Final answer:
ADP, or adenosine diphosphate, contains two phosphate groups. Energy is released through the process of dephosphorylation when ATP loses a phosphate group to become ADP.
Step-by-step explanation:
ADP, or adenosine diphosphate, has two phosphate groups. In the energy transfer process within cells, ATP (adenosine triphosphate) releases energy when it loses a phosphate group and becomes ADP. This process, known as dephosphorylation, involves the cleavage of the high-energy phosphoanhydride bonds between the phosphate groups, releasing energy for cellular activities. The negative charges on the phosphate groups repel each other, making the bonds energy-rich and inherently unstable, requiring energy to bond them together and releasing energy when these bonds are broken.