Science — Class 10 AI Notes

How chemical reactions are represented, balanced, and classified.

• A chemical reaction converts reactants into products with rearrangement of atoms — mass is conserved.
• Observable signs: change in state, change in colour, evolution of gas, change in temperature, formation of precipitate.
• A chemical equation is balanced when the number of atoms of each element is equal on both sides (law of conservation of mass).
• Steps to balance: write skeletal equation → balance metal atoms → non-metals → hydrogen → oxygen → add physical states (s, l, g, aq) → indicate conditions (Δ for heat, catalyst).
• Types of chemical reactions:
• Combination: two or more reactants → single product (e.g., CaO + H₂O → Ca(OH)₂, exothermic).
• Decomposition: single reactant → two or more products; thermal (CaCO₃ → CaO + CO₂), electrolytic (2H₂O → 2H₂ + O₂), photochemical (2AgCl → 2Ag + Cl₂).
• Displacement: more reactive element displaces less reactive one (Fe + CuSO₄ → FeSO₄ + Cu).
• Double displacement: exchange of ions between two compounds; usually forms a precipitate (Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl).
• Precipitation: an insoluble solid forms when two solutions are mixed.
• Neutralisation: acid + base → salt + water.
• Redox reactions: oxidation = gain of oxygen / loss of hydrogen / loss of electrons; reduction = loss of oxygen / gain of hydrogen / gain of electrons.
• In a redox reaction, oxidising agent gets reduced; reducing agent gets oxidised.
• Corrosion: oxidation of metals when exposed to air/water (e.g., rusting of iron); prevented by painting, oiling, galvanising, alloying.
• Rancidity: oxidation of fats/oils in food producing bad smell/taste; prevented by antioxidants, airtight packing, nitrogen flushing.

• Balanced equation: atoms of each element equal on both sides
• Types: combination, decomposition, displacement, double displacement, redox
• Oxidation (gain O / lose H / lose e⁻) vs Reduction (opposite)

• Reaction indicators → balancing → types → redox
• Corrosion (rusting) and rancidity
• Physical states and conditions on the arrow

• Balance in order: metals → non-metals → H → O.
• OIL RIG mnemonic: Oxidation Is Loss, Reduction Is Gain (of electrons).

• Changing subscripts to balance (only coefficients change).
• Ignoring physical states (s, l, g, aq).
• Reversing oxidation/reduction direction in redox.

1. Q. Why does silver chloride turn grey in sunlight?
   A. Photodecomposition: 2AgCl → 2Ag + Cl₂. Metallic silver deposition gives the grey colour (used in photography).
2. Q. Explain why rusting is called an electrochemical process.
   A. Iron gets oxidised at anode, oxygen gets reduced at cathode; water/electrolyte acts as medium — an electrochemical cell forms on the surface.
3. Q. Why do chips packets contain nitrogen gas?
   A. Nitrogen is inert; it displaces oxygen, preventing oxidation of fats — no rancidity.

Properties and reactions of acids and bases, pH, and salts used in daily life.

• Acids taste sour, turn blue litmus red, release H⁺ ions in water. Bases taste bitter, feel soapy, turn red litmus blue, release OH⁻ in water.
• Common indicators: litmus (blue↔red), methyl orange (red in acid, yellow in base), phenolphthalein (colourless in acid, pink in base). Olfactory indicators: onion, vanilla, clove.
• Acid + Metal → Salt + H₂↑ (except Cu, Ag with dilute acids).
• Acid + Metal carbonate/bicarbonate → Salt + CO₂↑ + H₂O.
• Base + Metal (amphoteric like Zn, Al) → Salt + H₂↑ (e.g. 2NaOH + Zn → Na₂ZnO₂ + H₂).
• Acid + Base → Salt + H₂O (neutralisation, exothermic).
• Metal oxides are basic (react with acids); non-metal oxides are acidic (react with bases).
• Strong acid/base: ionises completely (HCl, H₂SO₄, NaOH, KOH). Weak: partial (CH₃COOH, NH₄OH).
• pH = −log₁₀[H⁺]. pH < 7 acidic, = 7 neutral, > 7 basic. Universal indicator gives approximate pH by colour.
• Importance of pH in daily life: soil pH for plants, digestion (HCl in stomach), tooth decay (below pH 5.5), self-defence in animals (nettles, bee sting), antacids (mild base).
• Salts: pH depends on parent acid/base. Strong acid + strong base → neutral; strong acid + weak base → acidic; weak acid + strong base → basic.
• Important salts:
• Common salt (NaCl): from seawater/rock salt; raw material for many chemicals.
• Sodium hydroxide (NaOH) via chlor-alkali process: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ (electrolysis of brine).
• Bleaching powder Ca(OCl)Cl from slaked lime + chlorine; used to bleach cotton, disinfect water.
• Baking soda NaHCO₃: mild base, used in antacids, baking (with tartaric acid ⇒ CO₂ makes cake rise).
• Washing soda Na₂CO₃·10H₂O: from baking soda; softens hard water, used in glass/paper industry.
• Plaster of Paris CaSO₄·½H₂O from gypsum by heating at 373 K; used in casts, sculptures.
• Water of crystallisation: fixed number of water molecules in a salt's crystal (e.g., CuSO₄·5H₂O — blue; on heating turns white anhydrous).

• pH = −log[H⁺]
• Acid + Metal → Salt + H₂
• Acid + Carbonate → Salt + CO₂ + H₂O
• Acid + Base → Salt + H₂O (neutralisation)

• Indicators → properties → strength → pH
• Salts: preparation, uses (NaOH, bleaching powder, baking soda, washing soda, POP)
• Water of crystallisation

• Always add acid to water, never water to acid (highly exothermic).
• 'Strong' ≠ 'concentrated'; strong = fully ionised, concentrated = high amount per volume.

• Confusing bleaching powder Ca(OCl)Cl with slaked lime Ca(OH)₂.
• Assuming all salts are neutral.

1. Q. Why does dry HCl gas not turn blue litmus red?
   A. No water → HCl cannot dissociate → no H⁺ ions → no acidic behaviour.
2. Q. Why is Plaster of Paris stored in moisture-proof containers?
   A. It absorbs water and turns back into hard gypsum (CaSO₄·2H₂O), losing its usefulness.
3. Q. Fresh milk (pH ~6) becomes curd (pH ~4). Explain.
   A. Lactic acid formed by bacteria during fermentation → pH decreases → milk curdles.

Physical and chemical properties, reactivity series, extraction, and corrosion.

• Physical properties of metals: lustre, malleable, ductile, sonorous, good conductors of heat and electricity, high melting points (exceptions: Hg is liquid; Na, K are soft; Ga, Cs melt in palm).
• Physical properties of non-metals: dull (except iodine), brittle, non-sonorous, poor conductors (exception: graphite conducts).
• Metals react with oxygen → basic oxides (some amphoteric like Al₂O₃, ZnO which react with both acids and bases).
• Metals react with water: K/Na violently with cold water; Mg with hot water; Al/Zn/Fe with steam. Cu, Ag don't react.
• Reactivity series (decreasing): K, Na, Ca, Mg, Al, (C), Zn, Fe, Pb, (H), Cu, Hg, Ag, Au.
• Displacement rule: a more reactive metal displaces a less reactive one from its salt solution.
• Ionic (electrovalent) bond: formed by transfer of electrons — metal loses, non-metal gains. E.g. NaCl. Properties: high m.p., soluble in water, conduct electricity in molten/solution state.
• Extraction depends on reactivity:
• Highly reactive (K, Na, Ca, Mg, Al): electrolysis of molten chloride/oxide.
• Middle (Zn, Fe, Pb, Cu): roasting (sulphide ore + air) or calcination (carbonate ore + limited air) → oxide, then reduction with carbon.
• Low reactivity (Ag, Au): found free in nature or as sulphide; reduction not needed.
• Refining of metals: electrolytic refining (impure anode, pure cathode, salt solution as electrolyte).
• Corrosion of metals: iron rusts (Fe₂O₃·xH₂O), silver tarnishes (Ag₂S), copper turns green (basic carbonate).
• Prevention: painting, oiling, greasing, galvanisation (zinc coating), electroplating, alloying.
• Alloys: solid solutions of metals; better properties. Steel (Fe + C), Stainless steel (Fe + Cr + Ni), Brass (Cu + Zn), Bronze (Cu + Sn), Solder (Pb + Sn), Amalgam (Hg + metal).

• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au
• Roasting (sulphide + O₂) → oxide; Calcination (carbonate + Δ) → oxide
• Reduction: MO + C → M + CO

• Properties → reactivity → ionic bond → extraction → corrosion → alloys

• Higher in reactivity series → more vigorous with water and stronger displacement.
• Roasting = sulphide, Calcination = carbonate.

• Confusing roasting and calcination.
• Assuming all metals react with water.

1. Q. Why is sodium stored in kerosene?
   A. Sodium is highly reactive; reacts vigorously with air/moisture forming NaOH + H₂ (can ignite). Kerosene prevents contact.
2. Q. Why is aluminium used to make cooking utensils despite being reactive?
   A. It forms a thin, dense, protective layer of Al₂O₃ on its surface which prevents further reaction.
3. Q. Explain galvanisation.
   A. Coating iron with a thin layer of zinc; zinc is more reactive, so it corrodes preferentially (sacrificial protection).

Covalent bonding, catenation, hydrocarbons, functional groups, and important organic compounds.

• Carbon has 4 valence electrons — forms covalent bonds by sharing.
• Tetravalency + catenation (self-linking) + ability to bond with H, O, N, S, Cl → enormous variety of compounds.
• Allotropes of carbon: diamond (tetrahedral, hard, non-conductor), graphite (hexagonal layers, conducts, lubricant), fullerene C₆₀.
• Hydrocarbons: compounds of C and H only.
• Saturated (alkanes CₙH₂ₙ₊₂): only single bonds, less reactive.
• Unsaturated: alkenes CₙH₂ₙ (double bond), alkynes CₙH₂ₙ₋₂ (triple bond); more reactive.
• Isomers: same molecular formula, different structural formula (from C₄ onward; e.g., n-butane vs isobutane).
• Homologous series: family of compounds with same general formula, same functional group, successive members differ by −CH₂− (mass 14).
• Functional groups (name suffix / prefix): halo (−X), alcohol (−OH), aldehyde (−CHO), ketone (>C=O), carboxylic acid (−COOH).
• IUPAC naming: root (C count: meth, eth, prop, but, pent...) + suffix (−ane, −ene, −yne) + functional group modifier.
• Combustion: all hydrocarbons burn in air. Saturated → clean blue flame; unsaturated → sooty yellow flame (incomplete combustion).
• Oxidation: alcohols → carboxylic acids (using acidified KMnO₄ or alkaline K₂Cr₂O₇, which act as oxidising agents).
• Addition reactions: alkenes/alkynes + H₂ (Ni catalyst) → alkanes; used to hydrogenate vegetable oils into vanaspati.
• Substitution reactions: alkane + Cl₂ (sunlight) → chloroalkane + HCl.
• Ethanol C₂H₅OH: colourless liquid, used as solvent, in beverages; with sodium → sodium ethoxide + H₂; on heating with conc. H₂SO₄ at 443 K → ethene (dehydration).
• Ethanoic acid CH₃COOH (glacial): m.p. 290 K; used in vinegar; reacts with NaHCO₃ → CH₃COONa + CO₂ + H₂O; with ethanol + acid catalyst → ester (fruity smell) + H₂O (esterification).
• Soaps: sodium/potassium salts of long-chain carboxylic acids; form scum with hard water (Ca²⁺/Mg²⁺).
• Detergents: ammonium/sulphonate salts of long-chain hydrocarbons; work in hard water.
• Micelle: cluster of soap molecules with hydrophilic heads outside and hydrophobic tails inside — traps oil/dirt.

• Alkanes CₙH₂ₙ₊₂; Alkenes CₙH₂ₙ; Alkynes CₙH₂ₙ₋₂
• Combustion: hydrocarbon + O₂ → CO₂ + H₂O
• Ethanol → Ethene (H₂SO₄, 443 K, dehydration)
• CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (esterification)

• Covalent → allotropes → hydrocarbons → homologous series → functional groups
• Reactions: combustion, oxidation, addition, substitution, esterification
• Soaps vs detergents; micelle

• IUPAC name: count C, identify bond, identify group.
• Addition reaction only for unsaturated compounds; substitution only for saturated.

• Confusing addition vs substitution.
• Missing hydrogen atoms in structural formulas.
• Assuming detergents = soaps.

1. Q. Why do soaps not work well in hard water?
   A. Ca²⁺/Mg²⁺ ions form insoluble scum with soap → less lather → poor cleaning. Detergents avoid this because their calcium/magnesium salts are soluble.
2. Q. Distinguish saturated from unsaturated hydrocarbons chemically.
   A. Add bromine water: unsaturated decolourises it (addition); saturated doesn't react. Or burn: unsaturated gives sooty flame.
3. Q. Why is the conversion of ethanol to ethanoic acid an oxidation?
   A. Oxygen is added / hydrogen is removed. −OH group is converted to −COOH by the oxidising agent.

Nutrition, respiration, transport, and excretion in plants and animals.

• Life processes = basic functions maintaining life: nutrition, respiration, transportation, excretion, control-coordination, reproduction, growth.
• Autotrophic nutrition: organisms make food from simple inorganic substances (photosynthesis in plants).
• Photosynthesis: 6CO₂ + 6H₂O →(sunlight, chlorophyll) C₆H₁₂O₆ + 6O₂. Occurs in chloroplasts; site = stroma (Calvin cycle) & grana (light reaction).
• Steps of photosynthesis: absorption of light by chlorophyll → conversion to chemical energy → splitting of water (H₂ + O₂) → reduction of CO₂ to carbohydrate.
• Stomata: pores on leaves; open/close via guard cells; control gas exchange and transpiration.
• Heterotrophic nutrition: holozoic (ingesting, e.g., humans, Amoeba), saprophytic (dead matter, e.g., fungi), parasitic (host, e.g., Cuscuta).
• Human digestive system: mouth (saliva has amylase → starch to maltose) → oesophagus → stomach (HCl kills germs, activates pepsin → protein digestion, mucus protects) → small intestine (bile from liver emulsifies fats, pancreatic juice + intestinal juice complete digestion, absorption via villi) → large intestine (water absorption) → rectum (egestion).
• Respiration: breakdown of glucose to release energy (ATP).
• Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP.
• Anaerobic (yeast): glucose → ethanol + CO₂ + 2 ATP.
• Muscles (lack of O₂): glucose → lactic acid + 2 ATP → cramps.
• Human respiratory system: nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli (site of gas exchange, large surface area).
• Transportation in humans: heart (4 chambers), double circulation (pulmonary + systemic), keeps oxygenated & deoxygenated blood separate.
• Blood: plasma + RBCs (carry O₂ via haemoglobin) + WBCs + platelets. Blood vessels: arteries (thick, elastic, no valves), veins (thinner, valves), capillaries (single cell thick, exchange).
• Lymph: colourless, no RBCs; drains excess fluid to blood.
• Transportation in plants: xylem carries water + minerals up (transpiration pull, root pressure); phloem carries food (translocation, needs ATP, both directions).
• Excretion in humans: kidneys → nephrons filter blood (glomerulus + Bowman's capsule + tubule) → reabsorb useful substances → urine to bladder via ureter → out via urethra.
• Excretion in plants: gases via stomata, water via transpiration, waste in vacuoles/old xylem, gum/resin, fallen leaves.

• Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
• Anaerobic (yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

• Nutrition (auto/hetero) → digestion → respiration → transportation → excretion
• Xylem vs phloem
• Nephron & double circulation

• Xylem = water (one way, up); Phloem = food (both ways, needs ATP).
• Bile emulsifies fat; pancreatic juice digests all three (carb, protein, fat).

• Confusing anaerobic products (lactic acid in muscles vs ethanol in yeast).
• Left vs right heart chambers (left pumps to body, right to lungs).

1. Q. Why is double circulation necessary in humans?
   A. Keeps oxygenated and deoxygenated blood separate → efficient O₂ supply → supports high energy demands of warm-blooded animals.
2. Q. Why do we get cramps after heavy exercise?
   A. Insufficient O₂ in muscles → anaerobic respiration → lactic acid accumulates → cramps.
3. Q. How is the small intestine designed for absorption?
   A. Very long, highly folded, lined with villi (finger-like projections) with rich blood supply → huge surface area.

Nervous and hormonal control in animals; plant movements and hormones.

• Control and coordination in animals: nervous system + endocrine system.
• Neuron structure: dendrites → cell body → axon → axon terminals. Impulse travels dendrite→axon; passes to next neuron via synapse (chemical/neurotransmitter).
• Types of neurons: sensory (receptor→CNS), motor (CNS→effector), interneurons (within CNS).
• Reflex action: quick, automatic response — path: receptor → sensory neuron → spinal cord → motor neuron → effector (this is the reflex arc). No conscious thought needed → faster than voluntary action.
• Central Nervous System: brain + spinal cord. Brain regions: forebrain (thinking, memory, voluntary actions, hunger, sensory perception), midbrain (involuntary — pupil, reflexes to sound), hindbrain (cerebellum for balance, medulla for involuntary — heartbeat, breathing, pons).
• Peripheral Nervous System: cranial + spinal nerves; autonomic nervous system (sympathetic — fight/flight; parasympathetic — rest).
• Voluntary actions controlled by forebrain; involuntary by midbrain/hindbrain; reflex by spinal cord.
• Endocrine system: ductless glands secreting hormones directly into blood.
• Pituitary — 'master gland' — growth hormone (deficiency: dwarfism, excess: gigantism).
• Thyroid — thyroxine — regulates metabolism; needs iodine (deficiency: goitre).
• Adrenal — adrenaline — fight/flight response.
• Pancreas — insulin — controls blood sugar (deficiency: diabetes).
• Testes — testosterone; Ovaries — oestrogen; secondary sexual characters.
• Feedback mechanism: high blood sugar → pancreas releases insulin → glucose stored → sugar falls → insulin release stops.
• Plant control: no nervous system; controlled by chemical (hormones) and by growth movement (tropisms).
• Tropic movements (growth-dependent, directional): phototropism (toward light), geotropism (toward/against gravity), hydrotropism (toward water), chemotropism (toward chemicals, e.g., pollen tube to ovule), thigmotropism (touch, e.g., tendrils).
• Nastic movements (non-directional, quick): folding of Mimosa leaves on touch — due to change in turgor pressure.
• Plant hormones:
• Auxin — cell elongation, phototropism (moves to shaded side).
• Gibberellin — stem elongation.
• Cytokinin — cell division, delays ageing (found in fruits, seeds).
• Abscisic acid (ABA) — inhibitor; causes wilting, closes stomata (stress hormone).
• Ethylene — gaseous hormone; ripens fruits.

• Reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector
• Feedback: hormone → target effect → feedback stops secretion

• Nervous (CNS + PNS + ANS) + Endocrine
• Reflex vs voluntary vs involuntary
• Plant: tropic vs nastic; hormones auxin, gibberellin, cytokinin, ABA, ethylene

• Auxin bends plant toward light — moves to shaded side.
• Cerebellum = balance; medulla = involuntary essentials.
• Iodine deficiency → goitre.

• Confusing tropism types (phototropism vs geotropism).
• Placing adrenaline in the thyroid — it's from adrenal glands.

1. Q. Why do we not touch a hot object even after realising?
   A. Reflex action via spinal cord is quicker than conscious control via brain — hand is pulled back before pain is registered.
2. Q. How does auxin cause a shoot to bend toward light?
   A. Auxin migrates to the shaded side, causing cells there to elongate more → shoot bends toward light.
3. Q. A person's iodine intake is low. Predict a possible disorder.
   A. Goitre — thyroid enlarges because it cannot produce enough thyroxine without iodine.

Asexual and sexual reproduction in plants and humans, and reproductive health.

• Reproduction ensures continuity of species and variation via DNA copying.
• Asexual reproduction: single parent, offspring genetically identical (clones).
• Fission — binary (Amoeba), multiple (Plasmodium).
• Budding — Hydra, yeast.
• Fragmentation — Spirogyra.
• Regeneration — Planaria (specialised cells).
• Vegetative propagation — potato tuber (eyes), sugarcane, rose (cuttings), Bryophyllum (leaf buds); used commercially to preserve variety.
• Spore formation — Rhizopus (bread mould).
• Tissue culture — laboratory technique using totipotent cells.
• Sexual reproduction: two parents; gametes fuse (fertilisation); brings variation via meiosis + random fertilisation.
• Reproduction in flowering plants (angiosperms):
• Male: stamen (anther + filament). Anther makes pollen.
• Female: pistil (stigma + style + ovary). Ovary has ovules.
• Pollination: transfer of pollen from anther to stigma; self- or cross-pollination.
• Fertilisation: pollen tube grows through style → male gamete fuses with egg in ovule → zygote → embryo → seed; ovary → fruit.
• Reproduction in humans:
• Puberty: hormonal changes; secondary sexual characters develop.
• Male: testes (produce sperm & testosterone), vas deferens, seminal vesicles, prostate, urethra, penis.
• Female: ovaries (release ovum, produce oestrogen/progesterone), fallopian tubes (site of fertilisation), uterus (site of implantation and development), vagina.
• Menstrual cycle: 28-day cycle; ovulation ~day 14; if no fertilisation, uterine lining sheds (menstruation).
• Fertilisation in fallopian tube → zygote → embryo → implants in uterus → placenta forms (nutrition + gas exchange) → foetus → birth (~9 months).
• Reproductive health: safe sex prevents STDs (gonorrhoea, syphilis, HIV/AIDS). Contraceptive methods: barrier (condom), chemical (pills), surgical (vasectomy/tubectomy), IUCD.
• Sex determination: XX (female), XY (male); father's Y chromosome determines male offspring.

• Asexual: fission, budding, fragmentation, regeneration, vegetative, spore, tissue culture
• Sexual in plants: pollination → fertilisation → fruit/seed
• Sexual in humans: gametogenesis → fertilisation → placenta → foetus
• Reproductive health: STDs, contraception

• Asexual = clones (no variation); sexual = variation (advantage in evolution).
• Pollination is transfer only; fertilisation is fusion.

• Confusing pollination with fertilisation.
• Mixing up male vs female parts of a flower.

1. Q. Why is variation useful for a species?
   A. It allows the species to survive changing environments — some individuals may have traits suited to new conditions (drives natural selection).
2. Q. Why is DNA copying essential in reproduction?
   A. It transmits parental traits to offspring; small variations in copying create diversity that fuels evolution.
3. Q. Why is the male gamete smaller than the female gamete?
   A. Male gamete carries only genetic material and is designed for motility; the female gamete stores nutrients for the embryo.

Mendel's experiments, laws of inheritance, and sex determination.

• Heredity = transmission of traits from parents to offspring via genes on chromosomes.
• Mendel's work with garden pea (Pisum sativum) — 7 contrasting traits.
• Monohybrid cross (Tt × Tt): F1 all tall (Tt); F2 ratio 3 tall : 1 short — Law of Segregation (alleles separate during gamete formation).
• Dihybrid cross (RRYY × rryy): F1 all round-yellow (RrYy); F2 ratio 9:3:3:1 — Law of Independent Assortment (alleles of different genes segregate independently).
• Terminology: gene, allele (variants of a gene), dominant (masks the other), recessive (only expressed when both alleles same), homozygous (TT or tt), heterozygous (Tt), phenotype (visible trait), genotype (genetic makeup).
• Punnett square is used to predict offspring genotype/phenotype.
• Only traits controlled by genes are inherited; acquired traits (learnt skills, physical injuries) are NOT inherited (Lamarck's idea rejected).
• Sex chromosomes in humans: female XX, male XY. Mother gives X; father gives X or Y → 50% chance of each sex; father's contribution decides sex.
• Basis of evolution: variations arise → those beneficial in environment get selected → over generations, species change.
• Note: 'Evolution' portion beyond the basics has been rationalised in NCERT; focus on inheritance mechanism.

• Monohybrid F2: 3:1 (phenotype), 1:2:1 (genotype)
• Dihybrid F2: 9:3:3:1 (phenotype)
• Sex determination: XX (female), XY (male)

• Genes, alleles, dominant/recessive, genotype/phenotype
• Monohybrid → segregation; Dihybrid → independent assortment
• Punnett squares
• Sex determination in humans

• Dominant capital, recessive small (T, t).
• Sex chromosome: mother always X; father decides X (girl) or Y (boy).

• Believing acquired characters can be inherited.
• Assuming mother determines sex.

1. Q. Why is the sex of the child determined by the father?
   A. Mother contributes only X; father contributes X or Y. XX → girl, XY → boy — decided by father's gamete.
2. Q. Two tall pea plants (Tt) are crossed. What is the probability of a short offspring?
   A. Tt × Tt → TT, Tt, Tt, tt ⇒ P(short = tt) = 1/4 = 25%.
3. Q. Explain: 'A trait acquired during a lifetime is not inherited.'
   A. Only changes in DNA (in reproductive cells) pass on. A muscle built by exercise is not coded in DNA, so it cannot be inherited.

Reflection at curved surfaces, refraction through lenses, and sign convention.

• Light travels in straight lines; reflection follows i = r; incident ray, normal, reflected ray are coplanar.
• Spherical mirrors: concave (converging), convex (diverging). Terms: pole P, centre of curvature C, radius R, principal axis, focus F, focal length f = R/2.
• Image formation by concave mirror depends on object position (at infinity, beyond C, at C, between C & F, at F, between F & P). Practise the six cases.
• Convex mirror always produces virtual, erect, diminished image between P and F.
• Mirror formula: 1/v + 1/u = 1/f. Magnification m = −v/u = h'/h.
• Refraction: bending of light on going from one medium to another due to change in speed.
• Laws: incident ray, refracted ray, normal are coplanar; sin i / sin r = constant = ₁n₂ (Snell's law).
• Refractive index n = c/v (c in vacuum, v in medium); denser medium ⇒ higher n; light slows and bends toward normal.
• Lens: converging (convex) or diverging (concave). Focal length by convention: convex positive, concave negative.
• Lens formula: 1/v − 1/u = 1/f. Magnification m = v/u = h'/h.
• Power of a lens P = 1/f (with f in metres). Unit: dioptre (D). Combined power = P₁ + P₂ + ...
• New Cartesian sign convention: pole/optical centre is origin; incident light travels along +x direction; heights above principal axis are positive.
• Image characteristics table:
• Concave mirror: real & inverted (u beyond F); virtual & erect & magnified (u < F).
• Convex mirror: always virtual, erect, diminished.
• Convex lens: real & inverted for u > f; virtual & erect & magnified for u < f (magnifying glass).
• Concave lens: always virtual, erect, diminished.

• Mirror formula: 1/v + 1/u = 1/f; m = −v/u
• Lens formula: 1/v − 1/u = 1/f; m = v/u
• Snell: n₁ sin i = n₂ sin r; n = c/v
• Power P = 1/f (f in metres); unit: dioptre
• f = R/2

• Reflection (plane, spherical) → refraction → lenses
• Sign convention
• Image formation cases
• Power of lens

• New Cartesian: distances from pole, along incident light → +; opposite → −.
• m > 0 → erect virtual; m < 0 → inverted real (mirrors).

• Sign errors — especially for concave mirror/lens.
• Interchanging u and v.
• Using degrees vs radians in Snell (they don't matter individually — but consistency does).

1. Q. Object 20 cm before a concave mirror of f = −15 cm. Find image.
   A. 1/v = 1/f − 1/u = −1/15 − 1/(−20) = −4/60 + 3/60 = −1/60 ⇒ v = −60 cm (real, inverted, magnified 3×).
2. Q. A convex lens of f = 10 cm forms a virtual image 15 cm on the same side. Find object distance.
   A. 1/v − 1/u = 1/f ⇒ 1/(−15) − 1/u = 1/10 ⇒ 1/u = −1/15 − 1/10 = −1/6 ⇒ u = −6 cm.
3. Q. Power of a lens is +2 D. What kind and focal length?
   A. Positive → convex. f = 1/P = 0.5 m = 50 cm.

Structure and defects of the eye; refraction of light through prism; atmospheric optical phenomena.

• Eye parts: cornea (main refraction), aqueous humour, iris (controls pupil size), pupil, lens (fine focusing via ciliary muscles), vitreous humour, retina (image formation, contains rods and cones), optic nerve.
• Power of accommodation: ability of eye lens to adjust focal length. Least distance of distinct vision (near point) = 25 cm; far point = infinity (for a normal eye).
• Defects of vision:
• Myopia (short-sightedness): far point < ∞; distant objects blur; corrected with concave lens.
• Hypermetropia (long-sightedness): near point > 25 cm; nearby objects blur; corrected with convex lens.
• Presbyopia: age-related loss of accommodation; often needs bifocal lenses.
• Cataract: lens becomes cloudy; corrected by surgical replacement.
• Refraction through a glass prism: light bends toward base; splits (dispersion) into constituent colours (VIBGYOR) because different colours have different refractive indices — violet bends most, red least.
• Newton's experiment: white light passing through a prism separates into 7 colours; passing through an inverted second prism recombines to white.
• Rainbow: sunlight refracts, disperses and reflects internally in raindrops.
• Atmospheric refraction: apparent flattening of Sun near horizon, twinkling of stars (due to changing air density), advance sunrise & delayed sunset (~2 min each due to refraction).
• Scattering (Tyndall effect / Rayleigh): shorter wavelengths scatter more.
• Sky appears blue: blue scatters more than red.
• Sun appears reddish at sunrise/sunset: blue scattered away, red passes through longer atmospheric path.
• Danger signals red: least scattered → visible from far.

• P = 1/f (in dioptres, f in metres)
• Normal near point = 25 cm; far point = ∞

• Eye structure → accommodation → defects & correction
• Prism → dispersion → rainbow
• Atmospheric refraction & scattering

• Myopia → 'my-o' close → concave for far.
• Hypermetropia → 'hyper' far → convex for near.
• Rayleigh scattering ∝ 1/λ⁴.

• Confusing which defect uses which lens.
• Thinking stars twinkle due to their own brightness variation (it's atmospheric refraction).

1. Q. Why does the sky appear blue?
   A. Rayleigh scattering — shorter wavelengths (blue) are scattered more strongly by atmospheric molecules, so blue light reaches our eyes from all directions.
2. Q. Why don't planets twinkle like stars?
   A. Planets are closer and act as a collection of point sources; averaged refraction cancels twinkling. Stars are point sources whose light gets deflected slightly by moving air pockets.
3. Q. A person cannot read a book kept at 25 cm but can read it at 50 cm. Identify the defect and correction.
   A. Hypermetropia — corrected by a convex lens forming a virtual image of the book at his near point.

Current, potential difference, resistance, Ohm's law, and the heating effect of current.

• Electric current I = charge Q / time t. Unit: ampere (A). 1 A = 1 C/s. Conventional current flows from + to − (opposite to electron flow).
• Potential difference V between two points = work done to move unit charge = W/Q. Unit: volt (V).
• Ohm's law: V = IR (at constant temperature). R is the resistance of the conductor; unit: ohm (Ω).
• Resistance depends on length (∝ L), cross-section (∝ 1/A), and material (resistivity ρ): R = ρL/A. Unit of ρ: Ω·m.
• Conductors have low resistivity (metals like Cu, Ag); insulators have very high resistivity (rubber, glass).
• Resistors in series: same current I; total V = V₁ + V₂ + ...; equivalent Rₛ = R₁ + R₂ + R₃ + …
• Resistors in parallel: same voltage V across each; total I = I₁ + I₂ + ...; equivalent 1/Rₚ = 1/R₁ + 1/R₂ + 1/R₃ + …
• Parallel connection is preferred at home: appliances get full voltage, work independently, and total resistance decreases.
• Heating effect of current (Joule's law): H = I²Rt. Applications: bulb filament (tungsten, high m.p.), electric iron, heater, fuse.
• Electric power: P = VI = I²R = V²/R. Unit: watt (W). Commercial unit of energy: kilowatt-hour (kWh). 1 kWh = 3.6 × 10⁶ J.
• Electric fuse melts and breaks the circuit if current exceeds a safe value — protects against short circuits/overloading.

• I = Q/t
• V = IR (Ohm's law)
• R = ρL/A
• Series: R = R₁ + R₂ + …
• Parallel: 1/R = 1/R₁ + 1/R₂ + …
• P = VI = I²R = V²/R
• H = I²Rt (Joule's heating)

• Charge → current → potential difference → resistance
• Series vs parallel
• Heating effect, power, energy (kWh)

• Series: same current; parallel: same voltage.
• In parallel, equivalent resistance is less than the smallest resistor.

• Adding parallel resistances directly.
• Confusing 1 kWh with 1 kJ (1 kWh = 3.6 × 10⁶ J).
• Ignoring the effect of temperature on R.

1. Q. Three resistors 2 Ω, 3 Ω, 6 Ω are connected in parallel. Find equivalent.
   A. 1/R = 1/2 + 1/3 + 1/6 = 6/6 = 1 ⇒ R = 1 Ω.
2. Q. A 60 W bulb operates at 220 V. Calculate current and resistance.
   A. I = P/V = 60/220 ≈ 0.27 A; R = V/I ≈ 806.7 Ω (or V²/P = 806.7 Ω).
3. Q. Why is the filament of a bulb made of tungsten?
   A. Very high melting point (~3380 °C), high resistivity, and can emit light at high temperatures without breaking.

Magnetic fields due to current, force on a conductor, motor and generator, and domestic circuits.

• A current-carrying conductor produces a magnetic field around it (Oersted's experiment).
• Magnetic field lines: start N pole, end S pole outside a magnet; closed loops overall; never intersect; density represents strength.
• Field due to a straight current-carrying wire: concentric circles around the wire; direction from right-hand thumb rule (thumb = current, curled fingers = field).
• Field due to a circular loop: proportional to current, inversely proportional to radius; field at the centre is perpendicular to the plane of the loop.
• Field due to a solenoid: nearly uniform inside, like a bar magnet outside; direction by right-hand thumb rule around the loops.
• Electromagnet: soft iron core inside a solenoid; strong temporary magnet when current flows.
• Force on a current-carrying conductor in a magnetic field: F = BIL when I ⟂ B. Direction by Fleming's left-hand rule (thumb = force, forefinger = field, middle finger = current).
• Electric motor: converts electrical energy into mechanical (using force on current in magnetic field). Components: armature, split-ring commutator, brushes, magnets.
• Electromagnetic induction: EMF (and current) is induced in a coil when magnetic flux through it changes (Faraday's law).
• Electric generator: converts mechanical energy into electrical. AC generator has slip rings; DC has split-ring commutator. Direction by Fleming's right-hand rule.
• Domestic electric circuits: three wires — Live (red, ~220 V), Neutral (black, ~0 V), Earth (green, connected to ground for safety). Appliances connected in parallel.
• Safety devices: fuse (melts under overload), MCB (miniature circuit breaker), earthing (low-resistance path to ground so leakage doesn't shock the user).
• Short-circuit: live and neutral touch directly → very low resistance → very high current → heat/fire; fuse breaks the circuit and protects wiring.
• Overloading: too many appliances on one line → excessive current → fuse melts.

• Right-hand thumb rule (straight wire)
• Fleming's left-hand rule → motor (F, B, I)
• Fleming's right-hand rule → generator (induced current)
• Force on conductor F = BIL (perpendicular)

• Field from current: wire, loop, solenoid → electromagnet
• Force on current-carrying conductor
• Motor (electric → mechanical) vs generator (mechanical → electric)
• Domestic wiring: live, neutral, earth; fuse, MCB

• Left hand → motor (mnemonic: FBI order = thuMb–Forefinger–Middle).
• Right hand → generator (induced current).
• AC → slip rings; DC → split-ring commutator.

• Using the wrong hand rule.
• Confusing AC vs DC generator (slip rings vs commutator).

1. Q. Why is earthing important in electrical appliances?
   A. It provides a low-resistance path to ground; if the metal casing becomes live due to a fault, current flows to earth instead of through the user — preventing shocks.
2. Q. State one advantage of an electric fuse over a switch.
   A. A fuse automatically breaks the circuit under overload/short circuit, preventing fire; a switch requires manual action.
3. Q. How can the strength of an electromagnet be increased?
   A. Increase current, increase number of turns per unit length, or use a soft iron core.

Ecosystems, energy flow, waste management, and ozone depletion.

• Environment = biotic (living) + abiotic (non-living) surroundings.
• Ecosystem = a self-contained unit where organisms interact with each other and with abiotic components. Types: natural (forest, pond) and artificial (aquarium, crop field).
• Components: producers (autotrophs — plants), consumers (herbivores, carnivores, omnivores), decomposers (bacteria, fungi).
• Food chain: linear sequence — producer → primary consumer → secondary → tertiary. Each stage = trophic level.
• Food web = interconnected food chains; more realistic.
• 10% law of energy transfer (Lindeman): only ~10% of energy at one trophic level is passed to the next; the rest is lost as heat, in life processes.
• Because of the 10% law, food chains are usually limited to 3–4 trophic levels.
• Biomagnification: harmful chemicals (e.g., DDT, mercury) increase in concentration as they move up trophic levels — top predators are worst affected.
• Biodegradable substances: broken down by decomposers (vegetable peel, cotton, paper).
• Non-biodegradable: not decomposed (plastic, glass, DDT); accumulate as pollution.
• Impact: sewage in water bodies causes eutrophication and BOD rise; solid waste causes land pollution.
• Ozone layer (in stratosphere): protects Earth from harmful UV radiation.
• Ozone depletion: caused by CFCs (from refrigerators, aerosols). CFCs release Cl atoms that destroy ozone.
• Consequences: increased UV-B → skin cancer, cataracts, weakened immunity, damage to crops and marine life.
• Montreal Protocol (1987): international agreement to phase out ozone-depleting substances.
• Note: 'Sustainable management of resources' has largely been rationalised out of the chapter — focus on ecosystem + ozone content.

• 10% law: energy transferred between trophic levels
• Biomagnification: concentration ↑ up the chain

• Ecosystem components → food chain/web → energy flow
• Biodegradable vs non-biodegradable
• Ozone depletion (CFC → UV harm) → Montreal Protocol

• Only 10% up — so food chains rarely exceed 4 levels.
• Biomagnification hits top of chain hardest (birds of prey, humans).

• Thinking energy is cyclic (it flows one way; matter is cyclic).
• Confusing biodegradable with recyclable.

1. Q. Why are food chains usually limited to 3–4 trophic levels?
   A. Only 10% of energy passes to the next level; beyond 4 levels, insufficient energy remains to support another.
2. Q. How do plastics harm the environment?
   A. Non-biodegradable → accumulate as waste; when burnt release toxic gases; block drains; enter food chain as microplastics.
3. Q. Explain how CFCs deplete ozone.
   A. UV breaks CFCs, releasing Cl atoms; each Cl catalytically destroys many ozone molecules — thinning the ozone layer.