Cyclic photophosphorylation. (A) In this pathway, electrons from reduced ferredoxin are transferred to cytochrome bf rather than to ferredoxin–NADP⁺ reductase. The flow of electrons through cytochrome bf pumps protons into the thylakoid lumen. These protons flow through ATP synthase to generate ATP. Neither NADPH nor O₂ is generated by this pathway. (B) A scheme showing the energetic basis for cyclic photophosphorylation. Abbreviations: Fd, ferredoxin; Pc, plastocyanin.