The right answer is A. It stores energy until a cell needs it.
ATP is a ribose-linked adenine molecule that is attached to a chain of three phosphate groups.
The mechanism is the transfer of a phosphate group to another molecule and the ATP then becomes adenosine diphophate (ADP).
But a cell has very little ATP. And as it consumes permamently, it must constantly manufacture (synthesize) and it is including cellular respiration that provides the energy necessary for the manufacture of ATP by allowing phosphorylation (addition of a phosphate to the ADP).
