The energy molecule used by cells for all life activities is adenosine triphosphate (ATP).

Here's why:

* Universal Currency: ATP is like the "currency" of energy in the cell. It's the molecule that cells use to power nearly every process, from muscle contraction to protein synthesis.

* Energy Storage: ATP stores energy in the bonds between its phosphate groups. When these bonds are broken, energy is released.

* Rechargeable: ATP can be constantly regenerated through cellular respiration, a process that breaks down glucose and other fuels to produce ATP.

Let me know if you have any other questions!