The Na+/K+ ATPase pump moves which ions across the cell membrane?

• A. Calcium and Magnesium
• B. Chloride and Bicarbonate
• C. Potassium and Calcium
• D. Sodium and Potassium

Answer: (D)

This question tests understanding of how the Na+/K+ ATPase functions as a primary active transporter that establishes the essential sodium and potassium gradients across the plasma membrane. The pump uses one molecule of ATP to move three sodium ions out of the cell and two potassium ions into the cell with each cycle. This creates low intracellular Na+ and high intracellular K+, generating the electrochemical gradients that power secondary active transport and help maintain the resting membrane potential. It also helps regulate cell volume.

This pump is specific for sodium and potassium, and does not primarily transport calcium, magnesium, chloride, or bicarbonate—the other ions mentioned in the alternatives. The mechanism involves binding Na+ from the cytosol, phosphorylation-driven conformational change to expose Na+ to the outside and release it, binding K+ outside, dephosphorylation to revert to the original conformation, and release of K+ inside, continuing the cycle.