Photosynthesis uses CO2 and H2O to create C6H12O6 and O2 while cellular respiration uses glucose and oxygen to create CO2 and H2O. The relationship between the two is that photosynthesis makes the 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 hydrogen to form water. They rely on each other.
