HELPP In the cells of humans and other animals, a great deal of energy is dedicated to operating a pump that transports sodium (Na+) ions out of cells and potassium (K+) ions into cells. This transport creates a chemical and electrical gradient. Maintaining the proper balance of sodium and potassium is critical to ensuring that nerve cells work properly. Nerve cells drive muscle contractions—including heart muscles—and are responsible for animals’ abilities to sense their environment and for humans’ ability to think.

Scientists gain a better understanding of the sodium-potassium pump by creating models of what the pump accomplishes. Such models are used to examine many other complex processes as well.

This model of the sodium-potassium pump illustrates the process by which sodium is pumped out of cells and potassium is pumped in. The sodium-potassium pump moves the two different ions in opposite directions.

Where in a cell does this transport process take place?

A.
nucleus
B.
cell wall
C.
cell membrane
D.
vesicle