11th Class Biology Photosynthesis in Higher Plants

  • question_answer 4)
    RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in plants?  


    RuBisCO has a much greater affinity for CO2 than for O2. It is the relative concentration of O2 and CO2 that determines which of the two will bind to the enzyme. In plants some O2 does bind to RuBisCO and hence, CO2 fixation is- decreased. Here the RuBP instead of being converted to two molecules of PGA binds with O2 to form one molecule and phosphoglycolate in a pathway called photorespiration. In the photorespiratory pathway, there is neither synthesis of sugars, nor of ATP. Rather it results in the release of' CO2 with the utilization of ATP. In the photorespiratory pathway. There is no synthesis of ATP or NADPH. Therefore, photorespiration is a wasteful process. In plants, photorespiration does not occur. This is because they have a mechanism that increases the concentration of CO2 at the enzyme site. This takes place when the C4 acid from the mesophyll is broken down in the bundle cells to release this results in increasing the intracellular concentration of. In turn, this ensures that the RuBisCO functions as a carboxylase minimizing the oxygenase activity.  

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