Give comparison between the following :
(b) Cyclic and non-cyclic photophosphorylation
(b) Distinction between cyclic and non-cyclic photophosphorylation :
Cyclic photophosphorylation |
Non-cyclic photophosphorylation |
|
1. |
It is performed by PS I independently. |
It is performed by both PS I and PS II with the help of each other. |
2. |
An external source of electrons is not required because the same electrons get recycled. |
The process requires an external electron donor, because the same electron is not recycled. |
3. |
It is not connected with photolysis of water, therefore, no oxygen is evolved. |
It is connected with photolysis of water and liberation of oxygen. |
4. |
It synthesizes only ATP. |
ATP synthesis with the production of NADPH. |
5 |
Electron flow is cyclic. |
Electron flow is non-cyclic. |
RuBisCo enzymes acts as both carboxylase and oxygenase. It carries out more carboxylation in the C4 plants as these plants have special mechanism that increases the concentration of the CO2 at the enzyme site. There is no photorespiration in the C4 plants and thus oxygen does not bind to the RuBisCo enzyme. All this minimizes the oxygenase activity of the enzyme and increase the carboxylase activity.