What is the first acceptor of CO₂ in C₄ cycle ?

The correct answer is PEP.

Explanation:

• The C₄ cycle, also known as the Hatch-Slack pathway, is a photosynthetic process used by certain plants (e.g., maize, sugarcane, sorghum) to efficiently fix carbon dioxide (CO₂) in hot and dry conditions.
• In the C₄ cycle, the first stable product of carbon fixation is a four-carbon compound, oxaloacetic acid (OAA).
• Phosphoenolpyruvate (PEP), a three-carbon molecule, acts as the first acceptor of CO₂ in this cycle.
• CO2 combines with PEP to form oxaloacetic acid (OAA), a four-carbon compound.
• This reaction is catalyzed by the enzyme PEP carboxylase, which has a high affinity for CO2 and does not get inhibited by oxygen, making it efficient in fixing CO2 even in low concentrations.
• This process occurs in the mesophyll cells of C₄ plants, and the CO₂ fixation is catalyzed by the enzyme PEP carboxylase.

Key Points 

Other Options:

• RuBP:
  • Ribulose-1,5-bisphosphate (RuBP) is the primary acceptor of CO₂ in the C₃ cycle (Calvin cycle)
  • In the Calvin cycle, RuBP reacts with CO₂ to form two molecules of 3-phosphoglycerate (PGA).
  • This process occurs in C₃ plants or in the bundle sheath cells of C₄ plants after the initial fixation by PEP.
• PGA: PGA (3-phosphoglycerate) is an intermediate molecule formed during the Calvin cycle after the fixation of CO₂ by RuBP.
• OAA: Oxaloacetic acid (OAA) is the first stable product formed in the C₄ cycle after CO₂ is fixed by PEP and PEP carboxylase.