Q19 / 180 · AIIMS 2016 · Botany

Photosynthesis in $\mathrm{C}_4$ plants is relatively less limited by atmospheric $\mathrm{CO}_2$ levels because

  • A
    there is effective pumping of $\mathrm{CO}_2$ into bundle sheath cells
  • B
    RuBisCO in $\mathrm{C}_4$ plants has higher affinity for $\mathrm{CO}_2$
  • C
    six carbon acids are the primary initial $\mathrm{CO}_2$ fixation products
  • Correct answer
    D
    the primary fixation of $\mathrm{CO}_2$ is mediated via PEP carboxylase.

Solution

$\mathrm{CO}_2$ acceptor molecule in $\mathrm{C}_4$ plants is phosphoenol pyruvate (PEP). $\mathrm{C}_4$ plants are more efficient in picking up $\mathrm{CO}_2$ even when it is found in low concentration because of high affinity of PEP. PEP carboxylase (PEPcase) is the key enzyme which catalyses the primary fixation of $\mathrm{CO}_2$.

Hence, the correct answer is option: 'D'.

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