Bihar BSEB Intermediate Biology cheat sheet

Microsporangium tapetum nourishes developing pollen; each microspore mother cell undergoes meiosis to give four microspores, each forming a pollen grain with a generative and a vegetative cell.

In angiosperms the pollen tube enters the ovule through the micropyle (porogamy); double fertilization fuses one male gamete with the egg (2n zygote) and the other with two polar nuclei (3n primary endosperm nucleus).

Ovule after fertilization: integuments become seed coat, nucellus becomes perisperm, outer and inner integuments may form testa and tegma; ovary wall becomes pericarp.

Human spermatogenesis: spermatogonia to primary spermatocyte (meiosis I) to two secondary spermatocytes to four spermatids to spermatozoa; Sertoli cells provide nourishment, Leydig cells secrete testosterone.

Menstrual cycle: follicular phase driven by FSH, ovulation near day 14 triggered by LH surge, luteal phase sustained by progesterone from corpus luteum; menstruation occurs if no implantation.

Human gestation averages about 280 days from last menstrual period; implantation of blastocyst occurs about 6-7 days after fertilization; hCG from trophoblast maintains the corpus luteum.

Reproductive health: lactational amenorrhea, condoms, oral pills, IUDs (CuT, Lippes loop), tubectomy and vasectomy are contraceptive methods; MTP is legal in India up to 20 weeks under the Medical Termination of Pregnancy Act.

STDs of major concern include gonorrhea (Neisseria), syphilis (Treponema), chlamydiasis, genital herpes and HIV/AIDS; early detection and treatment prevent complications such as infertility and ectopic pregnancy.

Mendel's law of segregation: alleles separate during gamete formation; law of independent assortment applies to genes on different chromosomes; test cross with recessive parent reveals genotype.

Incomplete dominance (e.g., Snapdragon flower colour) gives intermediate heterozygote phenotype; codominance (AB blood group) expresses both alleles; multiple alleles exist for the ABO locus (IA, IB, i).

Sex-linked inheritance: colour blindness and haemophilia are X-linked recessive; affected males inherit the allele from carrier mothers; daughters of an affected male are carriers.

DNA structure: antiparallel double helix, 10 bp per turn, 3.4 nm pitch, 0.34 nm rise per base pair; A=T and G=C; Chargaff's rule states A/T = G/C = 1.

DNA replication is semi-conservative (Meselson-Stahl), requires DNA polymerase, origin of replication, and proceeds 5' to 3' with continuous leading strand and discontinuous lagging strand (Okazaki fragments).

Lac operon: lactose acts as inducer, binding repressor and allowing RNA polymerase to transcribe lacZ, lacY, lacA; absence of lactose keeps repressor bound and operon off.

Evolution evidence: homologous organs (divergent evolution), analogous organs (convergent evolution), fossils, embryology and molecular homology; Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, no selection and large population.

Natural selection types: directional, stabilizing and disruptive; industrial melanism in Biston betularia is a classic directional selection example; genetic drift is random allele frequency change in small populations.

Pathogen-disease matching: Plasmodium causes malaria (Anopheles vector), Wuchereria causes filariasis (Culex), Ascaris causes ascariasis, Salmonella typhi causes typhoid, HIV causes AIDS via reverse transcriptase.

Immunity: innate (barriers, phagocytes, inflammation) versus acquired (B and T lymphocytes); primary response is slow, secondary response is rapid due to memory cells; colostrum provides passive immunity to infants.

Antibody structure: H2L2, with two heavy and two light chains; IgG crosses placenta; IgA is in secretions; IgE mediates allergy; IgM is the first antibody in primary response.

Microbes in human welfare: Lactobacillus for curd, Saccharomyces for bread and ethanol, Aspergillus niger for citric acid, Penicillium for penicillin, Trichoderma polysporum for cyclosporin A, Monascus purpureus for statins.

Sewage treatment: primary (physical removal of solids) and secondary (aerobic sludge digestion by microbes) stages; biogas from anaerobic sludge digestion contains methane and is used as fuel.

Biofertilizers: Rhizobium (legume nodules), Azospirillum, Azotobacter (free-living nitrogen fixers), Anabaena and Nostoc (cyanobacteria), Glomus (mycorrhiza for phosphorus).

Apiculture, poultry and fisheries are animal husbandry practices; MOET and artificial insemination improve cattle; somatic hybridization and micropropagation (tissue culture) are plant breeding tools.

Single cell protein (SCP) from Spirulina and Methylophilus methylotrophus provides protein-rich feed; it reduces pressure on conventional agriculture and recycles waste.

Restriction enzymes recognize palindromic sequences; EcoRI cuts GAATTC between G and A producing sticky ends; ligase joins compatible sticky ends; DNA is negatively charged and moves toward the anode in gel electrophoresis.

PCR steps: denaturation (~94 C), annealing of primers (~50-60 C), extension by Taq polymerase (~72 C); Taq is thermostable because it comes from Thermus aquaticus.

Cloning vector features: origin of replication, selectable marker (e.g., ampicillin resistance), restriction sites; pBR322 has ori, ampR and tetR markers; insertional inactivation identifies recombinants.

Agrobacterium tumefaciens Ti plasmid delivers genes into dicot plants; gene gun (biolistics) is used for monocots; Bt cotton carries cry genes (cryIAc, cryIIAb) toxic to bollworm larvae.

RNA interference (RNAi) using dsRNA silences nematode Meloidogyne incognita in tobacco; Golden rice is biofortified with beta-carotene; Flavr Savr tomato had delayed ripening.

Insulin production: proinsulin has C peptide; mature human insulin has A and B chains linked by disulfide bonds; recombinant insulin avoids animal-source immune reactions.

Gene therapy: somatic cell gene therapy corrects genetic disease in patients (e.g., ADA deficiency); germline changes are heritable and generally not permitted; PCR-based diagnosis detects mutations early.

Transgenic animals (e.g., Rosie cow producing human alpha-lactalbumin) and molecular diagnosis using ELISA and PCR are major biotechnology applications; biopiracy concerns unlicensed use of bioresources.

Population growth: exponential dN/dt = rN; logistic dN/dt = rN(K-N)/K, where K is carrying capacity; r-selected species have high reproduction, K-selected species have low reproduction and parental care.

Population interactions: mutualism (+,+), competition (-,-), predation and parasitism (+,-), commensalism (+,0), amensalism (-,0); Gause's competitive exclusion principle applies to competing species.

Ecosystem energy flow is unidirectional; 10 percent law states only about 10 percent of energy transfers between trophic levels; pyramids of number, biomass and energy describe trophic structure.

Primary productivity: gross primary productivity minus respiration equals net primary productivity; ocean productivity is limited by light and nutrients, terrestrial by temperature and moisture.

Nutrient cycles: gaseous (carbon, nitrogen) and sedimentary (phosphorus, sulphur); decomposition involves fragmentation, leaching, catabolism, humification and mineralization.

Biodiversity hotspots in India include the Western Ghats, Eastern Himalayas, Indo-Burma and Sundaland; India has about 8 percent of global species diversity on 2.4 percent of land area.

In-situ conservation: biosphere reserves, national parks, sanctuaries; ex-situ: zoos, botanical gardens, seed banks, cryopreservation; Sacred groves are community-protected forests.

Environmental issues: ozone depletion by CFCs (Montreal Protocol), greenhouse gases (CO2, CH4, N2O, CFCs), eutrophication by nitrates and phosphates, biomagnification of DDT, and joint forest management.

Prokaryotic cell: 70S ribosomes, nucleoid without membrane, mesosomes for respiration; eukaryotic cell: 80S ribosomes, membrane-bound organelles, cytoskeleton and compartmentalization.

Fluid mosaic model (Singer and Nicolson): phospholipid bilayer with integral and peripheral proteins; membrane transport includes simple diffusion, facilitated diffusion, active transport (Na+/K+ ATPase) and osmosis.

Mitochondria are the site of aerobic respiration and ATP synthesis; chloroplasts carry out photosynthesis; lysosomes are acidic hydrolase-containing organelles; Golgi packages and modifies proteins.

Cell cycle: interphase (G1, S, G2) and M phase; DNA replicates in S phase; mitosis stages are prophase, metaphase, anaphase, telophase; cytokinesis differs in plant (cell plate) and animal cells (cleavage furrow).

Meiosis I is reductional (homologous separation, crossing over in pachytene); meiosis II is equational; synaptonemal complex forms in zygotene; chiasmata become visible in diplotene.

Biomolecules: amino acids linked by peptide bonds, proteins have primary to quaternary structure; enzymes lower activation energy and are affected by pH and temperature; competitive inhibitors bind the active site.

Nucleic acids: DNA deoxyribose, RNA ribose; ATP is the energy currency; carbohydrates include monosaccharides, disaccharides (sucrose, lactose) and polysaccharides (starch, cellulose, glycogen).

Cell theory: all living organisms are made of cells, cells arise from pre-existing cells; Virchow added the third postulate; cell size is limited by surface area to volume ratio.

Water potential = solute potential + pressure potential; water moves from higher to lower water potential; apoplast, symplast and transmembrane pathways carry water across roots; Casparian strip forces symplastic entry.

Transpiration pull (cohesion-tension theory) drives xylem sap upward; stomata open when guard cells are turgid due to K+ influx; transpiration is highest in dry, windy, bright conditions.

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

Photosynthesis: light reactions in thylakoids produce ATP and NADPH and split water (oxygen source); Calvin cycle in stroma fixes CO2 via RuBisCO; C4 plants use PEP carboxylase and bundle sheath cells; CAM plants fix CO2 at night.

Limiting factors: Blackman's law of limiting factors; light saturation and CO2 saturation curves; chlorophyll a and b absorb mainly blue-violet and red light, reflecting green.

Respiration: glycolysis in cytoplasm yields 2 ATP and 2 NADH per glucose; Krebs cycle in mitochondrial matrix; ETC and oxidative phosphorylation yield most ATP; anaerobic fermentation gives lactate or ethanol.

RQ values: carbohydrates 1.0, fats about 0.7, proteins about 0.9; RQ greater than 1 indicates organic acid respiration; aerobic respiration yields about 36-38 ATP per glucose.

Plant growth regulators: auxin (apical dominance, rooting), gibberellin (stem elongation, bolting), cytokinin (cell division, delay senescence), abscisic acid (stomatal closure, dormancy), ethylene (ripening, abscission).

Digestion: salivary amylase acts on starch at pH ~6.8; pepsin acts on proteins in acidic stomach; trypsin and chymotrypsin in alkaline duodenum; bile emulsifies fats; absorption of glucose and amino acids occurs in the small intestine.

Breathing: inspiration is active (diaphragm and external intercostals), expiration passive at rest; tidal volume about 500 mL, vital capacity about 3500-4500 mL; CO2 mainly transported as bicarbonate.

Blood: plasma without clotting factors is serum; RBCs lack a nucleus and live about 120 days; platelets number 1.5-3.5 lakh per cubic mm; SA node is the pacemaker; normal BP is about 120/80 mm Hg.

Excretion: nephron has glomerulus, Bowman's capsule, PCT, loop of Henle, DCT and collecting duct; glomerular filtration rate about 125 mL/min; ADH increases water reabsorption; aldosterone increases Na+ reabsorption.

Muscle contraction: sliding filament theory, actin and myosin, calcium release from sarcoplasmic reticulum, troponin-tropomyosin shift; ATP required for cross-bridge cycling and relaxation.

Neural control: resting potential about -70 mV maintained by Na+/K+ pump; action potential depolarizes to about +30 mV; myelin sheath speeds conduction; synapse uses neurotransmitters such as acetylcholine.

Hormones: insulin lowers blood glucose, glucagon raises it; thyroxine needs iodine; parathyroid hormone raises blood calcium; adrenaline is the fight-or-flight hormone; cortisol is a glucocorticoid.

Thermoregulation and homeostasis: hypothalamus is the thermostat; negative feedback maintains glucose, water and temperature balance; positive feedback occurs in oxytocin-driven uterine contractions.