Zoology 2025 Paper I 50 marks Discuss

Q4

(a) Draw a well-labelled diagram of testis and ovary in mammals, and discuss the functions of their hormones. 20 (b) Give an illustrated account of skull types in reptiles. 15 (c) Explain the types and significance of migration in fishes. 15

हिंदी में प्रश्न पढ़ें

(a) स्तनधारियों में वृषण और अंडाशय का सुचिहित चित्र बनाइए और उनके हार्मोनों के कार्यों पर चर्चा कीजिए। 20 (b) सरीसृपों में कपोटि के प्रकारों का एक सचित्र विवरण दीजिए। 15 (c) मछलियों में प्रवास के प्रकार और महत्व की व्याख्या कीजिए। 15

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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' in part (a) demands critical elaboration with balanced coverage of structure and function, while 'illustrated account' in (b) and 'explain' in (c) require visual integration and causal reasoning respectively. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure as: brief comparative introduction to vertebrate reproductive and structural diversity → systematic treatment of each sub-part with integrated diagrams → concluding synthesis on evolutionary trends in vertebrate adaptation.

Key points expected

  • Part (a): Testis structure showing seminiferous tubules, Leydig cells, Sertoli cells; ovary showing follicular stages, corpus luteum, stromal tissue; hormones (testosterone, estrogen, progesterone, inhibin, relaxin) with target organs and feedback mechanisms
  • Part (a): Hypothalamic-pituitary-gonadal axis integration and functional coordination between male and female hormonal systems
  • Part (b): Anapsid (turtle), Synapsid (mammal-like reptiles), Diapsid (lepidosaurian and archosaurian variants) skull types with temporal fenestrae number and position
  • Part (b): Evolutionary progression from anapsid to diapsid condition and secondary modifications in snakes and birds
  • Part (c): Anadromous (salmon, Hilsa ilisha), catadromous (eel), potamodromous (Indian major carps), oceanodromous migrations with specific Indian examples
  • Part (c): Physiological triggers (photoperiod, temperature, hormonal control via pituitary-thyroid axis), navigation mechanisms, and ecological/economic significance for fisheries management

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Accurately describes steroidogenesis pathway in gonads; correctly identifies temporal fenestrae homologies across reptilian skulls; precisely distinguishes migratory categories with correct life-cycle staging for Indian species like Hilsa and Cirrhinus mrigalaBasic hormonal functions stated without biosynthesis details; skull types named but fenestrae positions confused; migration types listed but physiological mechanisms oversimplifiedMajor errors such as confusing interstitial with Sertoli cell functions; anapsid/diapsid distinction reversed; conflates anadromous with catadromous patterns
Diagram / labelling20%10For (a): bilateral diagrams showing testicular lobules with cellular detail and ovarian follicular hierarchy; for (b): three skull types in lateral view with fenestrae shaded and labelled; all diagrams with proper orientation arrows and scale indicationDiagrams present but key structures unlabelled or mislabelled; skull diagrams lack fenestrae demarcation; ovarian follicle stages not sequentially arrangedDiagrams absent or unrecognizable; stick-figure representations; labels pointing to wrong structures; no attempt at skull fenestrae illustration
Examples & nomenclature20%10Cites specific Indian examples: Hilsa ilisha (anadromous), Anguilla bengalensis (catadromous), Labeo rohita (potamodromous); uses correct anatomical terminology (tunica albuginea, theca interna/externa, quadratojugal, supratemporal) and author citations (Goodrich for skull classification)Generic examples only (salmon, eel without species); some terminology present but inconsistent; Indian examples missing or incorrectNo valid examples; invented terminology; confuses reptilian skull bones with mammalian homologues; examples from birds or amphibians substituted
Process explanation20%10Elucidates spermatogenesis stages with hormonal regulation; explains jaw muscle attachment advantages of diapsid condition; details osmoregulatory challenges and thyroid-mediated metamorphosis in migratory fishes with smoltificationLists hormonal effects without mechanistic detail; describes skull types as static categories without functional interpretation; states migration occurs but not how fish navigateNo process explanation; confuses cause and effect in hormonal feedback; describes skull fenestrae as decorative rather than functional; attributes bird migration mechanisms to fishes
Evolutionary / applied context20%10Connects synapsid skull to mammalian ancestry; discusses conservation implications of dam construction on Hilsa migration; evaluates hormonal contraceptive applications; links skull kinesis to feeding ecology in snakesBrief mention of evolution without synthesis; generic statement on migration importance without specific conservation context; no applied relevance discussedNo evolutionary or applied context; presents all information as isolated facts; misapplies concepts (e.g., discusses bird evolution in reptile section)

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