Photosynthesis in Higher Plants

Cyclic and non-cyclic photophosphorylation

  • In cyclic photophosphorylation, which is performed by only Ps I system, the expelled electron from the photo centre of Ps I, is returned to it after carried away by a series of electron carriers.
  • Ps I contains a photo centre P700 and surrounded by antenna molecules (or) accessory pigments.
  • The released electron from P700 is passed through a series of electron carriers such as plastoquinone (PQ), Fe-s complex, Ferredoxin(Fd), cytochrome bb-f and plastocyanin.
  • ADP and inorganic phosphate are converted into ATP above cyt b6-f complex when an electron creates a proton gradient.
  • Ps I consists of chl 'a' which is more in number than chl 'b'.
  • If the expelled electron from the photo centre does not return back to it, then it is called as non-cyclic photophosphorylation, conducted by both Ps I and Ps II systems. Non-cyclic type is also known as 'Z-scheme'.
  • Ps II contains a photo centre, namely P680 which receives the electron that is released by photolysis of water and passes through electron carriers such as pheophytin, PQ, cyt b6-f and plastocyanin.
  • One ATP is produced above cyt b6-f complex.
  • From plastocyanin, one electron is passed onto Ps I complex (P700) to form NADHP from NADP+ with the help of an enzyme NADP- reductase.

View this video for the topic from 33:55 to 46:52

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