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NCERT-focused NEET Biology revision with chapter priority and concept linking.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Size | 0.1–5.0 μm (small) | 5–100 μm (large) |
| Nucleus | No true nucleus (nucleoid — naked DNA) | Well-defined nucleus with nuclear envelope |
| DNA | Circular, single chromosome; no histones | Linear chromosomes with histone proteins; multiple chromosomes |
| Ribosomes | 70S (50S + 30S) | 80S (60S + 40S); 70S in mitochondria & chloroplast |
| Membrane-bound organelles | Absent (no ER, Golgi, lysosomes, mitochondria) | Present (ER, Golgi, lysosomes, mitochondria, vacuoles, etc.) |
| Cell wall | Present (peptidoglycan/murein in bacteria) | Present in plants (cellulose), fungi (chitin); absent in animal cells |
| Plasmid | Present (extra-chromosomal circular DNA) | Absent |
| Reproduction | Binary fission (asexual) | Mitosis, meiosis, sexual reproduction |
| Examples | Bacteria, cyanobacteria, mycoplasma | Protists, fungi, plants, animals |
| Organelle | Structure | Function | Key Points |
|---|---|---|---|
| Mitochondria | Double membrane; inner folded into cristae; own DNA (mtDNA) & 70S ribosomes | ATP production (Krebs cycle, ETS, oxidative phosphorylation); "Powerhouse of cell" | Semi-autonomous; maternal inheritance; cristae increase surface area |
| Endoplasmic Reticulum | Rough ER: ribosomes attached; Smooth ER: no ribosomes | Rough ER: protein synthesis & modification; Smooth ER: lipid synthesis, detoxification | Continuous with nuclear membrane; involved in intracellular transport |
| Golgi Apparatus | Stack of flattened cisternae (cis, medial, trans faces); vesicles | Packaging, modification, sorting of proteins & lipids; secretion of glycoproteins | Also called "traffic police" of cell; forms lysosomes |
| Lysosomes | Single membrane; contain hydrolytic enzymes (acid hydrolases) | Intracellular digestion; autophagy (self-eating); apoptosis (programmed cell death) | Called "suicidal bags" (de Duve); pH ~5 (acidic) |
| Ribosome | 70S (prokaryotes) or 80S (eukaryotes cytosol); made of rRNA + proteins | Protein synthesis (translation) — site of mRNA decoding | Free ribosomes: cytoplasmic proteins; Bound ribosomes: membrane/secretory proteins |
| Nucleus | Double nuclear envelope with nuclear pores; contains nucleolus & chromatin | DNA storage, replication, transcription (RNA synthesis); controls cell activities | Nucleolus: rRNA synthesis & ribosome assembly; chromatin: DNA + histones |
| Chloroplast | Double membrane; thylakoid membranes stack into grana; stroma fluid | Photosynthesis: light reactions (thylakoid) + Calvin cycle (stroma) | Semi-autonomous; own DNA; found only in plant cells & algae |
| Vacuole | Single membrane (tonoplast); large central vacuole in plants | Storage (water, ions, waste), turgor pressure, osmoregulation | In plants: provides rigidity; in protists: contractile vacuole (osmoregulation) |
| Phase | Duration | Key Events | NEET Focus |
|---|---|---|---|
| G1 Phase | Variable (hours to days) | Cell growth; organelle duplication; synthesis of RNA & proteins; G1 checkpoint | G0 Phase: cells exit cycle (neurons, mature RBCs) — reversible (liver cells) or permanent |
| S Phase | 6–8 hours | DNA replication (each chromosome → 2 sister chromatids); histone synthesis; centrosome duplication | DNA content doubles (2n → 4n); chromosome number stays same (2n) |
| G2 Phase | 2–4 hours | Cell continues to grow; prepares for mitosis; protein synthesis; spindle formation preparation | G2 checkpoint: ensures DNA replicated correctly before mitosis begins |
| M Phase (Mitosis) | 1–2 hours | Prophase → Metaphase → Anaphase → Telophase → Cytokinesis | Prophase: chromatin condenses; Metaphase: chromosomes at equator; Anaphase: chromatids separate |
| Meiosis I | — | Homologous chromosomes separate (reductional division); crossing over in Prophase I | 2n → n; genetic variation via crossing over (Prophase I) and independent assortment (Metaphase I) |
| Meiosis II | — | Sister chromatids separate (equational division); similar to mitosis | 4 haploid cells (n) from 1 diploid cell (2n) — gametes in animals; spores in plants |
| Law | Statement | Diagonal Ratio | Key Concepts |
|---|---|---|---|
| Law of Dominance | In heterozygous condition, one allele is dominant and masks the expression of the other (recessive) | All F1 show dominant trait (3:1 in F2) | Dominant allele: expressed; Recessive: hidden in heterozygote but reappears in F2 |
| Law of Segregation | Allele pairs segregate (separate) during gamete formation so each gamete receives only one allele | Monohybrid ratio: 3:1 (Phenotypic); 1:2:1 (Genotypic) | Also called Law of purity of gametes; occurs in Anaphase I (Meiosis) |
| Law of Independent Assortment | Genes for different traits assort independently of one another during gamete formation | Dihybrid ratio: 9:3:3:1 (Phenotypic) | Only applies to genes on different chromosomes or far apart on same chromosome |
| Pattern | Description | Example | Ratio/Note |
|---|---|---|---|
| Incomplete Dominance | Heterozygote shows intermediate phenotype; neither allele is completely dominant | Snapdragon: Red (RR) × White (rr) = Pink (Rr) | 1:2:1 ratio in F2 (phenotypic & genotypic) |
| Co-dominance | Both alleles are fully expressed in heterozygote; no blending | Blood group AB (I^A I^B); sickle cell trait (HbA HbS) | Both traits visible simultaneously |
| Multiple Alleles | More than two alleles for a gene in population; individual has only 2 | ABO blood groups: I^A, I^B, i (3 alleles, 6 genotypes, 4 phenotypes) | IA & IB dominant over i; IA & IB co-dominant |
| Sex-linked Inheritance | Gene located on sex chromosome (usually X); shows different pattern in males & females | Colour blindness, Haemophilia, Duchenne muscular dystrophy (X-linked recessive) | Males express X-linked recessive more; females need 2 copies |
| Pleiotropy | One gene affects multiple, seemingly unrelated phenotypic traits | Phenylketonuria (PKU) — mental retardation + reduced hair/skin pigmentation | Single gene mutation → multiple effects |
| Polygenic Inheritance | Single phenotype controlled by multiple genes (additive effect) | Human skin colour, height, eye colour | Continuous variation; bell-shaped curve distribution |
| Epistasis | One gene masks/modifies the expression of another gene | Labrador coat colour: B gene (black/brown) + E gene (pigment deposition) | 9:3:4 ratio (recessive epistasis); 12:3:1 (dominant epistasis) |
| Disorder | Type | Karyotype | Features |
|---|---|---|---|
| Down Syndrome | Autosomal (Trisomy 21) | 47, XX/XY, +21 | Mental retardation, flat face, simian crease, protruding tongue, congenital heart defects |
| Klinefelter Syndrome | Sex chromosome (XXY) | 47, XXY | Male; tall, gynaecomastia, sterile, small testes, sparse body hair |
| Turner Syndrome | Sex chromosome (XO) | 45, X0 | Female; short stature, webbed neck, shield chest, underdeveloped ovaries, sterile |
| Patau Syndrome | Autosomal (Trisomy 13) | 47, XX/XY, +13 | Severe intellectual disability, cleft lip/palate, polydactyly, heart defects; high mortality |
| Edward Syndrome | Autosomal (Trisomy 18) | 47, XX/XY, +18 | Low birth weight, rocker-bottom feet, overlapping fingers, heart defects; high mortality |
| Jacobs Syndrome | Sex chromosome (XYY) | 47, XYY | Male; tall, normal fertility, mild learning difficulties; once called "super-male" |
| Metafemale Syndrome | Sex chromosome (XXX) | 47, XXX | Female; usually normal appearance, may have learning difficulties; fertile |
| Organ/Structure | Location | Function | Key Points |
|---|---|---|---|
| Mouth/Oral cavity | Begins digestive tract | Mechanical digestion (chewing), chemical (salivary amylase) | Salivary amylase: breaks starch → maltose; works best at pH 6.8 |
| Stomach | Left upper abdomen | Protein digestion (pepsin); churning; HCl (pH 1.5–3.5) | Gastric glands: Chief cells (pepsinogen), Parietal cells (HCl + IF), Mucous cells |
| Liver | Upper right abdomen | Bile production (emulsification of fats); metabolism; detoxification | Largest gland; bile has NO digestive enzymes; bile salts emulsify fats |
| Pancreas | Behind stomach | Pancreatic juice: trypsin, lipase, amylase; insulin & glucagon (endocrine) | Trypsinogen → trypsin (enterokinase activation); exocrine + endocrine gland |
| Small Intestine | Between stomach & large intestine | Complete digestion & absorption; villi & microvilli increase surface area | Duodenum, Jejunum, Ileum; bile + pancreatic juice + intestinal juice act here |
| Large Intestine | Terminal part of GI tract | Water absorption; feces formation; houses gut bacteria (vitamin K, B12) | Caecum (appendix), Colon (ascending, transverse, descending, sigmoid), Rectum |
| Component | Details | Key Facts |
|---|---|---|
| Heart | 4-chambered (2 atria + 2 ventricles); myogenic (self-excitatory); covered by pericardium | SA Node (pacemaker) → AV Node → Bundle of His → Purkinje fibers; 72 bpm normal |
| Cardiac Cycle | Atrial systole (0.1s) → Ventricular systole (0.3s) → Joint diastole (0.4s) = 0.8s at 75 bpm | Cardiac output = Heart rate × Stroke volume; normal ≈ 5 L/min |
| Blood Components | Plasma (55%) + Formed elements (45%: RBCs, WBCs, Platelets) | RBCs: biconcave, no nucleus (mammals), 120 days lifespan, EPO from kidney stimulates RBC production |
| Blood Groups | ABO: A, B, AB, O; Rh: + or −; 8 blood groups total | Universal donor: O− (RBC); Universal recipient: AB+ (plasma) — for RBC transfusion |
| Haemoglobin | Fe2+ containing; 4 polypeptide chains (2α + 2β); O2 transport (oxyhaemoglobin) | Normal: Males 14–18 g/dL; Females 12–16 g/dL; Fetal Hb has higher O2 affinity |
| Blood Clotting | Intrinsic (within blood) & Extrinsic (tissue factor) pathways → Common pathway → Fibrin clot | Factors: I (Fibrinogen), II (Prothrombin), III (Thromboplastin), VII, IX, X, XIII; Ca2+ (Factor IV) required |
| Double Circulation | Pulmonary (heart → lungs → heart) + Systemic (heart → body → heart) | Complete separation of oxygenated & deoxygenated blood; 4-chambered heart essential |
| Gland | Hormone(s) | Function | Key Points |
|---|---|---|---|
| Pituitary (Anterior) | GH, TSH, FSH, LH, ACTH, Prolactin, MSH | Growth, thyroid, gonads, adrenal cortex, milk secretion, skin pigmentation | "Master gland"; controlled by hypothalamic releasing/inhibiting hormones |
| Pituitary (Posterior) | ADH (Vasopressin), Oxytocin | Water reabsorption in kidneys; uterine contraction & milk ejection | ADH deficiency → Diabetes insipidus (excess urine, no glucose) |
| Thyroid | T3 (Triiodothyronine), T4 (Thyroxine), Calcitonin | BMR regulation, metabolism, growth, development; Ca2+ lowering | Hypothyroidism: goitre, cretinism (children), myxoedema (adults); Hyper: Graves' disease |
| Parathyroid | PTH (Parathyroid Hormone) | Increases blood Ca2+ (bone resorption, kidney reabsorption, activates vitamin D) | Hypoparathyroidism → Tetany (low blood Ca2+ → muscle spasms) |
| Adrenal Cortex | Glucocorticoids (Cortisol), Mineralocorticoids (Aldosterone) | Stress response, anti-inflammatory, Na⁺ & K⁺ balance (ACTH controls secretion) | Cushing's syndrome (excess cortisol); Addison's disease (deficient cortisol & aldosterone) |
| Adrenal Medulla | Adrenaline (Epinephrine), Noradrenaline | Fight or flight response: ↑ HR, BP, blood glucose; dilate pupils; bronchodilation | Emergency hormone; catecholamines; sympathetic nervous system activation |
| Pancreas (Islets) | Insulin (β cells), Glucagon (α cells), Somatostatin (δ cells) | Insulin: ↓ blood glucose; Glucagon: ↑ blood glucose; Somatostatin: inhibits both | Diabetes mellitus: Type 1 (autoimmune, no insulin); Type 2 (insulin resistance) |
| Ovary | Estrogen, Progesterone | Female secondary sexual characters, menstrual cycle, pregnancy maintenance | Estrogen: follicular phase; Progesterone: luteal phase; from corpus luteum after ovulation |
| Aspect | Light Reaction (Photo phase) | Dark Reaction (Calvin Cycle) |
|---|---|---|
| Site | Thylakoid membrane | Stroma of chloroplast |
| Light required | Yes (directly) | No (but needs products of light reaction: ATP, NADPH) |
| Pigments involved | Chlorophyll a, b, Carotenoids, Xanthophylls | No pigments; enzyme-driven |
| Key products | ATP (photophosphorylation), NADPH, O2 (photolysis) | G3P (triose phosphate) → Glucose; uses ATP + NADPH + CO2 |
| Processes | Photoexcitation → Electron transport → NADPH formation; Water splitting (photolysis) | CO2 fixation (RuBisCO) → Reduction → Regeneration of RuBP |
| Phases | PSII → ETC → PSI → NADP⁺ reductase; Cyclic & Non-cyclic photophosphorylation | C3 cycle: Carboxylation (RuBP + CO2), Reduction, Regeneration of RuBP |
| CO2 fixation enzyme | Not involved | RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) |
| O2 released from | Photolysis of water (H2O → 2H+ + 2e− + ½O2) | No O2 released |
| Feature | C3 Plants | C4 Plants | CAM Plants |
|---|---|---|---|
| CO2 fixation | RuBisCO fixes CO2 directly (C3 cycle) | PEP carboxylase fixes CO2 into oxaloacetate (C4 acid) in mesophyll; RuBisCO in bundle sheath | PEP carboxylase fixes CO2 at night (dark); RuBisCO operates during day |
| First stable product | 3-PGA (3-carbon compound) | Oxaloacetate (4-carbon compound) | Oxaloacetate (4-carbon compound) |
| Photorespiration | Significant (RuBisCO has affinity for O2 too); reduces efficiency by ~25% | Negligible (Kranz anatomy concentrates CO2 at RuBisCO site) | Minimal (CO2 stored as malic acid at night, released during day) |
| Kranz Anatomy | Absent | Present (bundle sheath cells arranged like a wreath around vascular bundle) | Absent; but large vacuoles for malic acid storage |
| Optimal temperature | 20–25°C | 30–40°C (tropical) | High temperatures; arid conditions |
| Examples | Wheat, Rice, Oats, Soybean, Potato, Cotton | Maize, Sugarcane, Sorghum, Amaranthus | Cactus, Pineapple, Orchids, Succulents (xerophytes) |
| Efficiency | Lower (photorespiration loss) | Higher (no photorespiration; higher water use efficiency) | Very high water use efficiency; slow growth |
| Theory | Scientist | Key Principles | Evidence/Experiments |
|---|---|---|---|
| Inheritance of Acquired Characters | Jean-Baptiste Lamarck | Use and disuse of organs → acquired traits are inherited | Giraffe's neck lengthening (use); disuse → vestigial organs — DISPROVEN (Weismann experiment) |
| Natural Selection | Charles Darwin | Variation exists; struggle for existence; survival of the fittest; natural selection acts on variation | Galapagos finches (adaptive radiation); peppered moth (industrial melanism); artificial selection (pigeons) |
| Mutation Theory | Hugo de Vries | Mutations are sudden, large, heritable changes; mutations cause speciation (not gradual) | Work on evening primrose (Oenothera lamarckiana); proposed "saltation" (single-step large mutation) |
| Modern Synthesis | Multiple scientists (Fisher, Haldane, Wright, Mayr) | Combines Darwin's natural selection with Mendelian genetics; population genetics + natural selection | Neo-Darwinism; gene pool, allele frequency, genetic drift, gene flow, non-random mating |
| Hardy-Weinberg Equilibrium | Hardy & Weinberg | p² + 2pq + q² = 1; allele frequencies remain constant if no evolutionary forces act | Conditions: large population, no mutation, no migration, random mating, no selection; used to test evolution |
| Cycle | Reservoir | Key Processes | Human Impact |
|---|---|---|---|
| Carbon Cycle | Atmosphere (CO2), Oceans (dissolved CO2, bicarbonates), Fossil fuels, Limestone | Photosynthesis (CO2 → organic); Respiration (organic → CO2); Decomposition; Combustion; Sedimentation | Burning fossil fuels ↑ atmospheric CO2 → greenhouse effect → global warming |
| Nitrogen Cycle | Atmosphere (N2 — 78%), Soil (nitrate, ammonium), Living organisms | N2 fixation (bacteria → NH3) → Nitrification (NH3 → NO2⁻ → NO3⁻) → Assimilation → Ammonification → Denitrification | Excess fertilizers → eutrophication; nitrogen oxides → acid rain, smog |
| Phosphorus Cycle | Rocks/soil (sedimentary), Ocean, Organisms (ATP, DNA, bones) | Weathering of rocks → plant uptake → animals → decomposition → sedimentation (slow cycle) | Eutrophication from phosphate detergents/fertilizers; non-gaseous cycle (no atmospheric phase) |
| Water Cycle | Oceans (97%), Ice caps (2%), Freshwater (1% — mostly groundwater) | Evaporation, transpiration, condensation, precipitation, infiltration, runoff, percolation | Deforestation → less transpiration; groundwater depletion; climate change alters precipitation patterns |
| Area | Application | Examples | Ethical/Concerns |
|---|---|---|---|
| Medicine | Therapeutic proteins, vaccines, gene therapy, stem cells | Insulin, GH, Interferon, Hepatitis B vaccine (recombinant) | Germline editing ethics, informed consent, genetic discrimination |
| Agriculture | GM crops with pest resistance, herbicide tolerance, nutritional enhancement | Bt Cotton (India), Bt Brinjal, Golden Rice, Roundup Ready soybean | Biodiversity loss, gene flow to wild relatives, corporate patents on seeds |
| Environment | Bioremediation, biofuels, waste treatment, biosensors | Oil spill cleanup bacteria, bioethanol from sugarcane/corn, biohydrogen | Release of GMOs into environment, unintended ecological effects |
| Forensics | DNA fingerprinting, paternity testing, criminal identification | Alec Jeffreys (1985); VNTR analysis; CODIS database | Privacy concerns, false positives, data security |
| Industry | Enzymes in detergents, food processing, bioplastic production | Proteases in detergents; rennet (chymosin) in cheese; PHA bioplastics | Environmental impact of industrial biotech waste |
| Topic | Diagram | Key Labels | Frequency |
|---|---|---|---|
| Cell Biology | Plant cell vs Animal cell | Cell wall, plastids, large vacuole (plant) vs centrioles, lysosomes (animal) | Very High |
| Cell Biology | Mitochondria (LS/TS) | Outer membrane, inner membrane, cristae, matrix, DNA | High |
| Genetics | Monohybrid cross (Punnett square) | P generation, F1, F2 (3:1 ratio); genotype & phenotype | High |
| Genetics | Pedigree chart | Circles (females), Squares (males), shaded (affected), carriers | Medium |
| Human Physiology | Human heart (external & LS) | 4 chambers, major blood vessels, valves, SA node, AV node, coronary arteries | Very High |
| Human Physiology | Nephron | Bowman's capsule, PCT, Loop of Henle, DCT, collecting duct, glomerulus | Very High |
| Human Physiology | Neuron | Dendrites, cell body, axon, myelin sheath, nodes of Ranvier, synaptic knobs | High |
| Plant Physiology | T.S. of Dicot Leaf | Upper/lower epidermis, palisade, spongy parenchyma, stomata, vascular bundle | High |
| Plant Physiology | T.S. of Dicot Stem | Epidermis, cortex, endodermis, pericycle, vascular bundles (xylem, phloem), pith | High |
| Plant Physiology | Root apex (LS) | Root cap, meristematic zone, zone of elongation, zone of maturation, root hair | Medium |
| Reproduction | Female reproductive system | Ovary, fallopian tube, uterus, cervix, vagina; follicle stages (primary, secondary, Graafian) | High |
| Reproduction | Male reproductive system | Testis, epididymis, vas deferens, seminal vesicle, prostate, urethra | High |
| Ecology | Pyramid of Energy | Trophic levels: Producers → Primary → Secondary → Tertiary consumers; 10% energy transfer | High |
| Evolution | Hardy-Weinberg graph | Allele frequencies; p², 2pq, q²; population genetics curve | Medium |
| Biotechnology | rDNA technology steps | Restriction enzyme cut, ligation, vector, transformation, selection | Medium |
| Chapter/Topic | Approx. Questions | Weightage | Priority |
|---|---|---|---|
| Human Physiology | 18–22 | 20–24% | HIGHEST — Digestion, Breathing, Body fluids, Excretory, Neural, Chemical coordination |
| Genetics & Evolution | 10–14 | 11–16% | VERY HIGH — Mendelian genetics, DNA, molecular basis, human health & disease, evolution |
| Plant Physiology | 8–12 | 9–13% | VERY HIGH — Photosynthesis, Respiration, Plant growth, Mineral nutrition |
| Reproduction (Plant + Human) | 8–10 | 9–11% | HIGH — Sexual reproduction in flowering plants, Human reproductive health |
| Biotechnology & Applications | 5–8 | 6–9% | HIGH — rDNA, PCR, Biotech in health & agriculture |
| Ecology & Environment | 6–8 | 7–9% | HIGH — Ecosystem, Biodiversity, Environmental issues |
| Cell Biology | 5–7 | 6–8% | HIGH — Cell structure, cell cycle, biomolecules |
| Diversity in Living World | 4–6 | 4–7% | MEDIUM — Classification, five kingdoms, plant & animal kingdoms |
| Structural Organisation in Plants/Animals | 3–5 | 3–6% | MEDIUM — Anatomy of flowering plants, Morphology, Animal tissues |
| Human Health & Disease | 4–5 | 4–6% | MEDIUM — Immunity, diseases (malaria, dengue, HIV, cancer), vaccines |
| Topic | Most Asked Sub-Topic | Example Question Pattern | Repeat Frequency |
|---|---|---|---|
| Genetics | Blood group inheritance | If father is A (heterozygous) and mother is B (heterozygous), possible blood groups of children? | Almost every year |
| Genetics | Chromosomal disorders | Identify the karyotype associated with Turner/Klinefelter/Down syndrome | Every alternate year |
| Human Physiology | Hormone deficiencies | Which hormone deficiency causes Diabetes insipidus / Tetany / Goitre / Addison's? | Every year |
| Human Physiology | Cardiac cycle | Duration of cardiac cycle / phases; SA node function; cardiac output calculation | Frequent |
| Plant Physiology | C3 vs C4 pathway | Which is true about C4 plants? / Kranz anatomy features | Very frequent |
| Plant Physiology | Photosynthesis pigments | Action spectrum vs absorption spectrum; Emerson effect; Red drop | Frequent |
| Ecology | Energy flow / 10% law | How much energy is available at 3rd trophic level if 1st level has 10,000 J? | Very frequent |
| Ecology | Biodiversity & conservation | Which is the biodiversity hotspot in India? / Red Data Book / IUCN categories | Every year |
| Cell Biology | Cell organelle function | Which organelle is called "powerhouse" / "suicidal bag" / "traffic police"? | Almost every year |
| Biotechnology | rDNA technology | Role of restriction enzymes / PCR / selectable markers / reporter genes | Very frequent |