Question

Photosynthesis in $C_4$ plants is relatively less limited by atmospheric $C{O}_2$ because

• A. Effective pumping of $C{O}_2$ into bundle sheath cells
• B. Rubisco in $C_4$ plants has higher affinity for $C{O}_2$
• C. Four carbon acids are primary initial $C{O}_2$ fixation products
• D. Primary fixation of $C{O}_2$ is mediated via PEP carboxylase

Answer 1

The correct option is D Primary fixation of $C{O}_2$ is mediated via PEP carboxylase

C${}_4$ plants can absorb CO${}_2$ even in a much low CO${}_2$ concentration while the C${}_3$ plants fail to avail it. C${}_4$ cycle is much more efficient photosynthetically. Primary Carboxylation of phosphoenolpyruvate acid (PEP) to form oxaloacetic acid (a 4- carbon compound) in presence of enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) is an additional step in the C${}_4$ plants that allow an efficient CO${}_2$ utilization. Secondary carboxylation to synthesize carbohydrates occurs in bundle sheath.

Hence, the correct answer is 'Primary fixation of CO${}_2$ is mediated via PEP carboxylase'.