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Botany Quick Revision

Plant kingdom, physiology, morphology, genetics & ecology.

Living world & classification

  • Whittaker's 5 kingdoms: Monera, Protista, Fungi, Plantae, Animalia.
  • Binomial nomenclature: Genus species (Linnaeus).
  • Taxonomic hierarchy: Kingdom→Phylum→Class→Order→Family→Genus→Species.
  • Virus: obligate parasite; TMV (RNA), bacteriophage (DNA).
  • Lichen = fungus + alga (symbiosis).

Plant kingdom

  • Algae: Chlorophyceae (green), Phaeophyceae (brown, laminarin), Rhodophyceae (red, floridean starch).
  • Bryophytes: 'amphibians of plant kingdom'; dominant gametophyte (moss, Marchantia).
  • Pteridophytes: first vascular; dominant sporophyte (fern, Equisetum).
  • Gymnosperms: naked seeds, no fruit (Cycas, Pinus).
  • Angiosperms: enclosed seeds; monocot vs dicot.
  • Alternation of generations: n gametophyte ↔ 2n sporophyte.

Morphology of flowering plants

  • Root: tap (dicot), fibrous (monocot); modifications — storage (carrot), pneumatophores (Rhizophora).
  • Stem modifications: tuber (potato), rhizome (ginger), stolon (mint).
  • Leaf venation: reticulate (dicot) vs parallel (monocot).
  • Phyllotaxy: alternate, opposite, whorled.
  • Inflorescence: racemose (indefinite), cymose (definite).
  • Aestivation: valvate, twisted, imbricate, vexillary.
  • Placentation: marginal, axile, parietal, free-central, basal.
  • Floral formula symbols: Br, ⚥, K, C, A, G.

Anatomy of flowering plants

  • Tissues: meristematic (apical, lateral, intercalary) & permanent.
  • Simple permanent: parenchyma, collenchyma, sclerenchyma.
  • Complex: xylem (tracheid, vessel, fibre, parenchyma), phloem (sieve tube, companion cell).
  • Dicot stem: open vascular bundles (with cambium), conjoint, collateral.
  • Monocot stem: closed, scattered VB, no secondary growth.
  • Kranz anatomy: bundle sheath cells of C4 plants.

Cell & cell division

  • Prokaryote: no membrane-bound organelles; 70S ribosome.
  • Eukaryote: nucleus + organelles; 80S ribosome (mito/chloro 70S).
  • Cell wall: cellulose (plants), chitin (fungi), peptidoglycan (bacteria).
  • Mitosis: PMAT — 2 identical diploid cells.
  • Meiosis I reductional (crossing over in pachytene), II equational.
  • Chiasma at pachytene of prophase I.

Biomolecules

  • Primary metabolites: sugars, amino acids, nucleotides.
  • Secondary: alkaloids (morphine), terpenoids, essential oils, pigments.
  • Enzymes lower Ea; Michaelis: V = Vmax[S]/(Km+[S]).
  • Cofactors: prosthetic groups (haem in catalase), coenzymes (NAD, FAD), metal ions.
  • DNA: double helix; A=T (2H), G≡C (3H); B-form 3.4 nm/turn, 10 bp.

Transport in plants

  • Water potential Ψw = Ψs + Ψp; pure water Ψw = 0.
  • Osmosis: water moves from high to low Ψw across semipermeable membrane.
  • Ascent of sap: cohesion–tension (transpirational pull).
  • Stomata open (guard cells turgid) → K⁺ influx → water in.
  • Phloem transport (Munch): source → sink (pressure flow).

Mineral nutrition

  • Essential elements: 17; macro (C,H,O,N,P,K,S,Ca,Mg) vs micro (Fe,Mn,Zn,Cu,B,Cl,Mo,Ni).
  • N cycle: fixation (Rhizobium in root nodules), nitrification, denitrification.
  • N deficiency: chlorosis; Mg: chlorosis between veins; Fe: young leaves chlorosis.
  • Nif genes code nitrogenase.

Photosynthesis

  • Chloroplast: thylakoids (light), stroma (Calvin).
  • Pigments: chlorophyll a (P680, P700), b, carotenoids, xanthophylls.
  • Z-scheme: PS-II → PQ → cyt b6f → PC → PS-I → Fd → NADP⁺.
  • Splitting of water at PS-II releases O₂.
  • Calvin cycle: RuBisCO fixes CO₂ → 3-PGA → G3P → glucose.
  • C4 (Hatch–Slack): PEPcase in mesophyll → OAA → malate → CO₂ in bundle sheath.
  • C4 advantages: no photorespiration, higher productivity in hot climate.
  • CAM (pineapple, cactus): CO₂ fixed at night.
  • Net: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O.

Respiration in plants

  • Glycolysis (cytoplasm): glucose → 2 pyruvate + 2 ATP + 2 NADH.
  • Link reaction: pyruvate → acetyl-CoA + CO₂ + NADH.
  • Krebs (matrix): per glucose 2 ATP + 6 NADH + 2 FADH₂ + 4 CO₂.
  • ETC (inner membrane): NADH→3 ATP, FADH₂→2 ATP; total ≈ 38 ATP.
  • Fermentation: pyruvate → ethanol (yeast) or lactate (2 ATP).
  • RQ = CO₂ released/O₂ consumed: carbs 1, fats <1, proteins ~0.9.

Plant growth & hormones

  • Growth: quantitative + irreversible; measured by auxanometer.
  • Auxin (IAA): apical dominance, rooting (IBA), parthenocarpy; discovered by Went.
  • Gibberellins (GA₃): bolting, seed germination, elongation.
  • Cytokinins: cell division, delay senescence, break dormancy.
  • Ethylene: fruit ripening, senescence (gaseous).
  • ABA: stress hormone, stomatal closure, seed dormancy.
  • Photoperiodism: short-day, long-day, day-neutral; florigen hypothesis.
  • Vernalisation: cold treatment to induce flowering (wheat).

Sexual reproduction in flowering plants

  • Microsporogenesis in anther → pollen (n).
  • Pollen wall: exine (sporopollenin, most resistant), intine (cellulose).
  • Megasporogenesis in ovule → 1 functional megaspore → embryo sac (7-celled, 8-nucleate).
  • Double fertilisation: 1 sperm+egg → zygote (2n); 1 sperm+2 polar nuclei → PEN (3n).
  • Endosperm develops before embryo.
  • Apomixis: seed without fertilisation; polyembryony (citrus).
  • Pollination: anemophilous (wind), entomophilous (insect), hydrophilous.

Principles of inheritance

  • Monohybrid ratio 3:1 (phenotype), 1:2:1 (genotype).
  • Dihybrid 9:3:3:1; law of independent assortment.
  • Test cross: F1 × recessive parent (1:1 if heterozygous).
  • Incomplete dominance (Snapdragon) → 1:2:1 phenotype.
  • Codominance (ABO blood): I^A I^B = AB blood.
  • Multiple alleles: ABO (3 alleles).
  • Linkage: genes on same chromosome inherited together (Morgan on Drosophila).
  • Sex determination: XX–XY (human), XX–XO (grasshopper), ZW (birds).
  • Haemophilia, colour-blindness: X-linked recessive.
  • Down (21 trisomy), Klinefelter (XXY), Turner (XO).

Molecular basis of inheritance

  • DNA structure: Watson–Crick; antiparallel; B-DNA right-handed.
  • Hershey–Chase (1952): DNA is genetic material (32P, 35S).
  • Replication semiconservative (Meselson–Stahl); Okazaki fragments on lagging strand.
  • Central dogma: DNA → RNA → protein.
  • Genetic code: triplet, universal, degenerate, non-overlapping, start AUG, stop UAA/UAG/UGA.
  • Lac operon (Jacob–Monod): inducible; repressor + inducer (lactose).
  • Human Genome Project: ~3.1×10⁹ bp, ~30,000 genes.

Evolution

  • Origin of life: Oparin–Haldane; Miller–Urey experiment.
  • Homologous (same origin) vs analogous (same function).
  • Darwin: natural selection + survival of fittest.
  • Hardy–Weinberg: p² + 2pq + q² = 1 (no evolution).
  • Evolutionary forces: mutation, migration, selection, drift, non-random mating.
  • Human evolution: Australopithecus → Homo habilis → erectus → sapiens.

Biotech & applications

  • Restriction enzymes (EcoRI) cut DNA at specific palindromes.
  • PCR: denaturation → annealing → extension (Taq polymerase).
  • Vectors: plasmid, phage; must have ori, selection marker, cloning site.
  • Agrobacterium tumefaciens Ti plasmid — plant transformation.
  • Bt cotton: Bacillus thuringiensis Cry proteins — insect resistance.
  • Golden rice: β-carotene (vit A).
  • Insulin (Humulin): recombinant A + B chain in E. coli.
  • Gene therapy: ADA deficiency first treated.

Ecology & environment

  • Population interactions: mutualism (+/+), predation (+/−), competition (−/−), commensalism (+/0).
  • Growth: exponential dN/dt = rN; logistic dN/dt = rN(K−N)/K.
  • Ecosystem: producers → consumers → decomposers; 10% law (Lindeman).
  • Ecological pyramids: number, biomass, energy (always upright).
  • Biogeochemical cycles: C, N, P, water.
  • Biodiversity hotspots (India): Western Ghats, Eastern Himalayas, Indo-Burma, Sundaland.
  • Ex-situ: zoo, seed bank; In-situ: national park, sanctuary, biosphere reserve.
  • IUCN Red List: extinct, EN, VU, NT, LC.
  • Ozone depletion: CFCs; Montreal Protocol 1987.

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