The thylakoid membrane contains a protein called atp synthase. As hydrogen ions pass through the protein, adp and a phosphate group are combined to form atp. What is the direct energy source, if any, for the movement of hydrogen ions and the formation of atp? a. The energy source is the high-energy electrons that accompany the hydrogen ions. B. The energy source is the concentration difference of hydrogen ions across the membrane. C. The energy source is a set of atp molecules that gather inside the thylakoid. D. There is no energy source; the process occurs without an energy input.