Q1
Answer the following in about 150 words each: (a) Describe the structure and functions of cyphellae and cephalodia in lichens. (b) What are prions? How are these different from viroids? How are prions transmitted? (c) Explain the structure of sporangiophore and dehiscence of sporangium of Rhizopus. (d) Enumerate the merits and demerits of numerical taxonomy. (e) Briefly discuss the distribution of gymnosperms in India.
हिंदी में प्रश्न पढ़ें
निम्नलिखित में से प्रत्येक का लगभग 150 शब्दों में उत्तर दीजिए : (a) लाइकेन के सिफेली (उपदर्श) व सिफेलोडिया की संरचना एवं कार्य का वर्णन कीजिए। (b) प्रायोन क्या हैं? ये वायरोइड से किस प्रकार भिन्न हैं? प्रायोन किस तरह से प्रसारित होते हैं? (c) राइजोपस के बीजाणुधानीधर की संरचना तथा बीजाणुधानी के स्फुटन का वर्णन कीजिए। (d) संख्याविषयक वर्गीकरण-विज्ञान के गुण व दोषों की परिगणना कीजिए। (e) भारत में अनावृतबीजी के वितरण का संक्षिप्त वर्णन कीजिए।
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.
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How this answer will be evaluated
Approach
This multi-part question requires approximately 30 words per sub-part (150 words total). Begin with (a) cyphellae/cephalodia structure-function in 25-30 words, then (b) prions vs viroids with transmission in 30 words, (c) Rhizopus sporangiophore and dehiscence in 25-30 words, (d) numerical taxonomy merits-demerits in 30 words, and (e) Indian gymnosperm distribution in 25-30 words. Prioritize precise terminology over elaboration; use diagrams for (a) and (c) if space permits.
Key points expected
- (a) Cyphellae: cup-shaped depressions on lower thallus surface for gas exchange; Cephalodia: gall-like structures containing Nostoc for nitrogen fixation in tripartite lichens like Peltigera aphthosa
- (b) Prions: infectious misfolded proteins (PrP^Sc) causing TSEs; differ from viroids (naked ssRNA, plant pathogens) in being protein-only, host-encoded, and mammalian pathogens; transmitted via ingestion of infected tissue, iatrogenic routes, or genetic mutation
- (c) Sporangiophore: unbranched, aerial hypha with swollen columella and apical sporangium; dehiscence by dissolution of deliquescent wall releasing sporangiospores
- (d) Merits: objectivity, computer-assisted analysis, phenetic relationships; Demerits: equal weighting of characters, ignores evolutionary history, operational taxonomic units may be artificial
- (e) Indian gymnosperms: Western Himalayas (Cedrus deodara, Pinus roxburghii), Eastern Himalayas (Abies spectabilis), Nilgiris (Podocarpus), Khasi Hills (Gnetum), with endemic Ginkgo biloba cultivation
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 25% | 12.5 | Accurately distinguishes cyphellae from cephalodia; correctly identifies prions as proteinaceous infectious particles without nucleic acid; precisely describes columella function in Rhizopus; understands phenetic vs cladistic approaches in numerical taxonomy; correctly maps gymnosperm distribution to Himalayan and Peninsular regions | Basic definitions correct but confuses cyphellae with apothecia or cephalodia with isidia; describes prions vaguely without contrasting with viroids; mentions sporangiophore but omits columella; lists merits/demerits superficially; general Himalayan mention without specificity | Fundamental errors like calling cephalodia reproductive structures, describing prions as viruses, confusing sporangiophore with conidiophore, or placing gymnosperms in Gangetic plains |
| Diagram / labelling | 15% | 7.5 | Clear labeled diagrams for (a) showing thallus cross-section with cyphellae and cephalodia positions, and for (c) depicting sporangiophore with columella, sporangium wall layers, and spore release; uses standard botanical conventions | Rough sketches without proper labeling or missing key structures like columella; diagrams present but anatomical details incorrect | No diagrams despite structural questions; or diagrams completely misrepresenting the morphology (e.g., showing asci in Rhizopus) |
| Examples & nomenclature | 20% | 10 | Cites specific lichens (Peltigera, Nephroma) for cephalodia; names prion diseases (CJD, kuru, BSE); mentions correct Rhizopus species (R. stolonifer); references Indian gymnosperm hotspots (Nanda Devi Biosphere, Silent Valley) with species like Pinus wallichiana, Taxus baccata | Generic examples without species names; mentions 'mad cow disease' without BSE; 'some Rhizopus'; vague 'Himalayan region' without specific areas | No valid examples; invents non-existent species or misattributes examples (e.g., placing Sequoia in India naturally) |
| Process explanation | 25% | 12.5 | Explains nitrogen fixation mechanism in cephalodia (Nostoc heterocysts); details prion conformational change (PrP^C to PrP^Sc) and propagation; describes precise enzymatic dissolution of sporangium wall and columella collapse mechanism; explains OTU clustering and phenetic distance calculation; correlates gymnosperm distribution with orographic rainfall and altitude | States processes occur without mechanistic detail; 'gas exchange happens' or 'spores are released' without explaining how; mentions computers used without explaining algorithms | No process explanation; confuses cause and effect (e.g., cyphellae cause nitrogen fixation); describes completely wrong mechanisms |
| Application / ecology | 15% | 7.5 | Links cephalodia to ecosystem nitrogen input in boreal forests; discusses prion surveillance in Indian livestock; connects Rhizopus to industrial fermentation and food spoilage; notes numerical taxonomy in biodiversity informatics; emphasizes gymnosperm conservation status (IUCN Red List) and climate vulnerability in Himalayas | Superficial mention of ecological roles without specific applications; generic 'important for ecosystem' statements | No applied or ecological context; or completely inappropriate applications (e.g., suggesting prions as biocontrol agents) |
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