What role does ATP play in cellular function?
The ATP stores energy.
ATP - adenosine triphosphate - has the function to "store" energy in the cell. It can easily reacts in other organelles, losing one phosphate and releasing some of this energy in order to ensure the cell keeps working normally.
Then, when has turned into ADP - Adenosine diphosphate - it will return to the mitochondria to receive the energy absorbed during the process of respiration of the cell.