Photosynthesis is where plants use sunlight, H2O, and CO2 to produce O2 and energy as sugar. Cellular respiration is where food is transformed to energy in the cells in the form of sugar. In photosynthesis, plants transform the light energy to chemical energy. It is used to convert H2O, CO2, and minerals to O2. In cellular respiration, the stored energy in sugar is being released and converted to energy that is being used by the cells. Glucose is carried to the blood and being taken up by each of the cells. The energy in photosynthesis is being used for food while the energy from cellular respiration in the form of ATP is used by the cells.