Correctly match the herbicide with its mode of development of resistance in
plants.
Herbicide Mode of development of resistance
P. Imidazolinones 1. Transformation of bacterial nitrilase gene
Q. Bromoxynil 2. Transformation of resistant version of acetolactate
synthetase
R. Glufosinate 3. Transformation of tfdA gene from Alcaligenes,
which encodes a dioxygenase
4. Transformation of bar gene from Streptomyces
hygroscopicus which encodes phosphinothricin
acetyltransferase
Options:
(A) P-2; Q-1; R-4
(B) P-2; Q-1; R-3
(C) P-1; Q-2; R-3
(D) P-4; Q-1; R-3
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.48)**
**1. Governing Concept**:
- **Topic**: Cell Biology & Active Membrane Transport (Sodium-Potassium Pump)
- The **$\text{Na}^+/\text{K}^+$-ATPase** is a primary active P-type transport pump located in the animal cell plasma membrane:
- For every molecule of ATP hydrolyzed by its intracellular catalytic domain:
$\text{ATP} + \text{H}_2\text{O} + 3\text{Na}^+_{\text{in}} + 2\text{K}^+_{\text{out}} \rightarrow \text{ADP} + \text{P}_i + 3\text{Na}^+_{\text{out}} + 2\text{K}^+_{\text{in}}$
- It pumps **3 $\text{Na}^+$ ions out of the cell** and **2 $\text{K}^+$ ions into the cell**.
- Because it exports 3 positive charges for every 2 positive charges imported, it is **electrogenic**, generating an inside-negative electrical potential and maintaining the cell resting membrane potential and osmotic volume.
**2. Option Analysis**:
- **Option (A) is CORRECT**: Exports exactly 3 $\text{Na}^+$ ions and imports 2 $\text{K}^+$ ions per hydrolyzed ATP molecule.
- **Option (B) is INCORRECT**: Inverts the ion transport stoichiometry ($2\text{Na}^+$ out, $3\text{K}^+$ in).
- **Option (C) is INCORRECT**: It pumps sodium outward against its electrochemical gradient, not inward.
- **Option (D) is INCORRECT**: Ion transport is unequal, making it electrogenic, not electroneutral.
**3. Final Answer**:
- **Correct Choice**: **A**
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