Agriculture 2021 Paper II 50 marks Describe

Q2

(a) Define cell. How is a plant cell different from an animal cell ? Describe a typical cell structurally and functionally, with a suitable diagram. 15 (b) Describe the physiological and molecular basis of heterosis. 15 (c) Classify types of male sterility and self-incompatibility system in plants. Describe the limitations of cytoplasmic genetic male sterility system in hybrid seed production. 20

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(a) कोशिका को परिभाषित कीजिए । पादप कोशिका जन्तु कोशिका से कैसे अलग है ? एक प्राकृतिक कोशिका का संरचनात्मक तथा कार्यात्मक आधार पर एक उपयुक्त आरेख सहित वर्णन कीजिए । 15 (b) संकर ओज के कार्यिकीय तथा आणविक आधारों का वर्णन कीजिए । 15 (c) पौधों में नर बंध्यता के प्रकारों तथा स्व-असंगति पद्धति को वर्गीकृत कीजिए । संकर बीज उत्पादन में कोशिकाद्रव्य आनुवंशिक नर बाँझपन प्रणाली की बाधाओं का वर्णन कीजिए । 20

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Directive word: Describe

This question asks you to describe. 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 'describe' demands comprehensive, structured exposition of structures, processes and mechanisms across all three sub-parts. Allocate approximately 25-30% time/words to part (a) covering cell definition, plant-animal differences and diagram; 30% to part (b) explaining heterosis mechanisms; and 40-45% to part (c) as it carries highest marks, ensuring detailed classification of male sterility types with limitations. Structure as: brief introduction → systematic treatment of (a), (b), (c) with clear sub-headings → concluding synthesis on application to hybrid seed technology.

Key points expected

  • Part (a): Precise cell definition; minimum 6-8 plant-animal differences (cell wall, chloroplasts, vacuoles, centrioles, lysosomes, plasmodesmata, cytokinesis, glyoxysomes); structural-functional description of organelles; neat labeled diagram
  • Part (b): Physiological basis—dominance, overdominance, epistasis hypotheses; molecular basis—gene expression networks, non-additive gene action, miRNA regulation, metabolic efficiency mechanisms
  • Part (c): Classification of male sterility—genetic (GMS), cytoplasmic (CMS), cytoplasmic-genetic (CGMS); sporophytic vs gametophytic self-incompatibility systems with examples
  • Part (c): Detailed limitations of CGMS—genetic vulnerability (T-cytoplasm in US maize blight 1970), restorer gene management, temperature sensitivity, negative pleiotropic effects on agronomic traits
  • Application linkage: Commercial exploitation of heterosis through CMS (e.g., rice, sorghum, pearl millet hybrids); need for alternative male sterility systems
  • Indian context: ICAR-developed hybrids (e.g., IRRI-ICAR rice varieties), A1/A2/A3 cytoplasm systems in pearl millet; NPT-1 rice lines; limitations in pigeonpea hybrid program

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11For (a): accurate cell definition per cell theory; precise organelle functions; no confusion between plant-animal structures. For (b): correctly distinguishes dominance vs overdominance vs epistasis; accurate molecular mechanisms. For (c): error-free classification of CMS types (T, S, C in maize; A1-A4 in pearl millet); correct distinction between sporophytic and gametophytic SIBasic definitions correct but some organelle functions misstated; heterosis hypotheses mentioned without clear distinction; male sterility types listed but classification criteria unclear or examples mismatchedFundamental errors (e.g., stating animal cells have cell walls); conflating heterosis with heterozygosity advantage without mechanism; confusing GMS with CMS; major classification errors
Quantitative reasoning12%6For heterosis: cites quantitative genetic parameters (mid-parent heterosis, better-parent heterosis, SCA/GCA ratios); mentions heritability estimates. For male sterility: references restoration percentages, threshold temperatures for breakdown; quantitative impact of 1970 maize blightMentions heterosis percentages in general terms without genetic basis; vague reference to yield advantages; limited quantitative treatment of male sterility breakdownNo quantitative data; purely descriptive without any numerical parameters, percentages or statistical measures
Indian context examples18%9Cites specific Indian developments: IR-20, Jaya, Padma rice hybrids; A1 cytoplasm (LRT 1) in pearl millet from Tifton; CMS-based sorghum hybrids (CSH series); ICAR-IARI research on CGMS limitations in pigeonpea; mentions PAU, TNAU, MPKV breeding programsGeneric mention of 'Indian rice hybrids' without naming; vague reference to 'research institutions'; no specific cytoplasm designations or varietal namesNo Indian examples; only foreign references (US maize, Chinese rice) or completely missing context
Diagram / process26%13For (a): neat, fully labeled plant cell diagram showing cell wall, plasma membrane, nucleus, nucleolus, ER, Golgi, mitochondria, chloroplasts, vacuole, ribosomes, plasmodesmata. For (c): schematic of CMS-CMS/Rf system or SI pollen rejection pathways. Clear process description of hybrid seed production using CGMSDiagram present but incompletely labeled (missing 2-3 key structures); diagram described but not drawn; process description verbal without visual representationNo diagram despite explicit requirement; diagram with major structural errors; no process illustration for male sterility system
Policy / extension angle22%11Discusses Seed Policy 2020, PPV&FR Act implications for hybrid breeding; need for diversified cytoplasm sources to prevent genetic vulnerability; role of ICAR-NSP in hybrid seed production; extension challenges in maintaining parental lines; mentions two-line or three-line system adoption in IndiaBrief mention of hybrid seed importance for food security; generic reference to 'government support' without specific policy instrumentsNo policy or extension linkage; purely academic treatment without connecting to seed industry, farmer adoption, or regulatory framework

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