When CO2 is added to PEP, the first stable product synthesised is:


The first stable product synthesized is OAA i.e. oxaloacetate.

In C4 plants, initial fixation of CO2 or carboxylation occurs in mesophyll cells. The chloroplasts of mesophyll cells possess enzyme PEP carboxylase for initial fixation of CO2. The primary acceptor of CO2 is phosphoenol pyruvate. PEP combines with CO2 in the presence of PEP carboxylase to form oxaloacetate.



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