Cellular respiration and photosynthesis are essentially opposite processes. Photosynthesis is the process by which organisms make high-energy compounds -- the sugar glucose in particular -- through the chemical "reduction" of carbon dioxide (CO2). Cellular respiration, on the other hand, involves the breakdown of glucose and other compounds through chemical "oxidation." Photosynthesis consumes CO2 and produces oxygen. Cellular respiration consumes oxygen and produces CO2.
