Botany 2025 Paper II 50 marks Discuss

Q4

(a) What is organic evolution? Discuss in detail the indirect evidences of organic evolution with suitable examples. (20 marks) (b) Describe the structure of chloroplast with labelled diagram and write about its functions. (15 marks) (c) Discuss in detail the role of mutations in plant breeding and crop improvement. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) जैविक विकास क्या है? जैविक विकास के अप्रत्यक्ष प्रमाणों पर उपयुक्त उदाहरणों द्वारा विस्तारपूर्वक चर्चा कीजिए। (20 अंक) (b) हरितलवक (क्लोरोप्लास्ट) की संरचना का नामांकित आरेख द्वारा वर्णन कीजिए तथा इसके कार्यों के बारे में लिखिए। (15 अंक) (c) पादप प्रजनन तथा फसल सुधार में उत्परिवर्तनों की भूमिका पर विस्तारपूर्वक चर्चा कीजिए। (15 अंक)

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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 critical, detailed examination with arguments and evidence. Allocate approximately 40% of time/words to part (a) given its 20 marks, 30% each to parts (b) and (c). Structure: brief introduction defining organic evolution; body covering indirect evidences with examples for (a), chloroplast ultrastructure with diagram for (b), and mutation types with breeding applications for (c); conclude with synthesis on how evolutionary mechanisms and cellular innovations drive crop improvement.

Key points expected

  • Part (a): Definition of organic evolution (descent with modification) and comprehensive coverage of indirect evidences—morphological (homologous and analogous organs), embryological (von Baer's laws, recapitulation), palaeontological (fossil horses, Archaeopteryx, Gondwana flora), physiological/biochemical (serological tests, universal genetic code), and biogeographical (continental drift, Wallace's line)
  • Part (a): Specific Indian examples—Birbal Sahni's work on Glossopteris flora establishing Gondwana connection, Siwalik fossil beds, or comparative anatomy of mangrove species (Rhizophora vs. Avicennia root modifications)
  • Part (b): Detailed chloroplast ultrastructure—double envelope membrane, stroma, thylakoid system (grana and stroma lamellae), presence of DNA, ribosomes (70S), and storage products (plastoglobuli); accurate labelled diagram showing spatial organization
  • Part (b): Functional aspects—light reactions (Z-scheme, ATP/NADPH production at thylakoid), carbon reactions (Calvin cycle in stroma), photorespiration, and chloroplast-nuclear signaling (retrograde signaling)
  • Part (c): Types of mutations—gene (point: transition/transversion, frameshift), chromosomal (deletion, duplication, inversion, translocation), and genomic (polyploidy); spontaneous vs. induced (physical: gamma rays, UV; chemical: EMS, sodium azide)
  • Part (c): Applications in Indian crop improvement—EMS-induced mutants in rice (TNAU varieties), gamma ray wheat mutants (Sharbati Sonora), BARC-developed groundnut varieties, role in creating genetic variability for drought/salinity tolerance, and limitations (pleiotropy, chimeras, linkage drag)
  • Synthesis: Connection between parts—how chloroplast endosymbiotic origin (evolutionary evidence) relates to organelle genetics in cytoplasmic inheritance, and how mutation provides raw material for artificial selection mimicking natural selection

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Precise definitions: organic evolution as gene frequency change in populations; correct distinction between homologous vs. analogous organs; accurate chloroplast membrane topology (intermembrane space vs. stroma); mutation classification by molecular mechanism and breeding application; no conflation of Darwinian evolution with LamarckismGenerally correct definitions with minor errors—e.g., confusing analogous with convergent evolution, vague on thylakoid lumen vs. stroma pH gradients, or mixing up transition and transversion mutations without clear examplesFundamental conceptual errors—defining evolution as 'progress' or 'ladder', labeling chloroplast diagram with mitochondrial features, or describing mutations only as harmful without recognizing neutral/beneficial roles in breeding
Diagram / labelling18%9Clear, proportionate chloroplast diagram with accurate ultrastructure: outer/inner envelope membranes, intermembrane space, stroma with circular DNA and ribosomes, granum stacks with thylakoid membranes, stroma lamellae connecting grana, and plastoglobuli; all labels aligned with lines; bonus for showing photosystem organization or division machineryRecognizable chloroplast shape with major structures labeled but missing details—no distinction between granal and stromal thylakoids, missing DNA or ribosome labels, or diagram too small for clarity; no attempt at evolutionary tree or mutation spectrum diagramAbsent or seriously flawed diagram; misdrawn organelle (mitochondrion or generic cell instead); labels pointing to wrong structures; illegible handwriting; or diagram copied without understanding (e.g., showing cristae in chloroplast)
Examples & nomenclature20%10Rich, specific examples: for (a) Archaeopteryx, horse evolution (Eohippus to Equus), Darwin's finches, Indian Gondwana fossils (Glossopteris, Gangamopteris), serological distance data; for (b) C3 vs. C4 chloroplast dimorphism; for (c) named Indian mutant varieties (Trombay groundnut, Pusa mutants), specific mutagens (EMS, gamma sources from BARC), and scientists (M.S. Swaminathan's mutation work)Generic examples without specificity—'fossils of horses' without naming stages, 'some Indian crops' without variety names, or 'radiation causes mutations' without distinguishing ionizing vs. non-ionizing; some nomenclature errors (e.g., 'thylakoid membrane' for lumen)No concrete examples, or invented/fictional ones; confused nomenclature (e.g., 'chlorophyll B' as structure, 'DNA mutation' as chromosomal type); irrelevant examples (human evolution dominating plant-focused question)
Process explanation22%11Clear mechanistic explanations: for (a) how fossilization preserves indirect evidence and dating methods (radioisotope, stratigraphy); for (b) chemiosmotic mechanism of photophosphorylation, Q-cycle, and Calvin cycle regeneration phase; for (c) mutation breeding protocol—M1-M3 generation handling, chimera dissociation, and selection strategies; logical flow with appropriate technical depthDescriptive rather than mechanistic—lists fossil types without explaining how they indicate ancestry, describes chloroplast 'making food' without light-dark reaction separation, or outlines mutation breeding steps without generational logic; some processes incomplete or jumbledNo process explanation—only definitions and lists; confused mechanisms (photosynthesis described as cellular respiration, mutation breeding conflated with hybridization); or complete omission of any biochemical/genetic process detail
Application / ecology18%9Strong applied dimension: for (a) evolutionary theory informing conservation prioritization (evolutionarily significant units) and crop domestication; for (b) chloroplast engineering for transgene containment (maternal inheritance), C4 rice project relevance; for (c) mutation breeding for climate resilience (heat/drought mutants), biofortification (high-iron pearl millet), and integration with genomic selection; mentions Indian agricultural context and ICAR achievementsSuperficial application—generic statement that 'evolution helps understand life', 'photosynthesis gives oxygen', or 'mutations create new varieties' without specific breeding objectives or ecological significance; no Indian policy/scheme connectionNo application or ecological context; or completely misapplied (e.g., suggesting mutation breeding for organic farming prohibition, or evolution as justification for social Darwinism); irrelevant digressions into animal breeding or human genetics

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