Zoology 2021 Paper I 50 marks Describe

Q3

(a) What is hypothalamo-pituitary axis? Draw a well-labelled diagram of pituitary gland and describe the functions of its hormones. (20 marks) (b) Define nephridium. Describe the various types of nephridia found in Pheretima. (15 marks) (c) Describe the respiratory organs and mechanism of respiration in Pila. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) हाइपोथैलेमो-पिट्यूटरी अक्ष क्या है? पीयूष (पिट्यूटरी) ग्रंथि का एक नामांकित चित्र बनाइए और इसके हार्मोनों के कार्यों का वर्णन कीजिए। (20 अंक) (b) वृक्क नलिका (नेफ्रिडियम) को परिभाषित कीजिए। फेरेटिमा में पाई जाने वाली विभिन्न प्रकार की वृक्क नलिकाओं (नेफ्रिडिया) का वर्णन कीजिए। (15 अंक) (c) पाइला में श्वसन अंगों और श्वसन की क्रियाविधि 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, structured exposition of structures and processes 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 introduction defining the hypothalamo-pituitary axis; body with well-labelled diagram of pituitary, followed by sequential treatment of nephridia in Pheretima and respiratory organs in Pila; conclude with functional integration of these systems in organismal physiology.

Key points expected

  • Part (a): Definition of hypothalamo-pituitary axis as functional and anatomical connection between hypothalamus and pituitary; portal hypophyseal system; neurosecretory cells
  • Part (a): Diagram showing pituitary lobes (adenohypophysis: pars distalis, pars intermedia, pars tuberalis; neurohypophysis: pars nervosa, infundibulum), correct labelling of hormones
  • Part (a): Functions of anterior pituitary hormones (GH, TSH, ACTH, FSH, LH, PRL) and posterior pituitary hormones (ADH, oxytocin) with their target organs
  • Part (b): Definition of nephridium as coelomic excretory organ; three types in Pheretima: septal/pharyngeal, integumentary, and enteronephric nephridia with structural differences
  • Part (b): Structural details: funnel-shaped nephrostome, ciliated canals, terminal duct; functional distinction between enteronephric (excrete into gut) and other types
  • Part (c): Respiratory organs in Pila: mantle cavity with gill (ctenidium) in aquatic phase, lung (pulmonary sac) in terrestrial phase; operculum and epiphragm
  • Part (c): Mechanism: aquatic respiration via ctenidial filament blood flow; aerial respiration via lung with vascularized wall; rhythmic opening/closing of pneumostome
  • Part (c): Adaptation significance: amphibious lifestyle, estivation/aestivation physiology, evolutionary transition from marine to freshwater to terrestrial habitats

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately defines hypothalamo-pituitary axis with portal circulation; correctly identifies all three nephridial types in Pheretima with their locations; precisely describes bimodal respiration in Pila including gill-to-lung transition; no factual errors in hormone targets or nephridial anatomyBasic definition of axis present but portal system details vague; identifies 2/3 nephridial types with minor anatomical errors; describes both respiratory organs but confuses mechanisms; some hormone functions misattributed to wrong lobesConfuses hypothalamo-pituitary with other axes; fails to distinguish nephridial types or describes non-existent types; conflates gill and lung function; major errors in hormone secretion sites (e.g., claims posterior pituitary synthesizes hormones)
Diagram / labelling18%9Clear, proportionate pituitary diagram with all lobes, portal vessels, and hypothalamic connections labelled; includes directional arrows for hormone transport; may include supplementary sketches for nephridial funnel or Pila mantle cavity cross-sectionDiagram present with major structures identifiable but some labels missing or misplaced (e.g., pars tuberalis unlabelled); portal system indicated but not clearly distinguished from general circulation; adequate but not exemplary presentationDiagram absent or unrecognizable; labels scattered without structure identification; no indication of vascular connections; messy or disproportionate drawing that impedes understanding
Examples & nomenclature16%8Uses correct zoological nomenclature: *Pheretima posthuma* (or *Pheretima* spp.), *Pila globosa*; employs precise terms like 'nephrostome', 'enteronephric', 'ctenidium', 'pneumostome', 'infundibulum', 'adenohypophysis/neurohypophysis'; cites Indian species contextUses generic common names interchangeably with scientific names; some terminology correct but inconsistent (e.g., 'earthworm' without genus, 'lung' instead of pulmonary sac); minor spelling errors in technical termsNo scientific names used; incorrect terminology (e.g., 'kidney' for nephridium, 'trachea' for Pila respiration); misspelled or invented terms; confuses *Pheretima* with *Lumbricus* or other genera
Process explanation22%11For (a): explains hypothalamic releasing/inhibiting hormones → portal system → adenohypophysis cascade; for (b): details ciliary action in nephridial filtration, enteronephric vs. exonephric excretion pathways; for (c): describes rhythmic mantle cavity ventilation, counter-current exchange in ctenidium, air-blood barrier in lungLists hormone functions without explaining regulatory cascade; describes nephridial structure without explaining urine formation or reabsorption; mentions both aquatic and aerial respiration but lacks mechanistic detail on transition between modesStatic description only—no processes explained; confuses secretion with synthesis for pituitary; cannot explain how nephridia actually function; describes Pila as having 'breathing' without anatomical mechanism
Evolutionary / applied context22%11For (a): mentions clinical relevance (diabetes insipidus, gigantism/dwarfism, hypopituitarism); for (b): relates enteronephric condition to water conservation in terrestrial annelids; for (c): discusses Pila as model for molluscan terrestrialization, parallels with pulmonary gastropod evolution, bioindicator value in Indian freshwater ecosystemsBrief mention of human relevance for pituitary without elaboration; notes Pheretima's soil habitat without evolutionary insight; mentions Pila's amphibious nature as 'adaptation' without evolutionary contextNo applied or evolutionary context provided; treats all three parts as isolated factual recall; misses opportunity to connect endocrine regulation with excretory/osmoregulatory integration

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