Zoology 2021 Paper I 50 marks 150 words Compulsory Write short notes

Q1

Write notes in about 150 words each for Q. Nos. 1(a) to 1(d) and answer Q. No. 1(e) : (a) Canal system in sponges (10 marks) (b) Nematocysts of Aurelia (10 marks) (c) Trochophore larva and its evolutionary significance (10 marks) (d) Origin of tetrapods (10 marks) (e) Draw a well-labelled diagram of avian brain. (10 marks)

हिंदी में प्रश्न पढ़ें

प्र० सं० 1(a) से 1(d) तक प्रत्येक पर लगभग 150 शब्दों में टिप्पणी लिखिए और प्र० सं० 1(e) का उत्तर दीजिए : (a) स्पंजों में नाल प्रणाली (10 अंक) (b) ऑरेलिया के निमेटोसिस्ट (10 अंक) (c) ट्रोकोफोर लार्वा और इसका विकासवादी महत्व (10 अंक) (d) चौपायों (टेट्रापोड्स) की उत्पत्ति (10 अंक) (e) पक्षी (एवियन) मस्तिष्क का एक नामांकित चित्र बनाइए। (10 अंक)

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Directive word: Write short notes

This question asks you to write short notes. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

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How this answer will be evaluated

Approach

The directive 'Write notes' demands concise, information-dense responses for parts (a)-(d) and a precise diagram for (e). Allocate approximately 25-28 minutes total: 4-5 minutes each for (a)-(d) producing 140-150 words per sub-part, and 5-6 minutes for (e) ensuring all 8-10 key neural structures are labelled. Structure each written part with a one-sentence definition followed by 3-4 bullet points covering types, functions, and significance; for (e), draw the dorsal view with clear demarcation of cerebrum, optic lobes, cerebellum, and medulla oblongata.

Key points expected

  • (a) Canal system: Distinguish ascon, sycon, and leucon types with examples (e.g., Leucosolenia, Sycon, Spongilla); mention choanocytes, spongocoel, and osculum; note flagellar current and filter-feeding efficiency.
  • (b) Nematocysts of Aurelia: Classify into atrichous isorhiza, holotrichous isorhiza, and heterotrichous microbasic euryteles; explain cnidocil discharge mechanism and prey capture function.
  • (c) Trochophore larva: Describe prototroch, metatroch, and telotroch ciliary bands; cite Polychaeta (e.g., Nereis) and Mollusca (e.g., Pila); explain trochaea theory and significance for Lophotrochozoa phylogeny.
  • (d) Origin of tetrapods: Trace fin-to-limb transition via Tiktaalik, Ichthyostega, and Acanthostega; mention pentadactyl limb homology and Devonian (Romer's gap) fossil evidence from Greenland and Pennsylvania.
  • (e) Avian brain diagram: Label cerebrum (smooth, no corpus callosum), large optic lobes, well-developed cerebellum (flight coordination), and elongated medulla; show cranial nerve roots (II, V, VII, IX, X).

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10For (a) correctly identifies leucon as most advanced with reduced spongocoel; for (b) distinguishes cnidocyte structure from nematocyst capsule; for (c) accurately describes blastopore fate in trochophore; for (d) correctly dates tetrapod origins to Late Devonian; for (e) shows correct proportional sizes of avian brain regions.Mixes up canal system types or confuses nematocyst categories; describes trochophore generally without ciliary band details; gives vague 'fish to land' narrative for tetrapods; diagram shows mammalian brain features.Fundamental errors such as calling sponges diploblastic, describing Aurelia nematocysts as absent (scyphozoan medusa reduction), or drawing reptilian brain with corpus callosum.
Diagram / labelling20%10For (e) produces clean dorsal view with 8+ accurately placed labels including olfactory lobes, cerebral hemispheres, optic lobes, cerebellum with folia, medulla oblongata, and at least two cranial nerve exits; uses pointer lines without label crowding.Diagram present but with 5-7 labels, missing either optic lobe detail or cerebellar foliation; some misplacement of structures or unclear demarcation between regions.No diagram, or sketch with <4 labels, confused orientation (ventral vs dorsal), or inclusion of non-avian features like neocortex or corpus callosum.
Examples & nomenclature20%10Cites specific genera: Leucosolenia/Sycon/Spongilla for canal types; Aurelia aurita; Nereis/Pila/Chaetopterus for trochophore; Tiktaalik roseae, Ichthyostega stensioei, Acanthostega gunnari for tetrapod origins; uses correct anatomical terms (prototroch, metatroch, rhombencephalon).Gives family-level or common names only (e.g., 'jellyfish', 'earthworm'); misspells scientific names; omits key fossil taxa for tetrapod transition.No scientific nomenclature; uses entirely vernacular terms; invents non-existent taxa or confuses Aurelia with Physalia.
Process explanation20%10For (a) explains water current pathway and choanocyte feeding; for (b) describes cnidocil trigger and operculum discharge; for (c) clarifies ciliary band locomotion and feeding currents; for (d) outlines limb bone homologies (humerus-radius-ulna vs stylopod-zeugopod); for (e) relates cerebellar size to flight precision.Lists structures without explaining function; describes nematocysts as 'stinging cells' without mechanism; mentions 'limbs evolved from fins' without bone correspondence.No process explanation; confuses cause and effect (e.g., claims sponges evolved complexity to become marine); describes avian brain as 'small' without functional interpretation.
Evolutionary / applied context20%10For (a) notes leucon grade as adaptive radiation; for (c) explicitly links trochophore to Lophotrochozoa clade and spiral cleavage; for (d) discusses Romer's gap and recent Indian fossil finds (e.g., Devonian tetrapod trackways); for (e) compares avian brain to reptilian/mammalian grades.Mentions 'evolutionary significance' as phrase without elaboration; gives generic 'common ancestor' statements; no reference to contemporary phylogenetic revisions.No evolutionary context; treats all features as static; includes creationist or Lamarckian language; claims tetrapods evolved 'to conquer land' teleologically.

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