Botany 2022 Paper II 50 marks Discuss

Q2

(a) Discuss the different processes by which solute moves across cell membrane. (10+10=20 marks) (b) What are B-chromosomes ? Describe their significance. (10+5=15 marks) (c) In a cross between pea plants with green and yellow coloured pods, the F₂ individual segregated into 787 green and 277 yellow pod coloured individuals. If you have to test that these results agree with the expected ratio 3 : 1, then apply Chi-square P = 5%. The control value of Chi-square at 0.05 for d_f = 2-1 = 1 is =3.84. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) विभिन्न प्रक्रियाओं की चर्चा करें जिनके द्वारा विलेय कोशिका झिल्ली के आर-पार गति करता है । (10+10=20 अंक) (b) बी-गुणसूत्र क्या हैं ? उनके महत्व का वर्णन करें । (10+5=15 अंक) (c) हरे और पीले रंग की फलियों वाले मटर के पौधों के बीच क्रॉस में F₂ पीढ़ी में 787 हरे और 277 पीले वाले रंग की पौधे बनते हैं । यदि आप को यह परीक्षण करना है कि ये परिणाम 3 : 1 के अपेक्षित अनुपात से मेल खाते हैं तो काई-स्क्वेयर P = 5% लागू करें । d_f = 2-1 = 1 के लिए 0.05 पर काई-स्क्वेयर का नियंत्रण मान 3.84 है । (15 अंक)

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Directive word: Discuss

This question asks you to discuss. 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 'discuss' demands a comprehensive, analytical treatment with balanced coverage across all three sub-parts. Allocate approximately 40% of time/words to part (a) on membrane transport (20 marks), and roughly 30% each to part (b) on B-chromosomes (15 marks) and part (c) on Chi-square analysis (15 marks). Structure with a brief introduction, then address each sub-part sequentially with clear sub-headings, ensuring part (c) includes complete step-by-step calculation with null hypothesis formulation, and conclude with integrated significance of these concepts in plant breeding and genetics research.

Key points expected

  • Part (a): Distinguish passive transport (simple diffusion, facilitated diffusion via channels and carriers, osmosis) from active transport (primary and secondary active transport, including Na⁺/K⁺-ATPase and proton pumps); include vesicular transport (endocytosis, exocytosis) and electrochemical gradient concepts
  • Part (a): Explain membrane structure relevance—fluid mosaic model, lipid bilayer properties, aquaporins, and the role of membrane potential in driving solute movement
  • Part (b): Define B-chromosomes as supernumerary, heterochromatic, non-essential chromosomes distinct from A-chromosomes; mention their occurrence in plants like maize, rye, and Indian species such as Coix and Plantago
  • Part (b): Elucidate significance—no phenotypic effect on viability but influence on recombination, nuclear volume, and evolutionary dynamics; mention their accumulation mechanisms and drive systems
  • Part (c): State null hypothesis (H₀: observed ratio fits 3:1), calculate expected values (green = 798, yellow = 266), compute Chi-square value using Σ(O-E)²/E, compare with tabulated value 3.84, and conclude regarding acceptance/rejection of H₀
  • Part (c): Demonstrate correct degrees of freedom calculation (n-1 = 1) and interpret P = 5% significance level appropriately in genetic context

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Accurately distinguishes all transport mechanisms with correct thermodynamic principles (ΔG, electrochemical gradients); precisely defines B-chromosomes with correct cytogenetic terminology; flawless Chi-square calculation with proper hypothesis formulation and correct arithmetic leading to valid conclusionBasic correct identification of transport types and B-chromosome definition; minor errors in gradient explanations or Chi-square calculation (wrong expected values or arithmetic mistakes) but correct final interpretationConfuses active and passive transport mechanisms; incorrect definition of B-chromosomes or confuses with sex chromosomes; major errors in Chi-square formula application, wrong degrees of freedom, or invalid statistical conclusion
Diagram / labelling18%9For (a): Clear labelled diagrams showing channel proteins, carrier proteins, Na⁺/K⁺ pump with conformational states, and vesicle formation; for (b): Karyotype sketch distinguishing A and B chromosomes; for (c): Well-structured calculation table with observed, expected, deviation columnsBasic diagrams for membrane transport with some labels missing; simple B-chromosome representation; calculation presented without proper tabular formatNo diagrams where essential (membrane transport); poorly drawn or unlabelled sketches; calculation without any tabular presentation
Examples & nomenclature16%8Cites specific examples: aquaporins (PIP family in plants), GLUT carriers, proton pumps in plant tonoplast; mentions B-chromosomes in maize, rye, Coix lacryma-jobi (Indian example), Plantago; uses precise genetic symbols and standard statistical notation (χ², df, p, H₀, H₁)General mention of plant/animal examples without specificity; basic B-chromosome examples; standard statistical symbols with minor inconsistenciesNo specific examples cited; confuses terminology (e.g., calls B-chromosomes 'accessory chromosomes' without clarification); incorrect or missing statistical notation
Process explanation24%12Detailed stepwise explanation of transport mechanisms including conformational changes in carriers, energy coupling in active transport; clear elucidation of B-chromosome accumulation mechanisms (mitotic/meiotic drive); systematic hypothesis testing procedure with explicit steps in Chi-square analysisSequential but superficial description of processes; basic explanation of B-chromosome behavior; correct but abbreviated steps in statistical testingDisorganized or fragmented explanations; no clear sequence in describing processes; jumps directly to calculation without stating hypothesis or showing intermediate steps
Application / ecology20%10Connects membrane transport to salinity tolerance in Indian crop varieties (e.g., salt-tolerant rice), nutrient uptake efficiency; links B-chromosomes to breeding programs and genome evolution; demonstrates how Chi-square validation underpins Mendelian genetics and plant breeding decisionsGeneral mention of agricultural relevance; basic connection between B-chromosomes and genetic diversity; acknowledges importance of statistical testing in genetics without specific applicationsNo applied context provided; treats topics as purely theoretical; fails to mention relevance to plant breeding, crop improvement, or ecological adaptation

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