Differences between C3 and C4 plants


 

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MECHANISM OF PHOTOSYNTHESIS

 The process of Photosynthesis is a complicated oxidation-reduction process ultimately resulting in the oxidation of water and reduction of CO2 to carbohydrates. The mechanism of photosynthesis can be studied with the following two processes : I. Primary Photochemical Reaction or Light reaction or Hill’s reaction, and II. Dark reaction or Blackman’s reaction or Path of carbon in photosynthesis Importance of two processes photosynthesis In the primary photochemical reaction, assimilatory powers (NADPH2 + ATP) are generated and O2 is released. These assimilatory powers are utilized in the dark reaction during which process CO2 is reduced to carbohydrates I. PRIMARY PHOTOCHEMICAL REACTION (OR) LIGHT REACTION (OR) HILL’S REACTION (Activities found in thylakoids or grana) In 1937, Robert Hill demonstrated that isolated chloroplasts evolved O2 when they were illuminated in the presence of suitable electron acceptors, such as ferricyanide. The ferricyanide is reduced to ferrocyanide by...
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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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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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