A) PGA
B) PEP
C) RuBP
D) OAA
Correct Answer: B
Solution :
In \[{{C}_{4}}\] plants initial \[C{{O}_{2}}\] fixation occurs in mesophyll cells of leaf. The first \[C{{O}_{2}}\] acceptor is a 3-C compound Phosphoenol Pyruvate (PEP). It combines with \[C{{O}_{2}}\] in the presence of PEP carboxylase to form 4-C compound oxaloacetic acid. \[PEP+C{{O}_{2}}+{{H}_{2}}O\xrightarrow{PEP\text{ }carboxylase}\] oxaloacetic acid \[+{{H}_{3}}P{{O}_{4}}\] Oxaloacetic acid is reduced to malic acid, Oxaloacetic-acid \[+NADPH\xrightarrow{dehydrcgenas}\] malic acid \[+NAD{{P}^{+}}\] In \[{{C}_{3}}\] plants the first \[C{{O}_{2}}\] acceptor is ribulose 1-5 biphosphate. It combines with \[C{{O}_{2}}\] to produce a transient intermediate compound called 2-carboxy 3-keto 1, 5 biphosphoribotol. It immediately splits to form two molecules of 3 phosphoglyceric acid or PGA. RuBP \[+C{{O}_{2}}\xrightarrow[Carboxylase]{RuBP}\]2-carboxy, 3-keto, 1, 5-biphosphoribotol 2 carboxy 3-keto 1-5 biphosphoribotol \[+{{H}_{2}}O\xrightarrow{{}}2\,PGA\].
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