Topic overview

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The electrochemical driving force combines chemical and electrical gradients; its Gibbs free-energy change indicates whether transport can occur spontaneously or needs energy input. The Nernst potential identifies the voltage at which one ion has no net flux, while the Goldman–Hodgkin–Katz framework accounts for multiple ions with differing permeabilities. Channels and carriers enable facilitated diffusion, whereas primary active transport uses energy directly and secondary transport couples uphill movement to another species moving downhill. Examples include the Na⁺/K⁺-ATPase, calcium pumps, and proton-motive-force-linked transport. The topic also introduces Donnan equilibrium, electrogenic transport, and the roles of ion gradients in membrane voltage.