Question

The reaction that is responsible for the primary fixation of CO${}_2$is catalysed by

• A. RuBP carboxylase and PEP carboxylase
• B. PEP carboxylase
• C. RuBP carboxylase
• D. PGA synthase

Answer 1

The correct option is A RuBP carboxylase and PEP carboxylase

RuBP Carboxylase :

RuBP carboxylase is the enzyme that is involved in the fixation of atmospheric carbon dioxide in the C3 cycle

• It catalyzes the reaction between the primary acceptor of $C{O}_2$, RuBP, with $C{O}_2$.
• However, it is found in both C3 and C4 plants.

PEP carboxylase:

• PEP carboxylase catalyzes the fixation of atmospheric carbon dioxide with phosphoenolpyruvate (PEP) in the C4 pathway.
• It is found only in C4 plants and not in C3 plants.

PGA synthase:

PGA synthase is the enzyme that catalyzes the conversion of L- glutamine to polyglutamic acid (PGA).

Summary:

Both RuBP carboxylase and PEP carboxylase are involved in the fixation of carbon dioxide. In the question, it is not mentioned specifically if it's about C3 or C4 plants. Thus the correct answer is option c.

Final answer:

RuBP carboxylase and PEP carboxylase.