During photosynthesis, plants make glucose and oxygen from carbon dioxide and water. To do this, they need energy in the form of light from the sun. While plants use glucose as energy, oxygen enters the atmosphere for use by other organisms.
During photosynthesis, a chemical called chlorophyll absorbs the light energy and encourages a reaction between carbon dioxide and water that results in glucose and oxygen. Oxygen is expelled as a waste product from the plant, and it enters the atmosphere. After producing glucose, plants convert it to pyruvate, which then generates adenosine triphosphate, or ATP, which is used as energy for cellular respiration.
This reaction is able to take place as water enters the plant's roots and carbon dioxide enters through the stomata on the leaves. There are cells guarding the stomata that allow carbon dioxide to enter and oxygen to leave. When light enters the plant, it excites the chlorophyll and causes it to lose an electron and generate a positive charge. It is during this process that the water molecules split and energy is transferred to ATP. The two chemical reactions involved are condensation, which involves the water molecule splitting, and oxidation, which promotes the electron transfer. In addition to light-dependent reactions, plants can go through light-independent reactions.