Final answer:
ATP is the readily available form of energy that cells can use to power cellular reactions.
Step-by-step explanation:
The molecule that is the readily available form of energy that cells can use is called adenosine triphosphate (ATP). ATP is a small, relatively simple molecule that contains the potential for a quick burst of energy that can be harnessed to perform cellular work. It is often referred to as the primary energy currency of cells and is used to power the majority of energy-requiring cellular reactions.