Q6
(a) Differentiate between enzymes and coenzymes and describe their mechanisms of action. (10+10=20 marks) (b) Define secondary metabolites. Discuss the importance of secondary metabolites to plants. (5+10=15 marks) (c) What is phloem ? Describe the various hypotheses concerning transportation in phloem. (5+10=15 marks)
हिंदी में प्रश्न पढ़ें
(a) प्रकिण्व (एंजाइम्स) और सहप्रकिण्व (कोएंजाइम्स) में भेद कीजिए और उनकी क्रियाविधि का वर्णन कीजिए । (10+10=20 अंक) (b) द्वितीयक उपापचयज को परिभाषित करें । द्वितीयक मेटाबोलाइट्स का पौधों के लिए क्या महत्व है । (5+10=15 अंक) (c) पोषवाह क्या है ? फ्लोएम में परिवहन से संबंधित विभिन्न परिकल्पनाओं का वर्णन कीजिए । (5+10=15 अंक)
Directive word: Differentiate
This question asks you to differentiate. 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 'differentiate' in part (a) demands clear contrastive analysis, while 'describe' in parts (a) and (c) and 'discuss' in part (b) require explanatory depth. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure as: brief comparative introduction for enzymes vs coenzymes, detailed mechanism descriptions with diagrams, definition and ecological significance of secondary metabolites with Indian examples, and systematic evaluation of phloem transport hypotheses with concluding synthesis on assimilate movement.
Key points expected
- Clear differentiation between enzymes (protein catalysts) and coenzymes (non-protein organic cofactors) with structural and functional distinctions for part (a)
- Mechanism of enzyme action: lock-and-key vs induced fit, activation energy reduction, active site specificity; coenzyme mechanisms: electron/proton transfer, group transfer reactions (NAD+, FAD, CoA) for part (a)
- Definition of secondary metabolites (not essential for growth/development, species-specific) and their classification into terpenoids, phenolics, alkaloids with Indian examples (neem azadirachtin, turmeric curcumin, opium alkaloids) for part (b)
- Ecological importance: defense against herbivores/pathogens, UV protection, pollinator attraction, allelopathy, nitrogen storage; economic importance for pharmaceuticals, agriculture for part (b)
- Phloem structure: sieve elements, companion cells, phloem parenchyma; definition as food-conducting tissue for part (c)
- Critical evaluation of transport hypotheses: Münch pressure flow (most accepted), electro-osmotic, cytoplasmic streaming, contractile proteins, surface tension; evidence for and against each with experimental support for part (c)
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 22% | 11 | Precise definitions distinguishing enzymes as protein catalysts from coenzymes as organic cofactors; accurate classification of secondary metabolites; correct phloem anatomy and critical evaluation of transport hypotheses with recognition of Münch theory's dominance | Generally correct definitions with minor errors in enzyme-coenzyme distinction; acceptable secondary metabolite classification; basic phloem structure with superficial or partially incorrect hypothesis coverage | Confusion between enzymes and coenzymes (e.g., calling coenzymes enzymes); incorrect definition of secondary metabolites; fundamental errors in phloem structure or transport mechanisms |
| Diagram / labelling | 18% | 9 | Clear diagrams for enzyme-substrate complex showing active site geometry; phloem tissue organization with sieve tube elements and companion cells; Münch pressure flow model diagram with source-sink gradient; proper labelling and integration with text | Basic diagrams present but lacking detail or partially mislabelled; generic representations without specific structural features; diagrams mentioned but not drawn | Missing or incorrect diagrams; no attempt to illustrate enzyme mechanism, phloem structure, or pressure flow model; diagrams contradict textual description |
| Examples & nomenclature | 18% | 9 | Specific coenzymes named (NAD+, FAD, CoA, TPP, PLP) with functions; Indian secondary metabolite examples (neem azadirachtin, turmeric curcumin, ashwagandha withanolides, cinchona quinine); correct biochemical nomenclature throughout | Some coenzymes named without functions; generic or non-Indian secondary metabolite examples; minor nomenclature errors | No specific coenzyme examples; missing or incorrect secondary metabolite examples; confused nomenclature (e.g., mixing cofactors and prosthetic groups) |
| Process explanation | 22% | 11 | Detailed enzyme catalytic mechanism (ES complex formation, transition state stabilization, product release); coenzyme participation in redox/group transfer; biosynthetic pathways for secondary metabolites (acetate-malonate, shikimate, mevalonate); stepwise evaluation of phloem loading, transport, and unloading mechanisms | General description of enzyme action without mechanistic detail; superficial coverage of secondary metabolite biosynthesis; basic pressure flow description without loading/unloading details | Vague or incorrect mechanistic descriptions; no explanation of how coenzymes function; missing process details for phloem transport; confused pathway descriptions |
| Application / ecology | 20% | 10 | Comprehensive ecological functions: secondary metabolites in plant-herbivore coevolution, antimicrobial defense, pollinator syndromes, allelopathy in Indian agroecosystems; agricultural and pharmaceutical applications; phloem transport relevance to crop productivity, grafting, phloem-feeding pest management | Some ecological roles mentioned without elaboration; limited application context; generic statements about economic importance | Missing ecological significance entirely; no application context; failure to connect basic concepts to plant fitness or human utility |
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