Botany 2021 Paper II 50 marks Compulsory Write short notes

Q1

Write short notes on the following : 10×5=50 (a) Cell adhesion molecules 10 (b) Ribosomal RNA processing in nucleolus 10 (c) Genetic consequences of Inversion 10 (d) Gene silencing 10 (e) Use of apomixis in plant breeding 10

हिंदी में प्रश्न पढ़ें

निम्नलिखित पर संक्षिप्त टिप्पणियाँ लिखिए : 10×5=50 (a) कोशिका आसंजन अणु 10 (b) राइबोसोमल आर.एन.ए. का केन्द्रक में प्रसंस्करण 10 (c) प्रतिलोमन के आनुवंशिक परिणाम 10 (d) जीन साइलेंसिंग 10 (e) पादप प्रजनन में असंगजन का उपयोग 10

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Directive word: Write short notes

This question asks you to write short notes. 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 'write short notes' demands concise, information-dense responses for each sub-part without elaborate introductions. Allocate approximately equal time and space (~150-180 words each) across all five parts since each carries equal marks. Structure each note with a precise definition, followed by key features, mechanism/process, and one relevant application or significance. No conclusion is needed; end each sub-part with its practical or evolutionary significance. Prioritize accuracy over elaboration.

Key points expected

  • (a) Cell adhesion molecules: Definition and major families (cadherins, integrins, selectins, immunoglobulin superfamily); their role in cell-cell and cell-ECM adhesion; importance in tissue morphogenesis and plant cell wall adhesion via plasmodesmata-associated proteins
  • (b) Ribosomal RNA processing in nucleolus: Organization of nucleolus (fibrillar center, dense fibrillar component, granular component); rRNA transcription by RNA Pol I; 45S pre-rRNA processing steps; assembly of 40S and 60S subunits; role of snoRNPs in methylation and pseudouridylation
  • (c) Genetic consequences of Inversion: Types of inversions (paracentric vs. pericentric); formation of inversion loops during pairing; reduced recombination in heterozygotes; position effects on gene expression; role in chromosomal evolution and speciation (e.g., Drosophila pseudoobscura)
  • (d) Gene silencing: Mechanisms including RNA interference (RNAi), transcriptional gene silencing (TGS), post-transcriptional gene silencing (PTGS); Dicer and RISC complex; epigenetic modifications; applications in functional genomics and crop improvement
  • (e) Use of apomixis in plant breeding: Types of apomixis (gametophytic and sporophytic); fixation of heterosis through apomixis; challenges (poor seed set, linkage with undesirable traits); examples from Pennisetum, Panicum; potential for hybrid variety development in rice and wheat

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Demonstrates precise understanding across all five sub-parts: correctly identifies CAMs as transmembrane proteins, distinguishes 45S/5S rRNA pathways, differentiates paracentric vs. pericentric inversions accurately, correctly describes siRNA/miRNA pathways in gene silencing, and accurately defines apomixis types without confusing with parthenogenesisShows generally correct concepts with minor errors: vague on CAM families, confuses some rRNA processing steps, mixes inversion types occasionally, oversimplifies gene silencing mechanisms, or conflates apomixis with vegetative propagationContains fundamental errors: describes CAMs as only extracellular matrix proteins, confuses nucleolus with nucleoplasm functions, fails to distinguish inversion types, describes gene silencing only as mutation, or defines apomixis incorrectly as self-pollination
Diagram / labelling15%7.5Includes at least 3 clear, well-labelled diagrams: nucleolus ultrastructure with FC/DFC/GC zones; inversion loop showing crossing-over pattern; and RNAi pathway with Dicer/RISC components; labels are precise and anatomically correctProvides 1-2 diagrams with basic labelling; diagrams are recognizable but lack detail (e.g., nucleolus shown without sub-compartments, simple inversion loop without chiasma positions); some labels missing or misplacedNo diagrams or very poorly drawn sketches; diagrams lack essential labels or show incorrect structures (e.g., showing mRNA instead of pre-rRNA in nucleolus, confusing inversion with translocation)
Examples & nomenclature20%10Uses specific nomenclature throughout: names CAM families (E-cadherin, α/β-integrins), cites snoRNPs (U3, U8), mentions specific inversions (In(2L)t in Drosophila), names RNAi components (Argonaute, Dicer), and cites Indian crop examples (Pennisetum squamulatum, ICRISAT breeding programs)Uses some correct terminology but lacks specificity: mentions 'cell adhesion proteins' without family names, refers to 'snoRNAs' generally, names Drosophila for inversion but not specific rearrangement, describes 'RNA interference' without component names, mentions apomictic grasses without speciesUses incorrect or no nomenclature: invents terms like 'cell glue proteins', confuses snoRNPs with snRNPs, no specific inversion examples, describes gene silencing only as 'gene blocking', no crop or species examples for apomixis
Process explanation25%12.5Explains dynamic processes with correct sequence: CAM-mediated signaling cascade; ordered 45S→18S,5.8S,28S processing with cleavage sites; stepwise inversion loop formation with recombination consequences; RNAi pathway from dsRNA to mRNA cleavage; apomictic embryo sac development bypassing meiosisDescribes processes in correct general order but lacks mechanistic detail; mentions rRNA processing without cleavage order, describes inversion effects without loop mechanics, outlines gene silencing without RISC action, sketches apomixis without developmental stagesProcesses confused or absent: describes CAMs only structurally, lists nucleolar components without processing sequence, cannot explain how inversion suppresses recombination, describes gene silencing as random mutation, no developmental explanation of apomixis
Application / ecology15%7.5Connects to practical significance: CAMs in cancer metastasis and plant grafting compatibility; rRNA processing defects in ribosomopathies; inversions in local adaptation and karyotype evolution; RNAi in crop protection (Bt cotton, papaya ringspot virus resistance) and functional genomics; apomixis for hybrid seed production and food security in IndiaMentions some applications superficially: notes CAMs in development, rRNA in protein synthesis generally, inversions in speciation vaguely, RNAi as 'useful tool', apomixis for 'cloning plants' without breeding contextNo practical connections or incorrect ones: CAMs only in cell structure, no disease relevance for rRNA processing, no evolutionary significance for inversions, no biotech applications for RNAi, describes apomixis only as 'asexual reproduction' without breeding value

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