Question

The first acceptor of CO₂ in a C₄ plant is

• A. Ribulose biphosphate
• B. Phosphoenol pyruvate
• C. Oxaloacetic acid
• D. 3-Phophoglyceric acid

Answer 1

The correct option is B

Phosphoenol pyruvate

The correct option is option B.

Explanations for the correct option:

1. C₄ plants are plants in which the first product of CO₂ fixation is a C₄ organic acid, oxaloacetate formed by the carboxylation of Phosphoenolpyruvate by Phosphoenolpyruvate carboxylase.
2. They fix CO₂ into carbon molecules and this mechanism is referred to as the Hatch-Slack pathway.
3. The oxaloacetate formed is transported to the bundle sheath cells where it is decarboxylated to generate CO₂ molecules for carbon assimilation.

Explanations for the incorrect options:

Option A:

1. Ribulose bisphosphate is involved in photosynthesis and acts as the principal CO₂ acceptor in autotrophic plants.
2. It is a product of the phosphorylation of ribulose-5-phosphate by ATP molecules in the Calvin cycle.

Option C:

1. Oxaloacetic acid is an intermediate of the citric acid cycle formed by the interaction of acetyl-CoA to generate citrate.
2. It is a four carbon compound involved in the TCA cycle.

Option D:

1. 3-Phosphoglyceric acid is an organic acid generated during glycolysis.
2. It is a three-carbon molecule formed as the first stable product during photosynthesis.

Final answer: The first acceptor of CO₂ in the C₄ plant is Phosphoenol pyruvate.