Question

Explain cyclic and non cyclic photo-phosphorylation.

Answer 1

Cyclic :-
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 :-

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 as non-cyclic photophosphorylation.

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

Answer 2

$\huge \: { \bold \: \: {answer}}$


$\huge{ \underline{ \bold{ \pink{ \: \: \: \: \: \: \: PHOTOPHOSPHORYLATION \: \: \: \: \: \: \: }}}}$


¤¤¤ The process of formation of high-energy chemicals [ ATP & NADPH ] in presence of light is called Photophosphorylation.

¤¤¤ It is of two types :-
▪ Non-Cyclic Photophosphorylation.
▪ Cyclic Photophosphorylation.

$\huge{ \bold{ \green{ = = Non-Cyclic \: Photophosphorylation. }}}$


¤¤¤ It occurs when two Photosystems work in a series [ first PS II and then PS I ] through are electron transport chain as seen in the Z - Scheme.


¤¤¤ Here, ATP & NADPH + H+ ion are synthesized .


¤¤¤ It is a non - cyclic process because the electrons lost by Photosystem II do not come back to it but pass on to NADP+ .


¤¤¤ It occurs on Thyllakoid.

$\huge{ \bold{ \green{ \: \: = = Cyclic \: \: Photophosphorylation. \: \: }}}$


¤¤¤ It occurs in stroma lamellae membrane when only PS I is a functional.


¤¤¤ The electron is circulated within the Photosystem and the ATP synthesis occurs due to cyclic flow of electrons.


¤¤¤ The lamellae of grana have PS I & PS II. The stroma lamellae membrane lack PS II & NADP reductase.


¤¤¤ The electron does not pass on to NADP+ but is cycled back to PS I complex through electron transport chain.


¤¤¤ Here, only ATP is synthesized [ No NADPH + H+ ] .


¤¤¤ Cyclic Photophosphorylation also occurs when only light of wavelengths beyond 680nm are available.