Tamil Nadu HSE Second Year Botany cheat sheet

Algae: chlorophyll-bearing thallophytes; storage forms - Chlorophyceae starch, Phaeophyceae laminarin and mannitol, Rhodophyceae floridean starch; cell walls - cellulose (green), cellulose plus algin (brown), cellulose plus pectin and polysulphate esters (red).

Brown algae show heteromorphic alternation: haploid gametophyte and diploid sporophyte differ in form; Fucus has diplontic life cycle with gametic meiosis.

Fungi: cell wall of chitin and polysaccharides; heterotrophic, mostly multinucleate coenocytic hyphae; reproduction by spores - conidia (asexual), ascospores/basidiospores (sexual); classes Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes.

Lichens are symbiotic associations of an alga (phycobiont) and a fungus (mycobiont); the fungus supplies shelter and minerals, the alga supplies carbohydrate; sensitive indicators of SO2 pollution.

Bryophytes: amphibious plants; gametophyte dominant and photosynthetic, sporophyte dependent; water needed for flagellate sperm; examples Marchantia (thalloid), Funaria and Polytrichum (leafy); Sphagnum is the peat moss.

Pteridophytes: first vascular plants with xylem and phloem; sporophyte dominant, gametophyte (prothallus) free-living and small; heterospory in Selaginella and Salvinia leads to seed habit; strobili in Equisetum.

Gymnosperms: naked ovules not enclosed in ovary; Cycas has coralloid roots with cyanobacteria, Pinus has mycorrhizal roots; Ginkgo biloba is a living fossil; Cycas circinalis is the Tamil Nadu state tree.

Life-cycle decision rule: algae and bryophytes - gametophytic/haplontic emphasis; pteridophytes - sporophyte dominant with independent gametophyte; gymnosperms and angiosperms - diplontic with reduced gametophyte retained on sporophyte.

Taxonomic hierarchy (descending): Kingdom, Division/Phylum, Class, Order, Family, Genus, Species; species is the basic unit, genus the basic category above it.

Binomial nomenclature by Carolus Linnaeus (Species Plantarum, 1753): genus name capitalised, specific epithet lower case, both italicised or underlined; author citation follows the name.

ICN rules: valid publication requires effective publication, Latin diagnosis or description, and designation of a type specimen; priority dates from the earliest valid name.

Suffixes: -phyta for division, -ae for class, -ales for order, -aceae for family; e.g., Poaceae, Fabaceae, Solanaceae.

Bentham and Hooker system (Genera Plantarum) - natural system, dicots first then monocots; Engler and Prantl - placed monocots before dicots.

Herbarium sheet label carries locality, date, collector and identification; type specimen (holotype) anchors the name permanently.

Three-domain classification (Woese): Archaea, Bacteria, Eukarya; five-kingdom system (Whittaker): Monera, Protista, Fungi, Plantae, Animalia.

Key identification characters: numerical taxonomy uses many equally weighted characters; cytotaxonomy uses chromosome number and karyotype; chemotaxonomy uses secondary metabolites.

Prokaryotic cell: 70S ribosomes, no membrane-bound organelles, single circular DNA, peptidoglycan wall in bacteria; eukaryotic cell: 80S ribosomes, nuclear envelope with pores, linear chromosomes.

Mitochondrion: double membrane, inner folds (cristae), own DNA and 70S ribosomes; site of Krebs cycle (matrix) and oxidative phosphorylation (inner membrane).

Chloroplast: double membrane, thylakoids stacked as grana, stroma with DNA and ribosomes; light reactions on thylakoid membranes, Calvin cycle in stroma.

Fluid mosaic model (Singer and Nicolson): phospholipid bilayer with integral and peripheral proteins; selective permeability; plasmodesmata connect adjacent plant cells.

Cell cycle: interphase G1, S (DNA replication), G2; M phase with karyokinesis and cytokinesis; plant cytokinesis by cell plate formation.

Mitosis: prophase (chromatin condenses, spindle forms), metaphase (chromosomes at equator), anaphase (centromeres split, chromatids move to poles), telophase (nuclear envelope reforms).

Meiosis I is reductional (homologous chromosomes separate), meiosis II is equational (sister chromatids separate); crossing over in pachytene of prophase I at chiasmata.

Prophase I stages in order: leptotene, zygotene (synapsis, synaptonemal complex), pachytene (crossing over), diplotene (chiasmata visible), diakinesis (terminalisation).

Law of segregation: alleles of a gene separate during gamete formation; monohybrid F2 phenotypic ratio 3:1, genotypic 1:2:1; test cross with recessive parent reveals genotype.

Law of independent assortment: genes on different chromosomes assort independently; dihybrid F2 ratio 9:3:3:1; does not hold for linked genes.

Incomplete dominance gives intermediate phenotype (Snapdragon flower colour, 1:2:1); codominance expresses both alleles; multiple alleles example - ABO blood group in humans.

Chromosomal basis: Sutton and Boveri; genes are linearly arranged on chromosomes; linkage and recombination frequency measure map distance in centimorgans.

Non-disjunction produces aneuploidy (trisomy 21, Turner XO, Klinefelter XXY); polyploidy is common in plants (triploid banana, tetraploid cotton).

DNA structure (Watson and Crick, 1953): antiparallel double helix, A pairs T with two hydrogen bonds, G pairs C with three; one turn of helix about 3.4 nm with 10 base pairs.

Semi-conservative replication: helicase unwinds, DNA polymerase adds nucleotides 5' to 3', leading strand continuous, lagging strand in Okazaki fragments; Meselson–Stahl experiment confirmed it.

Transcription in eukaryotes: RNA polymerase II makes mRNA from template strand; introns removed by splicing; translation on ribosomes uses triplet codons, AUG start, UAA/UAG/UGA stop.

Photosynthesis equation: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O; oxygen released comes from water (Rubin and Kamen, isotope experiment).

Light reactions: PSII (P680) splits water, electrons pass through plastoquinone, cytochrome complex, plastocyanin to PSI (P700); NADP+ reduced, ATP made by photophosphorylation.

Calvin cycle (C3): carboxylation by RuBisCO, reduction using ATP and NADPH, regeneration of RuBP; 3 ATP and 2 NADPH per CO2 fixed.

C4 pathway (Hatch–Slack): PEP carboxylase fixes CO2 in mesophyll as malate, decarboxylated in bundle sheath; Kranz anatomy; low photorespiration; examples maize, sugarcane.

CAM plants fix CO2 at night as malic acid, decarboxylate by day with stomata closed; examples Opuntia, pineapple; photorespiration is high in C3 plants at high O2 and temperature.

Glycolysis: glucose to 2 pyruvate in cytoplasm, net 2 ATP and 2 NADH; Krebs cycle in mitochondrial matrix yields 6 NADH, 2 FADH2, 2 ATP per glucose; ETS yields about 34 ATP; total about 38 ATP.

Water potential = solute potential + pressure potential; water moves from higher to lower water potential; plasmolysis occurs in hypertonic solution, deplasmolysis on return to hypotonic.

Mineral nutrition: macroelements N, P, K, Ca, Mg, S; microelements Fe, Mn, Zn, Cu, B, Mo, Cl, Ni; deficiency of Mg causes chlorosis, of N stunted growth; hydroponics detects deficiency.

Growth phases: lag, log (exponential), stationary; growth measurable by auxanometer or by fresh weight and cell number; growth is indeterminate in plants due to meristems.

Auxin (IAA): apical dominance, cell elongation, root initiation in cuttings, parthenocarpy; high concentration inhibits growth; 2,4-D used as herbicide.

Gibberellins: stem elongation, bolting, seed germination by inducing alpha-amylase in barley aleurone, delaying senescence in citrus.

Cytokinins: promote cell division and shoot bud formation, delay senescence (Richmond–Lang effect); kinetin was first isolated from autoclaved herring sperm DNA.

Abscisic acid: stress hormone, closes stomata, induces seed dormancy and abscission; ethylene: fruit ripening, epinasty, senescence; both are growth inhibitors.

Photoperiodism: short-day plants flower when dark period exceeds critical length (examples rice, soybean); long-day plants when dark period is shorter (wheat, radish); leaves perceive the photoperiod.

Phytochrome exists as Pr (absorbs red, 660 nm) and Pfr (absorbs far-red, 730 nm); Pfr is the active form; red light converts Pr to Pfr.

Vernalization: cold treatment of germinating seeds or young seedlings induces flowering in biennials such as winter wheat, cabbage and sugar beet; site of perception is the shoot apex.

Flower parts: calyx (sepals), corolla (petals), androecium (stamens - filament and anther with four microsporangia), gynoecium (carpels - stigma, style, ovary with ovules).

Microsporogenesis: microspore mother cell undergoes meiosis to form tetrads of microspores; each forms a pollen grain with vegetative and generative cells; pollen wall has exine of sporopollenin.

Megasporogenesis: one megaspore mother cell gives four megaspores, three degenerate; the functional one forms the 8-nucleate, 7-celled embryo sac (Polygonum type).

Double fertilization: one male gamete fuses with egg (syngamy → zygote), the other with two polar nuclei (triple fusion → 3n primary endosperm nucleus).

Pollination agents: anemophily (wind - grasses, light dry pollen), entomophily (insects - coloured, scented, nectar), hydrophily (water - Vallisneria, Zostera), ornithophily (birds).

Self-pollination ensures purity but reduces variation; cross-pollination increases variation; cleistogamy (closed flowers) ensures autogamy; dichogamy and self-incompatibility prevent it.

Seed: integuments become seed coat (testa and tegmen), ovule becomes seed, ovary becomes fruit; albuminous seeds retain endosperm (castor), non-albuminous use it up (bean).

Apomixis produces seeds without fertilization (nucellar embryony in Citrus); polyembryony is presence of more than one embryo per seed; parthenocarpy is fruit without fertilization (banana).

Ecosystem components: producers, consumers, decomposers, and abiotic factors; energy flow is unidirectional, 10 per cent law between trophic levels; pyramids of number, biomass, energy.

Primary productivity is organic matter fixed by producers; gross primary productivity minus respiration equals net primary productivity; ocean productivity is limited by nitrogen and phosphorus.

Nutrient cycling: gaseous cycles (carbon, nitrogen) have atmospheric reservoirs; sedimentary cycles (phosphorus, sulphur) have lithospheric reservoirs; decomposition releases nutrients.

Ecological succession: hydrarch (in water) and xerarch (on dry rock); pioneer species to climax community; primary succession starts on bare substrate, secondary after disturbance.

Biodiversity hotspots in India: Western Ghats and Eastern Himalaya; India is a megadiverse country with about 8 per cent of global species; in-situ conservation by national parks and biosphere reserves, ex-situ by zoos, seed banks, botanical gardens.

IUCN Red List categories: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern; Project Tiger and Project Elephant are Indian conservation programmes.

Pollution: BOD measures organic load in water; eutrophication from nitrate and phosphate; ozone hole caused by CFCs over Antarctica; greenhouse gases CO2, CH4, N2O, CFCs cause global warming.

Biological magnification increases concentration of non-degradable pollutants such as DDT and mercury along the food chain; biomagnification is highest in top carnivores.

Plant breeding steps: collection of variability (germplasm), evaluation and selection, hybridisation, and testing, release and commercialisation of varieties.

Selection methods: pure line selection for self-pollinated crops, mass selection, clonal selection for asexual crops; hybridisation may be emasculation followed by artificial pollination and bagging.

Green Revolution: semi-dwarf, fertiliser-responsive wheat and rice varieties (Norin-10 dwarfing gene); mutation breeding produced mung bean varieties resistant to yellow mosaic virus.

Somatic hybridisation: protoplast fusion with polyethylene glycol or electrofusion produces hybrids such as pomato from potato and tomato; micropropagation uses shoot tip culture for virus-free plants.

Transgenic plants: Bt cotton carries Bacillus thuringiensis cry genes (cry1Ac) for bollworm resistance; Golden Rice is engineered for beta-carotene; RNA interference used against nematode Meloidogyne in tobacco.

Biotechnology tools: restriction endonucleases cut DNA at specific palindromic sites; ligase joins; plasmid vectors with origin of replication and selectable markers; Agrobacterium tumefaciens Ti plasmid as vector.

PCR amplifies DNA using Taq polymerase, primers and thermal cycling (denaturation, annealing, extension); gel electrophoresis separates DNA by size, smaller fragments move farther.

Economic plants: rubber from Hevea brasiliensis, cinchona for quinine, Catharanthus roseus for vincristine, neem (Azadirachta indica) as biopesticide, coconut and sugarcane as major Tamil Nadu crops.

Microscopy: start with low power, focus with coarse adjustment, then fine adjustment under high power; always focus upward to avoid breaking the slide; draw labelled diagrams with title and magnification.

Sectioning: free-hand transverse sections of stem and root with a razor blade, stain with safranin (lignin red) or iodine (starch blue-black); mount in glycerine to prevent drying.

Tests: starch with iodine gives blue-black; reducing sugar with Benedict's reagent gives brick-red precipitate on heating; protein with Biuret gives violet; chlorophyll absorbs red and blue-violet light.

Osmosis experiment: potato osmoscope shows rise of sucrose solution level; plasmolysis in Rheo or Tradescantia peel with 1 M sucrose, reversible on return to water.

Photosynthesis experiments: hydrilla bubble count varies with light intensity; starch test on a variegated leaf shows starch only in green areas; Moll's half-leaf experiment shows CO2 necessity.

Respiration: germinating seeds in a flask with KOH raise water level in a delivery tube, proving CO2 release and O2 use; thermos flask experiment shows heat release.

Field study: quadrat method for frequency, density and abundance; herbarium preparation by pressing, drying and mounting with a label; record work includes aim, procedure, observation and inference.

Soil test and plant identification: pH by universal indicator, texture by feel method; identification uses floral formula and floral diagram symbols (K, C, A, G with fusion and adhesion signs).