Describe what a photo-system does for photosynthesis?

Answer 1

* Light is absorbed by the antenna pigments of photosystems II and I. * The absorbed energy is transferred to the reaction center chlorophylls, P680 in photosystem II, P700 in photosystem I. * Absorption of 1 photon of light by Photosystem II removes 1 electron from P680. * With its resulting positive charge, P680 is sufficiently electronegative that it can remove 1 electron from a molecule of water. * When these steps have occurred 4 times, requiring 2 molecules of water, 1 molecule of oxygen and 4 protons (H+) are released * The electrons are transferred (by way of plastoquinone - PQ in the figure) to the cytochrome b6/f complex where they provide the energy for chemiosmosis. * Activation of P700 in photosystem I enables it to pick up electrons from the cytochrome b6/f complex (by way of plastocyanin - PC in the figure) and raise them to a sufficiently high redox potential that, after passing through ferredoxin(Fd in the figure), * they can reduce NADP+ to NADPH. The sawtooth shifts in redox potential as electrons pass from P680 to NADP+ have caused this system to be called the Z-Scheme(although as I have drawn the diagram, it looks more like an "N"). It is also called noncyclic photophosphorylation because it produces ATP in a one-way process