Which statement best defines ATP in the context of cellular energy for exercise?

• A. An enzyme complex embedded in the inner mitochondrial membrane that catalyzes oxidative phosphorylation and synthesizes ATP by harnessing an electrochemical gradient across the membrane.
• B. A structural protein in muscle fibers responsible for force transmission and stabilization of sarcomeric alignment during contraction.
• C. A cellular carbohydrate polymer stored in muscle and liver that can be rapidly broken into glucose during exercise to supply ATP production in mitochondria and cytosol.
• D. Adenosine triphosphate, the cell's primary energy carrier that releases usable energy when a terminal phosphate bond is broken.

Answer: (D)