Tamil Nadu HSE Second Year Biology cheat sheet

Asexual reproduction in plants: vegetative propagules include runners (grass), rhizomes (ginger), tubers (potato), bulbs (onion), offsets (water hyacinth), and leaf buds (Bryophyllum).

Sexual reproduction in flowering plants: microsporangium (anther) produces microspores via meiosis; each microspore undergoes mitosis to form a pollen grain with generative and vegetative cells; the generative cell divides to form two male gametes.

Megasporogenesis: one megaspore mother cell (2n) undergoes meiosis to form four megaspores (n); usually only one survives and develops into the embryo sac (female gametophyte) with 8 nuclei and 7 cells (3 antipodal, 2 polar nuclei in central cell, 2 synergids, 1 egg).

Double fertilization: one male gamete fuses with egg (syngamy → zygote, 2n); the other fuses with two polar nuclei (triple fusion → primary endosperm nucleus, 3n).

Human male reproductive system: testes produce sperm and testosterone; sperm travel via epididymis, vas deferens, ejaculatory duct, urethra; accessory glands: seminal vesicles, prostate, bulbourethral.

Human female reproductive system: ovaries produce ova and estrogen/progesterone; fallopian tube is site of fertilization; uterus (endometrium) supports implantation; cervix opens into vagina.

Menstrual cycle: menstrual phase (days 1–5), follicular/proliferative phase (days 6–13), ovulation (~day 14), luteal/secretory phase (days 15–28); hormones: FSH, LH, estrogen, progesterone.

Reproductive health: contraception methods include barrier (condoms), hormonal (pills), IUDs (CuT), surgical (vasectomy/tubectomy); STDs include gonorrhea, syphilis, chlamydiasis, genital herpes, HIV/AIDS; ART includes IVF, ZIFT, GIFT, ICSI.

Apomixis: asexual seed formation without fertilization (e.g., Citrus, mango); polyembryony: presence of more than one embryo in a seed (e.g., citrus).

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

Monohybrid cross: F1 all tall (Tt); F2 phenotypic ratio 3:1 (tall: dwarf), genotypic ratio 1:2:1 (TT:Tt:tt). Dihybrid cross F2 phenotypic ratio 9:3:3:1.

Incomplete dominance: F1 intermediate phenotype (e.g., Snapdragon flower color); codominance: both alleles expressed (e.g., AB blood group).

Molecular basis: DNA structure (Watson-Crick double helix, antiparallel, base pairing A-T, G-C); replication semi-conservative (Meselson-Stahl); transcription (RNA polymerase); translation (ribosome, tRNA, genetic code triplet, start AUG, stop UAA/UAG/UGA).

Lac operon: inducible operon; lactose acts as inducer, binds repressor, allows transcription of lacZ, lacY, lacA; absence of lactose → repressor binds operator → no transcription.

Human genetics: sex determination (XX female, XY male); sex-linked disorders (hemophilia, color blindness); autosomal disorders (sickle cell anemia, phenylketonuria, thalassemia); chromosomal disorders (Down syndrome – trisomy 21, Klinefelter – XXY, Turner – XO).

Evolution: Darwin's natural selection; evidence from paleontology, comparative anatomy (homologous vs analogous organs), embryology, molecular phylogeny; Hardy-Weinberg principle: p² + 2pq + q² = 1.

Human evolution: Dryopithecus, Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Homo neanderthalensis, Homo sapiens; bipedalism and increasing brain size.

Types of natural selection: stabilizing (average phenotype favored), directional (one extreme favored), disruptive (both extremes favored).

Pathogens: Plasmodium (malaria), Entamoeba (amoebiasis), Ascaris (ascariasis), Wuchereria (filariasis), Salmonella typhi (typhoid), Streptococcus pneumoniae (pneumonia), HIV (AIDS), HPV (cervical cancer).

Immunity: innate (non-specific: barriers, phagocytes, inflammation) vs acquired (specific: B cells → antibodies, T cells → cell-mediated); active (vaccination) vs passive (antibodies transferred).

Vaccines: BCG (TB), DPT (diphtheria, pertussis, tetanus), polio (OPV/IPV), MMR (measles, mumps, rubella), hepatitis B; toxoid vaccines (tetanus, diphtheria).

Microbes in human welfare: Lactobacillus (curd), Saccharomyces cerevisiae (bread, beer), Aspergillus niger (citric acid), Penicillium (penicillin), Clostridium butylicum (butyric acid), Trichoderma polysporum (cyclosporin A), Monascus purpureus (statins).

Sewage treatment: primary (physical removal), secondary (biological, activated sludge), tertiary (chemical); biogas production by methanogens (e.g., Methanobacterium).

Plant breeding: steps include collection of variability, evaluation and selection, cross-hybridization, selection and testing of superior recombinants; methods: hybridization, mutation breeding, polyploidy, tissue culture.

Green revolution: introduction of high-yielding varieties of wheat (e.g., Kalyan Sona, Sonalika) and rice (e.g., IR-8, Taichung Native-1); use of fertilizers, pesticides, irrigation.

Biofortification: breeding crops with higher nutrients (e.g., Atlas 66 wheat – protein; golden rice – vitamin A; iron-fortified bajra).

Single Cell Protein (SCP): protein from microbes (e.g., Spirulina, Methylophilus methylotrophus) used as food supplement.

Genetic engineering tools: restriction enzymes (e.g., EcoRI, HindII), vectors (plasmids, bacteriophages, Ti plasmid), host organisms (E. coli, Agrobacterium), selectable markers, origin of replication.

Steps in recombinant DNA technology: isolation of DNA, fragmentation by restriction enzymes, isolation of desired gene, ligation into vector, transfer into host, selection and screening, multiplication and expression.

PCR (Polymerase Chain Reaction): denaturation (94°C), annealing (~55°C), extension (72°C) using Taq polymerase; amplifies DNA in vitro.

Gel electrophoresis: separates DNA fragments based on size; agarose gel; DNA migrates towards anode; staining with ethidium bromide and UV visualization.

Bioreactors: stirred-tank and sparged bioreactors for large-scale culture of cells; downstream processing for product purification.

Applications: insulin (Humulin from E. coli), gene therapy (ADA deficiency), vaccines (hepatitis B), transgenic animals (for human protein production), Bt crops (pest resistance), RNA interference (nematode resistance in tobacco).

Bt toxin: produced by Bacillus thuringiensis; cry genes (cryIAc, cryIIAb) encode insecticidal proteins; activated in alkaline gut of insects; used in Bt cotton, Bt corn.

Molecular diagnosis: PCR, ELISA, DNA fingerprinting; gene therapy: introduction of functional gene into cells (e.g., retroviral vectors).

Ethical issues: genetic engineering of humans, patenting of genes, biopiracy; biopatent and GM crops controversy.

Population attributes: density, natality, mortality, immigration, emigration, age distribution, sex ratio; growth models: exponential (J-shaped) and logistic (S-shaped, carrying capacity K).

Population interactions: mutualism (+,+), competition (–,–), predation (+,–), parasitism (+,–), commensalism (+,0), amensalism (–,0).

Ecosystem components: producers, consumers, decomposers; energy flow unidirectional; 10% law (Lindeman); ecological pyramids (number, biomass, energy).

Biogeochemical cycles: gaseous (carbon, nitrogen) and sedimentary (phosphorus, sulfur); nitrogen cycle includes nitrogen fixation, ammonification, nitrification, denitrification.

Biodiversity: levels (genetic, species, ecosystem); patterns (latitudinal gradient, species-area relationship); hotspots (e.g., Western Ghats, Eastern Himalayas); threats (habitat loss, overexploitation, invasive species, pollution, climate change).

Conservation: in situ (national parks, sanctuaries, biosphere reserves) and ex situ (zoos, seed banks, botanical gardens); IUCN categories (extinct, endangered, vulnerable, rare).

Environmental issues: air pollution (SO2, NOx, CO, particulates), water pollution (BOD, eutrophication), solid waste, ozone depletion (CFCs), greenhouse effect (CO2, CH4, N2O, CFCs).

Eutrophication: nutrient enrichment (N, P) → algal bloom → oxygen depletion → fish kill; biomagnification: increase in pollutant concentration at higher trophic levels (e.g., DDT).

Biodiversity hotspots in India: Western Ghats, Sri Lanka, Indo-Burma, Himalayas; global biodiversity: ~1.7 million species described.

Cell cycle: interphase (G1, S, G2) and M phase (mitosis/meiosis); mitosis stages: prophase, metaphase, anaphase, telophase; cytokinesis; checkpoints regulate cycle.

Meiosis: two divisions (I and II); prophase I includes synapsis, crossing over (recombination) at chiasmata; results in four haploid cells; sources of genetic variation.

Biomolecules: carbohydrates (mono-, di-, polysaccharides), proteins (amino acids, peptide bonds), lipids (fatty acids, glycerol), nucleic acids (DNA, RNA); enzymes are biocatalysts (lock-and-key, induced fit).

Cell organelles: nucleus (genetic material), mitochondria (ATP production, oxidative phosphorylation), chloroplast (photosynthesis), ribosome (protein synthesis), ER (rough – protein, smooth – lipid), Golgi (packaging), lysosome (digestion), peroxisome (detoxification).

Transport: diffusion (passive), osmosis (water), facilitated diffusion (carrier proteins), active transport (ATP, e.g., Na+/K+ pump), endocytosis/exocytosis.

Photosynthesis: light reaction (PSII, PSI, photolysis of water, ATP and NADPH) and Calvin cycle (dark reaction, RuBisCO, CO2 fixation); C3, C4, and CAM pathways.

Respiration: glycolysis (cytoplasm, 2 ATP, 2 NADH), Krebs cycle (mitochondrial matrix, 2 ATP, NADH, FADH2), electron transport chain (oxidative phosphorylation, ~34 ATP); anaerobic respiration (fermentation).

Photosynthetic pigments: chlorophyll a (primary), chlorophyll b, carotenoids; absorption spectrum; action spectrum; red and blue light most effective.

ATP: energy currency; structure (adenosine + 3 phosphate); hydrolysis releases energy (~7.3 kcal/mol).

Water potential (Ψ): Ψ = Ψs + Ψp; water moves from higher to lower water potential; pure water Ψ = 0; solute potential (Ψs) negative; pressure potential (Ψp) positive in turgid cells.

Transpiration: loss of water vapor through stomata; cohesion-tension theory (transpirational pull); factors: light, temperature, humidity, wind; stomatal opening by K+ influx.

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

Nitrogen fixation: symbiotic (Rhizobium in root nodules) and non-symbiotic (Azotobacter, cyanobacteria); nitrogenase enzyme; leghaemoglobin.

Plant growth regulators: auxins (apical dominance, rooting), 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 < critical), long-day plants (flower when day length > critical), day-neutral plants; phytochrome (Pr/Pfr) involved.

Vernalization: cold treatment promotes flowering (e.g., winter wheat); prevents precocious reproductive development.

Respiration in plants: aerobic (glycolysis, Krebs cycle, ETC) and anaerobic (fermentation); respiratory quotient (RQ) = CO2 released / O2 consumed; RQ for carbohydrates = 1, fats <1, proteins ~0.9.

Seed dormancy and germination: factors (water, oxygen, temperature, light); gibberellins break dormancy; abscisic acid induces dormancy.

Taxonomic hierarchy: Kingdom, Phylum/Division, Class, Order, Family, Genus, Species; binomial nomenclature (Carolus Linnaeus); rules of ICBN/ICZN.

Five kingdom classification (R.H. Whittaker): Monera, Protista, Fungi, Plantae, Animalia; basis: cell structure, thallus organization, mode of nutrition, reproduction, phylogenetic relationships.

Plant kingdom: algae (Chlorophyceae, Phaeophyceae, Rhodophyceae), bryophytes (amphibians of plant kingdom), pteridophytes (first vascular plants), gymnosperms (naked seeds), angiosperms (flowering plants).

Animal kingdom: phyla Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, Chordata; key features (symmetry, coelom, segmentation, notochord).

Fungi: classes Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes; symbiotic associations: lichens (algae + fungi), mycorrhiza (fungi + roots).

Microbes: viruses (TMV, bacteriophage), viroids (potato spindle tuber), prions (BSE), lichens; classification of bacteria based on shape (coccus, bacillus, spirillum, vibrio).

Binomial nomenclature examples: Mangifera indica (mango), Homo sapiens (human), Panthera leo (lion), Oryza sativa (rice).

Herbarium, botanical garden, museum, zoological park are taxonomic aids; key is a taxonomic aid for identification.

Whittaker's kingdom Monera includes archaebacteria (methanogens, halophiles, thermoacidophiles) and eubacteria (cyanobacteria, mycoplasma).