Zoology 2023 Paper I 50 marks Describe

Q2

(a) Define conjugation. Explain the mechanism of conjugation in Paramecium. Also give its significance. (20 marks) (b) Describe the different stages of life cycle of leech with the help of suitable diagram. (15 marks) (c) Describe the respiratory organs and mechanism of respiration in cockroach. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) संयुग्मन को परिभाषित कीजिए। पैरामीशियम में संयुग्मन की क्रियाविधि की व्याख्या कीजिए। इसका महत्व भी बताइए। (20 अंक) (b) जोंक के जीवन-चक्र की विभिन्न अवस्थाओं का उपयुक्त चित्र की सहायता से वर्णन कीजिए। (15 अंक) (c) तिलचट्टा (कॉक्रोच) में श्वसन अंगों और श्वसन की क्रियाविधि का वर्णन कीजिए। (15 अंक)

Evaluate your answer to this question → See all 2023 Zoology questions

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 structures and processes. Allocate approximately 40% of time/words to part (a) given its 20 marks, covering definition, mechanism and significance of conjugation; 30% each to parts (b) and (c). Structure: brief comparative introduction on asexual vs sexual reproduction in lower invertebrates → detailed body addressing each sub-part sequentially → concluding synthesis on evolutionary trends in reproduction and respiration across grades of organization.

Key points expected

  • Part (a): Precise definition of conjugation as temporary union of two individuals with reciprocal nuclear exchange; distinction from autogamy and endomixis in Paramecium
  • Part (a): Stepwise mechanism—prophase, metaphase, anaphase of micronuclei; formation of pronuclei; exchange and fusion; post-conjugation fissions; role of cytoplasmic bridge and paroral cone
  • Part (a): Significance—rejuvenation (Woodruff's experiment), genetic recombination, origin of new hereditary combinations, survival value; contrast with binary fission
  • Part (b): Complete life cycle of Hirudinaria (Indian cattle leech)—cocoon formation, direct development, juvenile stages, hermaphroditism and cross-fertilization; seasonal breeding pattern
  • Part (b): Diagrammatic representation showing cocoon structure, developing embryo, young leech emergence; annotation of spermatophore deposition and hypodermic impregnation
  • Part (c): Respiratory organs—tracheal system, spiracles (10 pairs), tracheoles, air sacs; cellular respiration at tracheole level
  • Part (c): Mechanism—abdominal and thoracic pumping, valve mechanism of spiracles, passive vs active ventilation; role of air sacs in flight metabolism
  • Part (c): Physiological adaptations—discontinuous gas exchange in desiccation-prone environments; comparison with aquatic respiration in other arthropods

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11For (a), correctly identifies conjugation as involving micronuclear meiosis and macronuclear disintegration; for (b), accurately describes hermaphroditic cross-fertilization and direct development without free larva; for (c), precisely distinguishes between tracheal ventilation and cellular gas exchangeBasic definitions correct but confuses micronuclear and macronuclear roles in (a); omits hypodermic impregnation in (b); conflates tracheae with tracheoles in (c)Fundamental errors—describes conjugation as fusion of whole organisms, states leech has trochophore larva, or claims cockroach has book lungs
Diagram / labelling18%9For (b), provides clear labelled diagram of leech life cycle showing cocoon, embryo and juvenile; for (a) and (c), includes schematic representations of conjugating paramecia or tracheal system with spiracle structure; all diagrams with proper titles and directional labelsDiagram present for (b) but incomplete labelling; missing structural details like spermatophore or tracheole endings; no diagrams for (a) or (c)No diagrams despite explicit requirement in (b); or diagrams without any labels; incorrect orientation or structures
Examples & nomenclature16%8Uses correct scientific names (Paramecium caudatum, Hirudinaria granulosa/quinquiesannulata, Periplaneta americana); cites Indian species; mentions Woodruff and Jennings for experimental evidence; distinguishes P. aurelia complex mating typesGeneric references to 'paramecium' and 'leech'; no species names; mentions scientists without connecting to specific experimentsWrong nomenclature (e.g., 'Pheretima' for leech); no indication of Indian fauna relevance; invents non-existent authorities
Process explanation24%12For (a), chronological explanation of nuclear events with timing; for (b), sequential developmental stages from cocoon deposition to juvenile emergence; for (c), integrated explanation of muscular pumping, spiracle valving and tracheole diffusion with physiological coordinationProcesses described but sequence unclear; missing key steps like pronuclear exchange or air sac function; no temporal or causal linkagesRandom listing of structures without process; confuses cause and effect; describes outcomes without mechanisms
Evolutionary / applied context20%10For (a), explains conjugation as evolutionary solution to clonal senescence; for (b), relates leech direct development to terrestrial adaptation and parental investment; for (c), discusses tracheal system as key innovation enabling insect terrestrial dominance and flight; mentions medical/leech therapy applicationsBrief mention of 'genetic variation' or 'adaptation' without elaboration; no synthesis across parts; misses applied significanceNo evolutionary or applied context; treats all topics as isolated facts; ignores significance component of (a) entirely

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 2023 Paper I