Zoology 2025 Paper I 50 marks 150 words Compulsory Write short notes

Q1

Write short notes on/Answer the following in about 150 words each: 10×5=50 (a) Metagenesis (b) Book lungs (c) Paedomorphosis (d) Torsion and detorsion in gastropods (e) Draw a well-labelled diagram of human eye and write its functions.

हिंदी में प्रश्न पढ़ें

निम्नलिखित में से प्रत्येक पर/का लगभग 150 शब्दों में संक्षिप्त टिप्पणी लिखिए/उत्तर दीजिए : 10×5=50 (a) संमेकांतरण (b) पुस्त फुप्फुस (c) शावकांतरण (d) गैस्ट्रोपोड में ऐटन (विमोटन) और अव्यावर्तन (e) मनुष्य की आँख का एक सुचिहित चित्र बनाइए और उसके कार्यों का वर्णन कीजिए।

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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 short notes' demands concise, information-dense responses for each sub-part. Allocate approximately 30 words/2 minutes per sub-part (a)-(d), reserving 30 words/3 minutes for part (e) which requires a diagram. Structure each note as: definition → key features → significance/example. For (e), prioritize a neat, correctly proportioned diagram with 8-10 labels over extensive text description.

Key points expected

(a) Metagenesis: Define as alternation of generations between sexual (medusa) and asexual (polyp) phases in Cnidaria; specify Obelia as classic example; note that metagenesis is distinct from true alternation of generations (no meiosis in spore formation).
(b) Book lungs: Identify as respiratory organs in arachnids (spiders, scorpions); describe stacked leaf-like lamellae in hemolymph-filled chamber; contrast with book gills in Limulus; note limitation for active metabolism.
(c) Paedomorphosis: Define as retention of juvenile traits in adult; distinguish neoteny (delayed somatic development) from progenesis (precocious sexual maturation); cite axolotl (Ambystoma mexicanum) and human 'fetalization' as examples.
(d) Torsion and detorsion: Explain 180° counter-clockwise rotation of visceral mass in gastropod larvae; describe consequences (asymmetry, loss of gill/auricle, torsion of nerve cords); note detorsion in some opisthobranchs and its evolutionary reversal.
(e) Human eye diagram: Include cornea, iris/pupil, lens, ciliary body, suspensory ligaments, retina (rods/cones), fovea, optic disc, sclera, choroid; briefly state photoreception and image formation functions.

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	20%	10	All five sub-parts demonstrate accurate core definitions: metagenesis correctly distinguished from metageny; book lungs correctly placed in Arachnida not Crustacea; paedomorphosis types precisely differentiated; torsion angle and direction stated correctly; eye structures anatomically accurate.	Most definitions correct but minor errors: metagenesis confused with alternation of generations in plants; book lungs mentioned without phylum; paedomorphosis types conflated; torsion direction vague; eye diagram has minor structural errors.	Fundamental misconceptions: metagenesis described as 'regeneration'; book lungs attributed to insects; paedomorphosis equated with metamorphosis; torsion described as coiling of shell; eye diagram shows serious anatomical errors like lens behind retina.
Diagram / labelling	20%	10	Part (e) presents a neat, proportionate sagittal section of human eye with 8-10 correctly placed labels; lines point precisely to structures; diagram drawn in pencil with clear boundaries; no time wasted on shading; other parts (a)-(d) may include small illustrative sketches enhancing clarity.	Part (e) diagram present but labels incomplete (6-7 structures) or lines misdirected; proportions slightly distorted (oversized lens, missing ciliary body); parts (a)-(d) lack supporting diagrams where helpful.	Part (e) diagram absent, extremely crude, or copied from memory with inverted anatomy; labels fewer than 5 or completely misplaced; diagram of book lungs or torsion also missing where expected; messy presentation affecting readability.
Examples & nomenclature	20%	10	Each sub-part cites specific, taxonomically correct examples: Obelia/Physalia for metagenesis; Araneae/Scorpiones for book lungs; Ambystoma mexicanum, Siren, or human evolution for paedomorphosis; Pila/Patella for torsion, Aplysia for detorsion; eye parts use standard anatomical terms (fovea centralis, ora serrata).	Some examples given but imprecise: 'jellyfish' for metagenesis without genus; 'spiders' without order; paedomorphosis example missing or generic 'tadpole' cited; torsion example as 'snail' without specificity; eye labels use colloquial terms.	Examples absent or wrong: metagenesis in 'earthworm'; book lungs in 'prawn'; paedomorphosis in 'caterpillar'; torsion in 'bivalves'; eye diagram labels use non-biological terms; demonstrates rote memorization without understanding.
Process explanation	20%	10	Clear sequential explanation of processes: metagenesis shows polyp→medusa→planula cycle; book lungs describe air entry through spiracles and gas exchange across lamellae; paedomorphosis explains hormonal (thyroxine) or environmental triggers; torsion explains 180° rotation in two 90° stages with mantle cavity repositioning; eye explains light path and accommodation mechanism.	Processes mentioned but sequence unclear or incomplete: metagenesis as 'alternation' without life cycle stages; book lungs as 'breathing organs' without mechanism; paedomorphosis as 'retention of features' without developmental basis; torsion as 'twisting' without developmental stages; eye function limited to 'seeing' without accommodation.	No process explanation or completely garbled: metagenesis described as 'metamorphosis'; book lungs confused with tracheal system; paedomorphosis as 'rapid growth'; torsion as 'shell coiling'; eye function absent or describes camera obscura principle instead of biological mechanism.
Evolutionary / applied context	20%	10	Demonstrates evolutionary significance: metagenesis as adaptation for dispersal (sessile polyp, mobile medusa); book lungs as terrestrial adaptation from aquatic ancestors; paedomorphosis as heterochronic evolution and speciation mechanism; torsion enabling coiled shell with anterior mantle cavity, detorsion as secondary simplification; eye structures showing camera-type evolution from simple eyespot.	Brief mention of significance without elaboration: metagenesis 'helps survival'; book lungs 'for land life'; paedomorphosis 'interesting phenomenon'; torsion 'evolutionary change'; eye 'important sense organ'—lacks specific evolutionary narrative.	No evolutionary or applied context; or incorrect statements: metagenesis as 'primitive feature to be eliminated'; book lungs 'inefficient so replaced by trachea'; paedomorphosis as 'disease'; torsion as 'mistake in development'; eye described with Lamarckian 'use and disuse' explanation.

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