Photosynthesis contributes to the oxygen supply on Earth by converting carbon dioxide and water into glucose and oxygen, utilizing sunlight as an energy source. This process occurs mainly in the chloroplasts of green plants through two stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). During photosynthesis, oxygen is released as a byproduct, replenishing atmospheric oxygen levels. This makes it vital for sustaining life, as many organisms rely on this oxygen for respiration.