Botany 2023 Paper II 50 marks Explain

Q7

(a) How can the reaction equilibria and reaction rates be explained by using free energy diagram in a simple enzymatic reaction ? 20 (b) Explain the following : 5+5=10 (i) Nitrate and nitrite reduction in the leaves of higher plants. 5 (ii) Protection of enzyme nitrogenase against oxygen and hydrogen damage. 5 (c) Comment on the following : 10+10=20 (i) Biosphere reserves 10 (ii) Red Data Book 10

हिंदी में प्रश्न पढ़ें

(a) एक साधारण एन्जाइमी अभिक्रिया में मुक्त ऊर्जा आरेख का उपयोग करके अभिक्रिया संतुलन और अभिक्रिया दरों को कैसे समझाया जा सकता है ? 20 (b) निम्नलिखित को समझाइए : 5+5=10 (i) उच्च पादपों की पत्तियों में नाइट्रेट और नाइट्राइट का अपचयन । 5 (ii) ऑक्सीजन और हाइड्रोजन क्षति के विरुद्ध एन्जाइम नाइट्रोजिनेज का संरक्षण । 5 (c) निम्नलिखित पर टिप्पणी कीजिए : 10+10=20 (i) जीवमंडल निचय 10 (ii) संकटग्रस्त जीव पुस्तिका 10

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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

Begin with a brief introduction linking enzymology, nitrogen metabolism and conservation biology. For part (a) carrying 20 marks, allocate approximately 40% of content—draw free energy diagrams showing substrate, transition state, enzyme-substrate complex and product with clear ΔG‡ and ΔG labels. For part (b) with 10 marks, spend ~20% covering nitrate reductase (NR) and nitrite reductase (NiR) pathways in leaves, then leghemoglobin and conformational protection mechanisms in nitrogenase. For part (c) with 20 marks, allocate ~40%—describe UNESCO MAB biosphere reserve structure (core, buffer, transition zones) with Indian examples like Nilgiri or Nanda Devi, and explain IUCN Red Data Book categories (CR, EN, VU, etc.) with Indian plant examples. Conclude by integrating how enzymatic efficiency, sustainable nitrogen fixation and conservation biology collectively address food security and biodiversity challenges.

Key points expected

  • Part (a): Free energy diagram showing uncatalyzed vs catalyzed reaction pathways with labeled activation energy (Ea or ΔG‡), transition state, enzyme-substrate complex (ES), and overall free energy change (ΔG); explanation of how enzymes lower activation energy without altering equilibrium constant (Keq)
  • Part (b)(i): Nitrate reduction pathway—nitrate reductase (NR, molybdenum-iron cofactor) converting NO₃⁻ to NO₂⁻ in cytosol; nitrite reductase (NiR, iron-sulfur center and siroheme) converting NO₂⁻ to NH₄⁺ in chloroplasts using reduced ferredoxin from photosynthesis
  • Part (b)(ii): Nitrogenase protection—leghemoglobin in root nodules (oxygen scavenging), respiratory protection (high respiration rate in bacteroids), conformational protection (Fe-protein conformational change), and heterocyst formation in cyanobacteria (thick cell wall, lack of PS-II)
  • Part (c)(i): Biosphere reserves—UNESCO MAB programme; zonation system (core, buffer, transition/manipulation zones); Indian examples (Nilgiri, Sunderbans, Nanda Devi, Gulf of Mannar); functions in conservation, research, education and sustainable development
  • Part (c)(ii): Red Data Book—IUCN publication; threat categories (Extinct, Extinct in Wild, Critically Endangered, Endangered, Vulnerable); Indian plant examples (Santalum album, Nepenthes khasiana, Saussurea obvallata/Brahma Kamal); significance for conservation prioritization and policy

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Accurately distinguishes ΔG‡ (activation energy) from ΔG (thermodynamic spontaneity); correctly states enzymes accelerate rates without changing Keq; precise about NR/NiR cofactors and cellular locations; accurate IUCN categories and biosphere reserve zonationBasic understanding of enzyme catalysis but confuses ΔG with ΔG‡; general description of nitrate reduction without cofactor specificity; knows Red Data Book exists but muddles threat categories; lists biosphere zones without functional clarityFundamental errors—claims enzymes alter equilibrium; states nitrite reductase operates in cytosol; conflates biosphere reserves with national parks or zoos; describes Red Data Book as listing only extinct species
Diagram / labelling20%10Clear free energy diagram with two curves (catalyzed/uncatalyzed), properly labeled axes (energy vs reaction coordinate), marked transition states, ES complex, products, with ΔG‡ and ΔG correctly indicated; may include nitrogenase structure or biosphere reserve zonation mapDiagram present but poorly labeled—missing ES complex or confusing activation energy with overall energy change; axes unlabeled or mislabeled; no attempt at structural diagrams for parts (b) or (c)No diagram despite explicit requirement in (a); or completely erroneous diagram showing enzymes increasing product energy; scribbled uninterpretable figures
Examples & nomenclature15%7.5Specific Indian biosphere reserves (Nilgiri, Nanda Devi, Gulf of Mannar); Indian Red Listed plants (Nepenthes khasiana, Saussurea obvallata, Santalum album); correct enzyme nomenclature (NR, NiR, nitrogenase Fe-Mo cofactor); mentions Meghalaya subtropical forests or Western Ghats endemismGeneric examples ('tiger reserve', 'some orchids'); vague references to 'northeast plants' without names; standard enzyme names without cofactor details; mentions India but no specific reservesNo Indian examples; foreign-only examples (Yellowstone, Amazon); incorrect plant names; confuses nitrogenase with nitrate reductase terminology
Process explanation25%12.5Stepwise electron flow in nitrate reduction (NADH→FAD→Mo→NO₃⁻; reduced ferredoxin→siroheme→NO₂⁻); detailed nitrogenase mechanism (Fe-protein reduces MoFe-protein, ATP hydrolysis, H₂ evolution as side reaction); logical progression through biosphere reserve functions and Red List assessment criteriaGeneral sequence described but missing electron donors/acceptors; knows nitrogenase is O₂-sensitive but unclear on protection mechanisms; descriptive about reserves without process logicNo coherent process—random facts listed; completely wrong biochemical pathway; describes biosphere reserves as 'places where animals are kept'
Application / ecology15%8Links enzymatic efficiency to agricultural productivity; connects biological nitrogen fixation to sustainable agriculture and reduced fertilizer use; integrates biosphere reserves with climate change mitigation and SDGs; discusses ex-situ conservation via Red Data Book informing seed banks (NBPGR) and protected area expansionBrief mention of 'agriculture important' or 'conservation needed'; superficial connection between nitrogen fixation and environment; no policy or practical integrationNo application or ecological context; purely theoretical treatment; or irrelevant digressions into unrelated environmental problems

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