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Question: Answered & Verified by Expert
Photosynthesis in $\mathrm{C}_4$ plants is relatively less limited by atmospheric $\mathrm{CO}_2$ levels because
BiologyPhotosynthesis in Higher PlantsJIPMERJIPMER 2007
Options:
  • A four carbon acids are the primary initial $\mathrm{CO}_2$ fixation products
  • B the primary fixation of $\mathrm{CO}_2$ is mediated via PEP carboxylase
  • C effective pumping of $\mathrm{CO}_2$ into bundle sheath cells
  • D RUBISCO in $\mathrm{CO}_4$ plants has higher affinity for $\mathrm{CO}_2$
Solution:
2216 Upvotes Verified Answer
The correct answer is: the primary fixation of $\mathrm{CO}_2$ is mediated via PEP carboxylase
The fixation of $\mathrm{CO}_2$ in $\mathrm{C}_4$ plants takes place in two places and by two different organic compounds. Phosphoenol pyruvate (PEP) is found in mesophyll cells which primarily fixes atmospheric $\mathrm{CO}_2$ into oxaloacetic acid (4C).
RUBISCO is present in bundle sheath cells where final fixation of $\mathrm{CO}_2$ in hexose sugars takes place. $\mathrm{CO}_2$ is primarily fixed by PEP carboxylase because this enzyme has greater affinity to $\mathrm{CO}_2$ than RUBISCO.

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