Differences between C3 and C4 plants


 

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Structure of photosynthetic Pigments

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Chlorophylls : * They are magnesium porphyrin compounds * The porphyrin ring consists of four pyrrole rings joined together by CH bridges. * A long chain of C atoms called as Phytol chain is attached to the porphyrin ring. * Molecular formulae :                         Both the chlorophylls (a and b) consist of : Mg-Porphyrin head which is hydrophilic in nature and a Phytol tail possessing lipophilic properly. Difference between two chlorophylls In chlorophyll b there is -CHO (aldehyde) group, instead of a _CH3 (acetyl) group in chlorophyll a molecule. Synthesis of Chlorophyll * Chlorophyll is formed from protochlorophyllide in the presence of light with the loss of two hydrogen atoms as follows :                       Protochlorophyll               →                Chlorophyll   ...
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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 step...
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