Zoology 2025 Paper II 50 marks Describe

Q8

(a) Describe the stages of fertilization in chick with diagram. (20 marks) (b) Draw structure of cholesterol and explain its role in health and diseases. (15 marks) (c) Discuss the role of ovarian hormones in female reproduction. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) चुजे में निषेचन के चरणों का चित्रों के साथ वर्णन कीजिए । (20 अंक) (b) कोलेस्ट्रॉल की संरचना बनायें एवं स्वास्थ्य तथा बीमारियों में इसकी भूमिका की व्याख्या कीजिए । (15 अंक) (c) मादा प्रजनन में अंडाशयी हार्मोनों की भूमिका की विवेचना 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 systematic, detailed exposition of biological processes and structures. 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 noting avian vs mammalian differences → sequential treatment of (a) fertilization stages with diagram, (b) cholesterol structure drawing with health applications, (c) ovarian hormone cascade with feedback loops → concluding synthesis on reproductive biology integration.

Key points expected

  • (a) Chick fertilization: sperm entry → germinal disc → pronuclear fusion → cleavage initiation; diagram showing infundibulum, magnum, isthmus, uterus sequence
  • (a) Polyspermy prevention mechanisms in birds (fast vs slow block) and early blastoderm formation
  • (b) Accurate steroid nucleus structure (four fused rings: three cyclohexane, one cyclopentane) with hydroxyl at C3 and alkyl side chain at C17
  • (b) Cholesterol roles: membrane fluidity, steroid hormone precursor, bile acid synthesis; diseases: atherosclerosis, familial hypercholesterolemia, gallstones
  • (c) Estrogen, progesterone, inhibin secretion patterns across follicular and luteal phases with hypothalamic-pituitary feedback
  • (c) Ovarian hormones in implantation, pregnancy maintenance, and menstrual/estrous cycle regulation in comparative context

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11For (a) correctly identifies acrosome reaction, syngamy, and polyspermy prevention in birds; for (b) accurately depicts steroid ring system with proper stereochemistry; for (c) precisely maps GnRH-FSH/LH-ovarian hormone axis with negative/positive feedback distinctionsBasic sequence correct but misses polyspermy details in (a), draws cholesterol skeleton without stereochemical accuracy in (b), confuses estrogen-progesterone dominance phases in (c)Fundamental errors such as mammalian-centric fertilization description ignoring avian peculiarities, incorrect ring fusion in cholesterol, or conflating ovarian with pituitary hormones
Diagram / labelling20%10For (a) clear sagittal section of oviduct with germinal disc, blastoderm layers labelled; for (b) neat steroid nucleus with numbered carbons, methyl groups, and hydroxyl positions; labels use standard anatomical/chemical terminologyDiagrams present but incomplete labelling—missing isthmus in oviduct, omitting carbon numbering in cholesterol, or unclear hormone feedback arrowsAbsent diagrams, unrecognizable sketches, or diagrams without any labels; failure to attempt required drawings despite explicit instruction
Examples & nomenclature18%9Uses precise terms: germinal disc (not blastodisc), zona pellucida/inner perivitelline layer distinction, LDL/HDL cholesterol fractions, estradiol-17β vs estrone, mentions Indian poultry breeds (Aseel, Kadaknath) or PCOS as applied exampleGeneric terminology without specificity—uses 'egg' ambiguously, 'female hormone' instead of specific estrogen, misses HDL/LDL distinctionIncorrect nomenclature such as 'oviduct' for uterus in mammals, confusing cholesterol with chitin, or 'progesterone' and 'prolactin' used interchangeably
Process explanation22%11For (a) sequential cellular/molecular events from sperm-egg binding to first cleavage; for (b) biosynthetic pathway from HMG-CoA to cholesterol to steroid hormones; for (c) hour-by-hour hormonal shifts triggering LH surge and corpus luteum transformationLists stages without causal mechanisms—what happens without how/why; static description lacking temporal or regulatory dynamicsDisordered sequence, no indication of cause-effect relationships, or complete omission of process description in favor of definitions only
Evolutionary / applied context18%9For (a) contrasts telolecithal cleavage with holoblastic patterns; for (b) discusses statin therapy, Indian dietary cholesterol concerns, evolutionary conservation of steroid synthesis pathway; for (c) links to assisted reproductive technologies, contraceptive development, or comparative reproductive strategiesBrief mention of applied relevance without elaboration—single sentence on heart disease or IVF without integrationNo applied or evolutionary perspective; purely descriptive answer treating each part as isolated factual recall without broader biological significance

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