Energy is initially released from ATP when the bond between its last two phosphate groups is broken in a reaction called hydrolysis , forming ADP and inorganic phosphate and freeing usable energy for the cell.

Core idea

  • ATP (adenosine triphosphate) has three phosphate groups linked by high‑energy phosphate bonds, especially the bond between the second and third (the “terminal” phosphate).
  • When a cell needs energy, water is used to break this terminal phosphate bond (ATP + H₂O → ADP + Pi), which releases free energy that can power cellular work.

How this powers cell processes

  • The released phosphate often attaches to another molecule, a step called phosphorylation , which changes that molecule’s shape or activity so a reaction can proceed (for example, the sodium‑potassium pump in membranes).
  • By coupling this exergonic ATP hydrolysis to endergonic reactions, cells drive processes like muscle contraction, active transport, and biosynthesis that would not occur spontaneously on their own.

TL;DR: Cells “spend” ATP by breaking its terminal phosphate bond through hydrolysis, releasing energy and a phosphate group that can be transferred to other molecules to make essential biological processes possible.