We could just Google this....but ATP adenosine triphosphate is the preferred energy source in the cellular energy cycle. A phosphate gets broken off when a cell

We could just Google this....but ATP adenosine triphosphate is the preferred energy source in the cellular energy cycle. A phosphate gets broken off when a cell uses it leaving ADP which is... Something something, I forget the rest. It's more expensive for the body to extract energy from ADP.