Zoology 2024 Paper I 50 marks Illustrate

Q4

(a) Give an illustrated account of integument and its derivatives in vertebrates with suitable diagrams. (20 marks) (b) What is Polymorphism ? Explain it with respect to life cycle of Obelia. (15 marks) (c) Describe the respiratory organs and mechanism of respiration in Sepia. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) कशेरुकियों में अध्यावरण एवं इसके व्युत्पादों का उपयुक्त रेखाचित्रों सहित विवरण दीजिए। (20 अंक) (b) बहुरूपता क्या है ? ओबीलिया के जीवन चक्र के संबंध में इसकी व्याख्या कीजिए। (15 अंक) (c) सीपिया में श्वसन अंगों और श्वसन की क्रियाविधि का वर्णन कीजिए। (15 अंक)

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Directive word: Illustrate

This question asks you to illustrate. 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 'illustrate' demands visual and descriptive clarity alongside conceptual depth. Allocate approximately 40% of time/words to part (a) given its 20 marks, with ~30% each to parts (b) and (c). Structure: brief comparative introduction on integument diversity across vertebrate classes; detailed body sections for each sub-part with integrated diagrams; concluding synthesis on adaptive significance of structural modifications in integument, polymorphism, and respiratory adaptations.

Key points expected

  • Part (a): Three-layered organization of vertebrate integument (epidermis, dermis, hypodermis) with class-specific derivatives—mammalian hair, glands, horns; avian feathers, scales; reptilian scales, claws; amphibian mucous glands; fish placoid/ctenoid scales and mucous cells
  • Part (a): Developmental origin of integumentary structures from ectoderm and mesoderm, with functional correlation to thermoregulation, protection, and sensory reception
  • Part (b): Definition of polymorphism as occurrence of structurally and functionally distinct forms within a single species; distinction between genetic and environmental polymorphism
  • Part (b): Obelia life cycle alternation between polyp (asexual, sessile) and medusa (sexual, free-swimming) stages; colonial organization with gastrozooids, dactylozooids, and gonozooids; metagenesis concept
  • Part (c): Sepia respiratory organs—paired mantle cavity, gills (ctenidia) with lamellar structure, branchial hearts, and accessory branchial hearts; counter-current exchange mechanism
  • Part (c): Mechanism of ventilation through mantle cavity contraction-inflation, role of siphon in directional water flow, and correlation with jet propulsion locomotion

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Accurately describes stratified epidermis with keratinization gradients across vertebrate classes; correctly distinguishes polymorphism from polyphenism in Obelia with precise metagenesis terminology; accurately identifies Sepia gill structure as ctenidium with primary and secondary lamellae and correct direction of blood/water flowBasic three-layer description present but confused about specific derivatives (e.g., mixing reptilian and avian scale types); defines polymorphism vaguely without metagenesis; describes 'gills' without structural detail or confuses Sepia with Octopus respiratory anatomyFundamental errors such as stating integument is mesodermal throughout; conflates polymorphism with alternation of generations in plants; describes tracheal respiration or incorrectly states Sepia has external gills
Diagram / labelling20%10Three high-quality diagrams: cross-section of mammalian integument showing epidermal strata and dermal papillae; Obelia colony with labelled zooid types and medusa bud; Sepia mantle cavity in sagittal section showing ctenidium, branchial heart, and water circulation arrows; all structures precisely labelled with anatomical terminologyDiagrams present but incomplete—missing hypodermis in integument, omitting gonozooids in Obelia, or showing generic 'cephalopod gill' without Sepia-specific features; some labels missing or incorrectDiagrams absent, poorly executed, or copied without understanding; labels confused or completely wrong; diagrams irrelevant to question (e.g., earthworm for Sepia)
Examples & nomenclature20%10Specific nomenclature: stratified squamous keratinized epithelium, Malpighian layer, stratum corneum; Indian examples like antelope horns (permanent cores) vs. deer antlers (seasonal); Obelia geniculata or O. dichotoma; Sepia officinalis or S. pharaonis with correct taxonomic placement in Class CephalopodaGeneric references to 'fish scales' without type specification; 'hydroid colony' without genus; 'cuttlefish' without scientific name; some terminology present but inconsistentNo scientific names; confused taxonomy (e.g., Obelia as scyphozoan); invented terms; examples from completely wrong phyla or classes
Process explanation20%10Clear sequential explanation: keratinization and shedding cycle in reptiles; Obelia reproductive cycle with planula larva settlement and colony development; Sepia ventilation mechanics—inhalant aperture closure, mantle contraction, pressure increase, exhalant jet with precise correlation to ctenidial gas exchange and accessory heart functionProcesses mentioned but sequence unclear or missing key steps; mechanical aspects of respiration described without pressure-flow relationships; life cycle stages listed without developmental logicNo process explanation; static descriptions only; completely wrong mechanisms (e.g., active gill pumping in Sepia); confused life cycle stages
Evolutionary / applied context20%10Evolutionary trends: integument from aquatic mucous protection to terrestrial keratinization and endothermy; adaptive significance of polymorphism in Obelia for dispersal and survival; Sepia respiratory efficiency enabling active predation and jet propulsion with reference to cephalopod success as marine predators; mention of cuttlebone buoyancy as applied aspectBrief mention of 'adaptation' without specific evolutionary context; generic statement about 'survival advantage' without linking structure to function; no applied significanceNo evolutionary or applied context; or completely irrelevant speculation; creationist statements; confused evolutionary relationships

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