question_answer

Electrons from excited chlorophyll molecule photosystem-II are accepted first by

A) cytochrome-b                  

B) cytochrome-f   

C) quinone              

D) ferredoxin

Correct Answer: C

Solution :

Photosystem-II is a photosynthetic pigment system along with some electron carriers that is located in/ the apressed part of grana thylakoids. Photocentre has a dimer of special chlorophyll-a molecules called \[{{\text{P}}_{\text{680}}}.\]\[{{\text{P}}_{\text{680}}}\]of photosystem-II absorbs light energy, gets excited and transfers its electrons to electron acceptor molecule phaeophytin. Phaeophytin on accepting electrons become strong reducing agent. It donates, its electrons to downstream component of ETC, ie, quinone, cyt-b cyt-f complex, plastocyanin. While passing over cytochrome complex, electron losses sufficient energy to synthesize ATP. Plastocyanin is a  copper containing soluble protein, which transfers electrons to Pyoo reaction centre of photosystem-L On geting excited, Pyoo hands over electrons to a special chlorophyll molecule X from where electrons are passed to membrane bound iron-sulphur protein for transfer to another soluble protein ferredoxin.