Photosynthesis and cellular respiration are the complete opposites of one another but are also complementary processes. In photosynthesis, producers such as plants take in carbon dioxide, water and sunlight to produce glucose and oxygen. With cellular respiration, organisms combine glucose and oxygen to produce carbon dioxide, water and energy.
The process of photosynthesis is used by plants and other photosynthetic organisms to produce energy, whereas the process of cellular respiration breaks down the energy for use. The balanced equation for photosynthesis is 6CO2 + 6H2O ---> C6H12O6 + 6O2 + energy. Cellular respiration is basically the reverse reaction of C6H12O6 + 6O2 ---> 6CO2 + 6H2O + energy. Both reactions are accomplished in organelles; chloroplasts are the sites of photosynthesis, and cellular respiration happens mainly in the mitochondria.
Only photosynthetic organisms can make glucose, but all organisms must be able to use that energy. This energy usually comes in the form of ATP, or adenosine triphosphate. Cellular respiration produces ATP. The glucose is burned to produce the ATP.
Cellular respiration consists of four steps. Glycolysis breaks glucose down into two molecules of pyruvic acid, producing two molecules of ATP. The transition reaction breaks down pyruvic acid. In the Krebs cycle, four more molecules of ATP are produced. The electron transport chain and chemiosmosis results in 32 ATP molecules.