Final answer:
Primary active transport uses ATP to move ions and create an electrochemical gradient, while secondary active transport uses the energy of this gradient to move other substances without directly using ATP.
Step-by-step explanation:
The question you've asked is about the difference between primary and secondary active transport. Primary active transport directly uses ATP to move ions across a cell membrane, thereby creating an electrochemical gradient. This process creates a difference in charge across the membrane, which is essential for the function of cells. On the other hand, secondary active transport does not directly use ATP. Instead, it utilizes the electrochemical gradient created by primary active transport to move substances across the membrane. Secondary active transport is indirectly dependent on ATP because it relies on the energy stored in the ion gradient built by primary active transport.
For example, the sodium-potassium pump is a well-known primary active transport mechanism that maintains the essential membrane potential by using ATP to pump sodium out of the cell and potassium into it. Then, substances such as glucose or amino acids can be brought into the cell through secondary active transport mechanisms, using the sodium gradient just established as an energy source.
So, the correct answer to your question is: a) Primary uses ATP, while secondary uses energy stored in the ion gradient.