What is active transport and how do pumps like the Na+/K+ ATPase contribute to membrane potential?

• A. Active transport uses energy to move substances against gradient; Na+/K+ ATPase pumps 3 Na+ out and 2 K+ in, maintaining membrane potential.
• B. Active transport moves substances along their gradient without energy; Na+/K+ pumps 2 Na+ out and 3 K+ in.
• C. Active transport is only used for nutrients; Na+/K+ ATPase has no effect on membrane potential.
• D. Active transport occurs only in plants.

Answer: (A)

Active transport uses energy to move substances against their gradient. The Na+/K+ ATPase is a classic example: it uses ATP to drive a cycle that exports three Na+ ions from the cell and brings in two K+ ions. This unequal exchange moves positive charge out of the cell, making the inside more negative and thus helping establish and maintain the membrane potential. It also maintains the necessary ion gradients—low intracellular Na+ and high intracellular K+—which are crucial for nerve signaling and for powering other transports.

This pump’s action is energy-dependent and electrogenic, which is why it helps set up the membrane potential. If substances were moved with no energy or along their gradient, there would be no sustained membrane potential. The idea that it moves ions in the opposite direction or lacks effect on membrane potential isn’t accurate, and the pump is not limited to plants—it’s essential in animal cells as well.