A great variety of living things on earth, including all green plants, synthesize their foods from simple molecules, such as carbon dioxide and water. For this process, the organisms require energy, and that energy is derived from sunlight.
Figure 1 shows the energy relationships in living cells. Light energy is captured in the chloroplast of plant cells and used to synthesize glucose molecules, shown as C 6H 12O 6. In the process, oxygen (O 2) is released as a waste product. The glucose and oxygen are then used in the mitochondrion of the plant and animal cell, and the energy is released and used to fuel the synthesis of ATP from ADP and P. In the reaction, C0 2 and water are released in the mitochondrion to be reused in photosynthesis in the chloroplast.