Question

Which of the following molecules is a primary acceptor of $C{O}_2$ in $C_4$ cycle?

• A. Pyruvate
• B. $3$-phosphoglycerate
• C. Phosphoenol pyruvic acid
• D. Oxaloacetate

Answer 1

Answer: (C)

Phosphoenol pyruvic acid

• Phosphoenol pyruvate (PEP) is a primary acceptor of $C{O}_2$ in photosynthesis. It is the first $C{O}_2$ acceptor in $C_4$ cycle.
• Phosphoenol pyruvic acid is a 3-carbon molecule. It is present in mesophyll cells of $C_4$ plants.
• In the $C_4$ cycle, $C{O}_2$ combines with phosphoenol pyruvic acid to form oxaloacetic acid.
• The enzyme that catalyzes this $C{O}_2$ fixation is PEP carboxylase or PEPcase. The mesophyll cells of $C_4$ plants lack the enzyme RuBisCO.4
  

So, the correct answer is option C.