The Na /K pump generates a membrane potential across the plasma membrane (PM) of the cell by transporting Na and K across the PM. The action of this pump results in the cell having a slightly charge inside the cell compared to the extracellular space.

NEGATIVE CHARGE can best fill in the gap

Explanation:

The Na /K pump functions to maintain resting potential so that the cells will be kept in a state of a low concentration of sodium ions and high levels of potassium ions within the cell.

The processes of Na - K pump illustrates active transport since it moves Na+ and K+ ions against their concentration gradient. The energy required is supplied by the breakdown of ATP (adenosine triphosphate) to ADP (adenosine diphosphate). In nerve cells the pump is used to generate gradients of both sodium and potassium ions.

How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?

The sodium-potassium pump forces out three (positive) Na+ ions for every two (positive) K+ ions it pumps in, thus the cell loses a positive charge at every cycle of the pump.