The answer is an energy of Sunlight.
In the process of photosynthesis, plants use the energy of Sunlight to convert water and carbon dioxide into glucose (which is a sugar) and oxygen (which is a byproduct). Pigment chlorophyll in the leaves of green plants absorbs sunlight and convert it into the chemical energy in the form of ATP or NADPH which is then used for conversion of carbon dioxide into carbohydrate glucose.
