Final answer:
The addition of a phosphate molecule to ADP to form ATP stores energy, which is then released when ATP is broken down into ADP and inorganic phosphate through hydrolysis.
Step-by-step explanation:
When a phosphate molecule is added to ADP to form ATP, energy is stored in the bonds between the phosphate groups of the ATP molecule. However, when ATP is broken down into ADP and inorganic phosphate through a process called hydrolysis, energy is released. This release of energy occurs because the products (ADP and phosphate ion) have less energy than the reactants (ATP and water).