Final answer:
The sodium-potassium pump (Na+/K+ ATPase) maintains the K+ concentration gradient by actively transporting K+ ions into the cell and Na+ ions out, using ATP hydrolysis for energy.
Step-by-step explanation:
Since the plasma membrane of a living cell is more "leaky" to K+ ions, the process or transporter that acts to maintain the K+ concentration gradient is the sodium-potassium pump (Na+/K+ ATPase).
This crucial pump uses energy derived from ATP hydrolysis to actively transport K+ ions into the cell and Na+ ions out of the cell, typically moving two K+ ions into the cell for every three Na+ ions expelled.
This action helps to maintain the electrochemical gradient, keeping the inside of the cell more negatively charged with respect to the extracellular fluid and ensuring proper concentrations of sodium and potassium ions.