The sodium-potassium pump is called an electrogenic pump because it:

• A. creates a net movement of charge across the membrane
• B. transports sodium and potassium ions at equal rates
• C. requires ATP to function
• D. moves ions down their concentration gradients

Answer: (A)

Verified step by step guidance

1. Understand the function of the sodium-potassium pump: It is a membrane protein that actively transports sodium (Na⁺) and potassium (K⁺) ions across the plasma membrane using energy from ATP hydrolysis.
2. Recall that the pump moves 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into the cell during each cycle. This creates an imbalance in the number of positive charges moved across the membrane.
3. Recognize that this imbalance in charge movement results in a net movement of positive charge out of the cell, which contributes to the membrane potential. This is why the pump is referred to as 'electrogenic.'
4. Eliminate incorrect options: The pump does not transport sodium and potassium ions at equal rates (it moves 3 Na⁺ out and 2 K⁺ in). It does require ATP to function, but this is not why it is called electrogenic. It also moves ions against their concentration gradients, not down them.
5. Conclude that the correct answer is: 'creates a net movement of charge across the membrane,' as this is the defining feature of an electrogenic pump.