Q5
Write on the following in about 150 words each : 10×5=50 (a) Block to polyspermy (10 marks) (b) Fate map of frog embryo (10 marks) (c) Activation energy based mechanism of enzyme action (10 marks) (d) Structure of dipeptide unit of a protein (10 marks) (e) Transmission of nerve impulse through synapse (10 marks)
हिंदी में प्रश्न पढ़ें
निम्नलिखित प्रत्येक पर लगभग 150 शब्दों में लिखिए : 10×5=50 (a) बहुशुक्राणुता का बाधित होना (10 अंक) (b) मेंढक भ्रूण का नियति मानचित्र (10 अंक) (c) एन्जाइम क्रिया की सक्रियण ऊर्जा आधारित क्रियाविधि (10 अंक) (d) प्रोटीन के एक डाई-पेप्टाइड इकाई की संरचना (10 अंक) (e) तंत्रिका आवेग का अंतर्प्रेरणी संचरण (10 अंक)
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 'write on' demands descriptive coverage with precise terminology across all five embryology, biochemistry and neurophysiology topics. Allocate approximately 30 words per sub-part (150 words total), spending roughly equal time on each since all carry equal marks. Structure each part as: definition → mechanism/structure → functional significance. For (a) and (e), emphasize sequential steps; for (b) and (d), prioritize accurate diagrams with labelling; for (c), focus on energy profile curves and transition state theory.
Key points expected
- (a) Block to polyspermy: Fast electrical block (depolarization of egg membrane) and slow permanent block (cortical granule exocytosis → zona pellucida modification/hardening); mention species-specific variations in amphibians vs mammals
- (b) Fate map of frog embryo: Presumptive germ layers on blastula surface (ectoderm—animal pole, mesoderm—marginal zone, endoderm—vegetal pole); reference Vogt's vital staining experiments; significance for developmental patterning
- (c) Activation energy mechanism: Enzyme lowers activation energy (Ea) by stabilizing transition state; Michaelis-Menten kinetics relevance; energy profile diagram showing uncatalyzed vs catalyzed reaction pathways
- (d) Dipeptide unit structure: Peptide bond formation (condensation/dehydration synthesis); planar trans configuration; phi and psi angles; Ramachandran plot constraints; partial double bond character restricting rotation
- (e) Synaptic transmission: Electrical vs chemical synapses; neurotransmitter release (Ca²⁺-dependent exocytosis), postsynaptic receptor binding, EPSP/IPSP generation; synaptic delay and one-way conduction
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 25% | 12.5 | Accurately describes fast and slow blocks to polyspermy with correct ionic basis; correctly identifies presumptive fates in frog fate map; properly explains transition state stabilization; accurately depicts peptide bond planarity; correctly sequences synaptic vesicle release and neurotransmitter action | Identifies major concepts with minor errors (e.g., confusing cortical reaction with acrosome reaction, or misplacing germ layer fates); vague on activation energy reduction mechanism; basic peptide bond description without stereochemical constraints | Fundamental misconceptions (e.g., polyspermy block as solely electrical, or dipeptide confused with disaccharide); incorrect synaptic directionality; conflates activation energy with free energy change |
| Diagram / labelling | 20% | 10 | Clean, proportionate diagrams for (b) frog blastula fate map with animal-vegetal axis and germ layer territories, and (d) dipeptide showing planar peptide linkage with correct bond angles; energy profile curve for (c) with labelled Ea and ΔG; synaptic structure for (e) with pre/post-synaptic elements | Rough sketches with partial labelling; missing key structural details (e.g., no indication of peptide bond planarity, or fate map without marginal zone demarcation); diagrams present but not integrated with text | Absent or irrelevant diagrams; diagrams without labels; confused representation (e.g., chemical synapse drawn like electrical synapse, or peptide bond showing free rotation) |
| Examples & nomenclature | 15% | 7.5 | Uses precise terminology: cortical granules, perivitelline space, zona pellucida/hardening; Vogt, Spemann-Mangold organizer; transition state, ground state, Michaelis complex; Ramachandran plot, phi/psi angles; synaptic cleft, SNARE proteins, ligand-gated channels; mentions Indian research (e.g., S. Chandrasekhar's work on amphibian development) | Generally correct terminology with occasional imprecision (e.g., 'enzyme fits substrate' instead of 'stabilizes transition state'); generic references without specific names; misses key eponyms | Incorrect or missing technical terms; invented nomenclature; confuses related concepts (e.g., acrosome reaction with cortical reaction, or EPSP with action potential) |
| Process explanation | 25% | 12.5 | Clear sequential logic: for (a) immediate depolarization followed by cortical granule cascade; for (b) how fate maps predict cell lineage; for (c) stepwise energy barrier reduction; for (d) condensation reaction mechanism; for (e) Ca²⁺ influx → vesicle fusion → neurotransmitter diffusion → receptor activation → postsynaptic potential | Describes processes in correct order but lacks causal connectors; mentions steps without explaining how they link; some processes incomplete (e.g., describes neurotransmitter release but not receptor consequence) | Disordered or missing steps; no indication of temporal sequence; describes structures without explaining dynamic processes; confuses cause and effect relationships |
| Evolutionary / applied context | 15% | 7.5 | Notes evolutionary significance: polyspermy block ensures diploidy maintenance; fate maps demonstrate developmental conservation across vertebrates; enzyme catalysis as evolutionary optimization of metabolic efficiency; peptide bond universality in life; synaptic plasticity as basis for learning; mentions clinical relevance (e.g., neurotransmitter-targeted drugs, enzyme inhibitors in therapy) | Brief mention of significance without elaboration; generic statements about 'importance in biology'; misses specific evolutionary or applied connections | No contextual framing; treats topics as isolated facts; misses why these mechanisms matter for organismal fitness or biomedical application |
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