Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologymediummcq1 pt

During one cycle the sodium-potassium pump exports three Na+ ions and imports two K+ ions while hydrolyzing one ATP. Why is this pump described as electrogenic?

A.The pump synthesizes ATP from ADP whenever ion flow reverses, so it generates current by running backward.
B.Electrogenic refers to the phosphate group attached to the pump during its cycle, because phosphate carries negative charge at cytosolic pH.
C.Each cycle leaves a net surplus of one positive charge outside, since three Na+ exit while only two K+ enter.
D.Any protein that binds ATP becomes electrically charged itself and transfers that charge onto the ions it carries.

Explanation

Core Concept

Each cycle moves a net surplus of one positive charge outward, three Na+ versus two K+. That charge separation helps make the cell interior negative relative to the exterior and contributes directly to the resting membrane potential. The pump also builds the Na+ and K+ concentration gradients that other transport processes exploit.

Correct Answer

CEach cycle leaves a net surplus of one positive charge outside, since three Na+ exit while only two K+ enter.

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