Synthase (generated ATP by thermal cycling of subunit during suspension in convection cell: thermosynthesis) → added membrane and Fo ATP Synthase moiety (generated ATP by change in electrical polarization of membrane during thermal cycling: thermosynthesis) → added metastable, light-induced electric dipoles in membrane (primitive photosynthesis) → added quinones and membrane-spanning light-induced electric dipoles (today's bacterial photosynthesis, which makes use of chemiosmosis). External proton gradient model Deep-sea hydrothermal vents, emitting hot acidic or alklaine water, would have created external proton gradients. These provided energy that primordial organisms could have exploited. To keep the flows separate, such an organism could have wedged itself in the rock of the hydrothermal vent, exposed to the hydrothermal flow on one side and the more alkaline water on the other. As long as the organism's membrane (or passive ion channels within it) is permeable to protons, the mechanism can function without ion pumps. Such a proto-organism could then have evolved further mechanisms such as ion pumps and ATP synthase. Meteoritic quinones A proposed alternative source to chemiosmotic energy developing across membranous structures is if an electron acceptor, ferricyanide, is within a vesicle and the electron donor is outside, quinones transported by carbonaceous meteorites pick up electrons and protons from the donor. They would release electrons across the lipid membrane by diffusion to ferricyanide within the vesicles and release protons which produces gradients above pH 2, the process is conducive to the development of proton gradients. See also Cellular respiration Citric acid cycle Electrochemical gradient Glycolysis Oxidative phosphorylation References Further reading Biochemistry textbook reference, from the NCBI bookshelf – A set of experiments aiming to test some tenets of the chemiosmotic theory – External links Chemiosmosis (University of Wisconsin) Cell biology Cellular respiration