Question

First $C{O}_2$ acceptor in $C_4$ plants is

• A. PEP
• B. PGA
• C. RuBP
• D. Pyruvic acid

Answer 1

Answer: (A)

In $C_4$ plants bundle sheath cells of leaf show $Kranz$ anatomy. In $C_4$ plants, the $C{O}_2$ first accepted in the mesophyll cells by PEP (phosphoenol pyruvate) and form a four carbon compound oxaloacetic acid.
Phosphoenol pyruvate $+C{O}_2\underset{\text{ Carboxylase }}{\stackrel{\text{ PEP }}{\to }}$ Oxaloacetic acid
In $C_3$ plants, the carboxylation (addition of $C{O}_2$ ) of RuBP (Ribulose 1,5 biphosphate) is catalyzed by an enzyme rubisco to form a 3-carbon compound phosphoglyceric acid (the first stable product of $C_3$ plants).
$RuBP+C{O}_2\stackrel{\text{ Rubisco }}{\to }3$-phosphoglyceric acid
Pyruvic acid is the end product of glycolysis During glycolysis one molecule of glucose is breakdown into two molecules of pyruvic acid.