Zoology 2021 Paper I 50 marks Describe

Q4

(a) Define double circulation. Give a comparative account of heart in reptiles, birds and mammals. (20 marks) (b) Describe habitat, habits and life history of Branchiostoma. (15 marks) (c) Give an illustrated account of life cycle of Leishmania. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) दोहरे परिसंचरण को परिभाषित कीजिए। सरीसृपों, पक्षियों और स्तनधारियों में हृदय का तुलनात्मक विवरण दीजिए। (20 अंक) (b) ब्रांकिओस्टोमा के आवास, आदतों और जीवन-इतिहास का वर्णन कीजिए। (15 अंक) (c) लीशमैनिया के जीवन-चक्र का सचित्र विवरण दीजिए। (15 अंक)

Evaluate your answer to this question → See all 2021 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 coverage of structures, processes and life histories. Allocate approximately 40% of time/words to part (a) given its 20 marks weightage, with 30% each to parts (b) and (c). Structure with brief definitions first, then comparative tables or systematic descriptions, followed by well-labelled diagrams for heart evolution, Branchiostoma anatomy, and Leishmania life stages. Conclude with evolutionary significance and medical relevance where applicable.

Key points expected

  • Part (a): Precise definition of double circulation (systemic + pulmonary circuits) with complete separation of oxygenated and deoxygenated blood
  • Part (a): Comparative cardiac anatomy showing 3-chambered heart in reptiles (except crocodiles with 4-chambered), 4-chambered in birds and mammals; noting interventricular septum completion as evolutionary advancement
  • Part (b): Habitat specifics of Branchiostoma (lancelet/Amphioxus) in sandy marine bottoms of Indian coasts (Gulf of Mannar, Palk Bay); filter-feeding habits and burrowing behavior
  • Part (b): Life history including metaplasia, retrogressive metamorphosis, and affinities showing primitive chordate characteristics (notochord, dorsal nerve cord, pharyngeal slits)
  • Part (c): Complete life cycle of Leishmania donovani (Kala-azar) showing promastigote in sandfly (Phlebotomus argentipes) and amastigote in human macrophages; alternation of hosts
  • Part (c): Illustrated stages including transformation in insect vector, infection of reticuloendothelial system, and clinical relevance to visceral leishmaniasis in endemic Indian regions (Bihar, Jharkhand, West Bengal)

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately defines double circulation with correct anatomical distinctions; precisely describes cardiac chambers, septation, and blood flow patterns across reptiles, birds and mammals; correctly identifies Branchiostoma systematic position and Leishmania morphological stages with accurate host-parasite relationshipsBasic definition of double circulation present but incomplete on septal evolution; heart comparisons lack precision on crocodilian exception; Branchiostoma description generic; Leishmania cycle confused on vector or stage terminologyMisdefines double circulation or confuses single/double circuits; major errors in chamber counts; misidentifies Branchiostoma as vertebrate or invertebrate; fundamental errors in Leishmania life cycle sequence or host specificity
Diagram / labelling20%10Three high-quality diagrams: (a) comparative heart sections showing sinus venosus, conus arteriosus, septal completeness across classes; (b) Branchiostoma sagittal section with notochord, nerve cord, gonads, atriopore; (c) Leishmania cycle with promastigote/amastigote ultrastructure and transmission arrows; all fully labelled with anatomical precisionDiagrams attempted for 2 of 3 parts with partial labelling; heart diagrams lack comparative dimension; Branchiostoma diagram missing key structures; Leishmania cycle diagrammatic but stages poorly distinguishedSingle diagram or none; crude sketches without anatomical accuracy; missing critical labels; diagrams contradict textual description
Examples & nomenclature18%9Cites specific examples: Crocodylus palustris for complete septation in reptiles; Branchiostoma lanceolatum/lanceolatum from Indian waters; Leishmania donovani with correct strain variations; mentions Phlebotomus argentipes as Indian vector; uses updated nomenclature (Amphioxus as synonym)Generic group names without species; mentions sandfly without species; uses outdated Amphioxus as primary name; Indian examples absent or vagueWrong species names; confuses Leishmania species (L. tropica vs L. donovani); misidentifies vector (Anopheles instead of Phlebotomus); no Indian examples
Process explanation22%11Clear sequential explanation: blood flow pathways in double circulation with pressure differentials; Branchiostoma feeding mechanism with ciliary currents and excretion via solenocytes; Leishmania transformation stages with physiological triggers (temperature, pH) for promastigote-amastigote interconversionDescribes structures but processes vague; blood flow described without pressure/functional implications; Branchiostoma feeding mentioned without mechanism; Leishmania stages listed without transformation triggersNo process explanation; static description only; confused sequence of developmental stages; incorrect physiological mechanisms attributed
Evolutionary / applied context18%9Explicitly links cardiac evolution to endothermy and metabolic demands (birds/mammals); positions Branchiostoma as cephalochordate showing probable chordate ancestor features; connects Leishmania to public health significance in India (WHO roadmap for elimination), diagnostic methods (rk39), and vector control strategiesBrief mention of evolution without functional explanation; notes Branchiostoma as 'primitive' without elaboration; mentions Kala-azar as disease without control contextNo evolutionary interpretation; no applied/medical relevance; misses significance of complete double circulation for endothermy; ignores Indian public health dimension

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 2021 Paper I