Question

In the Na⁺/glucose cotransporter, _____ moving down its gradient drives the transport of _____ against its gradient?

1) Na⁺ ions, K⁺ ions
2) Na⁺ ions, glucose
3) glucose, Na⁺ ions
4) glucose, K⁺ ions
5) K⁺ ions, glucose

Answer 1

Na⁺ ions moving down their gradient enable the cotransport of glucose against its concentration gradient in the Na⁺/glucose cotransporter. This is an instance of secondary active transport.

Step-by-step explanation:

In the Na⁺/glucose cotransporter, Na⁺ ions moving down its gradient drive the transport of glucose against its gradient. The correct answer to the student's question is option 2: Na⁺ ions, glucose. This is an example of secondary active transport where the sodium gradient maintained by Na⁺/K⁺ ATPases powers the uptake of glucose into cells. The Na+/glucose cotransporter is an example of a symport mechanism in cells. In this cotransporter, Na+ ions moving down their electrochemical gradient drives the transport of glucose against its concentration gradient.

The Na⁺ ions move down their electrochemical gradient into the cell from the tubular lumen. This exergonic process is energetically favorable and provides the necessary energy to transport glucose against its concentration gradient into the cell. Once inside, glucose diffuses across the basal membrane into the interstitial space and then into the blood.