Zoology 2023 Paper II 50 marks Explain

Q8

(a) Explain enzymes, their characteristics as well as induced-fit model of mechanism of enzyme action. (20 marks) (b) List various coagulation factors and describe their role in blood clotting. (15 marks) (c) Explain neoteny phenomenon taking suitable example. How is it different from paedogenesis? (15 marks)

हिंदी में प्रश्न पढ़ें

(a) प्रकिण्व एवं उनकी विशेषताओं के साथ-ही-साथ प्रकिण्व की क्रिया-विधि के प्रेरित-अनुरूप मॉडल की व्याख्या कीजिए। (20 अंक) (b) विभिन्न स्कंदन कारकों की सूची बनाएं एवं रक्त स्कंदन में उनकी भूमिका का वर्णन कीजिए। (15 अंक) (c) उपयुक्त उदाहरण लेते हुए चिरभूणता परिघटना की व्याख्या कीजिए। यह शावकीजनन से किस प्रकार भिन्न है? (15 अंक)

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Directive word: Explain

This question asks you to explain. 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 'explain' demands clear, logical exposition of mechanisms and phenomena across all three parts. Structure your answer with a brief introduction defining enzymes, then allocate approximately 40% of content to part (a) on enzyme characteristics and induced-fit model, 30% to part (b) on coagulation cascade with factor-wise listing, and 30% to part (c) on neoteny with Indian examples like Ambystoma and clear distinction from paedogenesis. Use diagrams for (a) and (b), and conclude with evolutionary significance where relevant.

Key points expected

  • Part (a): Definition of enzymes as biological catalysts; characteristics including specificity, reversibility, temperature/pH optima, catalytic efficiency; detailed explanation of induced-fit model (Koshland 1958) contrasting with lock-and-key, showing conformational change upon substrate binding
  • Part (a): Mention of enzyme nomenclature (IUBMB classification: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases) and factors affecting enzyme activity
  • Part (b): Complete listing of 13 coagulation factors (I-XIII) with Roman numerals and common names; intrinsic, extrinsic and common pathways; role of calcium (Factor IV), vitamin K-dependent factors (II, VII, IX, X), and final common pathway leading to fibrin clot formation
  • Part (c): Definition of neoteny as retention of juvenile traits in sexually mature adults; classic example of Ambystoma mexicanum (axolotl) or Necturus (mudpuppy) with external gills; evolutionary significance in human evolution (cranial features, hairlessness)
  • Part (c): Clear distinction from paedogenesis—neoteny involves somatic retardation with normal gonadal development, while paedogenesis is precocious sexual maturity in larval form (e.g., Micromalthus beetle or some salamanders); both represent heterochrony but differ in developmental timing

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Precise definitions of enzymes, coagulation factors numbered correctly with Roman numerals, accurate description of induced-fit conformational change, correct distinction between neoteny and paedogenesis with proper developmental biology terminologyGenerally correct definitions but minor errors in factor numbering, vague description of induced-fit without conformational emphasis, or conflation of neoteny with paedogenesisFundamental misconceptions such as treating enzymes as consumed in reactions, incorrect factor listings, confusing neoteny with progenesis or other heterochronic processes
Diagram / labelling18%9Clear hand-drawn diagram for induced-fit model showing enzyme-substrate complex with conformational change, and coagulation cascade flowchart with intrinsic/extrinsic/common pathways properly distinguished and labelledBasic diagrams present but lacking detail, missing labels for active site or cascade components, or poorly organized coagulation pathwayNo diagrams despite clear visual requirements, or diagrams with major errors that misrepresent mechanisms
Examples & nomenclature20%10Specific examples: Ambystoma mexicanum or Necturus for neoteny; Micromalthus or certain caecilians for paedogenesis; correct IUBMB enzyme classification; all coagulation factors named with both Roman numerals and common names (e.g., Factor VIII—antihemophilic factor)Generic or partially correct examples, some missing factor names, or incomplete enzyme classificationNo specific examples, incorrect naming of factors, or invented examples that do not demonstrate the phenomena
Process explanation22%11Stepwise explanation of induced-fit mechanism with energy considerations; detailed cascade sequence showing amplification at each step; clear developmental sequence showing how neoteny operates through delayed somatic development versus accelerated gonadal development in paedogenesisSequential but superficial coverage of processes, missing key steps in cascade, or unclear developmental timing mechanismsDisorganized or incorrect process description, failure to show cascade amplification, or complete absence of mechanistic explanation
Evolutionary / applied context18%9Evolutionary significance of neoteny in human evolution (retention of juvenile primate features), medical applications of coagulation knowledge (hemophilia treatment, warfarin mechanism), industrial enzyme applications; mention of heterochrony as evolutionary mechanismBrief mention of applications without elaboration, or generic statements about evolutionary importance without specific linkageNo evolutionary or applied context provided, or irrelevant digressions not connected to the specific biological phenomena

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