Osmosis is the process
of diffusion of water molecules across
a selectively permeable membrane. Chemiosmosis
is the process of diffusion of ions
(usually H+ ions, also known as
protons) across a selectively permeable membrane.
As in osmosis, chemiosmosis leads to a concentration
gradient of the diffusing ion across the membrane. A
concentration gradient is a form of potential energy
that can do work. In many cells, a proton gradient provides
the energy for the synthesis of ATP.