Photo Chemical Phase of Light Reaction

The photochemical phase is the light reaction's second half, and it is where the excitation energy generated during the photo-oxidation phase (13.9) is actually converted into usable chemical products. In this phase, electrons released from the reaction centres are passed along a chain of membrane-bound electron carrier molecules, and the energy released at each transfer step is used to generate the assimilatory power the dark reaction depends on: ATP and NADPH+H+. Because PS II's reaction centre loses electrons as part of this process, those electrons have to be replaced from somewhere, and that replacement comes from splitting water molecules - a process called photolysis, covered in 13.10.1 - which simultaneously regenerates the electrons PS II needs and releases oxygen as a byproduct. The full sequence by w …