Zoology 2022 Paper I 50 marks Explain

Q2

(a) Explain asexual and sexual modes of reproduction in Paramecium. (20 marks) (b) Write general features of egg laying mammals, pouched mammals and aquatic mammals. (15 marks) (c) Describe different types of scales in fishes with suitable diagrams. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) पैरामीशियम में अलैंगिक एवं लैंगिक जनन के तरीकों का वर्णन कीजिए । (20 अंक) (b) अंडा देने वाले स्तनधारियों, कोष्ठधारी स्तनधारियों एवं जलीय स्तनधारियों की सामान्य विशेषताओं के बारे में लिखिए । (15 अंक) (c) उपयुक्त रेखा-चित्रों द्वारा मछलियों में विभिन्न प्रकार के शल्कों की व्याख्या कीजिए । (15 अंक)

Evaluate your answer to this question → See all 2022 Zoology questions

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 causal reasoning and mechanistic detail across all three parts. Allocate approximately 40% of word budget to part (a) given its 20 marks, with ~30% each to parts (b) and (c). Structure as: brief comparative introduction on reproductive strategies and mammalian adaptations; detailed body covering binary fission/conjugation in Paramecium, monotreme/marsupian/cetacean features with Indian examples, and scale morphology with diagrams; conclude with evolutionary significance of reproductive and protective adaptations.

Key points expected

  • Part (a): Binary fission (transverse fission in P. aurelia, P. caudatum) with stages—karyokinesis followed by cytokinesis; conjugation—temporary union of compatible mating types, micronuclear meiosis, pronuclear exchange, separation, and exconjugant fission; autogamy and cytogamy as variations
  • Part (a): Distinction between vegetative reproduction (asexual) and genetic recombination (sexual); significance of nuclear dimorphism (macro- and micronucleus) in sexual processes
  • Part (b): Monotremata (Prototheria)—oviparous, cloaca, electroreception, milk patches without nipples; Marsupialia (Metatheria)—short gestation, altricial young, marsupium with teats, chorioallantoic placenta; examples: Tachyglossus, Ornithorhynchus, Macropus, Didelphis
  • Part (b): Aquatic mammals—Cetacea, Sirenia, Pinnipedia; adaptations: blowhole, blubber, fusiform body, modified limbs; Indian examples: Platanista gangetica (Ganges river dolphin), Neophocaena phocaenoides
  • Part (c): Cosmoid (fossil only, e.g., Coelacanth ancestors), placoid (sharks, rays—dermal denticles with enamel, dentine, pulp cavity), ganoid (Polypterus, Lepisosteus—rhomboid, ganoin-covered), ctenoid (Teleostei—bony, overlapping with comb-like posterior margin), cycloid (Teleostei—bony, smooth posterior margin)
  • Part (c): Functional correlation—placoid for protection and hydrodynamics, ctenoid/cycloid for flexibility and growth; evolutionary trend from heavy ganoid to lightweight teleost scales

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately describes transverse binary fission plane in Paramecium; correctly distinguishes micronuclear meiosis from macronuclear amitosis in conjugation; accurately classifies mammals by reproductive strategy (Prototheria/Metatheria/Eutheria) and identifies Cetacea/Sirenia/Pinnipedia as aquatic groups; precisely defines five scale types by histological composition and systematic distributionDescribes fission and conjugation but confuses nuclear roles or omits autogamy; lists mammal groups with minor classification errors (e.g., confusing pinnipeds with cetaceans); identifies 3-4 scale types with some histological inaccuraciesConfuses longitudinal with transverse fission; misidentifies conjugation as autogamy or permanent fusion; conflates marsupials with monotremes; describes scales only as 'bony' or 'cartilaginous' without type distinction
Diagram / labelling18%9Draws two clear diagrams: Paramecium in conjugation showing nuclear stages (meiosis, pronuclear exchange) and scale types (placoid vs. ctenoid/cycloid comparison); labels include macro/micronucleus, cytoplasmic bridge, pellicle, ganoin layer, basal plate, enamel, dentine with pulp cavity; uses proper shading for hard vs. soft tissuesProvides one adequate diagram (either conjugation or scales) with partial labelling; or two diagrams with missing key structures (e.g., no nuclear detail in conjugation, no histological layers in scales)No diagrams or unrecognizable sketches; labels missing or incorrect; confuses scale types (e.g., drawing placoid as overlapping)
Examples & nomenclature20%10Cites specific species: Paramecium caudatum, P. aurelia, P. bursaria for conjugation types; Tachyglossus aculeatus, Ornithorhynchus anatinus, Macropus rufus, Didelphis virginiana; Indian aquatic mammals Platanista gangetica, Neophocaena phocaenoides; scale examples from Polypterus, Lepisosteus, Catla, Labeo; uses correct higher taxa (Prototheria, Metatheria, Eutheria)Provides generic group names without species (e.g., 'kangaroo', 'platypus', 'dolphin'); mentions 2-3 scale examples; some taxonomic terms misspelled or outdatedNo specific examples or incorrect assignments (e.g., 'whale' as fish); confuses common names across groups; omits Indian examples entirely
Process explanation22%11Stepwise explanation: for binary fission—karyokinesis (macronuclear amitosis, micronuclear mitosis) before cytokinesis; for conjugation—prezygotic division, pronuclear exchange, synkaryon formation, postzygotic fission; for mammal reproduction—correlation of gestation length, yolk sac vs. chorioallantoic placenta, and developmental state; for scales—development from dermal papillae, incremental growth patterns, regenerationDescribes processes in general terms without clear sequence; mentions nuclear exchange in conjugation but not meiotic stages; notes marsupial pouch without placental detail; describes scale formation superficiallyNo sequential logic; confuses cause and effect (e.g., conjugation for asexual reproduction); describes mammal groups by habitat only without reproductive mechanism; no developmental context for scales
Evolutionary / applied context18%9Discusses evolutionary significance: conjugation as adaptive for genetic diversity in clonal populations; mammal reproductive strategies as adaptive radiation (fossil evidence from Mehrgarh for egg-laying mammals); scale reduction from heavy ganoid to lightweight ctenoid/cycloid as key teleost innovation; mentions conservation status of Platanista and anthropogenic threats to aquatic mammalsBrief mention of 'evolutionary advantage' without elaboration; notes scale lightness as 'helpful for swimming' without phylogenetic context; generic statement on mammal diversityNo evolutionary context; treats all features as isolated facts; no applied or conservation relevance; misrepresents evolutionary relationships (e.g., claiming monotremes evolved from marsupials)

Practice this exact question

Write your answer, then get a detailed evaluation from our AI trained on UPSC's answer-writing standards. Free first evaluation — no signup needed to start.

Evaluate my answer →

More from Zoology 2022 Paper I