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Question
Assertion :C4 photosynthetic pathway is more efficient than C3 pathway. Reason: Photorespiration is suppressed in C4 plants.
Assertion :C4 photosynthetic pathway is more efficient than C3 pathway. Reason: Photorespiration is suppressed in C4 plants.
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Solution
The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Photorespiration is a process which involves loss of fixed carbon as CO2 in plants in the presence of light. It is initiated in chloroplasts. This process does not produce ATP or NADPH and is a wasteful process. Photorespiration occurs usually when there is the high concentration of oxygen. Under such circumstances, RuBisCO, the enzyme that catalyses the carboxylation of RuBP during the first step of Calvin cycle, functions as an oxygenase. Some O2 does bind to RuBisCO and hence CO2 fixation is decreased. The RuBP binds with O2 to form one molecule of PGA (3C compound) and phosphoglycolate (2C compound ) in the pathway of photorespiration. There is neither the synthesis sugar nor of ATP. Rather, it results in the release of CO2 with the utilisation of ATP. It leads to a 25% loss of the fixed CO2.Photorespiration is suppressed inC4 plants by having a mechanism that increases the concentration of CO2 at the enzyme site. During the C4 pathway, when the C4 acid from the mesophyll cells is broken down in the bundle sheath cells, it releases CO2 - this results in increasing the intracellular concentration of CO2. This, in turn, ensures that the RuBisCO functions as a carboxylase minimizing the oxygenase activity. Therefore, C4 photosynthetic pathway is more efficient than C3 pathway. Thus, the correct answer is option A.
Photorespiration is a process which involves loss of fixed carbon as CO2 in plants in the presence of light. It is initiated in chloroplasts. This process does not produce ATP or NADPH and is a wasteful process. Photorespiration occurs usually when there is the high concentration of oxygen. Under such circumstances, RuBisCO, the enzyme that catalyses the carboxylation of RuBP during the first step of Calvin cycle, functions as an oxygenase. Some O2 does bind to RuBisCO and hence CO2 fixation is decreased. The RuBP binds with O2 to form one molecule of PGA (3C compound) and phosphoglycolate (2C compound ) in the pathway of photorespiration. There is neither the synthesis sugar nor of ATP. Rather, it results in the release of CO2 with the utilisation of ATP. It leads to a 25% loss of the fixed CO2.
Photorespiration is suppressed inC4 plants by having a mechanism that increases the concentration of CO2 at the enzyme site. During the C4 pathway, when the C4 acid from the mesophyll cells is broken down in the bundle sheath cells, it releases CO2 - this results in increasing the intracellular concentration of CO2. This, in turn, ensures that the RuBisCO functions as a carboxylase minimizing the oxygenase activity. Therefore, C4 photosynthetic pathway is more efficient than C3 pathway. Thus, the correct answer is option A.
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