Question

Match List-I with List-II
{ll} List-I (Herbicide) & List-II (Mechanism of Action)
(A) Glyphosate & (I) ACCase inhibitors
(B) Atrazine & (II) ALS/AHAS inhibitors
(C) Imazethapyr & (III) EPSP synthase
(D) Diclofop methyl & (IV) PS II inhibitors

Choose the correct answer from the options given below:

• (A) - (III), (B) - (IV), (C) - (II), (D) - (I)
• (A) - (III), (B) - (IV), (C) - (I), (D) - (II)
• (A) - (IV), (B) - (III), (C) - (II), (D) - (I)
• (A) - (IV), (B) - (II), (C) - (I), (D) - (III)

Hint:

- Glyphosate is uniquely associated with EPSP synthase inhibition.
- Triazines like Atrazine and Ureas like Diuron are classic Photosystem II (PS II) inhibitors.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Herbicides are classified by their mode of action, representing the primary biochemical site or enzyme they inhibit in plant metabolic pathways.

Step 2: Detailed Explanation:
Let us match each herbicide with its correct target enzyme/mechanism:
- (A) Glyphosate:
Glyphosate is a broad-spectrum, systemic, non-selective herbicide.
It inhibits EPSP synthase (5-enolpyruvylshikimate-3-phosphate synthase), an enzyme in the shikimate pathway essential for synthesizing aromatic amino acids (phenylalanine, tyrosine, tryptophan).
Thus, (A) matches with (III).
- (B) Atrazine:
Atrazine is a selective triazine herbicide that acts as a photosynthesis inhibitor.
It binds to the Qb-binding site of the D1 protein in Photosystem II (PS II), blocking photosynthetic electron transport.
Thus, (B) matches with (IV).
- (C) Imazethapyr:
Imazethapyr is an imidazolinone herbicide used in leguminous crops.
It inhibits ALS/AHAS (acetolactate synthase acetohydroxyacid synthase), blocking the synthesis of branched-chain amino acids (valine, leucine, isoleucine).
Thus, (C) matches with (II).
- (D) Diclofop methyl:
Diclofop methyl belongs to the aryloxyphenoxypropionate ("fop") group.
It acts as an ACCase inhibitor (acetyl-CoA carboxylase), blocking fatty acid synthesis in susceptible grass species.
Thus, (D) matches with (I).
Matching summary:
(A) $\rightarrow$ (III), (B) $\rightarrow$ (IV), (C) $\rightarrow$ (II), (D) $\rightarrow$ (I).

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