Photosynthesis and cellular respiration are connected through an important relationship. This relationship enables life to survive. The products of one process are the reactants of the other. Photosynthesis makes glucose that is used in cellular respiration to make ATP. The glucose is then turned back into carbon dioxide, which is used in photosynthesis. While water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with water to form water.
Photosynthesis and cellular respiration are also an important part of Carbon cycle.