Electrogenic ion transport contributes to membrane potential due to what capability?

• A. The diffusion of ions down their gradients
• B. The ability of adding/removing ions to the cell to maintain concentration gradients
• C. The opening of ion channels
• D. The movement of ions purely by diffusion irrespective of pumps

Answer: (B)

The main idea is that electrogenic transport creates membrane potential by actively moving ions across the membrane in a way that establishes or maintains an unequal distribution of charge on the two sides of the membrane. By actively adding or removing ions to maintain concentration gradients, the cell generates a net flow of charge across the membrane. This net movement of charge sets up a voltage difference: the interior becomes relatively more negative (or the exterior more positive) depending on which ions and transporters are involved. A classic example is the Na+/K+ ATPase, which pumps three Na+ out and two K+ in, producing a net outward current that contributes to the resting membrane potential.

Passive diffusion and the opening of ion channels involve ions moving down existing gradients and can produce currents, but they do not by themselves create or sustain the ion gradients that underlie membrane potential. They reflect the current flow once gradients exist, whereas electrogenic transport is about actively maintaining those gradients to generate voltage.