Tamil Nadu HSE First Year Botany cheat sheet

Taxonomic hierarchy in ascending order: Species → Genus → Family → Order → Class → Division (Phylum) → Kingdom; species is the basic unit of classification.

Binomial nomenclature (Linnaeus): genus name capitalised, species epithet lower-case, both italicised or underlined separately; author citation follows the species name.

Five-kingdom system (Whittaker, 1969) uses cell type, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships; Monera and Protista are prokaryotic/eukaryotic respectively.

Algae: Chlorophyceae (chlorophyll a, b; starch), Phaeophyceae (fucoxanthin; laminarin, mannitol), Rhodophyceae (r-phycoerythrin; floridean starch).

Bryophytes are amphibians of the plant kingdom: gametophyte dominant, sporophyte dependent on gametophyte, water needed for sperm transfer.

Pteridophytes are the first true vascular plants: sporophyte dominant, independent gametophyte (prothallus), homosporous or heterosporous; heterospory precedes seed habit.

Gymnosperms: ovules naked, no ovary; Cycas has coralloid roots with cyanobacteria, Pinus has mycorrhizal roots and needle-like leaves.

Angiosperms: flower is the reproductive organ, double fertilisation produces diploid zygote and triploid primary endosperm nucleus; dicots vs monocots differ in cotyledons, venation and vascular bundle arrangement.

Lichens are symbiotic associations of algae (phycobiont) and fungi (mycobiont); viruses are obligate intracellular parasites with nucleic acid core and protein capsid, not placed in five kingdoms.

Root modifications: tap roots → fusiform, conical, napiform (storage); pneumatophores in Rhizophora; prop roots in banyan; stilt roots in maize and sugarcane.

Stem modifications: rhizome (ginger), corm (Colocasia), tuber (potato), bulb (onion), tendril (grapevine), thorn (Citrus), phylloclade (Opuntia), cladode (Asparagus).

Leaf parts: petiole, lamina, stipules; phyllotaxy is alternate, opposite or whorled; venation is reticulate (dicots) or parallel (monocots).

Inflorescence: racemose (main axis unlimited, flowers acropetal) vs cymose (axis limited, flowers basipetal); examples: racemose-mustard; cymose-Jasminum.

Placentation types: marginal (pea), axile (China rose), parietal (mustard), free central (Dianthus), basal (sunflower).

Tissue systems: epidermal (protection, stomata, trichomes), ground tissue (parenchyma, collenchyma, sclerenchyma), vascular (xylem, phloem).

Xylem conducts water and minerals upward; phloem translocates food in both directions; xylem tracheids and vessels are dead at maturity.

Monocot stem: scattered vascular bundles, no secondary growth, closed bundles; dicot stem: bundles in a ring, open bundles with cambium.

Stomatal apparatus = guard cells + subsidiary cells; guard cells swell by K+ influx and water uptake to open the stoma.

Prokaryotic cell: no membrane-bound nucleus or organelles, 70S ribosomes, single circular DNA; eukaryotic cell: true nucleus, 80S ribosomes, membrane-bound organelles.

Cell theory (Schleiden, Schwann; Virchow added omnis cellula e cellula): all organisms are made of cells, cells are the basic unit, and new cells arise from pre-existing cells.

Fluid mosaic model (Singer and Nicolson): phospholipid bilayer with integral and peripheral proteins; transport is passive (diffusion, osmosis) or active (ATP-driven pumps).

Mitochondrion is the powerhouse: double membrane, cristae, matrix, site of aerobic respiration and ATP synthesis; chloroplast has thylakoids, grana and stroma for photosynthesis.

Endomembrane system includes ER, Golgi, lysosomes and vacuoles; ribosomes on rough ER synthesise proteins; Golgi modifies, packages and secretes them.

Biomolecules: carbohydrates (mono-, di-, polysaccharides), proteins (amino acids joined by peptide bonds), lipids (fatty acids + glycerol), nucleic acids (nucleotides).

Enzymes are protein biocatalysts that lower activation energy; they are specific, reusable, and affected by temperature and pH; competitive inhibitors bind the active site.

Nucleic acids: DNA is double-stranded with deoxyribose and thymine; RNA is single-stranded with ribose and uracil; nucleotides = nitrogen base + pentose sugar + phosphate.

Water is the most abundant cell component; it is a universal solvent due to its polar nature and high specific heat.

Mitosis stages: prophase → metaphase → anaphase → telophase; produces two genetically identical diploid daughter cells; cytokinesis follows.

Meiosis I (reductional) separates homologous chromosomes; meiosis II (equational) separates sister chromatids; crossing over occurs at pachytene of prophase I.

Prophase I substages: leptotene, zygotene (synapsis, synaptonemal complex), pachytene (crossing over), diplotene (chiasmata), diakinesis (terminalisation).

Plant growth is indeterminate and occurs at meristems: apical (length), lateral/cambium (girth), intercalary (in grasses).

Growth phases: lag (cell formation), log (cell elongation), plateau (cell differentiation), followed by senescence.

Growth regulators: auxin (cell elongation, apical dominance, rooting), gibberellin (stem elongation, bolting, seed germination), cytokinin (cell division, delaying senescence), abscisic acid (stomatal closure, dormancy), ethylene (fruit ripening, senescence).

Photoperiodism: short-day plants flower when night length exceeds a critical dark period; long-day plants flower when night is shorter; day-neutral plants flower regardless.

Vernalisation is promotion of flowering by low-temperature exposure (e.g., winter wheat); phytochrome mediates light responses.

Apical dominance is the inhibition of lateral buds by auxin from the terminal bud; decapitation releases lateral buds.

Overall photosynthesis: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O, driven by light energy trapped in chlorophyll.

Light reactions occur in thylakoid membranes: PS II (P680) and PS I (P700) drive non-cyclic photophosphorylation producing ATP, NADPH and O2 from water photolysis.

Cyclic photophosphorylation involves only PS I and produces ATP but no NADPH or O2; it occurs when NADP+ is limiting.

Calvin cycle (C3) in stroma: carbon fixation by RuBisCO, reduction of 3-PGA to G3P using ATP and NADPH, regeneration of RuBP.

C4 pathway (Hatch–Slack): PEP carboxylase fixes CO2 into oxaloacetate in mesophyll; Calvin cycle runs in bundle-sheath cells; examples maize, sugarcane.

Photorespiration: RuBisCO binds O2 at high O2/low CO2, wasting carbon; C4 and CAM plants reduce it; CAM plants fix CO2 at night into malate.

Aerobic respiration: glycolysis in cytoplasm (glucose → 2 pyruvate, net 2 ATP, 2 NADH); Krebs cycle in mitochondrial matrix; electron transport chain on inner membrane yields most ATP.

Net ATP from one glucose: glycolysis 2, Krebs cycle 2, ETC about 34, total about 38; anaerobic respiration yields 2 ATP and ethanol/lactate.

R.Q. = CO2 released / O2 consumed; carbohydrate ≈1.0, fat <1.0, protein ≈0.8.

Water potential (Ψw) = Ψs (solute) + Ψp (pressure); pure water at atmospheric pressure has Ψw = 0; solutes lower water potential (more negative).

Diffusion moves molecules down a concentration gradient; osmosis is diffusion of water across a semipermeable membrane from higher to lower water potential.

Plasmolysis occurs when a cell loses water in a hypertonic solution; deplasmolysis is reversal in a hypotonic solution.

Imbibition is absorption of water by hydrophilic colloids (e.g., dry seeds) causing swelling; it is the first step in water uptake.

Root pressure is positive hydrostatic pressure generated by active ion transport into xylem; it causes guttation in small plants.

Cohesion–tension theory explains ascent of sap: transpiration pull, cohesion of water molecules, adhesion to xylem walls, and continuous water column.

Transpiration is loss of water vapour through stomata; it cools the leaf and drives water transport but can cause wilting.

Phloem transport follows the pressure-flow (mass flow) hypothesis: loading at source, unloading at sink, driven by osmotic pressure gradient.

Mineral ions are absorbed actively against concentration gradients using energy; mycorrhizae and root hairs increase absorption surface.

Macronutrients (needed in large amounts): C, H, O, N, P, K, Ca, Mg, S; micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni.

Hydroponics is growing plants in nutrient solution without soil; it identifies essential elements and their deficiency symptoms.

Criteria for essentiality: element is necessary for normal growth and reproduction, its requirement is specific and not replaceable, and it is directly involved in plant metabolism.

Nitrogen is needed for proteins, nucleic acids and chlorophyll; deficiency causes chlorosis and stunted growth; legumes fix N2 via Rhizobium in root nodules.

Magnesium is the central atom of chlorophyll; deficiency causes interveinal chlorosis in older leaves.

Iron is required for chlorophyll synthesis and cytochromes; deficiency causes chlorosis of young leaves.

Boron is needed for pollen germination and sugar transport; calcium for cell wall (middle lamella) and membrane stability.

Mobile elements (N, P, K, Mg) show deficiency first in older leaves; immobile elements (Ca, Fe, B) show deficiency first in younger leaves.

Biological nitrogen fixation: nitrogenase enzyme (inhibited by O2) reduces N2 to ammonia; symbiotic (Rhizobium, Frankia) and free-living (Azotobacter, Clostridium, Anabaena).

Flower parts: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels); complete flower has all four whorls.

Microsporangium (anther) produces microspores by meiosis → pollen grains; megasporangium (ovule) produces one functional megaspore → embryo sac.

Megasporogenesis: one megaspore mother cell → meiosis → four megaspores; three degenerate, one forms the 8-nucleate, 7-celled embryo sac.

Double fertilisation: one male gamete fuses with egg (syngamy → zygote), the other with two polar nuclei (triple fusion → triploid endosperm).

Pollination: self (autogamy) vs cross (allogamy); agents are wind (anemophily), water (hydrophily), insects (entomophily), birds, bats.

Apomixis is seed formation without fertilisation (e.g., Citrus); parthenocarpy is fruit development without fertilisation (e.g., banana).

Embryo development stages: proembryo → globular → heart-shaped → torpedo → mature embryo; suspensor anchors and nourishes.

Seed germination: imbibition → enzyme activation → radicle emerges → plumule; epigeal (cotyledons above soil) vs hypogeal (cotyledons remain below).

Polyembryony is the occurrence of more than one embryo in a seed (e.g., Citrus); it is exploited in horticulture.

Mendel's law of segregation: alleles separate during gamete formation; law of independent assortment applies to genes on different chromosomes.

Monohybrid F2 ratio 3:1 (phenotypic), 1:2:1 (genotypic); dihybrid F2 ratio 9:3:3:1.

Test cross determines genotype by crossing with homozygous recessive; back cross is crossing with a parent.

Incomplete dominance (e.g., Snapdragon flower colour) gives intermediate phenotype; codominance (AB blood group) expresses both alleles.

DNA structure (Watson and Crick, 1953): double helix, antiparallel strands, base pairs A–T and G–C held by hydrogen bonds, sugar-phosphate backbone.

DNA replication is semi-conservative: each strand acts as template; enzymes include helicase, DNA polymerase, ligase.

Transcription: DNA → mRNA by RNA polymerase; translation: mRNA → protein at ribosomes via tRNA and codon–anticodon pairing.

Genetic code is triplet, degenerate, non-overlapping and universal; AUG is the start codon, UAA/UAG/UGA are stop codons.

Mutations: point (substitution, insertion, deletion) and chromosomal (deletion, duplication, inversion, translocation); sickle-cell anaemia is a point mutation.

Recombinant DNA technology: restriction endonucleases cut DNA at specific palindromic sites; DNA ligase joins fragments; vectors carry genes into host cells.

Common vectors: plasmids (pBR322), bacteriophages, and Ti plasmid of Agrobacterium tumefaciens for plant transformation.

PCR amplifies DNA in vitro using Taq polymerase, primers, dNTPs and thermal cycling (denaturation, annealing, extension).

Gel electrophoresis separates DNA fragments by size; smaller fragments migrate farther toward the positive electrode.

Bt cotton carries genes from Bacillus thuringiensis (cry genes) giving resistance to bollworm; golden rice is engineered for beta-carotene.

Tissue culture (micropropagation) uses totipotent explants on nutrient media with auxin and cytokinin; callus → plantlets; somaclonal variation arises in culture.

Plant breeding methods: selection, hybridisation, mutation breeding, and polyploidy breeding; hybrid vigour (heterosis) is exploited in crops.

Biofertilisers: Rhizobium, Azotobacter, Azospirillum (N-fixers), Glomus (mycorrhiza), and cyanobacteria (Anabaena, Nostoc) in rice fields.

Transgenic plants are tested for biosafety; gene therapy, DNA fingerprinting and ELISA are applications of biotechnology in diagnostics.

Taxonomic hierarchy in ascending order: Species → Genus → Family → Order → Class → Division (Phylum) → Kingdom; species is the basic unit of classification.

Binomial nomenclature (Linnaeus): genus name capitalised, species epithet lower-case, both italicised or underlined separately; author citation follows the species name.

Five-kingdom system (Whittaker, 1969) uses cell type, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships; Monera and Protista are prokaryotic/eukaryotic respectively.

Algae: Chlorophyceae (chlorophyll a, b; starch), Phaeophyceae (fucoxanthin; laminarin, mannitol), Rhodophyceae (r-phycoerythrin; floridean starch).

Bryophytes are amphibians of the plant kingdom: gametophyte dominant, sporophyte dependent on gametophyte, water needed for sperm transfer.

Pteridophytes are the first true vascular plants: sporophyte dominant, independent gametophyte (prothallus), homosporous or heterosporous; heterospory precedes seed habit.

Gymnosperms: ovules naked, no ovary; Cycas has coralloid roots with cyanobacteria, Pinus has mycorrhizal roots and needle-like leaves.

Angiosperms: flower is the reproductive organ, double fertilisation produces diploid zygote and triploid primary endosperm nucleus; dicots vs monocots differ in cotyledons, venation and vascular bundle arrangement.

Lichens are symbiotic associations of algae (phycobiont) and fungi (mycobiont); viruses are obligate intracellular parasites with nucleic acid core and protein capsid, not placed in five kingdoms.