Chemiosmotic theory states that ions will move across a membrane, down their concentration gradient. In bioenergetics, this relates to ATP synthesis. By following the change in ions across a membrane (the transmembrane potential), through a method such as patch clamping, cellular processes can be studied. ATP synthase allows the cell to convert a potential energy (the H+ gradient) into chemical energy (ATP), producing a useful source of energy that can be used directly in cellular processes (enzyme activation, channel opening, signalling, …). By studying the flow of charge across the membrane, the production of ATP can be determined, where the H+:ATP ratio is known.