Advanced Placement (AP) Biology Practice Exam

What type of reactions does ATP power within cells?

1. Only mechanical reactions

2. Only chemical reactions

3. Both anabolic and catabolic reactions

4. Only exergonic reactions

The correct answer is: Both anabolic and catabolic reactions

ATP, or adenosine triphosphate, serves as the primary energy carrier in cells, fueling a variety of biochemical processes. In this context, the correct response highlights the role of ATP in powering both anabolic and catabolic reactions. An anabolic reaction involves the synthesis of larger molecules from smaller ones, which requires an input of energy. ATP provides this necessary energy through the hydrolysis of its phosphate bonds, enabling the construction of complex macromolecules like proteins and nucleic acids. Conversely, catabolic reactions involve the breakdown of larger molecules into smaller units, releasing energy in the process. This released energy can also be captured and utilized in the synthesis of ATP, illustrating a dynamic interplay where ATP is essential for both energy-releasing and energy-consuming processes within the cell. The other options indicate a more restricted role for ATP, which does not accurately reflect its versatile function in bioenergetics. ATP is not limited to powering only mechanical or exclusively chemical reactions, nor is it confined to exergonic reactions, as it plays a crucial role in energizing endergonic processes as well. Overall, ATP's ability to support a broad spectrum of reactions underscores its importance in cellular metabolism.