Question

Phosphoenolpyruvate (PEP) is the primary CO2 acceptor in:

• A. C3 plants
• B. C4 plants
• C. C2 plants
• D. C3 and C4 plants

Answer 1

The correct option is B

C4 plants

The correct option is B:

Explanation of the correct answer:

1. Phosphoenolpyruvate (PEP) is the 3-Carbon compound and acts as the primary CO₂ acceptor in the mesophyll cells of C4 plants, leading to the formation of OAA (Oxaloacetic acid), C4 acid.
2. The enzyme PEP carboxylase or PEPcase catalyses this reaction.

Explanation of the incorrect options:

Option A:

1. RuBP (ribulose bisphosphate - 5C) acts as the primary CO₂ acceptor in C3 plants, leading to the formation of 2 molecules of 3-PGA (C3 acid).
2. The enzyme RuBP carboxylase-oxygenase (RuBisCO) catalyses the reaction.

Option C:

1. C2 cycle is also called photorespiration.
2. It is the light-dependent O₂ uptake and CO₂ release that occurs in photosynthetic organisms.
3. This process does not occur un C4 plants.

Option D:

1. PEP is the 3C compound and acts as the primary CO₂ acceptor in C4 plants only, not C3 plants.

Final answer: Phosphoenolpyruvate (PEP) is the primary CO2 acceptor in C4 plants.