Final answer:
The driving force on K+ is the difference between the equilibrium potential and the resting potential, which is -20 mV in this case, indicating a force that drives K+ into the cell.
Step-by-step explanation:
The driving force on K+ (potassium ions) is the difference in voltage between the equilibrium potential of potassium (EK) and the membrane resting potential. In this case, EK is -90 mV and the resting potential is -70 mV.
The driving force can be calculated by subtracting the resting potential from the equilibrium potential: Driving Force = EK - resting potential = -90 mV - (-70 mV) = -20 mV. This negative value indicates that the driving force is directing K+ ions to move into the cell.
Since potassium ions are higher inside the cell, they tend to move out of the cell through potassium channels due to the concentration gradient.
However, when the cell's membrane potential is closer to the potassium equilibrium potential (-90 mV), the drive for potassium to leave the cell is reduced, causing a shift in the direction of the driving force that now encourages K+ ions to enter the cell to bring the membrane potential back towards the equilibrium.