Figure 6.20: Noncyclic Electron Transport Uses Two Photosystems As chlorophyll molecules in the reaction centers of photosystems I and II absorb light energy, they pass electrons into a series of redox reactions, ultimately producing NADPH and ATP. The term “Z scheme” describes the path (blue arrows) of electrons as they travel through the two photosystems. In this scheme the vertical positions represent the energy levels of the molecules in the electron transport system.