Advanced Placement (AP) Biology Practice Exam

What is the main energy currency molecule that cells require for active transport?

1. NADH

2. ATP

3. ADP

4. FADH2

The correct answer is: ATP

The main energy currency molecule that cells require for active transport is adenosine triphosphate (ATP). ATP provides the necessary energy for the transport of substances against their concentration gradient, which is a key feature of active transport. The process involves hydrolysis of ATP, which releases energy that can be harnessed by transport proteins, or pumps, to move ions or molecules from areas of lower concentration to areas of higher concentration. This is essential for maintaining cellular homeostasis and facilitating processes such as nutrient uptake and waste elimination. In the context of the other options, while NADH and FADH2 are important for cellular respiration and involved in energy production, they primarily act in the electron transport chain rather than directly supplying energy for active transport. ADP, or adenosine diphosphate, is a product of ATP hydrolysis and is not used as the energy source for active transport, although it can be converted back to ATP. Therefore, ATP is uniquely suited as the energy currency that directly powers active transport mechanisms in cells.