Q4
(a) Discuss the mechanisms of absorption and translocation of mineral nutrients in plants. 20 (b) Define aneuploidy. Give an account of morphological and cytological functions of aneuploidy, and discuss its application in crop improvement. 20 (c) Explain the techniques involved in somatic hybridization in crop plants. 10
हिंदी में प्रश्न पढ़ें
(क) पौधों में खनिज पोषक-तत्वों के अवशोषण और स्थानांतरण (ट्रांसलोकेशन) की क्रियाविधि पर चर्चा कीजिए। 20 (ख) असुपुंजितता (एन्ड्यूप्लॉइडी) को परिभाषित कीजिए। असुपुंजितता के आकारिकीय एवं कोशिकीय कार्यों का विवरण दीजिए और फसल सुधार में इसके अनुप्रयोग का वर्णन कीजिए। 20 (ग) फसलीय पौधों में कायिक (दैहिक) संकरण से संबंधित तकनीकों की व्याख्या कीजिए। 10
Directive word: Discuss
This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.
See our UPSC directive words guide for a full breakdown of how to respond to each command word.
How this answer will be evaluated
Approach
The directive 'discuss' demands a comprehensive, analytical treatment with balanced coverage across all three sub-parts. Allocate approximately 40% of word budget to part (a) on mineral nutrition mechanisms, 35% to part (b) on aneuploidy covering definition, morphological/cytological features and crop improvement applications, and 25% to part (c) on somatic hybridization techniques. Structure with a brief integrated introduction, separate well-developed sections for each sub-part with clear sub-headings, and a concluding synthesis linking biotechnological advances to Indian agricultural challenges.
Key points expected
- Part (a): Active vs passive absorption mechanisms; role of carrier proteins, ion channels, and proton pumps; apoplastic and symplastic pathways of translocation; source-sink relationships in nutrient transport
- Part (a): Translocation via xylem (mass flow, transpiration pull) and phloem (pressure-flow hypothesis); remobilization of nutrients during senescence
- Part (b): Definition of aneuploidy as chromosome number variation from euploidy (2n±); types - nullisomy, monosomy, trisomy, tetrasomy; morphological effects like gigantism in trisomics, vigor changes; cytological effects including univalent formation, chromosome lagging, and segregation distortion
- Part (b): Applications in crop improvement - monosomics for gene mapping (Chinese Spring wheat), trisomics for locating genes on specific chromosomes, aneuploidy in developing substitution and addition lines; Indian examples like triticale development at IARI
- Part (c): Somatic hybridization techniques - protoplast isolation (enzymatic: cellulase, pectinase, hemicellulase), protoplast purification (density gradient centrifugation), fusion methods (PEG-mediated, electrofusion), selection of heterokaryons, regeneration of hybrid plants; applications in overcoming sexual incompatibility barriers
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 25% | 12.5 | Demonstrates precise understanding of membrane transport proteins (H+-ATPases, aquaporins), distinguishes apoplastic vs symplastic loading correctly; accurately defines aneuploidy types with correct chromosome formulas; explains protoplast fusion mechanisms with correct enzyme specifications and fusion agent chemistry | Covers basic absorption mechanisms but confuses active/passive transport details; defines aneuploidy broadly without distinguishing nullisomy/monosomy/trisomy; lists somatic hybridization steps but with errors in enzyme names or fusion methods | Fundamental errors like equating aneuploidy with polyploidy, confusing xylem/phloem transport mechanisms, or describing tissue culture instead of protoplast fusion |
| Quantitative reasoning | 15% | 7.5 | Includes quantitative parameters: Michaelis-Menten kinetics for ion uptake (Km, Vmax values), critical concentrations of nutrients; chromosome transmission rates in aneuploids (e.g., 50% transmission of monosomics); protoplast yields (10^6-10^7/g tissue) and fusion frequencies; cites relevant experimental data | Mentions quantitative aspects qualitatively without specific values; gives approximate chromosome numbers or transmission rates without precision | No quantitative treatment; purely descriptive answer with numbers avoided or incorrectly stated |
| Indian context examples | 20% | 10 | Cites Indian research: IARI work on wheat aneuploids (Sears' Chinese Spring derivatives), triticale development using aneuploidy; NBPGR protoplast fusion work; somatic hybrids developed in India (e.g., Brassica, rice); references to ICAR initiatives on biofortification linking mineral nutrition to crop improvement | Mentions generic Indian crops (wheat, rice) without specific institutional or researcher references; vague reference to 'Indian agriculture' without concrete examples | No Indian examples; entirely foreign examples or purely theoretical treatment |
| Diagram / process | 25% | 12.5 | Includes well-labeled diagrams: cross-section of root showing apoplastic/symplastic pathways; schematic of carrier-mediated transport; meiotic configurations in aneuploidy (univalent, trivalent formation); flowchart of somatic hybridization protocol from protoplast isolation to hybrid plant regeneration; diagrams enhance explanation significantly | Attempts diagrams but with incomplete labeling or minor errors; OR describes processes verbally without visual aids but with clear step-wise structure | No diagrams where essential; confusing verbal descriptions of processes; incorrect schematic representations |
| Policy / extension angle | 15% | 7.5 | Links to policy: PM-KISAN soil health card scheme for balanced nutrient management; National Innovations in Climate Resilient Agriculture (NICRA) for stress-tolerant crops via biotechnological tools; discusses regulatory framework for GM/somatic hybrids (GEAC guidelines); extension relevance of aneuploidy-based varieties and somatic hybridization for crop diversification | Brief mention of soil health or biotechnology policy without integration; generic statement on 'importance for food security' | No policy or extension linkage; purely academic treatment disconnected from agricultural application and farmer welfare |
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