Photosynthesis Question 12
12. Photosynthesis in $C_4$ plants is relatively less limited by atmospheric $CO_2$ levels because of :
[2005]
(a) Effective pumping of $CO_2$ into bundle sheath cells.
(b) Rubisco in $C_4$ plants has higher affinity for $CO_2$.
(c) Four carbon acids are the primary initial $CO_2$ fixation products.
(d) The primary fixation of $CO_2$ is mediated via PEP carboxylase.
Show Answer
Answer : d
Hints & Solution
(d) In $C_4$ plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of $CO_2$ is phosphoenol pyruvate or PEP. It combines with carbon dioxide in the presence of PEP carboxylase to form oxaloacetate. $C_4$ plants are more efficient in picking up $CO_2$ even when it is found in low concentration because of the high affinity of PEP case.
