UPSC Botany 2026 — Paper II

(a) A compact 150-word note defining frameshift mutation, explaining how insertion/deletion of a number of bases not a multiple of three shifts the reading frame, and stating its molecular consequences, causative mutagens and significance. 'Short note' means definition plus mechanism plus consequence plus an example, not an essay. (b) A 150-word note that must do two things explicitly asked: (i) describe the structure and occurrence of lampbrush chromosomes, and (ii) state their biological and cytogenetic significance. A labelled sketch of the chromomere-axis with paired lateral loops is expected. (c) A 150-word note defining reporter genes, listing the properties that make a gene a good reporter, naming the standard reporters with their gene symbols, sources, substrates and detection, and stating their applications in plant molecular biology. The distinction from selectable marker genes should be made. (d) A 150-word note covering both parts named in the question: (i) cell signalling as a perception-transduction-response sequence, and (ii) the classes of cell receptors, with named plant examples. Both halves must be present; an answer on signalling alone is incomplete. (e) A 150-word note on DNA fingerprinting: its basis in hypervariable repeat polymorphism, the classical Southern-blot/VNTR protocol and its modern PCR-STR successor, and its applications, with the plant/agricultural applications given due weight in a Botany paper.

• Definition: insertion or deletion of nucleotides not in multiples of three, shifting the reading frame
• Effect: altered codons downstream, premature stop, truncated non-functional protein; worked example
• Causes: acridine dyes (intercalation), polymerase slippage; named examples (CCR5-delta32, Tay-Sachs HEXA)
• Crick et al. 1961 T4 rII experiment proving the triplet code
• Occurrence: diplotene of meiotic prophase I in oocytes (amphibians, also birds, reptiles, insects); Flemming 1882, Rückert 1892
• Structure: bivalents with chiasmata, axis of chromomeres, paired lateral loops per chromatid with RNA-protein matrix
• Loops transcriptionally active; thin and thick ends
• Significance: stockpile of RNA for early embryo, model for transcription and RNA processing, gene mapping
• Definition: gene with easily assayed product used to monitor expression, promoter activity, transformation
• Properties: absent in host, sensitive quantitative assay, non-toxic, stable
• Examples with detection: lacZ, GUS, GFP, luciferase, CAT
• Uses (promoter analysis, protein localisation, screening) and difference from selectable markers
• Signalling steps: ligand, receptor, transduction, response, termination
• Types: endocrine, paracrine, autocrine, juxtacrine
• Transduction: second messengers (cAMP, Ca²⁺, IP3, DAG), phosphorylation cascades (MAPK)
• Receptors: cell-surface (GPCR, enzyme-linked, ion channel, plant RLKs) and intracellular (steroid, phytochrome, TIR1, GID1, PYR/PYL)
• Basis: hypervariable VNTR and STR repeats, individual-specific (Jeffreys 1984)
• Steps: DNA isolation, restriction digestion, electrophoresis, Southern blotting, probe hybridisation, autoradiography
• Modern STR-PCR with capillary electrophoresis
• Applications: forensics, paternity, disaster victims, wildlife, plant varieties; Indian pioneer Lalji Singh at CCMB

(a) 'Give a detailed account' requires a full, structured treatment of sex-linked inheritance: the chromosomal basis of sex determination (with plant systems), the pattern of transmission of genes on the X/Z and Y/W chromosomes, the classical experimental evidence, reciprocal-cross and criss-cross behaviour, dosage compensation, and the distinction from sex-limited and sex-influenced traits. (b) 'Explain' requires both halves: the four structural (intrachromosomal and interchromosomal) changes in chromosomes - deletion, duplication, inversion and translocation - with their types, meiotic behaviour and cytological detection, AND their genetic, evolutionary and applied significance. (c) 'Describe the role of biochemical and molecular basis of mutation' asks for the chemistry and molecular mechanism by which mutations arise: tautomerism and mispairing, the action of chemical and physical mutagens on DNA bases, spontaneous lesions, the role of repair or its failure, and the molecular categories and consequences of the resulting changes.

• Definition and types: X-linked recessive and dominant, Y-linked (holandric), pseudoautosomal, Z-linked in ZW systems, with human and other examples
• Morgan's Drosophila white-eye cross with ratios (3:1 with white all male; reciprocal cross criss-cross, 1:1:1:1); Bridges' non-disjunction
• Characteristics of X-linked recessive inheritance: hemizygous males, carrier females, criss-cross, skipping a generation
• Human examples with crosses (colour blindness, haemophilia A, DMD); dosage compensation and Lyon hypothesis; distinguish sex-limited and sex-influenced
• Deletion, duplication, inversion, translocation defined with subtypes
• Meiotic consequences: deletion loop, inversion loop with bridge and fragment, translocation ring or chain and semi-sterility
• Examples: cri-du-chat, Bar eye, Philadelphia chromosome, Robertsonian and familial Down syndrome
• Significance: evolution and speciation, disease and cancer, gene mapping, balancer chromosomes, alien gene transfer in breeding
• Biochemical basis: gene-enzyme link, inborn errors (alkaptonuria, PKU, albinism), sickle-cell amino acid change, auxotroph and Ames test
• Molecular basis: transitions, transversions, indels; spontaneous causes (tautomerism, depurination, deamination, slippage, transposons)
• Induced: base analogues, nitrous acid, EMS, acridines, UV, radiation; DNA repair systems
• Role: genetic disease and cancer, mutation breeding, mutagen screening, site-directed mutagenesis and evolution

(a(i)) 'Write in detail the chemical composition of microtubules' asks specifically for what microtubules are made of: the tubulin subunits, their molecular properties, nucleotide binding, the associated proteins and the drugs that bind them - together with the dimensions that follow from this composition. Functions are not asked here (they form part (ii)). (a(ii)) 'Elaborate the functions of cytoplasmic microtubules' asks for the roles of the non-axonemal, cytoplasmic microtubule arrays - in a Botany paper chiefly the four plant arrays (cortical, preprophase band, spindle, phragmoplast) plus intracellular transport, cell shape and signalling. The emphasis must be on function, not composition. (b) 'Explain the different means of passive transport across the plasma membrane' requires each mode of passive movement - simple diffusion, osmosis (including aquaporins), facilitated diffusion by carriers, and movement through ion channels - to be defined, mechanistically explained, and distinguished from one another and from active transport, with the driving force stated as the electrochemical potential gradient. (c(i)) 'Elaborate on the significance of molecular markers' asks primarily for the USES and value of DNA markers in plant science and breeding, supported by a brief statement of what a molecular marker is and the main classes. The weight must fall on significance, with concrete crop examples. (c(ii)) 'Explain the significance of polyploidy in agriculture' asks for the practical, crop-related value of auto- and allopolyploidy - named polyploid crops, the advantages they confer, the use of colchicine-induced polyploids and amphiploids in breeding - plus a brief statement of limitations. Theory of polyploid classification is background only.

• Tubulin as the main protein: alpha-beta heterodimer of about 55 kDa each, GTP bound to each, exchangeable GTP on beta
• 13 protofilaments forming a hollow tube of about 25 nm; polarity with plus and minus ends; gamma-tubulin ring complex nucleation
• Associated proteins: MAPs (tau, MAP2, MAP65), motor proteins kinesin and dynein, katanin
• Conditions and drugs: GTP and Mg²⁺ for assembly, colchicine and vinblastine inhibit, taxol stabilises; dynamic instability
• Cytoskeletal shape and support; organelle positioning
• Intracellular transport by kinesin and dynein
• Spindle formation in mitosis and meiosis; in plants preprophase band and phragmoplast
• Guidance of cellulose microfibril deposition by cortical microtubules; cilia, flagella and centrioles; drug targets
• Passive transport defined: down electrochemical gradient, no metabolic energy
• Simple diffusion of lipid-soluble molecules with factors affecting the rate (Fick's law, partition coefficient, size)
• Osmosis with aquaporins
• Facilitated diffusion: channel proteins (gated, selective, high rate) and carrier proteins (saturable, specific, Vmax and Km); comparison with active transport
• Definition and advantages over morphological markers (abundant, neutral, environment-independent)
• Diversity assessment, germplasm characterisation, variety identification and fingerprinting
• Linkage maps and QTL mapping
• Marker-assisted selection, gene pyramiding with examples (Improved Samba Mahsuri, Swarna-Sub1), hybrid purity, phylogeny
• Definition; autopolyploidy and allopolyploidy
• Gigas effect and seedlessness (triploid banana, watermelon)
• New crops: bread wheat, cotton, Brassica napus, triticale; fertility restoration of interspecific hybrids and fixation of hybrid vigour
• Induction by colchicine, oryzalin and temperature shock

(a) 'Discuss on the tools and techniques involved in PCR and FISH' requires two balanced halves: for PCR the reaction components (tools) and the thermal cycling steps with their temperatures (technique), plus variants and applications; for FISH the probes, labels, fluorochromes and microscope (tools) and the slide preparation, denaturation, hybridisation, washing and detection sequence (technique), plus variants such as GISH and their plant applications. (b) Two explicit halves: (i) the CAUSES of heterosis - the genetic theories of dominance, overdominance and epistasis with their evidence and the physiological/epigenetic basis; and (ii) its IMPACT in agriculture - hybrid crops, the male-sterility systems used to make them, yield gains, and the limitations. Define heterosis and its measures first. (c) 'Describe the various evidences supporting organic evolution' asks for a classified survey of the lines of evidence - morphological/comparative anatomy, palaeontological, embryological, biogeographical, physiological-biochemical, molecular, and direct experimental/observational - each illustrated with concrete examples, with botanical examples given prominence in a Botany paper.

• PCR tools: template, primers, Taq polymerase, dNTPs, Mg²⁺, buffer, thermal cycler
• PCR technique: denaturation 94-95 °C, annealing 50-65 °C, extension 72 °C, 25-35 cycles (2ⁿ), gel detection; variants (RT-PCR, qPCR, nested, multiplex) and uses
• FISH tools: labelled probes (direct fluorochrome or biotin/digoxigenin), chromosome or nuclei preparations, hybridisation reagents, DAPI, fluorescence microscope
• FISH technique: denaturation, hybridisation, stringent washes, detection and imaging; GISH, gene mapping, translocations, aneuploidy
• Definition of heterosis (Shull 1914)
• Dominance hypothesis with example genotypes and its objection
• Overdominance hypothesis (Shull, East) and epistasis; recent explanations
• Agricultural impact: hybrids in maize, sorghum, pearl millet, cotton, rice, vegetables; yield gain, male sterility systems; limitations (F2 breakdown, seed cost)
• Comparative anatomy: homologous, analogous, vestigial organs, atavism
• Embryology: von Baer, recapitulation in modified form
• Palaeontology: transitional forms (Archaeopteryx, Tiktaalik, horse, whale), living fossils, dating
• Biogeography, biochemistry and molecular evidence, selection (peppered moth, resistance), observed speciation

(a) A 150-word note on the Munch (pressure-flow) hypothesis of phloem translocation: its author, the mechanism of source-to-sink osmotically generated pressure gradient and mass flow, the supporting evidence including Munch's physical model and aphid stylet experiments, and the principal objections. A labelled diagram of the source-sink osmometer model is expected. (b) A 150-word biostatistics note covering BOTH terms: correlation (its definition, Karl Pearson's coefficient with formula and range, types, Spearman's rank correlation, test of significance) and regression (its definition, the regression equation and coefficients, their relation to r), followed by the key distinctions between the two and their use in plant science. (c) A 150-word note on heat shock proteins: their discovery, their nature as molecular chaperones, the major families with their functions, the HSF/HSE mechanism of induction, and their significance in thermotolerance and abiotic stress tolerance in plants. (d) A 150-word note defining the biogeochemical cycle, distinguishing gaseous from sedimentary cycles, outlining at least two named cycles (carbon and nitrogen being the expected ones, with phosphorus as the sedimentary example) with the organisms and processes involved, and stating the ecological significance and human perturbation. (e) A 150-word note on the regulation of nif genes: their organisation in Klebsiella pneumoniae, the functions of the structural and regulatory genes, the two-tier control by the ntr (NtrB/NtrC) system and by NifA with its antagonist NifL, the environmental signals of oxygen and fixed nitrogen, and the equivalent control in Rhizobium and Anabaena.

• Statement: mass flow of phloem sap driven by turgor pressure gradient from source to sink (Münch 1930)
• Loading of sucrose at source lowers water potential, water enters by osmosis, high turgor; unloading at sink lowers turgor
• Bulk flow through sieve tubes at 30-100 cm per hour; energy needed only for loading and unloading
• Evidence (aphid stylets, girdling, 14C) and objections (sieve plate resistance, two-way flow)
• Correlation: strength and direction of linear relationship; Pearson r formula; range -1 to +1; r² ; no causation
• Regression: dependence of y on x; y = a + bx; least squares; regression coefficient b = r·sy/sx
• Two regression lines and their coincidence at r = ±1
• Uses (prediction, calibration) and difference between the two
• Discovery: Ritossa 1962 (Drosophila puffs), Tissières 1974; conserved across organisms
• Induction by heat and other stresses through HSF binding heat shock elements
• Classes by size: HSP100, 90, 70, 60, small HSPs
• Functions as molecular chaperones (prevent aggregation, refold, translocation, degradation), thermotolerance
• Definition: cyclic movement of elements between organisms and the physical environment; reservoir and exchange pools
• Gaseous cycles (C, N, O, H): atmospheric reservoir, fast, self-regulating
• Sedimentary cycles (P, Ca, Fe, K): crustal reservoir, slow, loss to sediments
• Carbon and phosphorus cycles as examples; importance and human disturbance
• nif cluster in Klebsiella pneumoniae: about 20 genes, 7-8 operons, roles of nifHDK, nifENB, nifLA
• Sigma-54 dependent promoters activated by NifA
• nifLA activated by NtrC under nitrogen limitation; NifL inhibits NifA in presence of oxygen or fixed nitrogen
• Other controls: temperature, molybdenum, iron, ADP-ribosylation of Fe protein; FixL-FixJ in Rhizobium

(a(i)) Two linked demands: (i) explain the significance of Nod factors - their chemical nature, the nod genes that make them, their perception and the host specificity they confer; and (ii) describe the sequence of root nodule formation from flavonoid signalling to bacteroid and leghaemoglobin. Both must appear. (a(ii)) 'Describe the process of amino acid biosynthesis in nitrogen metabolism' requires the route from inorganic nitrogen to amino acids: nitrate reduction to ammonium, primary assimilation of ammonium by the GS/GOGAT cycle (with the subsidiary role of GDH), distribution of the amino group by transamination and amide synthesis, and the carbon-skeleton families of amino acids. Named enzymes, cofactors and reactions are expected. (b) 'Differentiate between' requires a point-by-point comparison of photophosphorylation and oxidative phosphorylation - site, energy source, electron donor and acceptor, direction of electron flow, carriers, direction of proton pumping, nature of the proton-motive force, ATP synthase, yield, inhibitors and uncouplers - preceded by a statement of what they have in common (chemiosmosis) and closed by the functional contrast. (c) 'Discuss the biochemical and physiological changes during fruit ripening' asks for both categories: the physiological changes (climacteric respiratory rise, autocatalytic ethylene, softening, membrane changes) and the biochemical changes (pigment conversion, cell-wall enzymes, starch to sugar, organic acid decline, loss of astringency, volatile synthesis), with the hormonal and genetic regulation and the postharvest applications.

• Nod factors: lipo-chitooligosaccharides made by nod genes (nodABC, nodD activated by flavonoids); host-specific decorations
• Significance: host specificity, LysM receptors, root hair curling, cortical division, infection thread, early nodulins
• Steps: flavonoid signal, attachment and curling, infection thread, cortical division and nodule primordium, bacteroid formation
• Symbiotic function: leghaemoglobin, nitrogenase, exchange of malate and fixed nitrogen; determinate and indeterminate nodules
• Nitrate reduction: nitrate reductase then nitrite reductase to ammonium
• Ammonium assimilation by GS-GOGAT cycle (reactions with cofactors); GDH minor route
• Transamination with PLP, amidation (asparagine synthetase)
• Amino acid families (glutamate, aspartate, pyruvate, serine, aromatic, histidine)
• Site: thylakoid versus inner mitochondrial membrane
• Energy source and electron donor and acceptor: light and water and NADP⁺ versus NADH, FADH₂ and oxygen
• Carriers and direction of electron flow (uphill Z-scheme versus downhill), cyclic and non-cyclic types
• Proton gradient and ATP synthase orientation (CF₀-CF₁ versus F₀-F₁), occurrence and use of ATP
• Climacteric and non-climacteric fruits; respiratory rise and ethylene autocatalysis (ACC synthase, ACC oxidase, ETR1, CTR1, EIN)
• Softening by pectin-degrading enzymes and cell wall loosening
• Colour change (chlorophyll loss, carotenoids, anthocyanins), sugar accumulation from starch, acid decrease
• Aroma volatiles, loss of astringency, membrane and gene-expression changes; control (1-MCP, controlled atmosphere, calcium)

(a(i)) 'Explain the factors affecting enzyme activity' requires each factor - substrate concentration, enzyme concentration, temperature, pH, cofactors and activators, inhibitors, and regulatory modifications - to be named AND its effect explained with the shape of the response curve and a plant example where possible. (a(ii)) 'Describe the mechanism of enzyme action' asks how an enzyme catalyses: lowering of activation energy through formation and stabilisation of the transition state, the enzyme-substrate complex, the lock-and-key and induced-fit models, the nature of the active site, the chemical strategies of catalysis, and a worked example such as the chymotrypsin catalytic triad or Rubisco. (b(i)) A 75-word explanation of acid rain: the definition by pH, the pollutants and chemistry that produce it, its effects on vegetation, soils, waters and monuments, and control measures. Brevity with precision is the requirement. (b(ii)) A 75-word explanation of why biocides act as pollutants: what biocides are, their persistence, bioaccumulation and biomagnification, their non-target ecological effects including on soil microflora and pollinators, resistance and resurgence, with named chemicals and incidents, and the remedies. (b(iii)) A 75-word explanation of photochemical smog: the conditions and precursors required, the photochemical reactions that generate ozone and PAN, the characteristic injury symptoms on plants (which matter most in a Botany paper) and on humans, and control measures. (c(i)) Two explicit demands in 120 words: (i) describe seed dormancy - define it and classify its types and causes; and (ii) explain how it is regulated, which means the hormonal ABA/GA balance, the DOG1 and light/temperature inputs, and the ways in which dormancy is naturally or artificially broken. (c(ii)) 'Explain biochemical changes taking place during seed germination' asks for the chemistry of germination: the three phases of water uptake and the resumption of metabolism, the hormonal signal for enzyme synthesis, and the mobilisation of starch, protein, lipid and phytin reserves with the enzymes and pathways involved.

• Substrate concentration (hyperbolic curve, Vmax, Km) and enzyme concentration
• Temperature (Q₁₀, optimum, denaturation) and pH (optimum, bell-shaped curve, examples)
• Inhibitors: competitive, non-competitive, irreversible with effect on Km and Vmax
• Activators and cofactors; product accumulation, allosteric and feedback control
• Lowering of activation energy; ES complex formation and E + S ⇌ ES → EP → E + P
• Lock-and-key (Fischer) and induced-fit (Koshland) models
• Catalytic strategies: proximity and orientation, transition-state stabilisation, acid-base, covalent, metal ion catalysis
• Example such as chymotrypsin triad; enzyme unchanged and equilibrium not altered
• Definition: rain with pH below 5.6; causes SO₂ and NOx
• Sources: coal power plants, smelters, vehicles; formation of H₂SO₄ and HNO₃
• Effects on lakes, soil, forests, crops, monuments
• Control measures
• Biocides defined (insecticides, herbicides, fungicides); spread by drift, run-off, leaching
• Persistence and biomagnification (DDT, BHC, aldrin)
• Effects on non-target organisms, resistance, water and health
• Alternatives: IPM, biopesticides, bans (Stockholm Convention)
• Conditions: sunlight, warm still air, heavy traffic
• Precursors: NOx and volatile organic compounds
• Reactions producing ozone, PAN and aldehydes
• Effects and control; contrast with London smog
• Definition and significance of seed dormancy
• Causes: hard seed coat, immature embryo, inhibitors, light and temperature requirement
• Regulation: ABA and GA balance, phytochrome, ABI3/ABI5, DOG1, ethylene, nitrate
• Methods of breaking: scarification, stratification, leaching, GA₃, KNO₃, light
• Imbibition, lag and radicle emergence; increased respiration and ATP
• Enzymatic mobilisation: alpha-amylase induced by GA in aleurone, proteases, lipases, glyoxylate cycle, phytase
• Transport of soluble products and synthesis of proteins, RNA and DNA from stored mRNA
• Hormone changes (ABA falls, GA and cytokinin rise); dry weight changes

(a(i)) A 75-word statement of the basic concept of phytogeography: its definition as the study of the distribution of plants in space and time, its main branches, its core concepts such as range, endemism, barriers and dispersal, and its founders. (a(ii)) 'Give a detailed account on various phytogeographical regions of India' asks for the classical regional division of India (Hooker's nine botanical regions as usually taught) with, for each region, its extent, climate, vegetation type and characteristic genera, and ideally a mention of the alternative frameworks - Rodgers and Panwar's biogeographic zones and the biodiversity hotspots. A sketch map is highly desirable. (b) 'Give an account on farmers' rights and intellectual property rights' requires both: the forms of intellectual property relevant to plants and the international framework (TRIPS, UPOV, CBD, Nagoya, ITPGRFA), and the concept and statutory content of Farmers' Rights, with India's Protection of Plant Varieties and Farmers' Rights Act, 2001 as the central example, plus the tension between the two. (c) Two explicit demands: (i) discuss the PRESENT STATUS of India's forest resources, which requires current India State of Forest Report data - extent, density classes, mangroves, growing stock, carbon stock, leading states and the trend; and (ii) list and explain the FACTORS RESPONSIBLE FOR DEFORESTATION, with consequences and remedial policy as useful additions.

• Definition: geographical distribution of plants and its causes
• Distribution non-random: climate, soil, topography, biotic factors
• Historical factors: continental drift, migration, barriers, speciation
• Branches (descriptive, ecological); endemism, disjunction
• Chatterjee's eight regions named: Western Himalaya, Eastern Himalaya, Indus plain, Gangetic plain, Assam, Malabar, Deccan, Andaman and Nicobar
• Characteristic vegetation and climate of each, with example species
• Floristic affinities and endemism (Eastern Himalaya, Malabar)
• Rodgers-Panwar ten biogeographic zones and biodiversity hotspots
• IPR types relevant to plants; TRIPS Art. 27.3(b) and India's sui generis choice
• Farmers' rights: FAO Treaty (2001) and rights to save, use, exchange, sell farm-saved seed
• PPV&FR Act 2001: registration categories, breeders' term (15/18 years), farmers' rights, benefit-sharing, Authority
• Biological Diversity Act 2002, Patents Act s.3(j), GI Act 1999; cases (neem, turmeric, basmati, TKDL)
• Present status with figures: forest cover 21.76%, tree cover 3.41%, total 25.17% (ISFR 2023); 33% policy goal
• Density classes, leading states, mangroves; quality versus extent
• Causes: agriculture and jhum, fuelwood and grazing, development projects, fires, encroachment, illegal felling
• Consequences and remedies (FCA 1980, FRA 2006, JFM, CAMPA/compensatory afforestation)