Final answer:
The sodium-potassium "pump" requires the constant expenditure of adenosine triphosphate (ATP) as a source of energy. Each cycle of the pump moves three sodium ions out of the cell and two potassium ions into the cell.
Step-by-step explanation:
The sodium-potassium "pump" requires the constant expenditure of adenosine triphosphate (ATP) as a source of energy. This protein pump moves sodium ions out of the cell and potassium ions into the cell against their concentration gradients. Each cycle of the pump uses one ATP molecule to pump out three sodium ions and pump in two potassium ions.