Class 11 Biology Photosynthesis In Higher Plants Cyclic and non-cyclic photo-phosphorylation

Cyclic and non-cyclic photo-phosphorylation

  • The process in which ATP is synthesised by cells in mitochondria and chloroplasts is named phosphorylation.
  • Photophosphorylation is the synthesis of ATP from ADP and inorganic phosphate in the presence of light.
  • When the two photosystems, first PS II and then the PS I, connected through an electron transport chain work in a series, the process is called non-cyclic photo-phosphorylation.
  • When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs due to cyclic flow of electrons in the stroma lamellae.
  • The stroma lamellae membranes lack PS II as well as NADP reductase enzyme, hence the excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain.
  • The cyclic flow results only in the synthesis of ATP, but not of NADPH + H+.


Fig. Cyclic phosphorylation

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