Which of the following is an example of secondary active co-transport?

The example of secondary active co-transport is represented by the sodium/glucose transport mechanism. In this process, glucose is transported into cells along with sodium ions. Here’s how it works: the sodium-potassium pump, which is classified as primary active transport, establishes a concentration gradient by pumping sodium ions out of the cell and potassium ions into the cell. This gradient creates a higher concentration of sodium outside the cell compared to the inside.

When sodium ions re-enter the cell through a co-transporter, they bring glucose along with them against its concentration gradient. This co-transport does not require direct energy in the form of ATP because it utilizes the energy stored in the sodium gradient created by the sodium-potassium pump. Thus, this mechanism exemplifies secondary active transport, where the transport of one substance (glucose) is coupled with the transport of another (sodium) that is moving down its concentration gradient.

In contrast, the other options do not represent secondary active co-transport in the same way. The sodium/potassium pump represents primary active transport, while the chloride/hydrogen exchanger and calciumsodium exchange are mechanisms that involve different ion movements that do not characterize them as secondary active co-transport for glucose absorption. This makes