The energy for glucose transport is provided by the active transport of which ion?

• A. Potassium into the cell
• B. Sodium out of the cell
• C. Sodium into the cell
• D. Potassium out of the cell

Answer: (B)

Glucose transport in many epithelia is powered by the sodium gradient across the apical membrane. Sodium moves from the lumen into the cell via a sodium-glucose cotransporter, bringing glucose with it. That gradient is maintained by the Na+/K+-ATPase actively pumping sodium out of the cell, using ATP. So the energy source for glucose uptake is sodium being pumped out of the cell, which creates the gradient that drives the secondary active transport of glucose. Potassium movements do not provide this energy for glucose transport.