Differences between C3 and C4 plants


 

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Differences between Cyclic and Non-cyclic photophosphorylation :

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S.No. Cyclic photophosphorylation                              Non-cyclic Photophosphorylation 1. Associated with PS I                                                     Associated with both PS I and PSII 2. Electron expelled from chl molecule                            Electron expelled from chl molecule is cycled back.                                                                   is not cycled back. Its loss is compensated                                                                                        by electrons coming from the photolysis of water. 3. Photolysis of water and O2                                         Photolysis of water and O2 evolution evaluation does not take place                                        take place. 4. Phosphorylation takes place at two places                Phosphorylation takes place only at one place. 5. Two ATP molecules are produced.                             one ATP and one NADPH2 are produced. 6. NADP is not reduced           
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Process of Photosynthesis

 Photosynthesis is an oxidation-reduction process in which water is oxidized and CO2 is reduced to carbohydrates and water, and O2 molecules are by-products. The reduction of CO2 to carbohydrate level needs assimilatory powers such as ATP and NADPH2 . Reduction of CO2 occurs in dark ( light-independent ) but the production of assimilatory powers takes place in the presence of light and the process is light-dependent. Thus, Photosynthesis consists of two phases : 1. Light-dependent phase (light reaction or Hill reaction) and ` 2. Light-independent phase (dark reaction or Blackman’s reaction).
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Crassulacean Acid Metabolism (CAM cycle)

 Under natural conditions, the acidity of green shoots of some non-halophytic succulents and semi-succulent plants increase at night and decrease during the daytime. This diurnal change in the acidity was first discovered in Bryophyllum belonging to the family Crassulaceae. Therefore, it is called Crassulacean Acid Metabolism (CAM) . This metabolism occurs only in green organs and it is quite common in the plants belonging to the families like Crassulaceae, Cactaceae, Orchidaceae, Bromeliaceae, Liliaceae, Asclepiadaceae, Vitaceae, and Euphorbiaceae. All such plants are called Crassulacean Acid Metabolism plants(CAM plants). Most CAM plants possess the succulent habit. A typical example of a commercial crop possessing a CAM pathway is pineapple. Mechanism of CAM cycle The sequence of reactions taking place in the CAM pathway is shown in Fig.20. 1. During the night when stomata are open, CO2 is fixed through the action of PEP carboxylase to Malic acid. This is accomplised in two steps :
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