 The electrons then flow to the cytochrome b6f complex, which uses their energy to pump protons across the thylakoid membrane in the chloroplast.These protons move back through the membrane as they drive the ATP synthase, as before.The electrons then flow through photosystem I and can then either be used to reduce the coenzyme NADP+, for use in the Calvin cycle, which is discussed below, or recycled for further ATP generation.