ATP is a molecule that serves as the universal energy source for all plants and animals. In your body, ATP breaks down into adenosine diphosphate plus a separate phosphate group. This releases energy, which is used to power your body's cells. During periods of inactivity, the reverse reaction takes place, and the phosphate group is reattached to the molecule using energy obtained from food. In this way, the ATP molecule is continuously being recycled by your body.