Zoology 2025 Paper I 50 marks Describe

Q3

(a) Describe the mechanism of parental care in amphibians with suitable examples. 20 (b) Describe the different stages of life cycle of Pheretima with the help of suitable diagrams. 15 (c) Discuss the various modes of nutrition in protozoa. 15

हिंदी में प्रश्न पढ़ें

(a) उभयचरों (एम्फिबियन) में पैतृक रक्षण की क्रियाविधि का उपयुक्त उदाहरणों सहित वर्णन कीजिए। 20 (b) फेरेटिमा के जीवन-चक्र की विभिन्न अवस्थाओं का उपयुक्त चित्रों की सहायता से वर्णन कीजिए। 15 (c) प्रोटोजोआ में पोषण के विभिन्न तरीकों पर चर्चा कीजिए। 15

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Directive word: Describe

This question asks you to describe. 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 'describe' demands detailed, systematic exposition of mechanisms and life cycles with visual support where specified. Allocate approximately 40% of time and words to part (a) given its 20 marks, 30% each to parts (b) and (c). Structure: brief comparative introduction on reproductive strategies across animal groups; for (a) categorize amphibian parental care types with mechanisms and Indian examples; for (b) draw and label 6-8 stages of Pheretima life cycle with developmental details; for (c) classify protozoan nutrition modes with cellular mechanisms. Conclude with evolutionary significance of these adaptations.

Key points expected

  • Part (a): Types of parental care in amphibians—egg attendance (Rhinoderma darwinii gastric brooding), transport (Phyllomedusa, Hyla), feeding (Neotropical poison frogs), and nest guarding (Indian bullfrog Hoplobatrachus tigerinus); hormonal and behavioural mechanisms
  • Part (a): Mechanistic details—male pregnancy in Syngnathidae analogues, skin feeding in Caecilian amphibians (Ichthyophis glutinosus from Western Ghats), oophagy and trophic egg production
  • Part (b): Complete life cycle stages of Pheretima posthuma—cocoon formation, embryonic development within cocoon, hatching as young worm, juvenile growth, sexual maturity; alternation of generations not applicable but direct development emphasized
  • Part (b): Diagrammatic representation showing: cocoon structure, cleavage stages, gastrulation, organogenesis, young worm emergence; accurate labelling of clitellum role in cocoon production
  • Part (c): Holozoic nutrition (ingestion, digestion, egestion—Amoeba, Paramecium), holophytic/autotrophic (Euglena with chloroplasts), saprozoic/saprophytic (absorption of dissolved organic matter—Trypanosoma), parasitic (Plasmodium, Entamoeba histolytica), mixotrophic and pinocytosis
  • Part (c): Cellular mechanisms—phagocytosis, food vacuole formation, intracellular digestion, contractile vacuole role in osmoregulation during nutrition

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11For (a): accurately distinguishes male vs. female parental investment, recognizes hormonal control (prolactin in amphibian brooding); for (b): correctly identifies Pheretima as direct developer without larval stage, knows clitellum function; for (c): precisely defines each nutritional mode with correct cellular basis, distinguishes phagotrophy from osmotrophyBasic definitions correct but confuses similar terms (e.g., saprozoic with saprophytic), minor errors in life cycle sequence, omits hormonal mechanisms in parental careFundamental misconceptions—states Pheretima has tadpole stage, confuses parental care types, misclassifies nutritional modes (calls Euglena holozoic), incorrect anatomical structures labelled
Diagram / labelling18%9For (b): draws neat, proportionate diagrams showing cocoon, cleavage stages (2-cell to blastula), gastrula with germ layers, young worm; for (a) and (c): includes schematic flowcharts where helpful; all diagrams titled, fully labelled with correct spellings; uses pencil for diagrams as per UPSC conventionDiagrams present but incomplete—missing stages in life cycle, poor proportions, partial labelling; diagrams mentioned in text but not clearly drawn; uses pen for diagramsNo diagrams for part (b) despite explicit requirement; diagrams drawn without labels; anatomically incorrect representations (e.g., showing metamorphosis in earthworm); illegible sketches
Examples & nomenclature20%10For (a): cites specific Indian examples—Hoplobatrachus tigerinus (nest guarding), Nasikabatrachus sahyadrensis (Western Ghats endemic with parental care), Ichthyophis sikkimensis; for (c): names correct genera for each mode—Amoeba, Paramecium, Euglena, Plasmodium, Trypanosoma; uses updated binomial nomenclatureGeneric examples only (frog, earthworm, amoeba), some Indian context missing, occasional outdated names (Euplotes instead of correct usage), misses key representative generaNo specific examples, incorrect scientific names, confuses organisms across phyla (e.g., names reptilian examples for amphibian question), vulgar names only
Process explanation22%11For (a): explains behavioural sequences—mate choice, egg deposition, transport mechanisms, feeding of tadpoles with unfertilized eggs; for (b): describes developmental processes sequentially with timing; for (c): details ingestion→digestion→egestion pathway, contractile vacuole dynamics, enzyme action in food vacuolesLists stages or modes without explaining how they occur; superficial behavioural descriptions; mentions food vacuole without explaining formation; chronological order present but mechanisms vagueRandom listing without sequence, no process description, confuses cause and effect, describes structures without explaining their role in the process
Evolutionary / applied context18%9For (a): discusses evolutionary drivers—predation pressure, aridification, K-selection in tropical amphibians; conservation implications for Indian amphibians; for (b): relates clitellum evolution to terrestrial adaptation in oligochaetes; for (c): connects mixotrophy to survival in fluctuating environments, medical importance of parasitic nutritionBrief mention of adaptation without explanation, generic statements about survival value, no Indian conservation context, misses applied significanceNo evolutionary or applied perspective, anthropomorphic explanations, irrelevant digressions into general ecology not tied to the specific taxa

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