Question

In C3 and C4 plants, primary carboxylation takes place with the help of?
(A) PEP carboxylase and pyruvate carboxylase
(B) RuBP carboxylase and PEP carboxylase
(C) PEP carboxylase and RuBP carboxylase
(D) RuBP carboxylase and pyruvate carboxylase

Answer 1

Hint:
Primary carboxylation is the first step of the C3 and C4 cycle. The molecule that first accepts carbon dioxide helps in primary carboxylation. In the C3 cycle, carbon dioxide reduction is the cyclic process and the first stable product in this compound is the 3-C compound. In the C4 cycle, the first stable compound is the 4-C compound.

Complete step by step answer:
In the Calvin cycle, the first stable product in this cycle is a 3-C compound 3- PGA (phosphoglyceric acid). Calvin cycle is divided into three distinct phases: Carboxylation, glycolytic reversal, and regeneration of RuBP. In this cycle, the carbon dioxide acceptor molecule is RuBP or RuDP (i.e., Ribulose1,5-biphosphate or Ribulose1,5-Diphosphate). There occurs covalent bonding of carbon dioxide to RuBP and the enzyme catalyzing this reaction is RuBP- carboxylase/oxygenase (Rubisco).
Carbon dioxide taken from the atmosphere is accepted by phosphoenolpyruvic acid(PEP) present in the chloroplasts of mesophyll cells of these leaves, leading to the formation of a 4-C compound, oxaloacetic acid (OAA). This acid is converted into another 4-C acid, the malic acid which enters into the chloroplast of bundle sheath cells and reacts with Ribuose-1,5-biphosphate(RuBP) already present in the chloroplasts of bundle sheath cells and Calvin cycle stars from here.

Option ‘B’ is correct

Note:
Calvin and Benson discovered the path of carbon in the Calvin cycle. The detailed study of the C4 cycle is introduced by M.D Hatch and C.R Slack in 1966. So it is called Hatch and Slack cycle. The stable product in C4 is a dicarboxylic substance.