Tamil Nadu HSE First Year Biology cheat sheet

Taxonomy hierarchy (broad to narrow): Kingdom → Phylum/Division → Class → Order → Family → Genus → Species; remember mnemonic 'King Philip Came Over For Good Soup'.

Binomial nomenclature by Carolus Linnaeus: genus name capitalized, species epithet lowercase, both italicized or underlined; e.g., Mangifera indica.

Five-kingdom classification (Whittaker, 1969): Monera (prokaryotic), Protista (eukaryotic unicellular), Fungi (chitinous cell wall, saprophytic), Plantae (multicellular autotrophs), Animalia (multicellular heterotrophs).

Three-domain system (Woese): Bacteria, Archaea, Eukarya; based on 16S rRNA differences; Archaea have ether-linked lipids and distinct RNA polymerase.

Virus, viroid, lichen: viruses are non-cellular obligate parasites (TMV, bacteriophage); viroids are naked RNA (potato spindle tuber); lichens are symbiotic association of algae and fungi.

Taxonomic aids: herbarium (pressed dried specimens), botanical garden (living plants), museum (preserved specimens), zoological park (living animals), key (analytical tool using contrasting characters).

Species is the basic unit of classification; a species is a group of individuals with fundamental similarities and capable of interbreeding.

ICBN (International Code for Botanical Nomenclature) and ICZN (International Code of Zoological Nomenclature) govern naming rules; type specimen is the reference for a species.

Systematics = taxonomy + phylogeny; it studies diversity and evolutionary relationships among organisms.

Algae: chlorophyll-bearing, autotrophic, mostly aquatic; examples: Chlorophyceae (green algae: Chlamydomonas, Volvox), Phaeophyceae (brown algae: Laminaria, Fucus), Rhodophyceae (red algae: Porphyra, Polysiphonia).

Bryophytes (amphibians of plant kingdom): lack vascular tissue, dominant gametophyte, require water for fertilization; examples: Marchantia, Funaria, Sphagnum.

Pteridophytes: first vascular plants, dominant sporophyte, need water for sperm; examples: Selaginella, Equisetum, Pteris, Adiantum.

Gymnosperms: naked seeds, no ovary enclosure; heterosporous; examples: Cycas, Pinus, Ginkgo, Ephedra; Cycas has coralloid roots with cyanobacteria.

Angiosperms: flowering plants with enclosed seeds (ovary → fruit); double fertilization and triple fusion produce diploid zygote and triploid endosperm.

Life cycle alternation: haploid gametophyte (n) produces gametes by mitosis; diploid sporophyte (2n) produces spores by meiosis; dominance shifts from gametophyte (bryophytes) to sporophyte (pteridophytes, gymnosperms, angiosperms).

Monocots vs dicots: monocots have one cotyledon, parallel venation, fibrous roots, trimerous flowers; dicots have two cotyledons, reticulate venation, tap roots, tetramerous/pentamerous flowers.

Economic importance: algae as food (Porphyra, Laminaria), agar from Gelidium and Gracilaria; Sphagnum as peat; gymnosperms as timber and resins.

Body plan terms: symmetry (asymmetrical, radial, bilateral), coelom (acoelomate, pseudocoelomate, coelomate), segmentation, and germ layers (diploblastic vs triploblastic).

Porifera (sponges): cellular level, ostia → spongocoel → osculum, choanocytes; e.g., Sycon, Spongilla.

Cnidaria (coelenterates): diploblastic, tissue level, cnidoblasts, polyp and medusa forms; e.g., Hydra, Aurelia, Physalia.

Platyhelminthes (flatworms): triploblastic, acoelomate, flame cells; e.g., Planaria, Fasciola, Taenia.

Aschelminthes (roundworms): pseudocoelomate, complete digestive tract; e.g., Ascaris, Wuchereria.

Annelida: true coelom, metameric segmentation, nephridia; e.g., Nereis, Pheretima, Hirudinaria.

Arthropoda: largest phylum, jointed appendages, chitinous exoskeleton, open circulation; e.g., insects, crustaceans, arachnids.

Mollusca: soft-bodied, mantle, shell (usually), radula; e.g., Pila, Sepia, Octopus; Echinodermata: spiny, water-vascular system, radial adults and bilateral larvae; e.g., Asterias.

Chordates: notochord, dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail; vertebrates (classes: Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia) have vertebral column.

Prokaryotic cell: no nucleus or membrane-bound organelles; 70S ribosomes; cell wall (peptidoglycan); examples: bacteria, cyanobacteria.

Eukaryotic organelles: nucleus (genetic control), mitochondria (ATP via oxidative phosphorylation), chloroplast (photosynthesis), ER (protein/lipid synthesis and transport), Golgi (modification, packaging), lysosome (hydrolytic enzymes), peroxisome (H2O2 metabolism).

Fluid mosaic model (Singer & Nicolson): plasma membrane is a phospholipid bilayer with embedded proteins; selective permeability.

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.

Biomolecules: carbohydrates (mono-, di-, polysaccharides), proteins (amino acids linked by peptide bonds), lipids (fatty acids + glycerol), nucleic acids (nucleotides: pentose sugar, phosphate, nitrogenous base).

Enzymes: biological catalysts, mostly proteins, lower activation energy; affected by temperature, pH, substrate concentration; lock-and-key and induced-fit models.

Cell cycle: interphase (G1, S, M-check G2) + M phase; mitosis produces two identical diploid cells; meiosis produces four haploid cells with crossing over in prophase I.

Mitosis stages: prophase (chromosome condensation), metaphase (alignment at equator), anaphase (sister chromatids separate), telophase (nuclear envelope re-forms); cytokinesis follows.

Meiosis significance: genetic variation via crossing over and independent assortment; reduces chromosome number by half.

Water potential (Ψ) = solute potential (Ψs) + pressure potential (Ψp); water moves from higher to lower water potential.

Transpiration pull-cohesion-tension theory explains ascent of sap in xylem; root pressure contributes at night.

Mineral nutrition: macronutrients (N, P, K, Ca, Mg, S) and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl, Ni); deficiency symptoms include chlorosis and necrosis.

Photosynthesis: light reactions in thylakoids produce ATP and NADPH; Calvin cycle (dark reaction) in stroma fixes CO2 via RuBisCO.

C3, C4, and CAM pathways: C4 plants (e.g., maize, sugarcane) use PEP carboxylase and have Kranz anatomy; CAM plants (e.g., cacti) fix CO2 at night.

Respiration: glycolysis (cytoplasm) → Krebs cycle (mitochondrial matrix) → electron transport chain (inner membrane); ATP yield ~36-38 per glucose in aerobic respiration.

Fermentation: anaerobic breakdown of glucose to lactic acid (animals) or ethanol + CO2 (yeast); yields 2 ATP per glucose.

Plant growth regulators: auxins (cell elongation, apical dominance), gibberellins (stem elongation, seed germination), cytokinins (cell division), abscisic acid (stress hormone, stomatal closure), ethylene (fruit ripening).

Photoperiodism: short-day plants flower when day length is below critical period; long-day plants flower when day length exceeds critical period; phytochrome mediates response.

Digestion: mechanical and chemical breakdown; enzymes-salivary amylase (starch), pepsin (protein in stomach), pancreatic lipase (fats), trypsin (protein); absorption mainly in small intestine villi.

Circulation: double circulation (pulmonary and systemic); heart has four chambers; SA node is pacemaker; ECG records electrical activity (P wave, QRS complex, T wave).

Blood components: plasma, RBCs (erythrocytes, hemoglobin for O2 transport), WBCs (leukocytes, immunity), platelets (thrombocytes, clotting).

Respiration: external (lungs) and internal (tissue) respiration; hemoglobin carries O2; CO2 transported mainly as bicarbonate; respiratory center in medulla oblongata.

Excretion: nephron is functional unit of kidney; filtration (glomerulus), reabsorption (tubules), secretion; urine formation; hormones ADH and aldosterone regulate water and salt balance.

Locomotion: skeletal system (bones, cartilage), muscle contraction via sliding filament theory (actin and myosin); joints (ball-and-socket, hinge, pivot).

Neural control: neuron structure (dendrites, cell body, axon); resting potential (-70 mV) and action potential; synapse transmission via neurotransmitters; brain regions (cerebrum, cerebellum, medulla).

Endocrine control: hormones from pituitary (growth hormone, TSH), thyroid (thyroxine), pancreas (insulin, glucagon), adrenal (adrenaline, cortisol), gonads (testosterone, estrogen, progesterone).

Homeostasis: maintenance of stable internal environment via feedback loops (e.g., blood glucose regulation by insulin and glucagon).

Asexual reproduction: fragmentation, budding, fission, spore formation, vegetative propagation; offspring genetically identical (clones).

Sexual reproduction in flowering plants: flower parts-sepals, petals, stamens (anther + filament), carpel (stigma, style, ovary); pollination (self vs cross), fertilization, seed and fruit formation.

Human male reproductive system: testes produce sperm and testosterone; epididymis, vas deferens, seminal vesicles, prostate, bulbourethral glands; penis.

Human female reproductive system: ovaries produce ova and estrogen/progesterone; fallopian tubes, uterus, cervix, vagina; menstrual cycle (~28 days) with ovulation around day 14.

Gametogenesis: spermatogenesis produces four sperm per primary spermatocyte; oogenesis produces one ovum and polar bodies; both involve meiosis.

Reproductive health: contraception methods (barrier, hormonal, IUD, surgical), STDs (gonorrhea, syphilis, HIV/AIDS), infertility treatments (IVF, ZIFT, GIFT).

Embryonic development: zygote → cleavage → blastocyst → implantation → gastrulation → organogenesis; placenta provides nourishment and gas exchange.

Apomixis and polyembryony: apomixis is seed formation without fertilization; polyembryony is presence of more than one embryo in a seed.

Mendel's laws: Law of Dominance, Law of Segregation (alleles separate during gamete formation), Law of Independent Assortment (genes on different chromosomes assort independently).

Monohybrid cross (3:1 phenotypic, 1:2:1 genotypic) and dihybrid cross (9:3:3:1) illustrate inheritance patterns.

Incomplete dominance (e.g., Snapdragon flower color) and codominance (e.g., AB blood group) deviate from simple dominance.

Chromosomal theory of inheritance (Sutton and Boveri): genes are located on chromosomes; sex-linked inheritance (e.g., color blindness, hemophilia) carried on X chromosome.

DNA structure: double helix (Watson and Crick, 1953), antiparallel strands, complementary base pairing (A-T, G-C), hydrogen bonds.

Central dogma: DNA → RNA (transcription) → protein (translation); genetic code is triplet, degenerate, and universal.

Mutation: change in DNA sequence; point mutations (substitution, insertion, deletion) can cause frameshift; chromosomal aberrations (deletion, duplication, inversion, translocation).

Evolution: Darwin's natural selection; evidence from fossils, homologous and analogous organs, embryology, and molecular homology; Hardy-Weinberg principle (p² + 2pq + q² = 1).

Human evolution: Homo sapiens arose in Africa; evolutionary trends include bipedalism, increased brain size, and reduced jaw.

Biotechnology: use of living organisms or their products for human welfare; recombinant DNA technology, gene cloning, and transgenic organisms.

Applications: insulin production (Humulin from E. coli), gene therapy, DNA fingerprinting, Bt crops (pest-resistant), and vaccine production.

Ecology: levels of organization-organism, population, community, ecosystem, biome, biosphere; abiotic and biotic factors.

Ecosystem: producers, consumers, decomposers; energy flow is unidirectional (10% law); nutrient cycles (carbon, nitrogen, phosphorus).

Biodiversity: variety of life; hotspots (e.g., Western Ghats, Eastern Himalayas); threats-habitat loss, pollution, overexploitation, invasive species; conservation (in situ and ex situ).

Environmental issues: air pollution (CO, SO2, NOx, particulate matter), water pollution, ozone depletion (CFCs), global warming (greenhouse gases), and eutrophication.

Sustainable development: meeting present needs without compromising future generations; renewable energy, afforestation, waste management, and bioremediation.

Plant tissue culture and micropropagation: growing plants from cells/tissues in sterile nutrient medium; used for cloning elite varieties and virus-free plants.

Biofertilizers: Rhizobium (nitrogen fixation in legumes), Azotobacter, Azospirillum, mycorrhizae (phosphate uptake).