A/An solution occurs when the solute concentration outside of the cell is higher than the solute concentration inside the cell Most cells have an electrical potential difference of between –40 and millivolts. is a determining force in water movement, and causes water to move from areas of high water concentration to low water concentration. In most cells, there are more molecules inside the cell and more sodium molecules outside the cell. A/An exists when different concentrations of a substance exist on either side of a membrane.