Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Sorghum is a C3 plant.
Reason (R): In Sorghum, the primary $\text{CO}_2$ acceptor is a 3-carbon molecule Phosphoenolpyruvate.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember that major tropical crop species like sugarcane, maize, sorghum, and millets are C4 plants, whereas wheat, rice, barley, and potatoes are C3 plants.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Plants are classified into $\text{C}_3$, $\text{C}_4$, or CAM groups based on their primary carbon fixation pathway and anatomical adaptations (such as Kranz anatomy).

Step 2: Detailed Explanation:
- Assertion (A) is false: Sorghum (Sorghum bicolor) is a highly efficient, drought-tolerant, tropical C4 grass, not a C3 plant.
- Reason (R) is true: In C4 plants like Sorghum, initial carbon fixation occurs in the mesophyll cells. The primary $\text{CO}_2$ acceptor is Phosphoenolpyruvate (PEP), which is a 3-carbon molecule. This carboxylation is catalyzed by the enzyme PEP carboxylase, forming oxaloacetate (a 4-carbon compound).
Thus, Assertion (A) is false, but Reason (R) is true.

Step 3: Final Answer:
The correct option is (D).