NEET 2025 • Class XII Biology

NCERT 2025–26: Class 12 Biology Hub — Notes, Figures, Summaries, Quizzes & Downloads

This hub brings together all five NCERT units — (VI) Reproduction, (VII) Genetics & Evolution, (VIII) Biology & Human Welfare, (IX) Biotechnology & its Applications, and (X) Ecology & Environment — with chapters 1–13 presented in a consistent, exam-ready format. Every chapter block follows the same layout: Notes → Figures → Quick Summary → 10-MCQ Quiz → Downloads. Use the sticky contents at left to jump between chapters, and the search box to filter chapters live on this page.

Syllabus verified • Updated: 06 Sep 2025

Unit Overview

This page is your master table of contents for NCERT Class XII Biology. Units are ordered as in NCERT, and each chapter block is self-contained for teaching and revision: topic-wise notes with definitions & logic, diagram callouts for labelling practice, a quick summary for last-minute revision, a 10-MCQ quiz for NEET pattern practice, and downloads (revision sheets, tables, diagrams). Progress chips flag weightage (High/Medium), diagram-heavy topics, and PYQ density to help you prioritise.

High-yield PYQs Diagram labelling 10-MCQ quizzes Quick revision sheets

01 Sexual Reproduction in Flowering Plants

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Androecium: Stamens with bilobed, dithecous, tetrasporangiate anthers. Microsporangium wall layers: epidermis, endothecium, middle layers, tapetum (nutrition).
  • Microsporogenesis: Sporogenous cells undergo meiosis → microspore tetrads → pollen grains (male gametophyte). Pollen wall: exine (sporopollenin, germ pores) and intine.
  • Pollen stage: Shed either at 2-celled (vegetative + generative) or 3-celled stage (vegetative + two male gametes).
  • Gynoecium: Pistil = stigma, style, ovary with ovules on placenta. Ovule: funicle, integument(s), micropyle, nucellus, MMC.
  • Megasporogenesis: MMC meiosis → four megaspores; typically one functional megaspore.
  • Embryo sac (monosporic, Polygonum type): 7-celled, 8-nucleate; egg apparatus (2 synergids + egg) at micropylar end, 3 antipodals at chalazal end, central cell with two polar nuclei.
  • Pollination: Autogamy, geitonogamy, xenogamy; agents abiotic (wind, water) and biotic (insects, birds, bats) with floral adaptations.
  • Pollen–pistil interaction: Recognition of compatibility; pollen germination on stigma → pollen tube through style to ovule.
  • Double fertilisation (unique to angiosperms): syngamy (egg + male gamete → zygote) and triple fusion (polar nuclei + male gamete → triploid PEN).
  • Post-fertilisation: Endosperm formation (usually precedes embryo; free-nuclear or cellular), embryo development (proembryo → globular → heart → mature), ovule → seed, ovary → fruit (pericarp).
  • Fruits: True (from ovary) vs false (thalamus contributes; apple). Parthenocarpy (banana etc.).
  • Seeds: Protection, dispersal, food reserve, independence from water for reproduction.
  • Apomixis: Seed formation without fertilisation (e.g., Asteraceae, grasses); useful for fixing hybrids.
  • Polyembryony: Multiple embryos in one seed (e.g., Citrus, Mango).
Important Figures
T.S. anther showing tetrasporangiate structure and wall layers
Anther: tetrasporangiate; wall layers with prominent tapetum.
Anatomy of ovule with micropyle, nucellus, integuments and embryo sac position
Ovule: micropyle, integuments, nucellus, embryo sac position.
Double fertilisation showing syngamy and triple fusion in embryo sac
Double fertilisation: syngamy and triple fusion pathway.
Quick Summary

Focus on anther and ovule structure, micro- and megasporogenesis, embryo sac organisation (7-celled, 8-nucleate), pollination types and agents, pollen–pistil compatibility, and the hallmark of angiosperms—double fertilisation—followed by endosperm/embryo development, seed and fruit formation, plus special cases like apomixis and polyembryony. Expect NEET questions on structures, stages, and process order.

Practice Quiz (3 MCQs)
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02 Human Reproduction

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Reproductive events after puberty: gametogenesis → insemination → fertilisation → implantation → gestation (embryonic & foetal development) → parturition → lactation.
  • Male system: testes in scrotum (cooling for spermatogenesis); seminiferous tubules (spermatogonia, Sertoli cells); interstitial Leydig cells → androgens. Ducts: rete testis → vasa efferentia → epididymis → vas deferens. Glands: seminal vesicles, prostate, bulbourethral → seminal plasma (fructose, Ca²⁺, enzymes). Penis enables erection & insemination.
  • Female system: ovaries (oogenesis, steroids); oviducts (infundibulum with fimbriae → ampulla → isthmus), uterus (perimetrium, myometrium, endometrium), cervix, vagina. External genitalia: mons pubis, labia majora/minora, clitoris, hymen (not a reliable indicator). Mammary glands for lactation.
  • Spermatogenesis: spermatogonia → primary spermatocytes (meiosis I) → secondary spermatocytes → spermatids (meiosis II) → spermatozoa (spermiogenesis); release by spermiation. Regulated by GnRH → LH (Leydig) & FSH (Sertoli).
  • Sperm structure: head (haploid nucleus + acrosome), neck, middle piece (mitochondria for motility), tail (flagellum).
  • Oogenesis: fetal oogonia → primary oocytes (prophase I arrest) within follicles → tertiary follicle (antrum) → primary oocyte completes meiosis I → secondary oocyte + first polar body; Graafian follicle ovulates secondary oocyte. Ovum formation ceases ~50 years.
  • Menstrual cycle (~28/29 d): menstrual (3–5 d) → follicular (FSH/LH rise; estrogen; endometrium proliferates) → ovulatory (LH surge ~day 14) → luteal (corpus luteum: progesterone; endometrium secretory). Pregnancy halts cycles.
  • Fertilisation & implantation: insemination → sperm reaches ampullary region; acrosomal enzymes penetrate zona pellucida; secondary oocyte completes meiosis II; male + female pronuclei fuse → zygote. Cleavage → morula → blastocyst (trophoblast + ICM) → implantation in endometrium.
  • Pregnancy & development: placenta (chorionic villi + uterine tissue) for exchange; endocrine: hCG, hPL, estrogens, progestogens; relaxin (ovary). Germ layers form; trimester milestones: heart (~1 mo), limbs/digits (~2 mo), major organs & external genitalia (~12 wks), movements & hair (~5 mo), eyelids separate & body hair (~24 wks), term ~9 mo.
  • Parturition: neuroendocrine reflex—foetal signals → maternal oxytocin → strong myometrial contractions → delivery → placenta expelled.
  • Lactation: milk production near late pregnancy; colostrum rich in antibodies—essential for neonatal immunity.
Important Figures
Labeled male reproductive system with testes, ducts, and glands
Male system: testes, ducts, accessory glands, penis.
Female reproductive tract with ovary, oviduct, uterus layers, cervix and vagina
Female system: oviduct (fimbriae–ampulla–isthmus), uterus layers.
Fertilisation and implantation sequence from zygote to blastocyst embedding
Fertilisation → cleavage → blastocyst → implantation.
Quick Summary

Covers anatomy of male/female systems, hormonal control of gametogenesis, phases of the menstrual cycle, site/timing of fertilisation, early embryogenesis and implantation, placental functions, and the physiology of parturition and lactation. NEET often tests hormone surges, cycle phases, sites (ampullary–isthmic junction), and placenta’s endocrine roles.

Practice Quiz (3 MCQs)
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03 Reproductive Health

Summative Weightage: Medium–High Updated: 08 Sep 2025
Chapter Notes
  • Meaning of reproductive health (WHO): total well-being in reproductive aspects—physical, emotional, behavioural, social.
  • India’s initiatives: Family Planning (1951) → RCH programmes; goals—awareness + access to services.
  • Strategies: school sex education; myth-busting on adolescence, safe practices, STIs; counselling; care for pregnant/new mothers; breastfeeding; gender equity; prevention of abuse/sex-related crimes.
  • Medical support: infrastructure and trained personnel for pregnancy/delivery care, contraception, STIs, MTP, menstrual issues, infertility.
  • Amniocentesis: prenatal genetic testing—legally banned for sex determination to curb female foeticide.
  • R&D and indicators: indigenous innovations (e.g., Saheli); improvements seen via higher institutional deliveries, lower MMR/IMR, small family norm adoption, better STI detection/cure.
  • Population stabilisation: causes of explosion (lower death/MMR/IMR, large reproductive cohort); measures—raise marriageable age, incentives, communication campaigns.
  • Contraceptives—key features: safe, effective, reversible, accessible, minimal side-effects, no interference with libido/act.
  • Methods: natural (periodic abstinence, withdrawal, lactational amenorrhea); barrier (condoms—also reduce STIs; diaphragms/cervical caps + spermicides); IUDs (non-medicated, Cu-releasing, hormone-releasing); oral pills (21-day combined/progestin; Saheli weekly, non-steroidal); injectables/implants; emergency contraception; surgical (vasectomy/tubectomy).
  • MTP: definition; legal framework in India with safeguards; safer in 1st trimester; risks rise in 2nd; danger of unqualified/illegal procedures; sex-selective misuse is illegal.
  • STIs: types—gonorrhoea, syphilis, chlamydiasis, trichomoniasis, genital herpes, genital warts, hepatitis-B, HIV/AIDS; modes—sexual contact, needles, instruments, transfusion, vertical; many curable if early; complications include PID, ectopic pregnancy, infertility.
  • Prevention of STIs: limit partners, use condoms, prompt medical care and complete treatment.
  • Infertility: multifactorial causes (male/female); evaluation of both partners.
  • ART options: IVF-ET (ZIFT ≤8-cell; IUT for >8-cell), GIFT, ICSI, AI/IUI; constraints—cost, expertise, ethics/social aspects; adoption as a valuable alternative.
Important Figures
Flowchart of contraceptive methods: natural, barrier, IUDs, hormonal, emergency, surgical
Contraceptive methods at a glance.
Infographic showing common STIs with transmission routes and prevention
Common STIs: routes, symptoms, prevention.
ART decision tree: IVF-ET, ZIFT, IUT, GIFT, ICSI, IUI
Assisted Reproductive Technologies (ART) overview.
Quick Summary

Covers policies and practices for a reproductively healthy society, population stabilisation, contraceptive choices and their mechanisms, the legal and medical aspects of MTP, the spectrum of STIs and prevention, and infertility management including ART. NEET favours questions on IUD types and actions, features of an ideal contraceptive, STI identification/prevention, and ART indications.

Practice Quiz (3 MCQs)
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04 Principles of Inheritance & Variation

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Foundations: Genetics studies heredity (inheritance) and variation; early domestication used artificial selection long before scientific genetics.
  • Mendel’s work: Pea crosses; factors (genes) in pairs; alleles; used statistics & probability.
  • Monohybrid crosses: F1 shows dominance; F2 phenotype 3:1, genotype 1:2:1. Test cross reveals unknown dominant genotype.
  • Laws: Dominance; Segregation (alleles separate during gametogenesis); Independent assortment (for unlinked genes in dihybrids).
  • Dihybrid: Classic F2 9:3:3:1 when genes assort independently.
  • Non-Mendelian patterns: Incomplete dominance (snapdragon pink F1); Co-dominance (ABO IA & IB both expressed); multiple alleles (IA, IB, i); pleiotropy; polygenic traits (height, skin colour).
  • Chromosomal theory: Sutton–Boveri; genes on chromosomes; Morgan’s Drosophila validation.
  • Linkage & recombination: Linked genes co-inherit; recombination frequency inversely related to linkage strength; map units for gene mapping.
  • Sex determination: XX/XY (human), XO, ZW (birds), haplodiploidy (honey bee).
  • Mutation: Point mutations (e.g., sickle-cell), chromosomal aberrations; induced by mutagens.
  • Genetic disorders: Pedigree analysis; Mendelian (colour blindness, haemophilia, sickle-cell anaemia, PKU, thalassemia) vs chromosomal (Down’s, Klinefelter’s, Turner’s); aneuploidy vs polyploidy.
Important Figures
Punnett square illustrating monohybrid cross with 3:1 F2 ratio
Punnett square: monohybrid cross (F2 3:1; 1:2:1 genotype).
Meiosis diagram aligning chromosome behavior with Mendel's laws
Chromosomal basis: pairing & segregation in meiosis.
Linkage map showing recombination frequencies
Linkage & recombination map units (cM) overview.
Quick Summary

Builds the logic of inheritance from Mendel’s laws to chromosomes, expands to dihybrids and independent assortment, and covers non-Mendelian patterns (incomplete/co-dominance, multiple alleles, polygenic traits). Adds gene mapping via recombination, mechanisms of sex determination, mutations, and human genetic disorders. NEET commonly probes ratios, test crosses, ABO genetics, linkage vs recombination, and pedigree logic.

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05 Molecular Basis of Inheritance

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Genetic material: DNA in most organisms; RNA in some viruses and as mRNA/tRNA/rRNA/catalyst elsewhere.
  • Nucleotide & polymers: base (A,G,C,T/U) + sugar (deoxy/ribose) + phosphate; 3′–5′ phosphodiester linkages; polarity 5′→3′.
  • DNA double helix: antiparallel strands; A=T (2 H-bonds), G≡C (3 H-bonds); ~10 bp/turn, 3.4 nm pitch; base stacking stabilises helix.
  • Central dogma: DNA → RNA → Protein (reverse flow in some viruses).
  • DNA packaging: Prokaryotic nucleoid loops; eukaryotic nucleosomes (histone octamer + ~200 bp DNA) → chromatin (eu-/heterochromatin).
  • Proof of DNA as genetic material: Griffith (transformation), Avery–MacLeod–McCarty (DNase sensitive), Hershey–Chase (32P enters).
  • Why DNA: more stable than RNA (no 2′-OH; thymine vs uracil); both replicate via complementarity.
  • RNA world: ancient catalytic & informational role; DNA evolved for stability + repair.
  • Replication: semiconservative (Meselson–Stahl); DNA pol synthesises 5′→3′; leading/lagging strands; ligase; origin(s); S-phase in eukaryotes.
  • Transcription: unit = promoter–gene–terminator; template vs coding strand; bacterial single RNA pol (σ/ρ); euk RNA pol I/II/III; hnRNA processing (capping, splicing, tailing).
  • Genetic code: triplet, degenerate, nearly universal; 61 sense + 3 stop; AUG initiator (Met); frameshift vs point mutations; tRNA as adaptor (anticodon, aminoacylation).
  • Translation: ribosome (two subunits); initiation–elongation–termination; 23S rRNA ribozyme activity in bacteria; UTR roles.
  • Regulation: primarily transcriptional; lac operon (negative regulation via repressor; inducer = lactose/allolactose).
  • HGP: goals, Sanger-based large-scale sequencing with BAC/YAC; ~3.16 Gb; <2% coding; 99.9% identical; SNPs abundant.
  • DNA fingerprinting: VNTR/minisatellite polymorphisms; restriction digest → gel → blot → probe hybridisation; forensic, paternity, population studies (PCR enhances sensitivity).
Important Figures
DNA double helix with antiparallel strands and base pairing
Watson–Crick double helix: antiparallel strands & base pairing.
Replication fork with leading and lagging strand, Okazaki fragments, ligase
Replication fork: leading/lagging synthesis & ligation.
Lac operon map showing promoter, operator, i, z, y, a genes
Lac operon organisation & induction logic.
Human Genome Project schematic with BAC/YAC cloning and sequencing
HGP workflow: clone → sequence → assemble → annotate.
Gel electrophoresis blot showing VNTR banding patterns for DNA fingerprinting
DNA fingerprinting: VNTR-based banding.
Nucleosome 'beads-on-a-string' chromatin diagram
Nucleosome & chromatin compaction.
Quick Summary

Establishes DNA/RNA chemistry, helix architecture, replication, transcription/translation mechanics, code logic, and gene regulation; then scales to genome projects and forensic tools. NEET favours replication directionality, enzyme roles, code properties, operon regulation, HGP facts, and DNA fingerprinting basics.

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06 Evolution

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Cosmic & Earth timeline: Universe ~13.8 bya (Big Bang); Earth ~4.5 bya; early reducing atmosphere (H2O, CH4, CO2, NH3); oceans/ozone formed as O2 accumulated; life ~4.0 bya.
  • Origin of life: Pasteur disproved spontaneous generation; Oparin–Haldane chemical evolution; Miller (1953) abiotically formed amino acids under simulated early Earth; first non-cellular life → first cells ~2.0 bya.
  • Darwinian theory: Branching descent + natural selection; individuals with higher fitness leave more progeny; Wallace’s similar view; Lamarck’s use/disuse rejected.
  • Evidences: Fossils (strata chronology, extinctions e.g., dinosaurs); comparative anatomy—homology (divergent evolution) vs analogy (convergent); embryology (limited); biochemical similarities; industrial melanism; rapid evolution of drug/pesticide resistance (stochastic, mutation based).
  • Adaptive radiation: One ancestor → many niches (Darwin’s finches, Australian marsupials); convergent forms among marsupials vs placentals (e.g., wolf–Tasmanian wolf).
  • Mechanisms of evolution: de Vries mutations (saltation) vs Darwin’s gradualism; population genetics—Hardy–Weinberg equilibrium p²+2pq+q²=1; forces changing allele freq: gene flow, genetic drift (founder effect), mutation, recombination, natural selection.
  • Brief life history: First O2-releasing cells; invertebrates by ~500 mya; plants then animals on land; lobefins → amphibians (~350 mya) → reptiles (amniotic eggs) → mammals (viviparous, intelligent); K–Pg extinction ~65 mya; continental drift shaped distributions.
  • Human evolution: ~15 mya Dryopithecus/Ramapithecus; 3–4 mya upright hominids; Australopithecus (~2 mya); Homo habilis (650–800 cc); H. erectus (~900 cc); Neanderthals (1400 cc); Homo sapiens arose 75k–10k ya in Africa → global spread; agriculture ~10k ya.
Important Figures
Timeline from Big Bang to origin of life and major evolutionary eras
Cosmic → Earth → life timeline.
Homologous vs analogous limbs/structures with divergent and convergent labels
Homology (divergent) vs analogy (convergent).
Industrial melanism moth frequency shift pre- and post-industrialization
Industrial melanism (selection in action).
Darwin’s finches showing beak diversity and diets
Adaptive radiation: Darwin’s finches.
Hardy–Weinberg equilibrium curve and forces disrupting equilibrium
Hardy–Weinberg & evolutionary forces.
Human evolution tree with cranial capacities and time scale
Evolution of humans (simplified tree).
Quick Summary

From chemical evolution to cellular life, evidence across fossils, anatomy and biochemistry supports descent with modification. Natural selection, drift, mutation, recombination, and gene flow shape diversity; adaptive radiation and convergence explain repeated forms. Human evolution highlights brain/language and cultural transitions.

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07 Human Health & Disease

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Health = complete physical, mental, social and psychological well-being; not just absence of disease.
  • Common infectious diseases: typhoid, cholera, pneumonia, dermatophytoses (skin fungi), malaria (P. falciparum may be fatal if untreated).
  • Prevention & control: public health (safe water, sanitation, waste management, vector control) + personal hygiene + immunisation.
  • Innate immunity: barriers (skin, mucosa), physiological (HCl, lysozyme in tears/saliva), cellular (phagocytes), cytokine-mediated defenses.
  • Acquired immunity: humoral (antibodies) and cell-mediated (T cells); features—specificity and memory; basis of vaccination.
  • Vaccination: active (antigen exposure) vs passive (preformed antibodies); schedules reduce disease burden at population level (herd protection).
  • AIDS: caused by HIV; transmission—unprotected sex, contaminated needles, transfusion, vertical (mother → child). Prevention by safe practices, screening, and education.
  • Cancer: uncontrolled cell division, loss of contact inhibition; benign vs malignant (metastasis). Risk factors include carcinogens, viruses, heredity. Detection (screening/biopsy), therapy (surgery, radiotherapy, chemotherapy, targeted/immune therapy).
  • Drug & alcohol abuse: rising in adolescents; drivers—peer pressure, stress, curiosity. Consequences—addiction, organ damage, accidents, social issues. Management—education, counselling, early medical help, rehabilitation, family support.
Important Figures
Infographic showing levels of prevention: sanitation, vaccination, vector control
Public health measures: sanitation → vaccination → vector control.
Diagram contrasting innate and acquired immunity arms
Innate vs acquired immunity at a glance.
HIV life cycle schematic and routes of transmission
HIV: life cycle & transmission routes.
Quick Summary

Defines holistic health, surveys major infections and their control, outlines innate/acquired immunity and vaccine logic, highlights AIDS and cancer essentials, and addresses substance abuse with prevention and rehabilitation strategies. NEET commonly tests vaccine types, immune memory, HIV transmission, and cancer basics.

Practice Quiz (10 MCQs)
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08 Microbes in Human Welfare

Summative Weightage: Medium–High Updated: 08 Sep 2025
Chapter Notes
  • Microbes are ubiquitous; besides pathogens many are beneficial and used daily by humans.
  • Household products: LAB ferment milk to curd; yeast (Saccharomyces cerevisiae) leavens bread; mixed fermentations in idli/dosa batter; specific microbes impart flavour/texture to cheeses.
  • Industrial products: organic acids (lactic, acetic), alcohols; antibiotics (e.g., penicillin from Penicillium) have transformed control of bacterial diseases.
  • Sewage treatment: primary → secondary (aeration tanks, activated sludge flocs of aerobic microbes) → effluent; part of sludge anaerobically digested.
  • Biogas: methanogenic archaea (e.g., Methanobacterium) degrade biomass in anaerobic digesters to methane-rich gas; widely used in rural energy schemes.
  • Biocontrol: using natural enemies/microbes (e.g., Bacillus thuringiensis toxins against insect larvae, Trichoderma as fungal biocontrol) reduces chemical pesticide reliance.
  • Biofertilisers: nitrogen fixers (symbiotic Rhizobium in legumes; associative Azospirillum; free-living Azotobacter) and cyanobacteria (Anabaena/Nostoc, Azolla–Anabaena) enrich soils and support sustainable agriculture.
Important Figures
LAB converting milk to curd with schematic of lactose to lactic acid
Curd formation by lactic acid bacteria.
Activated sludge tank showing aeration and microbial flocs
Activated sludge in secondary sewage treatment.
Biogas plant showing inlet, digester, gas holder, slurry outlet
Biogas digester: methanogenesis workflow.
Penicillin production flowchart from fermenter to purification
Industrial antibiotic production (penicillin).
Bt toxin mode of action on insect midgut epithelial cells
Bt biocontrol: crystal toxin action.
Biofertiliser examples: Rhizobium nodules, Azolla in paddy, cyanobacteria
Biofertilisers: Rhizobium, Azolla–Anabaena, cyanobacteria.
Quick Summary

Microbes power everyday fermentations, supply industrial chemicals and antibiotics, clean wastewater, generate renewable biogas, and act as eco-friendly biocontrol agents and biofertilisers—making them indispensable to health, industry, and sustainable agriculture. NEET often tests sewage/biogas steps, Bt logic, and examples of biofertilisers.

Practice Quiz (10 MCQs)
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09 Biotechnology — Principles & Processes

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Foundations: From traditional fermentations to modern EFB definition—integrating organisms/cells/molecular analogues for products & services; large-scale use of GMOs.
  • Pioneers: Boyer (restriction enzymes; sticky ends) + Cohen (plasmid isolation/transfer) → first rDNA (1972) by splicing into plasmids and transforming bacteria.
  • Core techniques: (i) Genetic engineering—precise gene-level modification to alter phenotype; (ii) Bioprocess engineering—aseptic scale-up to grow only desired cells for products.
  • ori & cloning: Alien DNA must link to a replicon with origin of replication (ori) to multiply in host (cloning).
  • First rDNA construct: Antibiotic-resistance gene ligated to plasmid (e.g., Salmonella) using restriction endonuclease + DNA ligase; replicated after transfer to E. coli.
  • Three GM steps: identify target DNA → introduce into host → maintain/express and pass to progeny.
  • Tools: restriction endonucleases, polymerases, ligases, vectors (plasmids/phages), competent host.
  • Restriction enzymes: endonucleases recognizing palindromic sites (e.g., Hind II); staggered cuts create sticky ends; ligase seals → recombinant DNA.
  • Fragment handling: agarose gel electrophoresis separates by size (−DNA → anode); EtBr staining under UV; desired band excised & eluted.
  • Cloning vectors: need ori, selectable marker(s) (e.g., ampR/tetR), unique cloning sites; insertional inactivation (e.g., pBR322; lacZ α-complementation for blue–white screening). Agrobacterium Ti (disarmed) for plants; retroviral vectors for animals.
  • Competent hosts & gene transfer: CaCl2 + heat shock; microinjection (animal nucleus); biolistics/gene gun (plants); disarmed vectors.
  • Process workflow: isolate DNA → cut with REs → separate & elute fragment → ligate into vector → transform host → select transformants → express product → scale up in bioreactors → downstream processing.
  • PCR amplification: primers + thermostable DNA pol (e.g., Taq) → denaturation–annealing–extension cycles produce billions of copies in vitro.
  • Bioreactors: controlled temperature, pH, O2, agitation; ports for sampling/foam control; batch/continuous cultures for high biomass/protein yields.
  • Downstream: separation & purification → formulation (stability/preservatives) → QC; for drugs, clinical validation before market.
Important Figures
Restriction enzyme cutting palindromic site to create sticky ends
Restriction endonuclease action & sticky ends.
Agarose gel electrophoresis image with DNA bands and UV visualization
Agarose gel: separation & band elution.
Plasmid vector map with ori, selectable markers, and MCS
Vector essentials: ori, markers, MCS.
Heat shock transformation steps with CaCl2-treated cells
Making bacteria competent & transformation.
PCR cycle diagram showing denaturation, annealing, extension
PCR cycles with thermostable polymerase.
Stirred-tank bioreactor with agitation and aeration systems
Stirred-tank bioreactor for scale-up.
Quick Summary

Covers the logic and workflow of rDNA technology—from restriction/ligation and vectors to competent hosts, PCR amplification, bioreactor scale-up, and downstream purification—anchored by the Boyer–Cohen breakthroughs and the requirement of an ori for cloning.

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10 Biotechnology & Its Applications

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Scope: Industrial-scale production of biopharmaceuticals/biologicals with GM microbes, plants, animals; areas—therapeutics, diagnostics, GM crops, processed foods, bioremediation, waste treatment, energy. Key R&D: better catalysts (enzymes/microbes), optimal bioprocess conditions, downstream purification.
  • Agriculture: Three pathways to raise output—agro-chemicals, organic, and GM-crop-based agriculture.
  • Tissue culture: Micropropagation → rapid clonal plants (tomato, banana, apple); meristem culture recovers virus-free plants; somaclones for uniformity.
  • Somatic hybridisation: Protoplast fusion (e.g., “pomato”); commercial use depends on desirable trait combinations.
  • GMOs & traits: Tolerance to abiotic stress (cold/drought/salt/heat), reduced pesticide use, less post-harvest loss, better mineral use, biofortification (e.g., vitamin A–enriched rice).
  • Pest resistance: Bt: Bt toxin genes from Bacillus thuringiensis expressed in crops (e.g., cotton); protoxin → activated in alkaline insect gut → binds midgut receptors → pore formation → lysis → death; target-specific to certain insect orders.
  • Pest resistance: RNAi: dsRNA-mediated gene silencing; e.g., nematode (Meloidogyne incognita) protection in tobacco via Agrobacterium-delivered constructs → degradation of nematode mRNA.
  • Medicine: rDNA enables safe, mass-produced therapeutics without strong immunogenicity of non-human products.
  • Human insulin (rDNA): Eli Lilly (1983) produced human insulin by expressing A and B chains separately in E. coli and combining them; bypasses proinsulin’s C-peptide processing problem.
  • Gene therapy: Add functional gene to correct defects; classic case—ADA deficiency (1990): patient lymphocytes engineered ex vivo with ADA cDNA; early embryonic gene addition could be permanent.
  • Molecular diagnosis: PCR detects low pathogen loads/mutations (early HIV/cancer detection); ELISA detects antigen/antibody via specific interactions; rDNA probes improve specificity.
  • Transgenic animals: Foreign gene insertion (mostly mice). Uses—physiology/development studies, disease models (cancer, CF, RA, Alzheimer’s), biological products (e.g., α1-antitrypsin; human α-lactalbumin “pharming”), vaccine safety testing, toxicity testing.
  • Ethics & regulation: Unpredictable ecological impacts of GMOs; oversight by bodies like GEAC (India) for GM research/release. Patents & benefit sharing controversies—biopiracy of traditional bio-resources/knowledge (e.g., basmati, turmeric, neem). Nations enact laws to prevent unauthorised exploitation and ensure equitable benefit sharing.
Important Figures
Bioprocess flow: strain → bioreactor → downstream processing → product
From engineered strain to purified product.
Bt toxin activation and pore formation in insect midgut
Bt mode of action in insect midgut.
RNA interference schematic showing dsRNA→RISC→mRNA cleavage
RNAi-mediated gene silencing.
Recombinant human insulin production showing A/B chains and disulfide bond formation
rDNA human insulin (A/B chains → insulin).
PCR amplification and ELISA antigen–antibody detection basics
PCR vs ELISA: diagnostic principles.
Transgenic mouse use-cases: disease model, pharming, vaccine safety
Transgenic animals: key applications.
Quick Summary

Biotechnology delivers trait-improved crops (Bt, RNAi), cloned plants, and breakthrough medicines (rDNA insulin), plus early diagnostics and gene therapy—while raising ethical and regulatory questions on GM release, patents, and biopiracy. NEET favours Bt/RNAi mechanisms, insulin production logic, PCR/ELISA basics, and roles of GEAC.

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11 Organisms & Populations

Summative Weightage: Medium–High Updated: 08 Sep 2025
Chapter Notes
  • Ecology: interactions among organisms and with abiotic environment; integrates organism → population → community → biome; Indian pioneer: Ramdeo Misra (father of Ecology in India).
  • Population: individuals of one species in a defined area, sharing resources and potentially interbreeding (includes asexual cohorts for ecological study).
  • Population attributes: birth rate (b), death rate (d), sex ratio, age distribution (age pyramids: expanding / stable / declining), and density N (number, biomass, % cover, or relative indices like catch per unit effort).
  • Density change: Nt+1 = Nt + [(B + I) − (D + E)]; processes—natality (B), immigration (I), mortality (D), emigration (E).
  • Growth models:
    • Exponential (J-curve): dN/dt = rN; solution Nt = N0ert when resources are unlimited; r = intrinsic rate of natural increase.
    • Logistic (sigmoid): dN/dt = rN[(K − N)/K]; K = carrying capacity; shows lag → acceleration → deceleration → asymptote at K.
  • Life-history strategies: semelparity (one-time breeding; salmon, bamboo) vs iteroparity (repeated breeding); many small offspring (oyster) vs few large (birds, mammals)—adapted to habitat constraints.
  • Population interactions (impact on species 1, species 2):
    • Predation (+,−): energy transfer, controls prey, maintains diversity; prey defenses—camouflage, toxins (e.g., monarch via Calotropis), thorns.
    • Competition (−,−): competitive exclusion (Gause); coexistence via resource partitioning.
    • Parasitism (+,−): host-specificity, high fecundity, reduced organs; ecto-/endo-parasites; complex cycles (flukes, malaria); brood parasitism (cuckoo–crow mimicry).
    • Commensalism (+,0): orchid–mango, barnacle–whale, egret–cattle, clownfish–anemone.
    • Mutualism (+,+): lichen, mycorrhiza; obligate pollination syndromes (fig–wasp; orchid sexual deceit).
    • Amensalism (−,0): one harmed, other unaffected.
  • Human impacts: anthropogenic pressures alter r, K, and interaction strengths; management relies on population metrics.
Important Figures
Age pyramids showing expanding, stable, and declining populations
Age pyramids: expanding vs stable vs declining.
Exponential and logistic growth curves with r and K marked
Growth: exponential (J) vs logistic (S) with K.
Matrix of species interactions: predation, competition, parasitism, mutualism, commensalism, amensalism
Interaction outcomes (+/−/0) across pairs.
Quick Summary

Defines populations and their unique attributes, quantifies density change via births, deaths, immigration and emigration, contrasts exponential vs logistic growth, outlines life-history strategies, and systematizes interspecific interactions from predation to mutualism, with notes on coexistence (resource partitioning) and human impacts.

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12 Ecosystem

Summative Weightage: Medium–High Updated: 08 Sep 2025
Chapter Notes
  • Definition: An ecosystem is a functional unit where organisms interact with each other and with abiotic factors. Scales vary—pond → forest → ocean; the biosphere is the global ecosystem.
  • Types: Terrestrial (forest/grassland/desert) and aquatic (pond/lake/river/sea); crop fields and aquaria are man-made ecosystems.
  • Structure:
    • Abiotic: light, temperature, water, soil, nutrients.
    • Biotic: producers (autotrophs), consumers (primary/secondary/tertiary), decomposers (bacteria, fungi, detritivores).
    • Species composition & stratification (e.g., forest: trees → shrubs → herbs).
  • Functional aspects: (i) Productivity (biomass formation) (ii) Decomposition (detritus → humus → minerals) (iii) Energy flow (unidirectional, trophic levels) (iv) Nutrient cycling (gaseous/sedimentary).
  • Pond model: Abiotic water/solutes/soil; producers = phytoplankton, algae, macrophytes; consumers = zooplankton, fish, benthos; decomposers abundant at bottom; solar input & daylength regulate processes; energy flows to higher levels and dissipates as heat.
  • Productivity: Primary production = plant biomass formed (g m−2 or kcal m−2). GPP – plant respiration (R) = NPP (food for heterotrophs). Secondary productivity = consumer biomass formation. Global NPP ≈ 170 billion tons (dry wt); oceans contribute ~55 billion tons.
  • Decomposition steps: fragmentation → leaching → catabolism → humification (humus, resistant/colloidal) → mineralisation. Faster when warm & moist; slower with lignin/chitin, cold, or anaerobic conditions.
  • Energy flow: Sun is primary source (except deep-sea vents); <50% radiation is PAR; plants capture ~2–10% PAR. Energy transfer up trophic levels follows thermodynamics; constant input required.
  • Food chains/webs:
    • Grazing food chain (GFC): producers → herbivores → carnivores (dominant in aquatic systems).
    • Detritus food chain (DFC): detritus → decomposers/detritivores → consumers (major in terrestrial systems).
    • Food web = interconnected chains; omnivores feed at multiple levels.
  • Ecological pyramids (numbers/biomass/energy): base = producers, apex = top consumers.
    • Upright: commonly in terrestrial systems (all three).
    • Inverted: e.g., biomass in oceans (small phytoplankton standing crop supports larger zooplankton/fish); numbers for tree → insects.
    • Energy pyramid is always upright due to heat loss at each transfer (~10% law).
    • Limitations: ignore decomposers and mixed trophic roles; oversimplify webs.
  • Nutrient cycling: repeated use/storage/movement of elements; reservoirs—atmosphere/hydrosphere (gaseous, e.g., C) or crust (sedimentary, e.g., P). Outputs of ecosystem processes deliver ecosystem services (e.g., water/air purification).
Important Figures
Pond ecosystem diagram showing producers, consumers, decomposers, and abiotic components
Pond ecosystem: components & flows.
Flowchart of decomposition: fragmentation, leaching, catabolism, humification, mineralisation
Decomposition pathway to humus & minerals.
Ecological pyramids of number, biomass, and energy; biomass inverted in ocean
Pyramids: upright vs inverted (ocean biomass).
Grazing and detritus food chains connected into a food web
GFC & DFC interlinked food web.
PAR fraction of solar spectrum and plant capture efficiency
PAR & plant capture (≈2–10%).
Nitrogen/carbon cycle arrows showing reservoirs and fluxes
Nutrient cycles: gaseous vs sedimentary.
Quick Summary

Ecosystems integrate abiotic–biotic structure with four core functions: productivity, decomposition, energy flow, and nutrient cycling. Energy moves one-way through trophic levels (≈10% transfer), shaping pyramids (energy always upright). DFC and GFC link into webs; decomposition regulates nutrient return; ecosystem services emerge from these processes.

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13 Biodiversity & Conservation

Summative Weightage: High Updated: 08 Sep 2025
Chapter Notes
  • Biodiversity (Edward O. Wilson): combined diversity across levels of biological organisation—genes, species, ecosystems.
  • Levels:
    • Genetic: within-species variation (e.g., reserpine potency in Rauwolfia; ~50k rice strains in India).
    • Species: variety of species (e.g., higher amphibian diversity in Western vs Eastern Ghats).
    • Ecological: ecosystem variety (deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, alpine meadows).
  • Global & Indian counts: IUCN (2004) >1.5 million described spp.; Robert May ≈7 million total. >70% animals (most = insects), plants ≈22%. India: a mega-diversity nation (8.1% of global species with 2.4% land area); ~45k plants and ~90k animals recorded; many more undiscovered. Prokaryote diversity vastly underestimated.
  • Latitudinal gradient: richness ↓ from equator → poles; tropics (23.5° N–S) richest (e.g., Amazon rainforest).
  • Species–area relationship (Humboldt): S ∝ AZ; on log scale: log S = log C + Z log A. Typical Z: 0.1–0.2 (small areas); 0.6–1.2 (continents; e.g., 1.15 for tropical frugivores).
  • Diversity–stability: more diverse communities are more productive and resistant to invasion/disturbance (Tilman). Rivet popper hypothesis (Ehrlich): loss of key species can cause functional collapse.
  • Loss of biodiversity: IUCN Red List (2004) — 784 extinctions in 500 yrs; >15,500 spp. threatened (12% birds, 23% mammals, 32% amphibians, 31% gymnosperms). Sixth mass extinction: 100–1000× background rates; major risks: ↓plant production, ↓resilience, ↑process variability.
  • Evil quartet: (i) habitat loss/fragmentation (e.g., rainforest shrinkage; Amazon clearing), (ii) over-exploitation (e.g., passenger pigeon), (iii) alien invasions (e.g., water hyacinth, Nile perch, Clarias gariepinus), (iv) co-extinctions (obligate partners lost).
  • Why conserve? Narrow utilitarian (food, fibre, medicines >25% drugs plant-derived); broad utilitarian (ecosystem services—O2 production, pollination, climate/flood regulation, pest control, aesthetics); ethical (intrinsic value, intergenerational equity).
  • Conservation:
    • In situ: protected areas, biodiversity hotspots (now 34; <2% land yet highly endemic). India: Western Ghats–Sri Lanka, Indo-Burma, Himalaya hotspots; ~14 biosphere reserves, 90 national parks, 448 sanctuaries; sacred groves conserve relic flora.
    • Ex situ: zoos, botanical gardens, safari parks; cryopreservation, seed banks, tissue culture, IVF/embryo transfer.
  • Global actions: Earth Summit (Rio, 1992) → CBD; WSSD (Johannesburg, 2002) → pledge to reduce biodiversity loss.
Important Figures
Map showing latitudinal gradient of species richness peaking in tropics
Latitudinal gradient: tropics are richest.
Log S vs Log A linear plot for species–area relationship
Species–area (log–log) with slope Z.
Diagram of the rivet popper hypothesis on an airplane wing
Rivet popper: losing ‘key’ species risks collapse.
India map with hotspots and protected areas marked
Hotspots & protected areas in India.
Flowchart of in situ and ex situ conservation methods
In situ vs ex situ conservation.
Examples of invasive species and habitat fragmentation
Alien invasions & habitat fragmentation.
Quick Summary

Biodiversity spans genes → species → ecosystems; peaks in the tropics and scales with area (S–A power law). Diversity underpins ecosystem stability and services but is rapidly eroding due to the “evil quartet”. Conservation blends in situ (hotspots, PAs, sacred groves) and ex situ (zoos, seed banks, cryo) approaches, driven by utilitarian and ethical imperatives.

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