What is the function of the structure labeled A?

The function of the structure that is labeled A is to make ATP. If you are not familiar with what ATP is, this is also known as Adenosine Triphosphate. This is where energy is stored and used within the cell. The structure of ATP will be composed of a nitrogenous base, ribose sugar, and three phosphate groups.

Cells will continuously break down in order to create ATP because once again, this is needed to get enough energy. ATP will also be synthesized from ADP and phosphate through the process of cellular respiration. Respiration is made up of a series of cellular reactions. The ATP in cells is normally produced by ATP synthase.