*information obtained from Human Body by D.K

Energy is needed for the functioning of body cells. This energy is produced by the breaking down food molecules in various chemical reactions, in particular the Krebs cycle that takes place within a cell’s mitochondria. Because the energy cannot be used directly by the cell, it is stored in a high-energy chemical bond, which links a molecule of ADP (Adenosine Triphosphate) The bond breaks, releasing the energy and converting ATP back into ADP.