Botany 2025 Paper II 50 marks Explain

Q8

(a) Define biodiversity. Explain the various ex situ and in situ methods of conserving biodiversity. (20 marks) (b) What are phytohormones? Briefly discuss the role of auxin in plant growth and development. Explain its mechanism of action. (15 marks) (c) Describe the various types of tropic movements in plants. Discuss their mechanism. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) जैव विविधता की परिभाषा दीजिए। जैव विविधता संरक्षण के विभिन्न बाह्य-स्थाने (एक्स सिटु) तथा स्व-स्थाने (इन सिटु) तरीकों की व्याख्या कीजिए। (20 अंक) (b) पादप हार्मोन क्या हैं? पौधों की वृद्धि एवं विकास में ऑक्सिन की भूमिका की संक्षेप में विवेचना कीजिए। इसकी क्रियाविधि को समझाइए। (15 अंक) (c) पौधों में विभिन्न प्रकार की अनुवर्ती गतियों (ट्रॉपिक मूवमेंट) का वर्णन कीजिए। उनकी क्रियाविधि पर विवेचना कीजिए। (15 अंक)

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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.

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How this answer will be evaluated

Approach

The directive 'explain' demands clear, logical exposition with cause-effect linkages. Structure: brief unified introduction defining biodiversity and phytohormones; body section (a) 40% word budget covering genetic/species/ecosystem diversity with detailed conservation methods including Indian initiatives like Project Tiger and cryopreservation at NBPGR; section (b) 30% on auxin biosynthesis, polar transport, and molecular mechanism via TIR1-Aux/IAA-SCF ubiquitin pathway; section (c) 30% on phototropism, geotropism, thigmotropism, chemotropism with Cholodny-Went model; conclude with integrated reflection on conservation-physiology linkages.

Key points expected

  • (a) Precise definition of biodiversity encompassing genetic, species and ecosystem levels with hierarchical organization
  • (a) Comprehensive coverage of in situ methods: protected areas (national parks, wildlife sanctuaries, biosphere reserves), sacred groves, community reserves with Indian examples like Nilgiri Biosphere Reserve
  • (a) Comprehensive coverage of ex situ methods: seed banks, field gene banks, in vitro conservation, cryopreservation, botanic gardens, zoos with institutions like NBPGR, FRLHT, Kew
  • (b) Definition of phytohormones as organic compounds regulating growth at low concentrations, distinguishing from nutrients
  • (b) Auxin roles: cell elongation, apical dominance, root initiation, vascular differentiation, fruit development with IAA, IBA, NAA, 2,4-D specifics
  • (b) Mechanism: polar transport via PIN proteins, acid growth hypothesis, and molecular pathway involving auxin receptor TIR1, ubiquitination of Aux/IAA repressors, ARF transcription factors
  • (c) Tropic movements: phototropism (blue light receptor phototropins), geotropism (starch-statolith hypothesis), thigmotropism (tendril coiling), chemotropism (pollen tube growth), hydrotropism
  • (c) Mechanistic explanations: Cholodny-Went model for phototropism, differential auxin distribution, calcium signaling, cytoskeletal reorganization

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately defines biodiversity with three hierarchical levels; correctly distinguishes in situ from ex situ; precisely defines phytohormones; accurately describes auxin transport (PIN-mediated polar transport) and signal transduction (SCF-TIR1-Aux/IAA-ARF pathway); correctly identifies tropic stimuli and responses without conflating tropism with nastic movementsBasic definitions correct but misses one level of biodiversity hierarchy; confuses some conservation categories; auxin mechanism oversimplified to 'acid growth' only; tropism descriptions generic without specifying receptors or signal componentsIncorrect definition of biodiversity (confused with ecosystem services); conflates in situ and ex situ methods; describes auxin only as 'growth promoter' without mechanism; confuses tropic with nastic movements; fundamental conceptual errors
Diagram / labelling18%9Clear labeled diagrams: (a) biodiversity hierarchy pyramid or conservation strategy flowchart; (b) auxin transport cell-to-cell showing PIN localization and efflux/influx carriers, OR mechanism showing TIR1-Aux/IAA-ARF interaction; (c) Cholodny-Went model with coleoptile tip removal/replacement experiment OR statolith repositioning in root cap; all diagrams fully labeled with structures and directional arrowsOne or two relevant diagrams present but labels incomplete; missing directional arrows for auxin transport; tropism diagram shows bending without cellular mechanism; diagrams support text but lack precisionNo diagrams or irrelevant sketches; diagrams without labels; copies from question without elaboration; diagrams contradict textual explanation
Examples & nomenclature18%9Specific Indian examples: for (a) names 4+ protected areas (Jim Corbett, Kaziranga, Sundarbans, Nanda Devi), NBPGR, FRLHT, sacred groves of Meghalaya; for (b) natural auxins (IAA, IBA) vs synthetic (NAA, 2,4-D) with applications; for (c) specific plant examples (Helianthus phototropism, Pisum geotropism, Cuscuta thigmotropism, lily pollen chemotropism); correct chemical nomenclature throughoutSome Indian examples mentioned but generic (only 'national parks' without naming); auxin examples limited to IAA; tropism examples common (sunflower, pea) without specificity; minor nomenclature errorsNo Indian examples; only foreign examples cited; confuses auxin with gibberellin or cytokinin examples; incorrect chemical names; no specific plant species mentioned for tropisms
Process explanation22%11Stepwise mechanistic clarity: (a) how in situ maintains evolutionary processes vs ex situ's genetic drift risks; (b) detailed auxin mechanism from biosynthesis (tryptophan-dependent pathways) through polar transport (AUX1 influx, PIN efflux) to signal transduction (ubiquitin-proteasome, transcriptional response); (c) precise cellular mechanisms: phototropin autophosphorylation, NPH3/RPT2, differential growth; statolith sedimentation triggering auxin redistribution; actin-microtubule dynamics in thigmotropismProcesses described in sequence but missing key molecular components; auxin mechanism stops at acid growth hypothesis; tropism explains 'bending toward light' without cellular basis; some steps logically connected but gaps evidentNo process explanation—only lists types; confused sequence of events; describes outcomes without causes; contradictory explanations across sub-parts
Application / ecology20%10Integrates conservation significance: (a) ecosystem services, climate resilience, sustainable development goals; critiques ex situ limitations (genetic erosion, cost); (b) auxin applications in agriculture—rooting hormones, herbicides (2,4-D), fruit setting, tissue culture; (c) ecological significance of tropisms—canopy competition avoidance, root foraging efficiency, pollination success; connects to crop improvement and ecosystem functionMentions applications superficially; conservation importance stated without ecological reasoning; auxin applications limited to 'rooting powder'; tropism significance as 'survival' without elaboration; weak integration across sub-partsNo application or ecological context; purely descriptive with no relevance to agriculture, conservation policy, or ecosystem dynamics; misses opportunity to connect biodiversity loss with hormonal stress responses

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