Photo-Oxidation Phase of Light Reaction

The photo-oxidation phase is the first half of the light reaction, and its job is simply to capture a photon and use its energy to excite a pigment molecule's electron. When a pigment molecule absorbs a photon, one of its electrons is bumped up to an excited, higher-energy state; if the light source is switched off, that same electron eventually falls back down to its normal, low-energy ground-state orbital as the molecule relaxes back to its original stable condition. Not all photons are equal in this respect: absorbing blue light excites chlorophyll to a higher energy state than absorbing red light does, because blue light has a shorter wavelength and therefore carries more energy per photon than red light. It is precisely this excited state of the reaction-centre chlorophyll molecule that ultimately gets used to drive phosphorylation - since the phosphorylation that follows is powered by a light-generated electron, it is specifically called photophosphorylation (detailed in section 13.11). What happens next to this excited electron - whether it simply relaxes back …