55) During oxidative phosphorylation, H2O is formed. Where does the oxygen for the synthesis of the water come from? 56) Which metabolic process is most closely associated with intracellular membranes? 57) In chemiosmotic phosphorylation, what is the most direct source of energy that is used to convert ADP + Pi to ATP? A) energy released as electrons flow through the electron transport system B) energy released from substrate-level phosphorylation C) energy released from ATP synthase pumping hydrogen ions against their concentration gradient D) energy released from movement of protons through ATP synthase E) No external source of energy is required because the reaction is exergonic. 58) Energy released by the electron transport chain is used to pump H+ ions into which location?