Chemiosmosis is the movement of ions across a selectively permeable membrane down an electrochemical gradients. In the context of cellular respiration, it refers to the diffusion of protons through ATP synthase. This process is coupled to the generation of ATP via oxidative phosphorylation. If the electrochemical gradient is disrupted for any reason, the electron transport chain is stopped.
Different electron carriers yield different amounts of ATP. On average, each NADH molecule results in the production of 3 ATP molecules, and each FADH2 molecule produces 2 ATP molecules.