What is the driving force of the membrane?

Answer 1

The driving force is explained by two factors: voltage gradient and concentration gradient. When there are more ions inside of a cell than outside of a cell, the concentration gradient is pushing the ion to exit the cell. This is simple diffusion. If that ion carries a negative charge then it also wants to exit the cell because the outside environment is slightly more positive.

So if you add both voltage gradient and concentration gradient you get the driving force. In the example above both gradients are pushing the ion outside of the cell. Sometimes you can have the gradients going in opposites and then the driving force will be determined on which gradient is stronger.

Answer 2

The driving force of the membrane is the concentration gradient of molecules or ions across the membrane. This gradient creates a potential difference that can drive the movement of substances across the membrane through processes like diffusion or active transport.