Zoology 2024 Paper I 50 marks Describe

Q3

(a) Describe the different larval forms of Crustaceans with suitable diagrams. (20 marks) (b) What are coral reefs ? Describe the different theories of coral reef formation. (15 marks) (c) Describe the evolution of kidney in relation to its function as an excretory organ. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) क्रस्टेशियंस के विभिन्न लार्वा रूपों का उपयुक्त रेखाचित्रों सहित वर्णन कीजिए। (20 अंक) (b) प्रवाल भित्तियाँ क्या हैं ? प्रवाल भित्ति निर्माण के विभिन्न सिद्धांतों का वर्णन कीजिए। (15 अंक) (c) उत्सर्जन अंग के रूप में इसके कार्य के संबंध में गुर्दे के विकास का वर्णन कीजिए। (15 अंक)

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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 structures, processes and theories across all three parts. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure: brief comparative introduction → detailed sequential description of crustacean larvae with diagrams → coral reef definition and three formation theories → evolutionary progression of excretory organs → concluding synthesis on adaptive significance.

Key points expected

  • Part (a): Sequential description of crustacean larval forms—nauplius, metanauplius, protozoea, zoea, mysis, megalopa/cypris—with distinguishing morphological features and taxonomic distribution (e.g., nauplius in Cirripedia, zoea in Decapoda)
  • Part (a): Correct labelling of larval appendages (antennules, antennae, mandibles in nauplius; thoracic legs in zoea; abdominal pleopods in mysis) and metamorphic transitions
  • Part (b): Definition of coral reefs as massive calcareous structures built by colonial anthozoans (primarily scleractinian corals) in shallow tropical waters
  • Part (b): Three classical theories of reef formation—Darwin's subsidence theory, Daly's glacial control theory, Murray's offshore bar theory—with their evidential basis and limitations
  • Part (c): Evolutionary progression of excretory organs—solennocytes in Platyhelminthes, protonephridia in rotifers/annelid larvae, metanephridia in adult annelids/arthropods, Malpighian tubules in insects, antennal/maxillary glands in crustaceans
  • Part (c): Functional correlation—ultrafiltration in solennocytes, selective reabsorption in metanephridia, modification for osmoregulation in marine/freshwater/terrestrial adaptations

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately describes all larval stages with correct developmental sequence for part (a); precisely defines coral reefs and accurately presents all three formation theories with their geographical predictions for part (b); correctly traces kidney evolution from solennocytes through metanephridia to specialized glands with functional adaptations for part (c)Describes major larval forms with minor sequence errors; defines coral reefs adequately but confuses elements of theories or omits one theory; outlines kidney evolution but conflates protonephridia and metanephridia or misses key functional shiftsConfuses larval forms (e.g., calls zoea a nauplius) or invents non-existent stages; defines coral reefs incorrectly or presents garbled theories; fundamentally misunderstands excretory evolution (e.g., claims insects have metanephridia)
Diagram / labelling18%9Provides clear, well-proportioned diagrams for part (a) showing nauplius, zoea and megalopa with accurate appendage labelling; includes schematic cross-sections for part (b) illustrating subsidence theory stages; draws comparative diagrams of solennocyte, flame cell and metanephridium for part (c)Draws recognizable larval diagrams with some labelling errors or omissions; provides basic reef diagrams without clear stratification; sketches kidney structures with minor anatomical inaccuraciesDiagrams absent or unrecognizable; mislabels critical structures (e.g., antenna vs antennule); provides irrelevant or copied diagrams without explanation
Examples & nomenclature18%9Cites specific examples: Artemia (nauplius), Penaeus/Cancer (zoea-megalopa sequence), Sacculina (kentrogon stage); names reef types (fringing, barrier, atoll) with Indian Ocean examples (Lakshadweep, Andaman atolls); identifies antennal glands in Astacus, maxillary glands in Daphnia, green glands in decapodsProvides generic crustacean examples without specificity; mentions Indo-Pacific reefs without naming specific formations; lists gland types without species associationsNo valid examples cited; confuses taxa (e.g., names insect larvae for crustaceans); invents non-existent glands or misattributes reef locations
Process explanation22%11Clearly explains metamorphic transitions and hormonal control (ecdysteroids) in part (a); logically explains how subsidence rate matches coral growth for Darwin's theory, sea-level changes for Daly's, and wave action for Murray's in part (b); explains ultrafiltration→selective reabsorption→secretion mechanisms and osmoregulatory challenges across habitats in part (c)Describes larval changes descriptively without explaining causal mechanisms; presents theories as lists without explaining their geological reasoning; states kidney functions without explaining how structure enables functionNo process explanation attempted; presents random facts without logical connection; fundamentally misunderstands mechanisms (e.g., claims active transport occurs in solennocytes)
Evolutionary / applied context20%10Synthesizes how larval dispersal strategies relate to adult habitat specificity; evaluates which reef theory best explains Indo-Pacific atolls versus Caribbean barriers; integrates kidney evolution with colonization of freshwater (antennal gland modification) and land (Malpighian tubule origin), citing Indian biodiversity applicationsMentions adaptive significance superficially; states that theories have been debated without evaluation; notes that different habitats need different excretion without evolutionary synthesisNo evolutionary or applied context provided; treats all topics as static descriptions; includes irrelevant material on conservation or fisheries without linking to question

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