Zoology 2025 Paper I 50 marks Describe

Q2

(a) Describe the comparative anatomy of digestive system in vertebrates. 20 (b) Give an illustrated account of reproduction in sponges. 15 (c) Describe the general features, distribution and social organization in termites. 15

हिंदी में प्रश्न पढ़ें

(a) कशेरुकियों में पाचन तंत्र के तुलनात्मक शारीर का वर्णन कीजिए। 20 (b) स्पंजों में प्रजनन का एक सचित्र विवरण दीजिए। 15 (c) दीमकों में सामान्य लक्षणों, वितरण और सामाजिक संगठन का वर्णन कीजिए। 15

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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.

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How this answer will be evaluated

Approach

The directive 'describe' demands systematic, detailed exposition with appropriate illustrations. Allocate approximately 40% of time/words to part (a) given its 20 marks, and 30% each to parts (b) and (c). Structure: brief comparative introduction, then detailed anatomical progression from cyclostomes to mammals for (a); illustrated life cycle with gemmule formation for (b); caste system and symbiotic digestion for (c). Conclude with evolutionary significance across all three parts.

Key points expected

  • Part (a): Progressive complexity from agnathans (cyclostomes with intra-oral tongue and keratinized teeth) through gnathostomes—fish (J-shaped stomach), amphibians (short intestine, liver, pancreas), reptiles (complete septum, muscular stomach), birds (gizzard, crop, cloaca), to mammals (differentiated dentition, complex stomach in ruminants, elongated intestine with caecum and vermiform appendix); mention Indian species like Labeo rohita, Naja naja, Bos indicus
  • Part (a): Accessory digestive glands—liver (hepatic portal system), pancreas (exocrine and endocrine functions), gall bladder; their comparative development across vertebrate classes
  • Part (b): Asexual reproduction—budding (external/internal), fragmentation, gemmule formation (thesocytes, spicule coat, Indian freshwater sponges like Eunapius/Ephydatia); sexual reproduction—oviparous vs viviparous species, spermatozoa transfer via water currents, internal fertilization, amphiblastula and parenchymula larvae with fate of cell layers
  • Part (c): General features—soft-bodied, polymorphic, hemimetabolous, cryptic habitat; distribution—tropical to temperate, Indian species (Coptotermes, Odontotermes) causing agricultural damage; social organization—reproductive caste (king, queen, neotenics), sterile castes (workers, soldiers with mandibulate/nasute types), pheromonal regulation, trophallaxis
  • Part (c): Symbiotic digestion—flagellates (Trichonympha, Holomastigotoides) in hindgut for cellulose breakdown; mound architecture in Odontotermes; economic importance as pests and soil engineers

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Accurately describes digestive tract regionalization (foregut, midgut, hindgut) across vertebrate classes; correctly identifies sponge reproductive structures (choanocytes giving rise to gametes, archeocytes forming thesocytes); precisely defines termite caste differentiation and eusocial characteristics without confusing with HymenopteraBasic anatomical descriptions with minor errors (e.g., confusing amphibian and reptile liver structure); general sponge reproduction without gemmule details; termite castes mentioned but without functional differentiationFundamental misconceptions such as attributing spiral valve to mammals, calling sponges hermaphroditic without qualification, or equating termite soldiers with ant workers; significant factual errors across multiple parts
Diagram / labelling20%10For (a): labeled comparative diagrams showing alimentary canal of fish, frog, pigeon and rabbit; for (b): gemmule structure with spicule types (amphidiscs/monaxons), larval stages; for (c): caste differentiation diagram, gut with flagellate location; neat, proportional, with directional arrows and magnification indicatorsRough sketches for 1-2 parts with partial labeling; missing critical structures like spiral valve, cloaca, or flagellate pouch; diagrams present but not integrated with textAbsent or irrelevant diagrams; unlabeled sketches; confusion between diagrams (e.g., drawing honeybee caste for termites); diagrams contradict textual description
Examples & nomenclature20%10Specific Indian examples: Petromyzon (Cyclostomata), Labeo/Channa (Teleostei), Bufo/Rana (Amphibia), Uromastix/Naja (Reptilia), Passer/Corvus (Aves), Funambulus/Rattus (Mammalia); Euspongia/Spongilla for marine/freshwater sponges; Coptotermes heimi, Odontotermes obesus for Indian termites; correct scientific names with authorities where relevantGeneric examples (fish, frog, bird) without specificity; common sponge names only; termite examples limited to 'white ant' without genusWrong examples (e.g., Octopus as vertebrate, coral as sponge); no Indian context; invented scientific names; confusion between related taxa
Process explanation20%10Clear sequential explanation: for (a) mechanical→chemical digestion progression with enzyme sources; for (b) gemmule formation steps (archeocyte aggregation→spongin coat→spicular envelope→germination conditions), fertilization to larval metamorphosis; for (c) pheromone-mediated caste regulation, stepwise cellulose digestion (endogenous+symbiotic enzymes), trophallactic food flowDescriptive rather than process-oriented; some steps mentioned but not causally linked; missing critical transitions like metamorphosis or molt-dependent caste determinationStatic descriptions without process; confused sequences (e.g., larva before fertilization); no mention of enzymatic or hormonal mechanisms
Evolutionary / applied context20%10For (a): evolutionary trends—jaw origin from pharyngeal arches, stomach diversification with diet, herbivore gut elongation; for (b): retention of ancestral totipotency, gemmules as dormancy adaptation; for (c): convergent evolution of eusociality with haplodiploidy vs chromosome fusion, termites as ecosystem engineers in Indian agriculture, biocontrol using entomopathogenic fungiBrief mention of 'evolution' or 'pest' without elaboration; generic statements about adaptation without specific mechanismsNo evolutionary perspective; missing applied significance; or irrelevant digressions into unrelated evolutionary theory

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