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  • The C4 carbon cycle is a CO2 concentrating mechanism evolved to reduce photorespiration. The following ar stated as important features of C4 pathway:  <

The C4 carbon cycle is a CO2 concentrating mechanism evolved to reduce photorespiration. The following ar stated as important features of C4 pathway: 

P. The leaves of C4 plants have Kranz anatomy that distinguishes mesophyll and bundle sheath cells.

Q. In the peripheral mesophyll cell, atmospheric CO2 Is fixed by phosphoenolpyruvate carboxylase yielding a four-carbon acid.

R. In the inner layer of mesophyll, NAD-malic enzyme decarboxylates four-carbon acid and releases CO2.

S. CO2 is again re-fixed through the Calvin cycle in the bundle sheath cells.

Which one of the following combinations is correct?

 

Option: 1

Q, R and S

 


Option: 2

P. Q and R


Option: 3

P, Q and S

 


Option: 4

P, R and S


Answers (1)

best_answer

NAD-malic enzyme does not decarboxylate a four-carbon acid in the inner layer of mesophyll.

In C4 plants, which have a specialised carbon fixation pathway, decarboxylation of a four-carbon acid (malate or aspartate) occurs in the bundle sheath cells, not in the inner layer of mesophyll. The decarboxylation process is carried out by the enzyme NADP-malic enzyme, not NAD-malic enzyme.

In C4 plants, the mesophyll cells fix carbon dioxide into a four-carbon acid (either malate or aspartate) using an enzyme called phosphoenolpyruvate carboxylase (PEP carboxylase). The four-carbon acid is then transported to the bundle sheath cells, where it undergoes decarboxylation by NADP-malic enzyme. This decarboxylation reaction releases carbon dioxide (CO2), which is then utilised in the Calvin cycle for the synthesis of sugars.

So, the correct statement would be:

In the bundle sheath cells of C4 plants, NADP-malic enzyme decarboxylates the four-carbon acid and releases CO2. Hence, the correct answer is option 3. 

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