Zoology 2022 Paper II 50 marks Discuss
Q8
(a) What is stem cell? Discuss the types of stem cells and their application in therapeutic uses in human. 20 (b) Explain the mechanism of spermatogenesis in mammals with suitable diagram. 15 (c) Describe the hormonal regulation of metamorphosis in amphibians. 15
हिंदी में प्रश्न पढ़ें
(a) मूल कोशिका क्या होती है? मूल कोशिकाओं के प्रकारों एवं मनुष्य के रोग निवारण में उनके अनुप्रयोग की व्याख्या कीजिए। 20 (b) उपयुक्त आरेख के साथ स्तनपायी में शुक्रजनन की प्रक्रिया की व्याख्या कीजिए। 15 (c) उभयचरों में कायांतरण के हार्मोनी नियमन का वर्णन कीजिए। 15
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 a comprehensive treatment with critical elaboration, while parts (b) and (c) require 'explain' and 'describe' respectively—meaning mechanistic clarity and systematic coverage. Allocate approximately 40% of time/words to part (a) given its 20 marks, with ~30% each to parts (b) and (c). Structure: begin with a unified introduction on developmental biology, then address each part sequentially with dedicated sub-headings, ensuring part (b) includes a well-labelled diagram, and conclude with a brief synthesis on the significance of developmental processes in medicine and evolution.
Key points expected
- Part (a): Definition of stem cells (totipotency, pluripotency, multipotency); classification into embryonic (ESCs), adult/somatic (ASCs), and induced pluripotent stem cells (iPSCs); therapeutic applications including regenerative medicine, treatment of blood disorders (thalassemia, leukemia via bone marrow transplant), Parkinson's disease, diabetes, and Indian contributions (e.g., stem cell research at CCMB, NCRM)
- Part (b): Complete sequence of spermatogenesis—spermatogonia (A dark, A pale, B types), primary spermatocytes, meiosis I and II, spermiogenesis (acrosome formation, flagellar development, nuclear condensation), Sertoli cell role, blood-testis barrier; diagram showing seminiferous tubule cross-section with labelled stages
- Part (c): Hypothalamic-pituitary-thyroid axis in amphibian metamorphosis; TRH from hypothalamus, TSH from pituitary, T3/T4 from thyroid; synergistic role of corticosteroids; tissue-specific responses (tail resorption via apoptosis, limb development, gut remodeling); contrasting neoteny in axolotl and its hormonal basis
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 22% | 11 | Demonstrates precise understanding across all three parts: for (a) correctly distinguishes potency levels and iPSC generation; for (b) accurately describes meiotic divisions and spermiogenesis stages; for (c) correctly identifies the hormonal cascade and distinguishes T3/T4 roles, with no factual errors in any sub-part | Shows generally correct concepts but with minor errors—e.g., confuses pluripotency with totipotency in (a), mislabels meiotic divisions in (b), or omits corticosteroid synergy in (c) | Contains significant conceptual errors—e.g., equates stem cells with cancer cells, describes mitosis instead of meiosis in spermatogenesis, or attributes metamorphosis control solely to pituitary without thyroid involvement |
| Diagram / labelling | 18% | 9 | Provides a clear, accurate diagram for part (b) showing seminiferous tubule organization with distinct cell types (spermatogonia, primary/secondary spermatocytes, spermatids, Sertoli cells) and stage-specific arrangements; labels are precise and anatomically correct; may include supplementary flowchart for hormonal axis in (c) | Diagram present but incomplete—shows general tubule structure but lacks specific cell identification, or has minor labelling errors; diagram supports explanation but does not enhance it significantly | Diagram absent, poorly executed, or fundamentally incorrect; labels missing or wrong; diagram contradicts written explanation; no attempt to visualize the process |
| Examples & nomenclature | 18% | 9 | Uses specific, accurate nomenclature throughout: names stem cell types correctly (e.g., hematopoietic stem cells, mesenchymal stem cells), cites Indian research institutions or clinical applications; for (b) uses proper terminology (spermatogonia A dark/pale, spermatids, spermatozoa); for (c) names specific hormones (TRH, TSH, thyroxine, triiodothyronine) and species examples (Xenopus, axolotl) | Uses generally correct terms but lacks specificity—e.g., refers to 'embryonic stem cells' without subtypes, uses 'sperm cells' instead of precise stage names, or mentions 'thyroid hormone' without specifying T3/T4; few examples provided | Incorrect or absent nomenclature; confuses terms (e.g., spermatogenesis vs. spermiogenesis, metamorphosis vs. morphogenesis); no examples cited; generic language throughout |
| Process explanation | 22% | 11 | Explains mechanisms with clear causal logic: for (a) details how iPSCs are generated (Yamanaka factors) and how stem cell differentiation is directed; for (b) sequences the entire process with timing (duration of spermatogenesis in humans ~74 days) and cellular transformations; for (c) explains hormone receptor mechanisms, tissue-specific gene activation, and programmed cell death in tail resorption | Describes processes in correct order but lacks mechanistic depth—mentions stages without explaining transitions, or lists hormones without explaining their interaction; chronological but not causal | Process description fragmented or backward; confuses sequence of events; provides only static descriptions without explaining how one stage leads to next; major gaps in explanation |
| Evolutionary / applied context | 20% | 10 | Integrates broader significance: for (a) discusses ethical considerations in stem cell research, India's Stem Cell Research Guidelines, and future of personalized medicine; for (b) briefly notes evolutionary significance of spermatogenesis efficiency in mammalian reproduction; for (c) explains adaptive value of metamorphosis and evolutionary persistence of neoteny; demonstrates awareness of current research frontiers | Mentions applications superficially—lists therapeutic uses without discussing challenges, or notes metamorphosis as 'important' without evolutionary analysis; applied context present but underdeveloped | No applied or evolutionary context provided; treats all parts as purely descriptive without connecting to medicine, conservation, or evolutionary biology; misses opportunity to demonstrate integrative understanding |
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