(A) piRNAs silence transposable elements in germ cells
(B) piRNA is the abbreviation of P-element interacting RNA
(C) piRNAs modify the 2′-OH of ribose with methyl group
(D) piRNA is a long non-coding RNA
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.16)**
**1. Governing Concept**:
- **Topic**: Plant Physiology & C4 Carbon Fixation Anatomy (Kranz Anatomy)
- In $\text{C}_4$ plants (e.g. maize, sugarcane):
- Photosynthesis is spatially compartmentalized between **mesophyll cells** and **bundle sheath cells** (Kranz anatomy).
- In mesophyll cells: Atmospheric $\text{CO}_2$ (as $\text{HCO}_3^-$) is fixed by **PEP carboxylase** to form 4-carbon oxaloacetate, which is converted to malate/aspartate.
- Malate is transported to bundle sheath cells, where it is decarboxylated by **malic enzyme** to release concentrated $\text{CO}_2$ around **RuBisCO**, suppressing the oxygenase reaction (photorespiration).
**2. Option Analysis**:
- **Option (A) is INCORRECT**: PEP carboxylase is localized in mesophyll cells, not bundle sheath cells.
- **Option (B) is INCORRECT**: RuBisCO is strictly localized in bundle sheath cells in C4 plants, absent from mesophyll cells.
- **Option (C) is CORRECT**: Spatial separation concentrates $\text{CO}_2$ in bundle sheath cells, virtually eliminating RuBisCO oxygenation and photorespiration.
- **Option (D) is INCORRECT**: Primary carbon fixation produces 4-carbon oxaloacetate, not 3-PGA.
**3. Final Answer**:
- **Correct Choice**: **C**
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