All of the above
Proof:
Photosynthesis occurs in two stages. The first stage is called light reactions because it requires light energy. During light reactions, chlorophyll absorbs light energy and converts it into chemical energy. Chemical reactions in this stage split water into oxygen and hydrogen. The hydrogen remains in the plant while the oxygen is released as a by-product through the stomata. The oxygen released by plants is very important to the animal life on our planet. Plants are the only common source of atmospheric oxygen on earth.