Question

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

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

Answer 1

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

In $C_4$ plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of $C{O}_2$ is phosphoenol pyruvate or PEP. It combines with carbon dioxide in the presence of PEP carboxylase or PEPcase to form oxaloacetate.
$C_4$ plants are more efficient in picking up $C{O}_2$ even when it is found in low concentration because of the high affinity of PEPcase.