Zoology 2024 Paper II 50 marks Explain

Q6

(a) Explain the structure of nephron and its role in urine formation. Add a note on hormonal regulation of urine formation. (15+5=20 marks) (b) Classify hormones and write down the process of steroid hormone biosynthesis. (15 marks) (c) What do you mean by teratogenesis? Explain the genetic and induced teratogenesis. (5+10=15 marks)

हिंदी में प्रश्न पढ़ें

(a) वृक्काणु (नेफ्रॉन) की संरचना एवं मूत्र-निर्माण में इसकी भूमिका की व्याख्या कीजिए। मूत्र-निर्माण के हार्मोनी नियमन पर एक टिप्पणी लिखिए। (15+5=20 अंक) (b) हार्मोनों का वर्गीकरण कीजिए तथा स्टेरॉयड हार्मोन के जैव संश्लेषण की प्रक्रिया को लिखिए। (15 अंक) (c) विकृजनन से आप क्या समझते हैं? आनुवंशिक एवं प्रेरित विकृजनन की व्याख्या कीजिए। (5+10=15 अंक)

Evaluate your answer to this question → See all 2024 Zoology questions

Directive word: Explain

This question asks you to explain. 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

Begin with a brief introduction linking renal physiology, endocrinology, and developmental biology. For part (a), spend ~40% time (20 marks) detailing nephron ultrastructure, glomerular filtration, tubular reabsorption/secretion, and hormonal control by ADH, aldosterone, ANP. For part (b), allocate ~30% (15 marks) classifying hormones by chemical nature and source, then tracing steroidogenesis from cholesterol through pregnenolone to corticosteroids, androgens, and estrogens with key enzymes. For part (c), use remaining ~30% (15 marks) defining teratogenesis, then contrasting genetic mechanisms (chromosomal aberrations, single-gene mutations) with induced causes (thalidomide, retinoic acid, radiation, infections). Conclude by integrating how endocrine disruption links to teratogenesis.

Key points expected

  • Part (a): Nephron structure—renal corpuscle (glomerulus + Bowman's capsule), PCT, Henle's loop (descending/ascending limbs), DCT, collecting duct; urine formation via filtration, reabsorption, secretion; hormonal regulation—ADH (vasopressin) on collecting ducts, aldosterone on DCT, ANP antagonism
  • Part (b): Hormone classification by chemical nature (peptide/protein, steroid, amino acid derivatives) and by source (hypothalamic, pituitary, peripheral); steroid biosynthesis pathway—cholesterol → pregnenolone → progesterone → corticosteroids/androgens/estrogens with CYP11A1, 3β-HSD, 17α-hydroxylase, aromatase
  • Part (c): Teratogenesis definition—structural/functional defects from prenatal insults; genetic teratogenesis—trisomies (Down, Edwards, Patau), monosomy X (Turner), single-gene defects; induced teratogenesis—teratogens (thalidomide phocomelia, isotretinoin, alcohol fetal syndrome, rubella, radiation), critical periods, dose-response
  • Integration: Endocrine disruptors as teratogens—DES (diethylstilbestrol) causing vaginal adenosis, thyroid hormone deficiency causing cretinism
  • Applied relevance: Kidney disease burden in India (CKD hotspots), steroid hormone therapeutics, prevention of birth defects through folic acid supplementation and teratogen avoidance

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately describes nephron segments with correct epithelial types (podocytes, proximal tubule brush border, thin/thick limbs); precise Starling forces for GFR; correct hormone receptors (V2, mineralocorticoid); accurate steroidogenic enzyme locations (mitochondrial CYP11A1 vs smooth ER enzymes); teratogen mechanisms (thalidomide binding cereblon)Basic nephron structure correct but confuses cortical vs juxtamedullary nephrons; hormonal actions described without receptor specificity; steroid pathway broadly correct but enzyme order confused; teratogenesis examples listed without mechanismFundamental errors—confuses filtration with secretion, states ADH acts on glomerulus, reverses androgen/estrogen synthesis, conflates teratogenesis with mutagenesis
Diagram / labelling18%9Clear labeled diagram of nephron with vascular supply (afferent/efferent arterioles, peritubular capillaries, vasa recta); second diagram for steroidogenic pathway showing organelle transitions; teratogen timing diagram showing critical windows; neat handwriting, proper proportionsSingle nephron diagram with most parts labeled but missing juxtaglomerular apparatus or vasa recta; steroid pathway as flowchart without structural drawings; no temporal diagram for teratogenesisNo diagrams or unlabeled sketches; confused representation (e.g., glomerulus drawn as tube); messy, uninterpretable; diagrams contradict text
Examples & nomenclature18%9Precise terminology—podocyte foot processes, mesangial cells, macula densa, juxtaglomerular cells; specific enzymes (CYP11A1, 17α-hydroxylase/17,20-lyase, aromatase); named teratogens with Indian relevance—endemic cretinism (iodine deficiency in Himalayan belt), thalidomide history, Bhopal methyl isocyanateGeneric hormone names without specific compounds; enzymes mentioned as 'hydroxylases' without specificity; common teratogens listed (alcohol, smoking) without Indian public health contextIncorrect nomenclature—'kidney tubes,' 'cortisone' for all steroids; no specific examples; confuses teratogens with carcinogens
Process explanation22%11Stepwise urine formation—Starling equation for filtration, fractional reabsorption percentages (65% Na+ in PCT, water follows osmotic gradient in descending limb, active transport in ascending), countercurrent multiplication explained; steroidogenesis with compartmentalization (mitochondria to ER); teratogen dose-timing relationship with specific developmental events (organogenesis windows)Sequential description of urine formation without quantitative aspects; steroid pathway as list of conversions; teratogenesis as list without explaining why critical periods matterNo process logic—random facts assembled; confuses reabsorption with secretion; steroid synthesis described backwards; no understanding of developmental timing
Evolutionary / applied context20%10Evolutionary—nephron adaptation to terrestrial life (mammalian kidney vs fish pronephros/mesonephros); Henle's loop length correlating with habitat aridity; steroid hormone conservation across vertebrates; clinical—CKD epidemic in India (Uddanam nephropathy, Sri Lankan agricultural nephropathy), steroid therapeutics (hydrocortisone for Addison's, dexamethasone for preterm labor), national programs (Rashtriya Bal Swasthya Karyakram for birth defects)Brief mention of kidney evolution or clinical relevance without specifics; generic statement on steroid drugs; awareness of birth defects without program namesNo evolutionary or applied perspective; purely descriptive answer; irrelevant digressions into unrelated diseases

Practice this exact question

Write your answer, then get a detailed evaluation from our AI trained on UPSC's answer-writing standards. Free first evaluation — no signup needed to start.

Evaluate my answer →

More from Zoology 2024 Paper II