Question

How is the intracellular levels of $K^{+}$ are higher than extracellular levels in animal cells?

Answer 1

The membrane is permeable to potassium ions, they will flow down their concentration gradient; i.e. towards the outside of the cell. There is also a concentration gradient favouring sodium diffusion in the opposite direction but the membrane is not permeable to sodium. Accordingly, after a few potassium ions have moved out of the cell, the cell will have an excess of negative charge, whereas the outside solution will have an excess of positive charge; i.e., a potential difference will exist across the membrane. The potential difference itself influences the movement of potassium ions. They (being positive) are attracted by the negative charge on the intra cellular side of the membrane and are repelled by the positive charge on the extracellular side of the membrane.