Question

Primary CO$_2$ acceptor in C$_4$ plants

• A. Phospho enol pyruvic acid
• B. Ribulose 1,5 bis phosphate carboxylase
• C. Oxalo acetic acid
• D. Phospho glyceric acid

Hint:

C$_4$ plants use PEP as the primary CO$_2$ acceptor in mesophyll cells, reducing photorespiration and enhancing efficiency under stress.

Answer 1

The Correct Option is A

In C$_4$ plants, the initial fixation of carbon dioxide occurs in the mesophyll cells. The primary CO$_2$ acceptor is Phosphoenol Pyruvate (PEP).
The enzyme PEP carboxylase catalyzes the reaction between CO$_2$ and PEP to form oxaloacetic acid (OAA). This adaptation allows C$_4$ plants to efficiently fix carbon even under conditions of high light intensity and temperature, minimizing photorespiration.
By contrast, in C$_3$ plants, the primary acceptor of CO$_2$ is Ribulose-1,5-bisphosphate (RuBP), and the enzyme involved is Rubisco.
Hence, in C$_4$ plants, the correct primary CO$_2$ acceptor is Phospho enol pyruvic acid (PEP).

Answer 2

Primary CO₂ acceptor in C₄ plants:

C₄ plants have a specialized mechanism to efficiently fix carbon dioxide, especially under conditions of high temperature and light intensity. Unlike C₃ plants, where CO₂ is directly fixed by ribulose bisphosphate, in C₄ plants the initial CO₂ acceptor is a 3-carbon compound called phosphoenolpyruvic acid (PEP).

PEP is a 3-carbon compound that reacts with CO₂ to form a 4-carbon compound, oxaloacetic acid, catalyzed by the enzyme PEP carboxylase. This process helps in concentrating CO₂ in bundle sheath cells, reducing photorespiration and increasing photosynthetic efficiency.

Therefore, phosphoenolpyruvic acid (PEP) acts as the primary CO₂ acceptor in C₄ plants, marking a key difference between C₃ and C₄ photosynthetic pathways.

Correct Answer: Phosphoenolpyruvic acid