The living cell＇s electric potential and the electromotive force of a galvanic cell are described here using a nonvolume work thermodynamics and are shown to develop and operate on thr same principle, which is that in both external forces perform work at the expense of the system＇s free energy. The role of the membrane as external-force transmitter could be allowed for only after the momentum conservation principle had been incorporated into the thermostatic description of membrane equilibria and transport. For that it was necessary to introduce an additional term to a species＇ chemical potential that accounts for its potential interaction with the membrane. Then membrane equilibria, in particular the Nernst equilibrium potential, the Donnan potential, and osmotic pressure, could be properly described. The electric equivalent circuit method supplemented with an electric energy diagram is applied for describing steady-state transport across ion-selective membranes. Then it becomes evident that the system＇s free energy can be spent on moving across one type of ion when there is free passage for another type of ion. This is due to electric coupling between ionic fluxes accomplished via the resting membrane potential, which is thus to be viewed as an electromotive force, rather than just the electric potential difference.