenishment. For passing into photosynthetic cells,CO2 dissolves in water.Aquatic plants also depend upon dissolved carbon dioxide present in water.
Water is a raw material for all photosynthetic organisms except bacteria.Water is used as a reluctant and oxygen is evolved from water.
During photosynthesis carbon dioxide is chemically reduced to carbohydrate. Water molecule splits in presence of sunlight and is called photolysis and oxygen is released. Thus released oxygen comes from water and not from carbon dioxide. Food is the source of energy needed by animal and plant life. And this food is manufactured by green plants from inorganic substances with the aid of sunlight energy during photosynthesis. Food represents the stored energy during photosynthesis. The oxygen needed by human beings and animals for respiration continues to be supplied by photosynthesis.