Botany 2024 Paper II 50 marks Describe

Q7

(a) Define leaf senescence. Describe important physiological and biochemical changes taking place during this process. Comment upon the regulation of senescence by phytohormones. 20 (b) Describe the molecular organization of chloroplast ATP synthase. Explain its mechanism of action. 10+5=15 (c)(i) Discuss the causes, consequences and control of eutrophication. 8 (c)(ii) In present Indian scenario, explain the importance of biosphere reserves in bio-diversity conservation. 7

हिंदी में प्रश्न पढ़ें

(a) पत्ती जीर्णता को परिभाषित कीजिए । इस प्रक्रिया के दौरान होने वाले क्रियात्मक तथा जैवरासायनिक परिवर्तनों का वर्णन कीजिए । पादप हार्मोन द्वारा जीर्णता के विनियमन पर टिप्पणी कीजिए । 20 (b) हरित लवक (क्लोरोप्लास्ट) ATP synthase की आणविक संरचना का वर्णन कीजिए । इसकी कार्यविधि को स्पष्ट कीजिए । 10+5=15 (c)(i) यूट्रोफिकेशन के कारणों, परिणामों तथा नियंत्रण पर चर्चा कीजिए । 8 (c)(ii) वर्तमान भारतीय परिदृश्य में जैव विविधता संरक्षण में संरक्षित जीवमंडल की उपयोगिता को समझाइए । 7

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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 'describe' demands systematic, detailed exposition of structures, processes and mechanisms. Allocate approximately 40% of time/words to part (a) on leaf senescence (20 marks), 30% to part (b) on chloroplast ATP synthase (15 marks), and 30% to part (c) combining eutrophication and biosphere reserves (15 marks). Structure: begin with precise definitions for each sub-part, followed by detailed physiological/biochemical/molecular descriptions, then regulatory mechanisms and ecological applications, concluding with integrated conservation significance.

Key points expected

  • Part (a): Definition of leaf senescence as programmed cell death in leaves; physiological changes including chlorophyll degradation, protein hydrolysis, nutrient remobilization; biochemical markers like ROS accumulation, lipid peroxidation, enzyme activities (proteases, nucleases); phytohormonal regulation by ethylene and ABA (promoters) vs. cytokinins and auxins (inhibitors)
  • Part (b): Molecular organization of CF1CF0 complex—CF1 (α3β3γδε) catalytic head and CF0 (a, b, b', c-ring) membrane-embedded proton channel; mechanism involving proton-motive force, rotational catalysis, binding change mechanism with three catalytic sites (L, T, O conformations)
  • Part (c)(i): Eutrophication causes (agricultural runoff, sewage discharge, industrial effluents); consequences (algal blooms, hypoxia, biodiversity loss, fish kills); control measures (tertiary sewage treatment, buffer strips, biomanipulation, phosphorus removal)
  • Part (c)(ii): Indian biosphere reserves (Nilgiri, Sundarbans, Nanda Devi, Gulf of Mannar) as UNESCO MAB sites; importance in in-situ conservation, sustainable development, research and monitoring, protecting endemic species like lion-tailed macaque, Bengal tiger
  • Integration: Link senescence nutrient recycling to ecosystem productivity; connect ATP synthase bioenergetics to primary productivity sustaining aquatic and terrestrial food webs subject to eutrophication pressures

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately defines senescence as PCD distinct from necrosis; correctly identifies CF1CF0 subunit stoichiometry and rotary mechanism; precisely distinguishes oligotrophic vs. eutrophic conditions; correctly states UNESCO MAB designation criteria for Indian biosphere reservesBasic definitions correct but confuses senescence with aging generally; mixes mitochondrial and chloroplast ATP synthase features; oversimplifies eutrophification as merely 'pollution'; lists biosphere reserves without MAB contextFundamental errors like treating senescence as pathological death; incorrect subunit composition (e.g., missing c-ring stoichiometry); conflates eutrophication with thermal pollution; confuses biosphere reserves with national parks or zoos
Diagram / labelling18%9Draws detailed CF1CF0 complex with stalk (γ, δ, ε), peripheral stalk (b, b'), and c-ring (10-14 subunits) with proton flow arrows; includes catalytic site conformations; may include senescence-associated vacuole or chloroplast ultrastructure changesSimplified CF1CF0 sketch missing subunit labels or proton gradient indication; generic leaf cross-section without senescence-specific features; no diagrams for eutrophication or biosphere reserve zonationAbsent or incorrect diagrams; mislabels CF1 as membrane-bound or CF0 as extrinsic; diagrams unrelated to question content
Examples & nomenclature18%9Cites specific phytohormones (ethylene via EIN3/EIL1, cytokinin via ARR genes); names ATP synthase subunits (ATP1, ATP2, ATP4, ATP6, ATP9); identifies Indian eutrophic water bodies (Dal Lake, Hussain Sagar); specifies Nilgiri BR as first Indian MAB site (1986) with core-buffer-transition zonesGeneric hormone names without specific regulators; mentions 'F0F1' without chloroplast-specific CF designation; general reference to 'lakes' without Indian examples; lists biosphere reserves without establishment dates or zonesIncorrect nomenclature (e.g., 'F1F0 ATPase' for synthase); no Indian examples; confuses biosphere reserves with Project Tiger reserves or Ramsar sites
Process explanation22%11Elucidates senescence SAG gene activation, Rubisco degradation, chlorophyll catabolism via PAO pathway; explains chemiosmotic coupling, proton translocation, γ-subunit rotation, ATP synthesis stoichiometry (3H+/ATP); details eutrophication cascade from P/N loading to anoxia; explains BR zonation functioningLists changes without mechanistic linkage; describes ATP synthase as 'enzyme making ATP' without rotary catalysis; sequential but superficial eutrophication description; mentions BR zones without functional explanationNo mechanistic understanding; confuses ATP synthesis with hydrolysis; describes eutrophication as single-step process; no understanding of BR zonation concept
Application / ecology20%10Links senescence nutrient recycling to crop yield and stay-green varieties; connects ATP synthase efficiency to C3/C4 productivity and climate resilience; evaluates biomanipulation and constructed wetlands for eutrophication control; assesses BR effectiveness in landscape-level conservation with community participation (e.g., Pachmarhi BR)Mentions agricultural relevance without specific applications; notes photosynthesis importance generally; lists control measures without evaluation; states conservation importance without critical assessment of BR challengesNo applied or ecological perspective; purely descriptive without significance; no mention of management or conservation outcomes

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