Cyclic and Non cyclic Photo phosphorylation – Class 11 | Chapter – 13 | Biology Short Notes Series PDF

Cyclic and Non cyclic Photo phosphorylation: Photophosphorylation is the process of utilizing light energy from photosynthesis to convert ADP to ATP. It is the process of synthesizing energy-rich ATP molecules by transferring the phosphate group into ADP molecule in the presence of light.

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Photophosphorylation is of two types:

  • Cyclic Photophosphorylation
  • Non-cyclic Photophosphorylation

Cyclic and Non cyclic Photo phosphorylation

Cyclic Photophosphorylation

The photophosphorylation process which results in the movement of the electrons in a cyclic manner for synthesizing ATP molecules is called cyclic photophosphorylation.

In this process, plant cells just accomplish the ADP to ATP for immediate energy for the cells. This process usually takes place in the thylakoid membrane and uses Photosystem I and the chlorophyll P700.

During cyclic photophosphorylation, the electrons are transferred back to P700 instead of moving into the NADP from the electron acceptor. This downward movement of electrons from an acceptor to P700 results in the formation of ATP molecules.

Non-Cyclic Photophosphorylation

The photophosphorylation process which results in the movement of the electrons in a non-cyclic manner for synthesizing ATP molecules using the energy from excited electrons provided by photosystem II is called non-cyclic photophosphorylation.

This process is referred to as non- cyclic photophosphorylation because the lost electrons by P680 of Photosystem II are occupied by P700 of Photosystem I and are not reverted to P680. Here the complete movement of the electrons is in a unidirectional or in a non- cyclic manner.

During non-cyclic photophosphorylation, the electrons released by P700 are carried by primary acceptor and are finally passed on to NADP. Here, the electrons combine with the protons – H+ which is produced by splitting up of the water molecule and reduces NADP to NADPH2.

Difference between Cyclic and Non cyclic Photo phosphorylation

Following are the important differences between Cyclic and Non cyclic Photo phosphorylation:

Cyclic Photophosphorylation Non-Cyclic Photophosphorylation
Only Photosystem I is involved. Both Photosystem I and II are involved.
P700 is the active reaction centre. P680 is the active reaction centre.
Electrons travel in a cyclic manner. Electrons travel in a non – cyclic manner.
Electrons revert to Photosystem I Electrons from Photosystem I are accepted by NADP.
ATP molecules are produced. Both NADPH and ATP molecules are produced.
Water is not required. Photolysis of water is present.
NADPH is not synthesized. NADPH is synthesized.
Oxygen is not evolved as the by-product Oxygen is evolved as a by-product.
This process is predominant only in bacteria. This process is predominant in all green plants.

 

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