| Substrate | Enzyme | Product |
| I. Phosphoenol pyruvate | PEP Carboxylase | \[{{C}_{4}}\]acid |
| II. Malate | Malic enzyme | \[{{C}_{4}}\]acid |
| III. RuBP | Ribulose 5-phosphate Kinase | \[{{C}_{3}}\]acid |
| IV. Pyruvate | Pyruvate dikinase | \[{{C}_{3}}\]acid |
A) III and IV
B) I and II
C) II and III
D) I and IV
Correct Answer: D
Solution :
In \[{{C}_{4}}\]plants \[C{{O}_{2}}\]taken from the atmosphere is accepted by Phosphoenolpyruvic acid (PEP), presents in the chloroplasts of mesophyll cells of these leaves, leading to the formation of 4-C compound. Atmospheric \[C{{O}_{2}}+\text{ }PEP\](3-C compound)\[\xrightarrow[{}]{PEP\,carboxylase}\] \[\underset{(\text{4-C compound})}{\mathop{\text{Oxaloacetic acid (OAA)}}}\,\]OAA is converted into malic acid (4-C) which enters into bundle sheath cells where it undergoes oxidative decarboxylation yielding pyruvic acid (3-C) compound). Pyruvic acid reenters mesophyll cells and regenerates PEP with the help of an enzyme pyruvate orthophosphate dikinase.
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