The role of H2O, or water, in photosynthesis, is essential to ATP, which is the energy process that drives photosynthesis. It is also important in the making of food; hydrogen atoms found in water make up part of the glucose molecules that plants use as nourishment.
Photosynthesis occurs in two stages, both of which require water.
The first part of photosynthesis is ATP. Sunlight, absorbed by the chloroplasts in the plant's leaves, splits the water into hydrogen and oxygen atoms. The hydrogen atoms are used to make the chemical energy ATP, a type of fuel that enables the cells to produce food. Oxygen is then excreted from the plant.
The second stage of photosynthesis is the production of food, or glucose, a type of sugar made from hydrogen, carbon and oxygen. The hydrogen atoms come from water, while the carbon and oxygen come from carbon dioxide, which is absorbed through the pores on the plant's leaves. The water and carbon dioxide combine in a chemical reaction, resulting in sugar and oxygen. The sugar is sent from the leaves to the rest of the plant through tissue called "phloem," which nourishes the plant. The oxygen is then released from the plant.