Biology Marking Period 3 Practice Test 2026 - Free Biology Practice Questions and Study Guide

This question tests how the Na+/K+-ATPase uses energy to move ions and maintain the membrane potential. The pump uses one ATP molecule to move three sodium ions from inside the cell to the extracellular space and two potassium ions from outside to inside. This specific 3 Na+ out/2 K+ in stoichiometry is essential because it creates a net export of positive charge, helping keep the cell interior negative relative to the outside and sustaining the ion gradients the cell relies on for various processes. The pump is an active transporter embedded in the plasma membrane, powered by ATP hydrolysis, which drives conformational changes that alternately expose binding sites to either side of the membrane. It is not a passive channel, so statements claiming passive transport or energy-free movement are incorrect, and it does not directly synthesize ATP.