GATE BT 2024 • Q49
MSQ • 2 Marks
Section 2: General Biotechnology
Biomolecules, enzyme kinetics
Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which of the following is/are synthetic auxin(s) that does/do NOT occur naturally?
Options:
-
(A) 2,4-Dichlorophenoxyacetic acid
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(B) Indole-3-acetic acid
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(C) Indole-3-butyric acid
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(D) 1-Naphthaleneacetic acid
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.49)**
**1. Governing Concept**:
- **Topic**: Plant Physiology & Synthetic Auxins
- **Auxins** promote cell elongation, apical dominance, and root initiation:
- **Natural Auxins**: Synthesized endogenously by plants:
- Indole-3-acetic acid (IAA) — primary natural auxin.
- Indole-3-butyric acid (IBA) — endogenous in many species.
- 4-Chloroindole-3-acetic acid (4-Cl-IAA).
- Phenylacetic acid (PAA).
- **Synthetic Auxins**: Man-made compounds not naturally synthesized in plants:
- 2,4-Dichlorophenoxyacetic acid (**2,4-D**).
- 1-Naphthaleneacetic acid (**NAA**).
- 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T).
- Dicamba, Picloram.
**2. Option Analysis**:
- **Option (A) [2,4-D (2,4-Dichlorophenoxyacetic acid)] is CORRECT**: A purely synthetic chlorinated phenoxy auxin widely used as a herbicide and in callus induction.
- **Option (B) [Indole-3-acetic acid (IAA)] is INCORRECT**: The primary endogenous natural auxin of all vascular plants.
- **Option (C) [Indole-3-butyric acid (IBA)] is INCORRECT**: Naturally occurring auxin found in plant tissues.
- **Option (D) [1-Naphthaleneacetic acid (NAA)] is CORRECT**: A synthetic naphthalene-ring auxin not occurring naturally in plants.
**3. Final Answer**:
- **Correct Options**: **A, D**
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