Question

The first carbon dioxide acceptor in C4-plants is

• A. PEP (Phosphoenol pyruvate)
• B. RuBP (Ribulose biphosphate)
• C. Oxaloacetic acid
• D. 3-PGA (3-Phosphoglyceric acid)

Answer 1

The Correct Option is A

The question asks about the first carbon dioxide acceptor in C4 plants. Understanding the process of photosynthesis in C4 plants is crucial for answering this.

C4 plants have a unique pathway for photosynthesis that helps them thrive in high light intensity and high-temperature environments. This pathway is known as the C4 cycle or the Hatch-Slack pathway.

In C4 plants, the first step of carbon fixation involves the enzyme phosphoenolpyruvate carboxylase, which catalyzes the combination of carbon dioxide with phosphoenol pyruvate (PEP) to form oxaloacetate. Thus, PEP is the first carbon dioxide acceptor in the C4 pathway.

Let's evaluate each option:

• PEP (Phosphoenol pyruvate): Correct choice as it is the initial molecule that accepts CO₂ in C4 plants via the enzyme PEP carboxylase.
• RuBP (Ribulose biphosphate): While it is involved in the Calvin cycle (a part of the photosynthesis process), it is not involved in the initial CO₂ fixation step in C4 plants.
• Oxaloacetic acid: This is the first stable product formed after PEP accepts CO₂, not the initial CO₂ acceptor.
• 3-PGA (3-Phosphoglyceric acid): This is an intermediary molecule formed in the Calvin cycle and unrelated to the initial CO₂ acceptance in C4 plants.

Thus, the correct answer is PEP (Phosphoenol pyruvate). This understanding showcases that PEP's role as the primary acceptor is central to differentiating how C4 plants efficiently capture atmospheric CO₂ under stress environmental conditions.