If ATP loses one phosphate group, the resulting molecule is called ADP.

• A. Adenosine Diphosphate
• B. Adenosine Tetraphosphate
• C. Adenosine Monophosphate
• D. Adenosine Triphosphate

Answer: (A)

ATP is the molecule that stores energy in cells, and its name tells you how many phosphate groups it has. It contains adenosine plus three phosphate groups. When one phosphate is removed, you’re left with two phosphates, so the molecule is called ADP—adenosine diphosphate. The other names don’t fit because they imply different numbers of phosphate groups: three would be triphosphate, one would be monophosphate, and four would be tetraphosphate.