Here's the breakdown:

* ATP (adenosine triphosphate) is a high-energy molecule that acts as the primary energy currency of cells. It has three phosphate groups attached to an adenosine molecule.

* When ATP is broken down, a phosphate group (Pi) is removed, releasing energy. This process is called hydrolysis, which involves the addition of a water molecule.

* The remaining molecule is ADP (adenosine diphosphate), which has only two phosphate groups.

So, the complete breakdown of ATP looks like this:

ATP + H2O → ADP + Pi + energy