The pumping of hydrogen ions (protons) across membranes during chemiosmosis is an example of which type of cellular transport?

active

facilitated diffusion

osmosis

endocytosis

I believe the correct answer from the choices listed above is the second option. Chemiosmosis is the process of using a hydrogen concentration and electrochemical gradient to move hydrogen ions through a specialized protein channel, thus driving a chemical process. Therefore, it is a facilitated diffusion which uses regular diffusion as the driving force (i.e. the molecule moves from high to low concentration), but unlike regular diffusion does so only through specialized channels.