Final answer:
The Na+/glucose cotransporter moves glucose and Na+ into the cell by utilizing the energy stored in the ionic Na+ gradient, which makes it an example of secondary active transport.
Step-by-step explanation:
The Na+/glucose cotransporter is a membrane protein that facilitates the transport of glucose into cells. This transport is coupled with the movement of sodium ions (Na+) and is an example of secondary active transport. The correct characteristic of the Na+/glucose cotransporter from the options provided is that it is driven by the potential energy stored in the ionic Na+ gradient (choice b). Glucose is moved into the cell down its concentration gradient concurrently with Na+, which is moving into the cell down its electrochemical gradient. This is not an example of primary active transport because the cotransporter does not use ATP directly. Instead, it relies on the energy from the Na+ gradient, which is typically established by the Na+/K+ ATPase, a primary active transport mechanism. Additionally, the cotransporter does not exchange Na+ for glucose; it brings both into the cell. And while it transports glucose efficiently, it typically does not transport fructose.