Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

Important questions and answersमहत्वपूर्ण प्रश्न और उत्तर

1. Rest, motion and frame of reference

• A body is at rest or in motion only relative to a frame of reference (a point of view with a clock and coordinate axes).
• Motion can be one-dimensional (a car on a straight road), two-dimensional (a projectile) or three-dimensional (a flying bird).

2. Distance and displacement

• Distance – total length of path; scalar; never negative.
• Displacement – shortest straight-line change in position with direction; vector; can be zero or negative. Displacement ≤ distance.
• Example: one full round of a circular track → distance = 2πr, displacement = 0.

3. Speed and velocity

• Average speed = total distance ÷ total time. Average velocity = displacement ÷ time.
• Instantaneous velocity v = dx/dt (slope of the x–t graph at that instant).
• Uniform motion: equal displacements in equal intervals of time.

4. Acceleration

• a = dv/dt; SI unit m s⁻². Negative acceleration opposite to velocity is called retardation.
• Uniform acceleration: velocity changes equally in equal times.

5. Graphs

• x–t graph: slope = velocity. A straight line means uniform velocity; a curve means acceleration.
• v–t graph: slope = acceleration, area = displacement.
• a–t graph: area = change in velocity.

6. Equations of uniformly accelerated motion

• v = u + at
• s = ut + ½at²
• v² = u² + 2as
• Distance in the n^th second: s_n = u + (a/2)(2n − 1)
• They follow from a = dv/dt and v = dx/dt by integration (calculus method) or from the v–t graph.

7. Motion under gravity

• Near Earth, freely falling bodies have a = g ≈ 9.8 m s⁻² downward (air resistance ignored).
• Dropped from rest: v = gt, h = ½gt². Thrown up with u: time to top = u/g, maximum height = u²/2g, total time of flight = 2u/g.

8. Relative velocity

• Velocity of A relative to B: v_AB = v_A − v_B.
• Same direction: subtract speeds. Opposite directions: add speeds.

Important questions and answers

1. Scalars and vectors

• Scalar – magnitude only (mass, time, speed, work). Vector – magnitude and direction (displacement, velocity, force), added by vector rules.
• Types: zero (null) vector, unit vector â = A/|A| (î, ĵ, k̂ along x, y, z), equal vectors (same magnitude and direction), negative vector (same magnitude, opposite direction), collinear and coplanar vectors, position vector r = xî + yĵ + zk̂.

2. Addition and subtraction

• Triangle law and parallelogram law.
• Resultant: R = √(A² + B² + 2AB cosθ); direction tan α = B sinθ / (A + B cosθ).
• Maximum R = A + B (θ = 0°), minimum R = |A − B| (θ = 180°).
• Subtraction: A − B = A + (−B). Addition is commutative and associative.

3. Resolution of vectors

• In a plane: A_x = A cosθ, A_y = A sinθ; A = A_xî + A_yĵ.
• In 3D: A = A_xî + A_yĵ + A_zk̂, |A| = √(A_x² + A_y² + A_z²).
• Analytical addition: add the x, y and z components separately.

4. Products of vectors

• Dot (scalar) product: A·B = AB cosθ = A_xB_x + A_yB_y + A_zB_z. Commutative. î·î = 1, î·ĵ = 0. Example: work W = F·s.
• Cross (vector) product: A×B = AB sinθ n̂ (right-hand rule). Not commutative: A×B = −B×A. î×ĵ = k̂, ĵ×k̂ = î, k̂×î = ĵ, î×î = 0. Example: torque τ = r×F.
• Two vectors are perpendicular if A·B = 0, and parallel if A×B = 0.

5. Projectile motion

• A body thrown at an angle moves under gravity only. Horizontal velocity u cosθ stays constant; vertical motion has acceleration g downward. The two motions are independent.
• Time of flight T = 2u sinθ/g; maximum height H = u² sin²θ/2g; horizontal range R = u² sin 2θ/g.
• Maximum range at θ = 45°: R_max = u²/g. Angles θ and (90° − θ) give the same range.
• Path is a parabola: y = x tanθ − gx²/(2u² cos²θ).
• Projected horizontally from height h: time t = √(2h/g), range = u√(2h/g).
• Air drag reduces both the range and the height.

6. Uniform circular motion

• Speed is constant but direction changes, so it is accelerated motion.
• Angular velocity ω = θ/t, v = rω, time period T = 2π/ω, frequency ν = 1/T.
• Centripetal acceleration a_c = v²/r = rω², always towards the centre.

Important questions and answers

1. Force and inertia

• Aristotle wrongly thought a force is needed to keep a body moving. Galileo’s inclined-plane experiments showed a body keeps moving unless friction or another force stops it.
• Inertia – tendency to resist change in the state of rest or motion. Types: of rest, of motion, of direction. Mass is the measure of inertia.

2. Newton’s laws

• First law: a body stays at rest or in uniform motion unless an external force acts (law of inertia).
• Linear momentum p = mv (vector).
• Second law: F = dp/dt; for constant mass F = ma. 1 newton = force giving 1 kg an acceleration of 1 m s⁻². Component form: F_x = ma_x, etc. The second law is the “real” law – the first and third can be derived from it.
• Impulse J = F × Δt = Δp. A cricketer pulls hands back while catching to increase time and reduce force.
• Third law: to every action there is an equal and opposite reaction; they act on different bodies, so they never cancel. Examples: walking, rocket propulsion, swimming.

3. Conservation of linear momentum

• If no external force acts, the total momentum of a system stays constant.
• Recoil of a gun: m_bv_b + m_gv_g = 0 → v_g = −m_bv_b/m_g.
• Frames: an inertial frame is at rest or moves with constant velocity; Newton’s laws hold only in it. An accelerated frame is non-inertial.

4. Apparent weight in a lift

• Moving up with acceleration a: R = m(g + a) (feels heavier).
• Moving down with acceleration a: R = m(g − a) (feels lighter).
• Uniform velocity: R = mg. Free fall (a = g): R = 0 (weightlessness).

5. Equilibrium and free body diagrams

• Concurrent forces meet at one point; for equilibrium their vector sum is zero.
• A free body diagram (FBD) shows all forces acting on one body – weight, normal reaction, tension, friction – used to write F = ma.

6. Friction

• Force opposing relative motion between surfaces in contact.
• Static friction is self-adjusting: it equals the applied force until it reaches the limiting value f_s = μ_sN.
• Kinetic friction f_k = μ_kN; μ_k < μ_s. Rolling friction is the smallest.
• Angle of friction λ: tan λ = μ_s. Angle of repose α: tan α = μ_s, so λ = α.
• On a rough incline, sliding acceleration a = g(sinθ − μ_kcosθ).
• Pulling a roller is easier than pushing it, because pulling reduces the normal reaction.
• Friction is a “necessary evil”: it lets us walk and brakes work, but causes wear and heat. Reduce it with lubricants, ball bearings and polishing.

7. Dynamics of circular motion

• A body in a circle needs a centripetal force F = mv²/r towards the centre (provided by tension, friction, gravity, etc.).
• Car on a level curve: friction provides it, so v_max = √(μrg).
• Banked road (no friction): tan θ = v²/rg. With friction: v_max = √[rg(μ + tanθ)/(1 − μ tanθ)].
• Centrifugal force is a pseudo-force felt only in a rotating (non-inertial) frame, equal to mv²/r outward.

Important questions and answers

1. Work

• W = F·s = Fs cosθ; scalar; unit joule (J).
• Positive work: θ < 90° (force along motion). Negative: θ > 90° (friction). Zero: θ = 90° (centripetal force, a coolie carrying a load on a level road) or no displacement.
• Work by a variable force W = ∫F dx = area under the F–x graph.

2. Conservative and non-conservative forces

• Conservative (gravity, spring force): work does not depend on path; work in a closed loop is zero.
• Non-conservative (friction, air drag): work depends on path; energy is lost as heat.

3. Energy

• Forms: mechanical, heat, light, sound, electrical, chemical, nuclear.
• Kinetic energy K = ½mv² = p²/2m.
• Work–energy theorem: net work done = change in kinetic energy.
• Potential energy: gravitational U = mgh; spring U = ½kx². Force F = −dU/dx.
• Mass–energy equivalence: E = mc².
• Conservation of energy: total energy of an isolated system is constant. With only conservative forces, K + U = constant.

4. Power

• P = W/t; instantaneous P = F·v; unit watt (W). 1 horsepower = 746 W. 1 kWh = 3.6 × 10⁶ J (a unit of energy).

5. Collisions

• Momentum is conserved in all collisions.
• Elastic: momentum and KE both conserved. Inelastic: only momentum conserved. Perfectly inelastic: bodies stick together.
• 1-D elastic collision, body 2 at rest: v₁ = (m₁ − m₂)u₁/(m₁ + m₂), v₂ = 2m₁u₁/(m₁ + m₂). Equal masses exchange velocities.
• Coefficient of restitution e = speed of separation ÷ speed of approach; e = 1 elastic, e = 0 perfectly inelastic, 0 < e < 1 inelastic.

6. Motion in a vertical circle

• Minimum speed at the top: √(gr); at the bottom: √(5gr) (for a string).
• Tension is maximum at the bottom and minimum at the top.

Important questions and answers

1. Rigid body and centre of mass

• A rigid body keeps the distances between its particles fixed – a useful ideal model.
• Centre of mass: x_cm = Σm_ix_i/Σm_i (similarly y, z). Two particles: x_cm = (m₁x₁ + m₂x₂)/(m₁ + m₂). Uniform rod: at its middle.
• The CM moves as if the whole mass were there and all external forces acted on it: F_ext = Ma_cm. Internal forces do not change the motion of the CM.
• If no external force acts, v_cm stays constant (e.g. fragments of an exploding shell).
• Centre of gravity = centre of mass when g is uniform.

2. Torque and equilibrium

• Torque τ = r × F, magnitude rF sinθ (N m). It causes rotation.
• A couple is two equal, opposite, parallel forces; it causes only rotation.
• Equilibrium of a rigid body: ΣF = 0 (no translation) and Στ = 0 (no rotation). Principle of moments: clockwise moments = anticlockwise moments (lever, see-saw).
• Work by torque W = τθ; power P = τω.

3. Moment of inertia

• I = Σm_ir_i² (kg m²) – rotational inertia; depends on mass and how it is spread about the axis.
• Radius of gyration K: I = MK².
• Perpendicular axis theorem (plane lamina): I_z = I_x + I_y.
• Parallel axis theorem: I = I_cm + Md².
• Standard values: thin rod about centre ML²/12, about one end ML²/3; ring about its axis MR²; disc about its axis MR²/2; solid sphere about a diameter 2MR²/5; hollow sphere 2MR²/3.

4. Rotational kinematics and dynamics

• Analogues: x ↔ θ, v ↔ ω, a ↔ α, m ↔ I, F ↔ τ, p ↔ L.
• ω = ω₀ + αt; θ = ω₀t + ½αt²; ω² = ω₀² + 2αθ. v = rω, a_t = rα.
• τ = Iα (Newton’s second law for rotation).

5. Angular momentum

• L = r × p; for a rigid body L = Iω. τ = dL/dt.
• Conservation: if τ_ext = 0, Iω = constant. A skater or diver pulls in arms → I decreases → ω increases. Planets move faster near the Sun.

6. Rotational KE and rolling

• KE_rot = ½Iω².
• Rolling without slipping: v = Rω; total KE = ½mv²(1 + K²/R²).
• Rolling down an incline: a = g sinθ/(1 + K²/R²). Solid sphere (K²/R² = 2/5) reaches the bottom before a disc (1/2), which beats a ring (1).

Important questions and answers

1. Kepler’s laws

• Law of orbits: planets move in elliptical orbits with the Sun at one focus.
• Law of areas: the line from Sun to planet sweeps equal areas in equal times (areal velocity is constant – because angular momentum is conserved). So a planet moves fastest when nearest the Sun.
• Law of periods: T² ∝ a³ (a = semi-major axis).

2. Universal law of gravitation

• F = Gm₁m₂/r², always attractive, acts along the line joining the masses.
• G = 6.67 × 10⁻¹¹ N m² kg⁻² (universal constant, first measured by Cavendish).
• Gravitational field intensity E = F/m = GM/r² (towards the mass). Forces and fields add by the superposition principle.

3. Acceleration due to gravity

• g = GM/R² ≈ 9.8 m s⁻².
• At height h (h ≪ R): g_h ≈ g(1 − 2h/R). At depth d: g_d = g(1 − d/R); g = 0 at the centre.
• g is less at the equator than at the poles, because of Earth’s rotation and its bulge at the equator.
• Mass of Earth M = gR²/G.

4. Potential and potential energy

• Gravitational potential V = −GM/r (zero at infinity; negative because gravity is attractive).
• Potential energy of two masses U = −GMm/r.

5. Satellites

• Orbital speed v₀ = √(GM/r); near the surface v₀ = √(gR) ≈ 7.9 km/s. Period T = 2π√(r³/GM).
• Geostationary satellite: period 24 h, moves west to east in the equatorial plane at about 36,000 km height – looks fixed in the sky; used for TV and communication.
• Polar satellite: low orbit (about 500–800 km) passing over the poles; covers the whole Earth; used for mapping, weather and remote sensing.
• Total energy of a satellite E = −GMm/2r; binding energy = +GMm/2r.
• Astronauts feel weightless because they and the satellite are in continuous free fall.

6. Escape velocity

• Minimum speed to escape Earth’s gravity: v_e = √(2GM/R) = √(2gR) ≈ 11.2 km/s. v_e = √2 × v₀.
• The Moon’s escape speed is only about 2.4 km/s, so gas molecules escape easily – the Moon has no atmosphere.
• Maximum height reached by a body thrown up with speed v (large v): h = v²R/(2gR − v²).

Important questions and answers

1. Elasticity

• Elasticity – property of regaining original shape after the deforming force is removed. Plasticity – no tendency to regain shape (putty, clay).
• Due to intermolecular forces: stretching changes molecular separation, and a restoring force develops.

2. Stress and strain

• Stress = restoring force per unit area = F/A (N m⁻² = Pa).
• Types: longitudinal (tensile or compressive), shearing (tangential force), volume/hydraulic (uniform pressure).
• Strain (no unit): longitudinal ΔL/L, shearing θ (angle), volume ΔV/V.

3. Hooke’s law and the stress–strain curve

• Within the elastic limit, stress ∝ strain; stress/strain = modulus of elasticity.
• Curve: proportional limit → elastic limit (yield point) → plastic region → ultimate tensile strength → fracture point.
• Ductile materials (copper, aluminium) have a long plastic region and can be drawn into wires. Brittle materials (glass, cast iron) break soon after the elastic limit. Elastomers (rubber) stretch hugely but do not obey Hooke’s law.

4. Moduli of elasticity

• Young’s modulus Y = (F/A)/(ΔL/L) = FL/(AΔL). Steel has a larger Y than rubber, so steel is more elastic. Measured by Searle’s method.
• Bulk modulus B = −p/(ΔV/V); compressibility = 1/B. Solids have the largest B, gases the smallest.
• Modulus of rigidity η = (F/A)/θ; only solids have it.
• Poisson’s ratio σ = lateral strain/longitudinal strain (no unit; theoretically between −1 and 0.5).
• Elasticity decreases with rise in temperature, and impurities can increase or decrease it.

5. Elastic potential energy and thermal stress

• Energy stored in a stretched wire U = ½ × F × ΔL; energy per unit volume = ½ × stress × strain.
• A rod clamped between walls and heated or cooled develops force F = YAαΔT.

6. Applications

• Crane ropes are made of many thin wires twisted together for flexibility and strength; thickness is chosen from the yield strength.
• Girders and rails are I-shaped – they resist bending well while saving material and weight.
• The maximum height of a mountain on Earth (about 10 km) is limited by the elastic limit of rocks.

Important questions and answers

1. Thrust and pressure

• Thrust – total normal force on a surface. Pressure P = F/A (scalar; Pa). Fluids exert only normal forces at rest.
• Pressure at depth h: P = P₀ + ρgh; same at all points at the same depth.
• Atmospheric pressure ≈ 1.013 × 10⁵ Pa (76 cm of mercury). Gauge pressure = P − P₀. Measured with a mercury barometer and open-tube manometer.
• Density ρ = m/V; relative density = density of substance ÷ density of water (no unit).

2. Pascal’s law

• Pressure applied to an enclosed fluid is transmitted equally in all directions.
• Hydraulic lift: F₂ = F₁ × A₂/A₁. Also used in hydraulic brakes and presses.

3. Buoyancy and floatation

• Archimedes’ principle: a body in a fluid loses weight equal to the weight of fluid displaced (buoyant force acts at the centre of buoyancy).
• Law of floatation: a floating body displaces fluid equal to its own weight. Fraction submerged = ρ_body/ρ_liquid.

4. Viscosity

• Internal friction between fluid layers: F = ηA(dv/dx); η = coefficient of viscosity (Pa s; CGS unit poise).
• For liquids η decreases with temperature; for gases it increases.
• Stokes’ law: F = 6πηrv. Terminal velocity v_t = 2r²(ρ − σ)g/9η (ρ = body, σ = fluid). Explains slow fall of rain drops and parachutes.
• Poiseuille’s formula: volume flow per second Q = πPr⁴/(8ηl).

5. Fluid flow

• Streamline (laminar) flow – every particle follows the path of the one before; turbulent – irregular eddies.
• Reynolds number R_e = ρvD/η: roughly below 1000 streamline, above 2000 turbulent.
• Ideal liquid: incompressible and non-viscous.
• Equation of continuity: A₁v₁ = A₂v₂ – liquid flows faster in narrower parts.
• Bernoulli’s theorem: P + ½ρv² + ρgh = constant along a streamline (pressure + kinetic + potential energy per volume).
• Applications: lift on aeroplane wings, swing of a spinning ball (Magnus effect), atomiser/sprayer, roofs blown off in storms, Venturimeter.
• Torricelli’s theorem: speed of efflux from a hole at depth h, v = √(2gh).

6. Surface tension

• S = F/l (N m⁻¹) = surface energy per unit area (J m⁻²). Due to cohesive forces; surface acts like a stretched membrane.
• Drops and bubbles are spherical (minimum surface area). Excess pressure: drop 2S/R, soap bubble 4S/R.
• Angle of contact: acute for water–glass (water wets glass, concave meniscus); obtuse for mercury–glass (convex meniscus).
• Capillarity: h = 2S cosθ/(ρrg). Water rises, mercury falls in a glass capillary.
• S decreases with temperature and with detergents (so soap water cleans better).

Important questions and answers

1. Heat, temperature and scales

• Heat is energy that flows due to a temperature difference; temperature tells how hot a body is.
• Scales: C/100 = (F − 32)/180 = (K − 273.15)/100. −40° is the same on Celsius and Fahrenheit.
• Ideal gas equation PV = nRT; absolute zero is 0 K = −273.15 °C.

2. Thermal expansion

• Linear: ΔL = αLΔT. Area: ΔA = βAΔT. Volume: ΔV = γVΔT. For solids β = 2α, γ = 3α.
• Applications: gaps in railway tracks, loose electric wires in summer, bimetallic strip in thermostats.
• Density decreases with temperature: ρ_T ≈ ρ₀(1 − γΔT).
• Anomalous expansion of water: water contracts from 0 °C to 4 °C and has maximum density at 4 °C, so lakes freeze from the top and fish survive below.

3. Specific heat and calorimetry

• Q = mcΔT. Water has a high specific heat (≈ 4186 J kg⁻¹ K⁻¹), so it is used as a coolant and makes coastal climate moderate.
• Molar specific heat C = Q/(nΔT).
• Principle of calorimetry (method of mixtures): heat lost by the hot body = heat gained by the cold body.

4. Change of state and latent heat

• Q = mL. Latent heat of fusion of ice ≈ 3.33 × 10⁵ J/kg; of vaporisation of water ≈ 22.6 × 10⁵ J/kg.
• Temperature stays constant during a change of state (flat parts of the heating curve).
• Pressure raises the boiling point (pressure cooker) and lowers the melting point of ice (regelation). Triple point of water: 273.16 K.

5. Conduction

• Heat flow H = KA(T₁ − T₂)/L; K = thermal conductivity (W m⁻¹ K⁻¹). Temperature gradient = ΔT/L.
• Thermal resistance R = L/KA; in series R = R₁ + R₂.

6. Convection

• Heat moves with the actual movement of fluid. Natural (density difference) or forced (fan, pump).
• Examples: sea breeze by day, land breeze by night, trade winds.

7. Radiation

• Needs no medium; travels at the speed of light.
• Perfectly black body absorbs all radiation. Kirchhoff’s law: good absorbers are good emitters.
• Stefan’s law: E = σT⁴ (σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴); for a real body E = eσAT⁴.
• Newton’s law of cooling: rate of cooling ∝ (T − T_s) for small temperature differences.
• Wien’s law: λ_mT = b (≈ 2.9 × 10⁻³ m K); hotter bodies glow bluer.
• Greenhouse effect: CO₂ and other gases trap Earth’s heat radiation and warm the planet.

Important questions and answers

1. Basic terms

• System – the part under study; surroundings – everything else. State variables: P, V, T, U.
• Thermal equilibrium: no net heat flow. Zeroth law: if A and B are each in equilibrium with C, then A and B are in equilibrium with each other – this defines temperature.
• Heat and work are path-dependent; internal energy U is a state function (depends only on the state).

2. First law of thermodynamics

• ΔQ = ΔU + ΔW (heat given = rise in internal energy + work done by the system). It is the law of conservation of energy.
• Work done by a gas W = PΔV (area under the P–V curve).
• Specific heats of gases: C_p > C_v; Mayer’s relation C_p − C_v = R; γ = C_p/C_v.
• Limitation: it does not tell the direction of heat flow or whether a process is possible.

3. Thermodynamic processes

• Isothermal (T constant): ΔU = 0, Q = W = nRT ln(V₂/V₁), PV = constant.
• Adiabatic (no heat exchange): Q = 0, PV^γ = constant, W = nR(T₁ − T₂)/(γ − 1). Adiabatic expansion cools a gas.
• Isobaric (P constant): W = PΔV. Isochoric (V constant): W = 0, Q = ΔU.
• The adiabatic curve is steeper than the isothermal curve (by factor γ).

4. Second law and reversibility

• Kelvin–Planck: no engine can convert all heat taken from a source into work. Clausius: heat cannot flow by itself from a colder to a hotter body.
• Reversible processes can be retraced exactly (ideal, very slow, no friction). Real processes are irreversible.

5. Heat engines and refrigerators

• Heat engine: takes Q₁ from a hot source, does work W, rejects Q₂ to a sink. Efficiency η = W/Q₁ = 1 − Q₂/Q₁.
• Carnot engine (two isothermal + two adiabatic steps) is the most efficient: η = 1 − T₂/T₁. η = 100% only if T₂ = 0 K, which is impossible.
• Refrigerator / heat pump: coefficient of performance β = Q₂/W = T₂/(T₁ − T₂).

Important questions and answers

1. Postulates of kinetic theory

• A gas consists of a very large number of tiny molecules in continuous random motion.
• Molecules are like point masses; their own volume is negligible.
• Collisions with each other and the walls are perfectly elastic, and collision time is negligible.
• No intermolecular forces except during collisions. Gravity is ignored.

2. Gas laws and ideal gas

• Boyle: PV = constant (T fixed). Charles: V ∝ T (P fixed). Gay-Lussac: P ∝ T (V fixed).
• Ideal gas obeys PV = nRT = Nk_BT at all P and T. Real gases behave ideally at low pressure and high temperature.
• R = 8.314 J mol⁻¹ K⁻¹; Boltzmann constant k_B = R/N_A = 1.38 × 10⁻²³ J K⁻¹; Avogadro number N_A = 6.022 × 10²³ mol⁻¹.

3. Pressure and molecular speed

• Pressure of an ideal gas: P = (1/3)ρv_rms² = (1/3)(N/V)mv_rms².
• Root-mean-square speed v_rms = √(3RT/M) = √(3k_BT/m) (M in kg/mol).
• Average KE per molecule = (3/2)k_BT. So temperature measures the average KE of molecules; at 0 K it would be zero.
• The kinetic theory explains all the gas laws and diffusion.

4. Mean free path

• Average distance between two successive collisions: λ = 1/(√2 πd²n), where d = molecular diameter, n = number density.

5. Degrees of freedom and specific heats

• Degrees of freedom: monatomic 3 (translation); diatomic 5 (3 translation + 2 rotation), 7 if vibration is included.
• Law of equipartition of energy: each degree of freedom gets ½k_BT per molecule.
• Monatomic: U = (3/2)nRT, C_v = 3R/2, C_p = 5R/2, γ = 5/3 ≈ 1.67.
• Diatomic (rigid): C_v = 5R/2, C_p = 7R/2, γ = 7/5 = 1.4.
• Solids (Dulong–Petit law): molar specific heat ≈ 3R.

Important questions and answers

1. Periodic and oscillatory motion

• Periodic: repeats after equal intervals (Earth around the Sun). Oscillatory: to-and-fro about a mean position (pendulum). Every oscillation is periodic, but not every periodic motion is oscillatory.
• Needs a restoring force and inertia.
• Period T, frequency ν = 1/T (hertz), angular frequency ω = 2πν. sin and cos functions are periodic.

2. Simple harmonic motion (SHM)

• Restoring force ∝ displacement and opposite to it: F = −kx, so a = −ω²x.
• Displacement x = A sin(ωt + φ); A = amplitude, (ωt + φ) = phase, φ = initial phase.
• Velocity v = ω√(A² − x²): maximum Aω at the mean position, zero at the extremes.
• Acceleration: maximum ω²A at the extremes, zero at the mean position.
• SHM is the projection of uniform circular motion on a diameter.

3. Energy in SHM

• KE = ½k(A² − x²), PE = ½kx², total E = ½kA² = ½mω²A² (constant).
• KE = PE when x = A/√2.

4. Spring systems

• Horizontal or vertical spring: T = 2π√(m/k).
• Springs in series: 1/k = 1/k₁ + 1/k₂. In parallel: k = k₁ + k₂.

5. Simple pendulum

• For small angles: T = 2π√(l/g), independent of mass and amplitude.
• Seconds pendulum: T = 2 s, l ≈ 0.99 m on Earth.
• In a lift accelerating up, g_eff = g + a, so T decreases; in free fall, the pendulum doesn’t oscillate.

6. Damped and forced oscillations

• Free oscillations happen at the natural frequency. Damped: amplitude falls due to friction or air resistance.
• Forced: an external periodic force drives the system. Resonance: when the driving frequency equals the natural frequency, the amplitude becomes very large (soldiers break step on bridges; tuning a radio). Less damping gives sharper resonance.

Important questions and answers

1. Waves and wave motion

• A wave is a disturbance that carries energy from one place to another without carrying matter.
• Mechanical waves need a medium (sound); electromagnetic waves do not (light).
• Transverse: particles vibrate perpendicular to the wave (waves on a string); crests and troughs. Longitudinal: particles vibrate along the wave (sound); compressions and rarefactions.

2. Terms

• Wavelength λ, frequency ν, period T, amplitude A; wave speed v = νλ.
• Phase difference = (2π/λ) × path difference.
• Progressive wave: y = A sin(kx − ωt), k = 2π/λ (angular wave number), ω = 2πν. Particle velocity ≠ wave velocity.

3. Speed of waves

• Transverse wave on a string: v = √(T/μ) (T = tension, μ = mass per unit length).
• Longitudinal wave: v = √(E/ρ) (E = elastic modulus). In gases, Newton assumed isothermal change: v = √(P/ρ) ≈ 280 m/s (too low). Laplace correction (adiabatic): v = √(γP/ρ) ≈ 331 m/s at 0 °C.
• Effects: pressure has no effect (at constant T); v ∝ √T; humidity increases v (moist air is lighter). Sound is faster in solids than in liquids and gases.
• In a gas, v_sound = √(γ/3) × v_rms.

4. Superposition, interference and beats

• Superposition: resultant displacement = sum of individual displacements.
• Interference: constructive when path difference = nλ, destructive when (n + ½)λ.
• Beats: two sounds of slightly different frequencies give periodic rise and fall of loudness; beat frequency = ν₁ − ν₂. Used to tune instruments and find an unknown frequency.

5. Reflection and standing waves

• Reflection from a rigid (closed) end: phase change of π (crest becomes trough). From a free (open) end: no phase change.
• Stationary waves form when two identical waves travel in opposite directions: nodes (zero amplitude) and antinodes (maximum). Node-to-node distance = λ/2. No net transfer of energy.

6. Strings and pipes

• String fixed at both ends: ν_n = nv/2L (n = 1, 2, 3…) – all harmonics.
• Laws of a vibrating string: ν ∝ 1/L, ν ∝ √T, ν ∝ 1/√μ; verified with a sonometer.
• Closed organ pipe: ν = (2n − 1)v/4L – only odd harmonics (1 : 3 : 5).
• Open organ pipe: ν = nv/2L – all harmonics (1 : 2 : 3), so it sounds richer.
• End correction ≈ 0.6r at each open end (r = radius of the pipe).

7. Doppler effect (for competitive exams)

• The apparent change in frequency when the source and observer move relative to each other: the pitch rises as they approach and falls as they move apart (a passing train’s horn). Used in radar, speed guns and astronomy (red shift).

Important questions and answers

1. Fundamental particles

• Electron – discovered by J.J. Thomson (cathode rays); charge −1.6 × 10⁻¹⁹ C (Millikan’s oil drop); mass 9.1 × 10⁻³¹ kg.
• Proton – from canal (anode) rays (Goldstein); charge +1.6 × 10⁻¹⁹ C; mass 1.67 × 10⁻²⁷ kg.
• Neutron – discovered by Chadwick (1932); no charge; mass slightly more than a proton.
• Atomic number Z = number of protons; mass number A = protons + neutrons. Isotopes: same Z, different A (¹H, ²H, ³H). Isobars: same A, different Z (⁴⁰Ar, ⁴⁰Ca). Isotones: same number of neutrons.

2. Atomic models

• Thomson: positive sphere with electrons embedded (plum pudding).
• Rutherford’s α-scattering (gold foil): most α-particles passed straight (atom is mostly empty), a few deflected, about 1 in 20,000 bounced back → a tiny, heavy, positive nucleus.
• Drawbacks of Rutherford’s model: could not explain the stability of the atom (a revolving electron should radiate energy and fall into the nucleus) or line spectra.

3. Electromagnetic radiation and quantum theory

• c = νλ; wave number ν̄ = 1/λ.
• Planck’s quantum theory: energy is emitted or absorbed in packets (quanta): E = hν, h = 6.626 × 10⁻³⁴ J s.
• Photoelectric effect: electrons are emitted only if ν ≥ threshold frequency ν₀; hν = hν₀ + ½mv². Number of electrons depends on intensity; their KE depends on frequency.

4. Atomic spectra

• Emission spectrum of hydrogen has lines in series: Lyman (n₁ = 1, UV), Balmer (2, visible), Paschen (3, IR), Brackett (4), Pfund (5).
• Rydberg formula: ν̄ = R_H(1/n₁² − 1/n₂²), R_H = 109,677 cm⁻¹.

5. Bohr’s model (H and H-like atoms)

• Electrons move in fixed circular orbits (stationary states) without losing energy.
• Angular momentum is quantised: mvr = nh/2π.
• Energy is absorbed or emitted only when an electron jumps between orbits: ΔE = hν.
• E_n = −2.18 × 10⁻¹⁸ (Z²/n²) J = −13.6 Z²/n² eV; radius r_n = 0.529 n²/Z Å.
• Limitations: fails for multi-electron atoms, can’t explain splitting of lines (Zeeman, Stark effects), and ignores the wave nature of electrons.

6. Quantum mechanical model

• de Broglie: every moving particle has a wave nature, λ = h/mv (noticeable only for tiny particles like electrons).
• Heisenberg’s uncertainty principle: Δx·Δp ≥ h/4π – position and momentum can’t both be known exactly, so fixed orbits are not possible.
• An orbital is the region where the probability of finding an electron is high.
• Quantum numbers: principal n (shell, size); azimuthal l = 0 to n − 1 (s, p, d, f – shape); magnetic m_l = −l to +l (orientation); spin m_s = +½ or −½.
• Shapes: s – spherical; p – dumbbell (p_x, p_y, p_z); d – mostly clover-leaf. Nodes: radial = n − l − 1, angular = l.

7. Filling of electrons

• Aufbau principle: fill orbitals in increasing energy, using the (n + l) rule: 1s 2s 2p 3s 3p 4s 3d 4p 5s…
• Pauli exclusion principle: no two electrons in an atom have all four quantum numbers the same – an orbital holds at most 2 electrons with opposite spins.
• Hund’s rule: in orbitals of equal energy, electrons first occupy singly with parallel spins, then pair up.
• Exceptions due to the extra stability of half-filled and fully-filled subshells: Cr = [Ar] 3d⁵ 4s¹, Cu = [Ar] 3d¹⁰ 4s¹.

Important questions and answers

1. Early classification

• Döbereiner’s triads: the middle element’s atomic mass is about the average of the other two (Li, Na, K).
• Newlands’ law of octaves: every eighth element had similar properties (worked only up to calcium).
• Mendeleev: properties are periodic functions of atomic mass. He left gaps and predicted eka-aluminium (gallium) and eka-silicon (germanium), and corrected some atomic masses.

2. Modern periodic law and table

• Moseley showed atomic number is more fundamental. Modern law: properties are periodic functions of atomic number.
• Long form: 18 groups and 7 periods. Blocks: s (groups 1–2), p (13–18), d (3–12, transition), f (lanthanoids and actinoids, inner transition).
• Period number = outermost shell; for s and p blocks, group relates to the number of valence electrons.
• IUPAC names for Z > 100 use roots: 0 nil, 1 un, 2 bi, 3 tri, 4 quad, 5 pent… e.g. 104 = unnilquadium (Unq).

3. Classification of elements

• Metals (left), non-metals (upper right), metalloids along the zig-zag line (B, Si, Ge, As, Sb, Te). Noble gases in group 18.

4. Periodic trends

• Atomic radius: decreases across a period (nuclear charge increases), increases down a group (new shells).
• Ionic radius: cation < parent atom; anion > parent atom. For isoelectronic species, more nuclear charge → smaller size: O²⁻ > F⁻ > Na⁺ > Mg²⁺.
• Ionisation enthalpy: increases across a period, decreases down a group. Exceptions: Be > B and N > O (stable filled 2s² and half-filled 2p³). Successive IEs increase (IE₂ > IE₁).
• Electron gain enthalpy: becomes more negative across a period; halogens have the most negative values. Cl is more negative than F because F is very small and its incoming electron is repelled.
• Electronegativity (Pauling scale): increases across, decreases down; F is the highest (4.0).
• Metallic character decreases across and increases down. Oxides change from basic (Na₂O) → amphoteric (Al₂O₃) → acidic (Cl₂O₇) across a period.
• Valence: s and p block elements usually show valence = number of valence electrons or 8 minus that number.

5. Anomalous behaviour and diagonal relationship

• Second-period elements (Li to F) behave differently from their group members because of small size, high electronegativity and no d-orbitals.
• Diagonal relationship: Li–Mg, Be–Al, B–Si show similar properties.

Important questions and answers

1. Why atoms combine

• To gain a stable noble-gas configuration (octet rule; duplet for H). Limitations: incomplete octet (BF₃), expanded octet (PCl₅, SF₆), odd-electron molecules (NO).

2. Ionic bond

• Formed by transfer of electrons (NaCl). Favoured by low ionisation enthalpy of the metal, very negative electron gain enthalpy of the non-metal and high lattice enthalpy.
• Ionic compounds: high melting points, soluble in water, conduct in molten or dissolved state.

3. Covalent bond

• Formed by sharing electrons (Lewis/Kossel approach). Single, double and triple bonds.
• Formal charge = valence electrons − lone-pair electrons − ½ bonding electrons.
• Polarity: unequal sharing gives a polar bond. Dipole moment μ = charge × distance (debye). CO₂ and BF₃ have μ = 0 (symmetrical); H₂O (1.85 D) and NH₃ are polar; NH₃ has a larger μ than NF₃.
• Fajans’ rules: covalent character in an ionic bond increases with a small, highly charged cation and a large anion (e.g. LiI is more covalent than NaCl).

4. Resonance and coordinate bond

• Resonance: when one structure can’t show a molecule fully, several structures are drawn; the real molecule is a hybrid (O₃, CO₃²⁻, benzene). It makes molecules more stable.
• Coordinate (dative) bond: both shared electrons come from one atom (NH₄⁺, H₃O⁺).

5. Hydrogen bond

• Weak attraction between H bonded to a very electronegative atom (F, O, N) and another such atom.
• Intermolecular (between molecules): high boiling point of H₂O and HF; ice floats. Intramolecular (within one molecule): o-nitrophenol, which is more volatile than p-nitrophenol.

6. Shapes – VSEPR theory

• Electron pairs repel and stay as far apart as possible; repulsion order: lone pair–lone pair > lone pair–bond pair > bond pair–bond pair.
• BeCl₂ linear (180°); BF₃ trigonal planar (120°); CH₄ tetrahedral (109.5°); NH₃ pyramidal (107°); H₂O bent (104.5°); PCl₅ trigonal bipyramidal; SF₆ octahedral.

7. Valence bond theory and hybridisation

• Bonds form by overlap of half-filled orbitals. Sigma (σ) bond: head-on overlap, stronger. Pi (π) bond: sideways overlap, weaker.
• Hybridisation: mixing of orbitals of similar energy. sp (linear, BeCl₂, C₂H₂); sp² (trigonal, BF₃, C₂H₄); sp³ (tetrahedral, CH₄); sp³d (trigonal bipyramidal, PCl₅); sp³d² (octahedral, SF₆).

8. Molecular orbital theory

• Atomic orbitals combine to form bonding (lower energy) and antibonding (higher energy) molecular orbitals.
• Bond order = (N_b − N_a)/2. Higher bond order → shorter, stronger bond. Bond order 0 → molecule doesn’t exist (He₂).
• H₂: BO 1. N₂: BO 3. O₂: BO 2 and paramagnetic (two unpaired electrons) – explained by MOT, not by Lewis structures.

Important questions and answers

1. Basic concepts

• System and surroundings. Open system exchanges matter and energy; closed – only energy; isolated – neither.
• State functions depend only on the state (U, H, S, G, P, V, T); q and w are path functions.
• Extensive properties depend on amount (mass, volume, U, H); intensive do not (temperature, pressure, density).

2. First law

• ΔU = q + w. Sign convention in chemistry: heat absorbed by the system and work done on the system are positive. (Physics uses ΔQ = ΔU + ΔW with W done by the system – same law, different sign convention.)
• Expansion work w = −p_extΔV.

3. Enthalpy and heat capacity

• H = U + PV; at constant pressure ΔH = q_p. ΔH = ΔU + Δn_gRT (Δn_g = moles of gaseous products − reactants).
• Heat capacity C = q/ΔT; C_p − C_v = R for an ideal gas. Bomb calorimeter measures ΔU; coffee-cup calorimeter measures ΔH.
• Exothermic: ΔH < 0. Endothermic: ΔH > 0.

4. Thermochemistry

• Standard state: 1 bar, usually 298 K (ΔH°).
• Enthalpies of: formation (1 mol compound from elements; zero for elements in standard state), combustion (always negative), neutralisation (≈ −57.1 kJ/mol for a strong acid + strong base), atomisation, bond dissociation, solution, phase changes (fusion, vaporisation).
• ΔH_reaction = ΣΔH_f(products) − ΣΔH_f(reactants) = Σ bond enthalpies broken − Σ bond enthalpies formed.
• Hess’s law: total enthalpy change is the same whether the reaction occurs in one step or many.

5. Second and third laws; spontaneity

• Entropy S measures randomness. For a spontaneous process, ΔS_total > 0. ΔS increases on melting, vaporisation, dissolving and heating.
• Gibbs energy: ΔG = ΔH − TΔS. ΔG < 0 spontaneous; ΔG = 0 equilibrium; ΔG > 0 non-spontaneous.
• ΔH −, ΔS + → always spontaneous. ΔH +, ΔS − → never. Other combinations depend on temperature.
• ΔG° = −RT ln K = −2.303 RT log K.
• Third law: entropy of a perfectly crystalline substance at 0 K is zero.

Important questions and answers

1. Physical and chemical equilibrium

• Equilibrium is dynamic: forward and backward processes go on at equal rates, so concentrations stay constant.
• Physical examples: ice ⇌ water at 0 °C, water ⇌ vapour in a closed vessel, solid ⇌ solution in a saturated solution; Henry’s law – solubility of a gas ∝ its pressure (soda bottles).
• Chemical equilibrium can be reached from either side.

2. Law of mass action and equilibrium constant

• Rate ∝ product of active masses (Guldberg and Waage).
• For aA + bB ⇌ cC + dD: K_c = [C]^c[D]^d/[A]^a[B]^b. For gases, K_p = K_c(RT)^Δn.
• Large K → mostly products; small K → mostly reactants. Pure solids and liquids are left out of K.
• Reaction quotient Q: if Q < K the reaction goes forward; Q > K backward; Q = K at equilibrium.

3. Le Chatelier’s principle

• A system at equilibrium shifts to reduce the effect of any change.
• Adding a reactant → shifts forward. Raising pressure → shifts to the side with fewer gas moles. Raising temperature → favours the endothermic direction (K of an exothermic reaction decreases). A catalyst does not shift equilibrium, it only speeds it up.
• Haber process (N₂ + 3H₂ ⇌ 2NH₃, exothermic): high pressure (about 200 atm), moderate temperature (about 700 K), iron catalyst.

4. Acids and bases

• Arrhenius: acid gives H⁺, base gives OH⁻ in water.
• Brønsted–Lowry: acid = proton donor, base = proton acceptor; conjugate pairs differ by one H⁺ (HCl/Cl⁻, NH₄⁺/NH₃).
• Lewis: acid accepts an electron pair (BF₃, AlCl₃, H⁺), base donates one (NH₃, OH⁻).

5. Ionisation of water and pH

• K_w = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 298 K (increases with temperature).
• pH = −log[H⁺]; pH + pOH = 14. Neutral pH 7, acidic < 7, basic > 7.
• Weak acid: K_a; degree of ionisation α ≈ √(K_a/C); [H⁺] = √(K_aC).
• Common ion effect: adding an ion already present suppresses ionisation of a weak electrolyte (NH₄Cl suppresses NH₄OH).

6. Buffers and solubility product

• Buffer: resists change in pH. Acidic buffer CH₃COOH + CH₃COONa; basic buffer NH₄OH + NH₄Cl. Henderson equation: pH = pK_a + log([salt]/[acid]).
• Solubility product K_sp: for AB, K_sp = s²; for AB₂, K_sp = 4s³. A precipitate forms when the ionic product exceeds K_sp.

7. Hydrolysis of salts and indicators

• Strong acid + weak base salt (NH₄Cl) → acidic. Weak acid + strong base salt (CH₃COONa) → basic. Strong acid + strong base salt (NaCl) → neutral.
• Indicators: phenolphthalein (pH 8.3–10, colourless → pink), methyl orange (pH 3.1–4.4, red → yellow).

Important questions and answers

1. Oxidation and reduction

• Classical: oxidation = addition of oxygen or removal of hydrogen; reduction = the opposite.
• Electronic: oxidation = loss of electrons, reduction = gain of electrons (memory aid: OIL RIG).
• The oxidising agent gets reduced; the reducing agent gets oxidised. Both always happen together (redox).
• Example: Zn + Cu²⁺ → Zn²⁺ + Cu. Zn is oxidised (reducing agent); Cu²⁺ is reduced (oxidising agent).

2. Oxidation number rules

• Free element = 0. Monatomic ion = its charge.
• Oxygen −2 (but −1 in peroxides like H₂O₂, +2 in OF₂). Hydrogen +1 (but −1 in metal hydrides like NaH). Fluorine always −1.
• Sum of oxidation numbers = 0 for a molecule, or the charge for an ion.
• Examples: Cr in K₂Cr₂O₇ = +6; Mn in KMnO₄ = +7; S in H₂SO₄ = +6.
• Increase in oxidation number = oxidation; decrease = reduction.

3. Types of redox reactions

• Combination: C + O₂ → CO₂. Decomposition: 2KClO₃ → 2KCl + 3O₂.
• Displacement: metal (Zn + CuSO₄) or non-metal (Cl₂ + 2KBr → 2KCl + Br₂).
• Disproportionation: the same element is both oxidised and reduced: 2H₂O₂ → 2H₂O + O₂ (O: −1 → −2 and 0).

4. Balancing redox reactions

• Oxidation number method: find the change in oxidation numbers, make the increase equal to the decrease, then balance O with H₂O and H with H⁺ (acid) or OH⁻ (base).
• Half-reaction (ion–electron) method: write oxidation and reduction halves separately, balance atoms and charge with electrons, multiply to equalise electrons, and add.
• Example (acidic): MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O.

Important questions and answers

1. Organic compounds and carbon

• Organic chemistry is the chemistry of carbon compounds (except CO, CO₂, carbonates, etc.).
• Carbon is tetravalent and shows catenation (forms long chains and rings).
• Hybridisation: sp³ (25% s, single bonds), sp² (33% s, double bond), sp (50% s, triple bond). More s-character → more electronegative carbon.

2. Representation and classification

• Structural formulas: complete, condensed (CH₃CH₂OH) and bond-line.
• Classification: acyclic (open chain) and cyclic – alicyclic, aromatic (benzene) and heterocyclic (pyridine).
• Functional group: the atom or group deciding properties (–OH, –CHO, >C=O, –COOH, –NH₂).
• Homologous series: same functional group, successive members differ by CH₂ (14 u), similar chemical properties, gradual change in physical properties.

3. IUPAC nomenclature

• Choose the longest chain containing the functional group; number it to give the lowest locants; add prefixes (substituents) and suffixes (functional group).
• Examples: CH₃CH₂OH ethanol; CH₃CHO ethanal; CH₃COCH₃ propanone; CH₃COOH ethanoic acid; (CH₃)₂CHCH₃ 2-methylpropane.

4. Isomerism

• Structural: chain (butane/2-methylpropane), position (propan-1-ol/propan-2-ol), functional (ethanol/methoxymethane), metamerism.
• Stereoisomerism: geometrical (cis/trans) and optical.

5. Reaction mechanisms

• Homolytic fission → free radicals. Heterolytic fission → carbocation (C⁺) and carbanion (C⁻).
• Carbocation stability: 3° > 2° > 1° > methyl.
• Nucleophiles are electron-rich (OH⁻, CN⁻, NH₃); electrophiles are electron-poor (H⁺, NO₂⁺, AlCl₃).
• Electronic effects: inductive (−I: –NO₂, halogens; +I: alkyl groups), resonance/mesomeric, electromeric (temporary, on attack of a reagent) and hyperconjugation (explains stability of alkyl carbocations and alkenes).
• Types of reactions: substitution, addition, elimination and rearrangement.

6. Purification

• Crystallisation, sublimation (camphor, naphthalene), distillation (simple, fractional, under reduced pressure, steam distillation), differential extraction, and chromatography (R_f = distance moved by substance ÷ distance moved by solvent).

7. Analysis

• Lassaigne’s test (sodium fusion extract): nitrogen → Prussian blue; sulphur → violet colour with sodium nitroprusside; halogens → with AgNO₃: white AgCl, pale yellow AgBr, yellow AgI.
• Quantitative: C and H by Liebig’s combustion; N by Dumas or Kjeldahl method; halogens by Carius method.

Important questions and answers

1. Classification

• Alkanes (saturated, C_nH_2n+2), alkenes (one C=C, C_nH_2n), alkynes (one C≡C, C_nH_2n−2) and aromatic hydrocarbons (benzene and its relatives).

2. Alkanes

• Preparation: hydrogenation of alkenes or alkynes with Ni/Pt/Pd; Wurtz reaction 2RX + 2Na → R–R + 2NaX (dry ether); decarboxylation of sodium salts with soda lime; Kolbe’s electrolysis.
• Reactions: free-radical halogenation in light (CH₄ + Cl₂ → CH₃Cl + HCl), combustion (gives CO₂, H₂O and heat), cracking.
• Conformations of ethane: staggered (more stable) and eclipsed.

3. Alkenes

• Preparation: dehydration of alcohols (conc. H₂SO₄, heat); dehydrohalogenation of alkyl halides with alcoholic KOH; partial reduction of alkynes (Lindlar’s catalyst → cis-alkene; Na in liquid NH₃ → trans-alkene).
• Geometrical isomerism: cis- and trans-but-2-ene.
• Addition reactions: H₂, halogens (decolourising bromine water is a test for unsaturation), HX.
• Markovnikov’s rule: H goes to the carbon that already has more H atoms: propene + HBr → 2-bromopropane. Peroxide effect (anti-Markovnikov, only with HBr): → 1-bromopropane.
• Baeyer’s reagent (cold, dilute, alkaline KMnO₄) is decolourised → diol. Ozonolysis breaks the C=C to give aldehydes or ketones. Polymerisation: ethene → polythene.

4. Alkynes

• Preparation: CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂; from vicinal dihalides with alcoholic KOH.
• Acidic nature of terminal alkynes: the sp carbon (50% s) holds electrons strongly, so H is released to Na or NaNH₂ → sodium acetylide.
• Additions: H₂, X₂, HX, H₂O. Cyclic polymerisation: 3 C₂H₂ → C₆H₆ (red-hot iron tube, 873 K).

5. Aromatic hydrocarbons – benzene

• C₆H₆: Kekulé structure; resonance; six delocalised π electrons make it very stable.
• Hückel rule: a planar, cyclic, fully conjugated system with (4n + 2) π electrons is aromatic (benzene: 6).
• Undergoes electrophilic substitution (not addition): nitration (conc. HNO₃ + conc. H₂SO₄, electrophile NO₂⁺), halogenation (Cl₂/FeCl₃), sulphonation, Friedel–Crafts alkylation and acylation (anhydrous AlCl₃).
• Directive influence: –OH, –NH₂, –CH₃ (activating) and halogens (deactivating) are ortho/para directing; –NO₂, –CHO, –COOH, –CN are meta directing.

6. Carcinogenicity and toxicity

• Benzene and polynuclear hydrocarbons (more than two fused benzene rings, e.g. benzopyrene) are toxic and cancer-causing. They form from incomplete burning of tobacco, coal and petroleum.

Important questions and answers

1. Five kingdom classification

• R.H. Whittaker (1969): Monera, Protista, Fungi, Plantae, Animalia.
• Criteria: cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationships.

2. Kingdom Monera (bacteria)

• Prokaryotes. Shapes: coccus (spherical), bacillus (rod), vibrio (comma), spirillum (spiral).
• Structure: cell wall of peptidoglycan, no nuclear membrane (nucleoid), plasmids, 70S ribosomes, flagella, pili. Gram-positive and Gram-negative types.
• Archaebacteria live in extreme places: halophiles (salty), thermoacidophiles (hot springs), methanogens (marshes, cattle gut – produce methane/biogas).
• Eubacteria: cyanobacteria (photosynthetic; Nostoc, Anabaena fix nitrogen in heterocysts; cause water blooms), chemosynthetic autotrophs, and heterotrophs (decomposers).
• Reproduction: mainly binary fission; spores in bad conditions; DNA transfer (conjugation, transformation, transduction).
• Mycoplasma: no cell wall, smallest living cells, can live without oxygen; many are pathogens.
• Uses: curd (Lactobacillus), antibiotics, nitrogen fixation (Rhizobium), retting of fibres. Diseases: cholera, typhoid, tetanus, citrus canker.

3. Kingdom Protista

• Single-celled eukaryotes, mostly aquatic; link between plants, animals and fungi.
• Chrysophytes (diatoms, desmids): silica walls; deposits form diatomaceous earth (used in polishing, filtration); chief producers in oceans.
• Dinoflagellates: two flagella, cellulose plates; Gonyaulax causes red tides and releases toxins.
• Euglenoids: flexible pellicle, photosynthetic in light, heterotrophic in dark (Euglena).
• Slime moulds: saprophytic, form plasmodium; spores with cell walls.
• Protozoans: amoeboid (Amoeba, Entamoeba), flagellated (Trypanosoma – sleeping sickness), ciliated (Paramoecium), sporozoans (Plasmodium – malaria).

4. Kingdom Fungi

• Heterotrophic (saprophytes, parasites, symbionts); cell wall of chitin; body of thread-like hyphae forming a mycelium (coenocytic if without septa).
• Reproduction: vegetative (fragmentation, budding), asexual spores (conidia, sporangiospores, zoospores), sexual (plasmogamy → karyogamy → meiosis). In ascomycetes and basidiomycetes a dikaryon stage occurs.
• Phycomycetes: aseptate hyphae; Mucor, Rhizopus (bread mould), Albugo.
• Ascomycetes (sac fungi): septate; ascospores in asci; yeast, Penicillium, Aspergillus, Neurospora (genetics), morels.
• Basidiomycetes (club fungi): basidiospores; mushrooms, bracket fungi, rust (Puccinia), smut (Ustilago).
• Deuteromycetes (imperfect fungi): only asexual stage known; Alternaria, Colletotrichum, Trichoderma.
• Lichens: symbiosis of an alga (phycobiont, makes food) and a fungus (mycobiont, gives shelter and water); good pollution indicators. Mycorrhiza: fungus + plant roots, helps absorb nutrients.

5. Viruses, viroids and prions

• Viruses: non-cellular, made of protein coat (capsid) + nucleic acid (DNA or RNA); inert crystals outside a host, active only inside living cells (obligate parasites).
• Ivanowsky (1892) studied tobacco mosaic; Beijerinck called it ‘contagium vivum fluidum’; Stanley crystallised it. TMV has RNA; bacteriophages usually have double-stranded DNA.
• Diseases: mumps, smallpox, herpes, influenza, AIDS.
• Viroids (Diener, 1971): free RNA without protein coat; potato spindle tuber disease.
• Prions: abnormally folded proteins; mad cow disease (BSE) and Creutzfeldt–Jakob disease in humans.

Important questions and answers

1. Algae

• Simple, thalloid, mostly aquatic, chlorophyll-bearing plants.
• Reproduction: vegetative (fragmentation), asexual (zoospores), sexual – isogamous (similar gametes, Ulothrix, Spirogyra), anisogamous (different sizes, Eudorina), oogamous (large egg + small sperm, Volvox, Fucus).
• Chlorophyceae (green): chlorophyll a, b; food stored as starch; cellulose wall; pyrenoids. Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
• Phaeophyceae (brown): chlorophyll a, c and fucoxanthin; food as laminarin/mannitol; mostly marine, large (kelps). Ectocarpus, Laminaria, Fucus, Sargassum, Dictyota. Give algin.
• Rhodophyceae (red): chlorophyll a, d and r-phycoerythrin; food as floridean starch; can live deep in the sea. Polysiphonia, Porphyra, Gracilaria, Gelidium (give agar) and carrageen.
• Uses: half of Earth’s photosynthesis; food (Porphyra, Laminaria); Chlorella as a protein-rich food supplement, even for space travellers.

2. Bryophytes

• Called the ‘amphibians of the plant kingdom’ – live on land but need water for fertilisation.
• Plant body is a thallus with rhizoids; no true roots, stems or leaves; no vascular tissue.
• The main plant is the haploid gametophyte. Sex organs: antheridium (male), archegonium (female). The diploid sporophyte (foot, seta, capsule) is attached to and depends on the gametophyte.
• Liverworts: Marchantia – vegetative reproduction by gemmae in gemma cups.
• Mosses: Funaria, Polytrichum, Sphagnum; life cycle has a protonema stage. Sphagnum forms peat (fuel) and is used to pack plants as it holds water.
• Mosses and lichens are pioneers on bare rocks and prevent soil erosion.

3. Pteridophytes

• First terrestrial plants with vascular tissue (xylem and phloem).
• Main plant is the sporophyte with true roots, stem and leaves (small microphylls in Selaginella, large macrophylls in ferns).
• Sporangia on sporophylls, sometimes in cones (strobili: Selaginella, Equisetum).
• Most are homosporous; Selaginella and Salvinia are heterosporous (micro- and megaspores) – a step toward the seed habit.
• Gametophyte is a small, free-living prothallus; water is needed for fertilisation.
• Examples: Psilotum, Lycopodium, Selaginella, Equisetum, Dryopteris, Pteris, Adiantum.

4. Gymnosperms

• ‘Naked seed’ plants – ovules are not enclosed in an ovary.
• Roots: tap roots; Cycas has coralloid roots with nitrogen-fixing cyanobacteria; Pinus has mycorrhiza.
• Leaves: needle-like in conifers (less water loss, thick cuticle, sunken stomata).
• Heterosporous: male cones (microsporangia → pollen) and female cones (megasporangia → ovules). Wind pollination; water is not needed for fertilisation.
• Gametophytes are reduced and depend on the sporophyte. Examples: Cycas, Pinus, Ginkgo (living fossil). Sequoia is one of the tallest trees.

Important questions and answers

1. Basis of classification

• Level of organisation: cellular (Porifera), tissue (Cnidaria), organ (Platyhelminthes), organ system (others).
• Symmetry: asymmetrical (most sponges), radial (Cnidaria, Ctenophora, adult echinoderms), bilateral (most others).
• Germ layers: diploblastic (Cnidaria, Ctenophora) or triploblastic (Platyhelminthes onward).
• Coelom: acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), coelomate (Annelida onward).
• Segmentation (metamerism, e.g. earthworm) and presence of a notochord (chordates).

2. Non-chordate phyla

• Porifera (sponges): pores (ostia), canal system, osculum, choanocytes, spicules/spongin; Sycon, Spongilla, Euspongia.
• Cnidaria: stinging cnidoblasts, gastrovascular cavity, polyp and medusa forms; metagenesis in Obelia; Hydra, Physalia, Adamsia, corals.
• Ctenophora (comb jellies): eight rows of ciliated comb plates, bioluminescence; Pleurobrachia, Ctenoplana.
• Platyhelminthes (flatworms): flame cells for excretion, mostly hermaphrodite, many parasites; Taenia (tapeworm), Fasciola (liver fluke), Planaria (high regeneration).
• Nematoda (roundworms): pseudocoelom, sexes separate; Ascaris, Wuchereria (filaria), Ancylostoma (hookworm).
• Annelida: metameric segmentation, nephridia, closed circulation; Nereis (parapodia), Pheretima (earthworm), Hirudinaria (leech).
• Arthropoda: largest phylum; jointed legs, chitin exoskeleton, open circulation, Malpighian tubules; Apis, Bombyx, Anopheles, Locusta, Limulus (living fossil).
• Mollusca: second largest; soft body with mantle and shell, radula for feeding; Pila, Octopus, Sepia, Loligo.
• Echinodermata: spiny skin, water vascular system with tube feet, radial adults and bilateral larvae; Asterias, Echinus, sea cucumber.
• Hemichordata: worm-like, stomochord; Balanoglossus.

3. Phylum Chordata

• Features: notochord, dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail (at least at some stage).
• Urochordata: notochord only in the larval tail (Ascidia, Salpa). Cephalochordata: notochord throughout life (Branchiostoma/Amphioxus). Vertebrata: notochord replaced by a backbone.

4. Vertebrate classes

• Cyclostomata: jawless, circular sucking mouth; Petromyzon (lamprey).
• Chondrichthyes: cartilaginous skeleton, no air bladder; Scoliodon (dogfish), Pristis (sawfish), Torpedo (electric ray).
• Osteichthyes: bony skeleton, air bladder, gills with operculum; Labeo (rohu), Catla, Hippocampus (sea horse).
• Amphibia: moist skin, three-chambered heart, eggs in water; frog, toad, Salamandra, Ichthyophis (limbless).
• Reptilia: dry scaly skin, three-chambered heart (four in crocodiles), shelled eggs on land; turtles, snakes, lizards, crocodiles.
• Aves: feathers, beak, forelimbs as wings, pneumatic (hollow) bones, four-chambered heart, warm-blooded; crow, pigeon, ostrich.
• Mammalia: mammary glands, hair, external ears (pinna), four-chambered heart, mostly viviparous (platypus lays eggs); bat, whale, human.

Important questions and answers

1. The root

• Tap root (dicots: mustard), fibrous roots (monocots: wheat), adventitious roots from other parts (grass, banyan, maize).
• Regions: root cap, meristematic zone, zone of elongation, zone of maturation (root hairs).
• Modifications: storage (carrot, turnip, sweet potato), prop roots (banyan), stilt roots (maize, sugarcane), pneumatophores for breathing in swamps (Rhizophora).

2. The stem

• Has nodes, internodes and buds; develops from the plumule.
• Underground storage: tuber (potato), rhizome (ginger, turmeric), corm (Colocasia), bulb (onion).
• Tendrils (cucumber, grapevine) for climbing; thorns (Citrus, Bougainvillea) for protection; phylloclade – flat green stem (Opuntia).
• Vegetative spread: runners (grass), stolons (strawberry, mint), offsets (Pistia, Eichhornia).

3. The leaf

• Parts: leaf base, petiole, lamina. Venation: reticulate (dicots) or parallel (monocots).
• Simple or compound – pinnately compound (neem) or palmately compound (silk cotton).
• Phyllotaxy: alternate (china rose, mustard), opposite (Calotropis, guava), whorled (Alstonia).
• Modifications: tendrils (pea), spines (cactus), fleshy storage leaves (onion), insect-catching pitcher (pitcher plant).

4. Inflorescence

• Racemose: main axis keeps growing; flowers in acropetal order (youngest at top).
• Cymose: main axis ends in a flower; flowers in basipetal order (oldest at top).

5. The flower

• Symmetry: actinomorphic – radial (mustard, datura, chilli); zygomorphic – bilateral (pea, gulmohur, bean); asymmetric (canna).
• Position of ovary: hypogynous – superior (mustard, china rose, brinjal); perigynous – half-inferior (plum, rose, peach); epigynous – inferior (guava, cucumber, ray florets of sunflower).
• Aestivation (arrangement of sepals/petals in bud): valvate (Calotropis), twisted (china rose, cotton), imbricate (Cassia, gulmohur), vexillary/papilionaceous (pea, bean).
• Androecium (stamens): epipetalous (attached to petals – brinjal), epiphyllous (to perianth – lily); monoadelphous (one bundle – china rose), diadelphous (two – pea), polyadelphous (many – citrus).
• Gynoecium (carpels): apocarpous – free (lotus, rose); syncarpous – fused (mustard, tomato).

6. Placentation

• Marginal (pea), axile (china rose, tomato, lemon), parietal (mustard, Argemone), free central (Dianthus, Primrose), basal (sunflower, marigold).

Important questions and answers

1. Meristematic tissues

• Actively dividing cells. Apical (root and shoot tips – increase length), intercalary (at internodes of grasses – regrowth after grazing), lateral (cambium – increase girth).

2. Simple permanent tissues

• Parenchyma: thin-walled living cells; storage, photosynthesis (chlorenchyma), secretion.
• Collenchyma: living cells thickened at the corners with pectin; mechanical support to young dicot stems and petioles.
• Sclerenchyma: dead cells with thick lignified walls; fibres (long) and sclereids (stone cells in nut shells and guava pulp).

3. Complex tissues

• Xylem (conducts water and minerals): tracheids, vessels (absent in most gymnosperms), xylem fibres, xylem parenchyma. First-formed protoxylem, later metaxylem. Stems: endarch (protoxylem towards centre); roots: exarch (towards the outside).
• Phloem (conducts food): sieve tubes, companion cells, phloem parenchyma, phloem fibres. Gymnosperms have albuminous cells and sieve cells instead.

4. Tissue systems

• Epidermal: epidermis with cuticle, stomata (bean-shaped guard cells in dicots, dumb-bell shaped in grasses, with subsidiary cells), trichomes and root hairs.
• Ground: cortex, pericycle, pith, medullary rays; mesophyll in leaves.
• Vascular: radial bundles in roots (xylem and phloem on different radii); conjoint collateral in stems and leaves. Open bundles have cambium (dicots); closed bundles do not (monocots).

5. Roots

• Dicot root: epidermis with root hairs, cortex, endodermis with Casparian strips, pericycle, 2–4 xylem and phloem bundles (diarch to tetrarch), small or no pith.
• Monocot root: more than six bundles (polyarch), large pith, no secondary growth.

6. Stems

• Dicot stem (sunflower): collenchymatous hypodermis, endodermis (starch sheath), bundles arranged in a ring, conjoint, collateral and open; large pith.
• Monocot stem (maize): sclerenchymatous hypodermis, scattered bundles surrounded by a bundle sheath, closed, water-containing cavities, no distinct pith.

7. Leaves

• Dicot leaf (dorsiventral): palisade parenchyma on the upper side, spongy below; more stomata on the lower surface.
• Monocot leaf (isobilateral): undifferentiated mesophyll, stomata on both surfaces; grasses have bulliform cells that make leaves roll up in water stress.

Important questions and answers

1. Habit and morphology

• Common Indian frog: Rana tigrina (now Hoplobatrachus tigerinus). Cold-blooded (poikilothermic); shows hibernation (winter sleep) and aestivation (summer sleep); can change colour to hide (camouflage).
• Body: head and trunk, no neck or tail. Skin moist and slimy (mucus), smooth; frogs don’t drink water – they absorb it through the skin.
• Eyes with nictitating membrane; tympanum (ear drum) behind the eye; forelimbs with 4 digits, hind limbs with 5 webbed digits.
• Males have vocal sacs and a copulatory pad on the first digit of the forelimb.

2. Digestive system

• Short alimentary canal (carnivore). Bilobed, sticky tongue catches insects. Mouth → buccal cavity → pharynx → oesophagus → stomach → intestine → rectum → cloaca.
• Liver secretes bile (stored in gall bladder); pancreas secretes pancreatic juice. Digested food is absorbed by villi and microvilli.

3. Respiratory and circulatory systems

• Cutaneous respiration (through skin) in water and during hibernation; lungs and buccal cavity on land.
• Closed circulation. Heart has three chambers: two atria, one ventricle; also a sinus venosus and conus arteriosus.
• Hepatic portal and renal portal systems. Lymphatic system present. RBCs are nucleated.

4. Excretion, nervous system and senses

• Ureotelic (excretes urea). Two kidneys; in males, the ureter works as a urinogenital duct; all open into the cloaca.
• Brain: forebrain, midbrain, hindbrain; 10 pairs of cranial nerves. Spinal cord in the vertebral column.
• Sense organs: eyes (simple), ears (hearing and balance), taste buds, nasal epithelium (smell), touch receptors.

5. Reproduction and ecological importance

• Sexes separate. Fertilisation is external in water; development through a larva called a tadpole, which undergoes metamorphosis into an adult.
• Frogs eat insects and protect crops, keep the ecosystem balanced as part of food chains, and their legs are eaten as food in some countries.

Important questions and answers

1. Cell theory and cell size

• Schleiden (plants) and Schwann (animals): all living things are made of cells. Virchow: new cells come only from pre-existing cells (omnis cellula e cellula).
• Sizes: Mycoplasma is the smallest cell (about 0.3 µm); bacteria 3–5 µm; the ostrich egg is the largest single cell; nerve cells are the longest.

2. Prokaryotic vs eukaryotic; plant vs animal

• Prokaryotic: no membrane-bound nucleus or organelles, 70S ribosomes (bacteria). Eukaryotic: true nucleus, membrane-bound organelles, 80S ribosomes.
• Plant cells: cell wall, plastids, large central vacuole, usually no centrioles. Animal cells: no cell wall, centrioles present, small vacuoles.

3. Cell wall and plasma membrane

• Plant cell wall: cellulose, hemicellulose, pectins; middle lamella (calcium pectate) joins neighbouring cells; plasmodesmata connect cytoplasm.
• Fluid mosaic model (Singer and Nicolson, 1972): a lipid bilayer with proteins floating in it.
• Transport: passive (diffusion, osmosis – no energy) and active (uses ATP, e.g. Na⁺/K⁺ pump).

4. Endomembrane system

• Endoplasmic reticulum: rough ER (with ribosomes – protein synthesis) and smooth ER (lipid and steroid synthesis).
• Golgi complex (Camillo Golgi): stacks of cisternae with cis (forming) and trans (maturing) faces; packages materials; forms glycoproteins and glycolipids.
• Lysosomes: sacs of hydrolytic enzymes working at acidic pH; digest worn-out parts (‘suicide bags’).
• Vacuoles: bounded by the tonoplast; may fill up to 90% of a plant cell; contractile vacuole in Amoeba removes excess water.

5. Mitochondria and plastids

• Mitochondria: double membrane, inner one folded into cristae; matrix has its own DNA and 70S ribosomes; site of aerobic respiration – ‘powerhouse’ of the cell (ATP).
• Plastids: chloroplasts (grana of thylakoids + stroma; photosynthesis; own DNA), chromoplasts (carotenoids – colour of fruits, flowers), leucoplasts (colourless storage: amyloplasts – starch, elaioplasts – oils, aleuroplasts – proteins).

6. Ribosomes, cytoskeleton, cilia, centrosome

• Ribosomes (Palade): RNA + protein, no membrane; 70S = 50S + 30S; 80S = 60S + 40S; site of protein synthesis.
• Cytoskeleton: microtubules, microfilaments, intermediate filaments – support, shape and movement.
• Cilia and flagella: 9 + 2 arrangement of microtubules (axoneme) from a basal body.
• Centrosome: two centrioles with a cartwheel of 9 triplet microtubules; form spindle fibres in animal cells.
• Microbodies: peroxisomes and glyoxysomes.

7. Nucleus and chromosomes

• Discovered by Robert Brown (1831). Double nuclear envelope with pores; nucleoplasm; nucleolus (rRNA synthesis); chromatin (DNA + histone proteins).
• Chromosomes have a centromere with kinetochores. Types by centromere position: metacentric (middle), sub-metacentric (slightly off-centre), acrocentric (near one end), telocentric (at the end). Some have a satellite.

Important questions and answers

1. Carbohydrates

• Made of C, H, O. Monosaccharides: glucose, fructose, ribose. Disaccharides: sucrose (glucose + fructose), lactose, maltose – joined by glycosidic bonds.
• Polysaccharides: starch (plant storage), glycogen (animal storage), cellulose (plant cell walls, made of β-glucose), chitin (fungal walls, arthropod skeletons).

2. Proteins

• Polymers of amino acids (20 kinds; essential ones must come from food) joined by peptide bonds.
• Structure: primary (sequence), secondary (α-helix, β-sheet held by hydrogen bonds), tertiary (3-D folding), quaternary (several chains, e.g. haemoglobin with 4 subunits).
• Functions: enzymes, hormones (insulin), transport (haemoglobin), antibodies, structure (collagen – most abundant animal protein). RuBisCO is the most abundant protein in the biosphere.

3. Lipids

• Insoluble in water. Fatty acids (saturated – no double bonds; unsaturated – with double bonds) + glycerol → triglycerides (fats and oils), joined by ester bonds.
• Phospholipids form cell membranes; steroids include cholesterol.

4. Enzymes

• Biological catalysts, mostly proteins (ribozymes are RNA enzymes). The substrate binds at the active site. Enzymes lower the activation energy.
• Mechanism: lock and key (Fischer) and induced fit (Koshland) models; enzyme–substrate complex forms, then products are released.
• Factors: temperature and pH (each enzyme has an optimum; high temperature denatures it), substrate concentration (rate rises to a maximum, V_max).
• Inhibition: competitive (inhibitor resembles the substrate, e.g. malonate inhibits succinic dehydrogenase) and non-competitive.
• Six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.

5. Cofactors and isoenzymes

• Holoenzyme = apoenzyme (protein part) + cofactor.
• Cofactors: prosthetic groups (tightly bound, e.g. haem in peroxidase), coenzymes (loosely bound organic molecules, often from vitamins, e.g. NAD from niacin), metal ions (Zn²⁺ in carboxypeptidase).
• Isoenzymes: different forms of an enzyme doing the same reaction (lactate dehydrogenase has five).

6. Primary and secondary metabolites

• Primary: needed for normal life (sugars, amino acids, lipids).
• Secondary: not essential for basic life but useful: alkaloids (morphine, codeine), terpenoids, essential oils, drugs (vinblastine, curcumin), rubber, gums, pigments.

Important questions and answers

1. Cell cycle

• Interphase (about 95% of the time): G₁ (growth), S (DNA replication – DNA doubles, chromosome number stays the same), G₂ (preparation for division).
• M phase: karyokinesis (nucleus divides) + cytokinesis (cytoplasm divides).
• A human cell takes about 24 h; yeast about 90 minutes. Non-dividing cells enter the G₀ (quiescent) stage.

2. Mitosis (equational division)

• Prophase: chromatin condenses into chromosomes, spindle begins to form; nuclear envelope and nucleolus disappear by the end.
• Metaphase: chromosomes line up at the equatorial (metaphase) plate – best stage to study their shape.
• Anaphase: centromeres split; sister chromatids move to opposite poles.
• Telophase: chromosomes reach the poles, nuclear envelopes and nucleoli reappear.
• Cytokinesis: a furrow in animal cells; a cell plate in plant cells.
• Significance: growth, repair and replacement of cells; daughter cells are identical with the same chromosome number.

3. Meiosis (reductional division)

• Occurs in reproductive cells; one diploid cell gives four haploid cells.
• Prophase I: leptotene (chromosomes condense), zygotene (homologous chromosomes pair – synapsis, bivalents), pachytene (crossing over between non-sister chromatids), diplotene (homologues start separating; X-shaped chiasmata visible), diakinesis (terminalisation of chiasmata).
• Metaphase I: bivalents at the plate. Anaphase I: homologous chromosomes separate (chromatids stay together). Telophase I, then a short interkinesis.
• Meiosis II is like mitosis: sister chromatids separate.

4. Significance and differences

• Meiosis halves the chromosome number (so it stays constant from generation to generation after fertilisation) and creates variation through crossing over and independent assortment.
• Mitosis vs meiosis: one vs two divisions; 2 identical diploid cells vs 4 different haploid cells; no pairing vs synapsis and crossing over; somatic vs germ cells.
• Animal vs plant mitosis: animal cells have centrioles and asters and divide by furrowing; plant cells lack centrioles and form a cell plate.

Important questions and answers

1. Basics

• Overall: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O (in light, with chlorophyll).
• Site: chloroplast – light reaction in the grana (thylakoids), dark reaction in the stroma.
• Pigments: chlorophyll a (main, reaction-centre pigment), chlorophyll b, carotenoids and xanthophylls (accessory pigments – widen absorption and protect chlorophyll). Most absorption in the blue and red regions.

2. Light reaction

• Two photosystems: PS II (reaction centre P680) and PS I (P700), each with light-harvesting complexes.
• Photolysis of water at PS II: 2H₂O → 4H⁺ + O₂ + 4e⁻. The oxygen released comes from water.
• Non-cyclic photophosphorylation (Z-scheme): both PS II and PS I; produces ATP and NADPH and releases O₂.
• Cyclic photophosphorylation: only PS I, in stroma lamellae; produces only ATP.

3. Chemiosmotic hypothesis (Peter Mitchell)

• Electron transport pumps H⁺ into the thylakoid lumen, and water splitting adds more H⁺ there.
• H⁺ flows back to the stroma through ATP synthase (CF₀–CF₁), and the energy makes ATP.

4. Dark reaction – Calvin cycle (C₃ pathway)

• Carboxylation: RuBP + CO₂ → 2 molecules of 3-PGA (first stable product), catalysed by RuBisCO.
• Reduction: PGA → sugar, using ATP and NADPH. Regeneration of RuBP.
• For each CO₂: 3 ATP + 2 NADPH. For one glucose: 18 ATP + 12 NADPH.

5. C₄ pathway (Hatch and Slack)

• In maize, sugarcane, sorghum. Leaves have Kranz anatomy (large bundle-sheath cells).
• In mesophyll, PEP carboxylase fixes CO₂ into oxaloacetic acid (OAA, 4-carbon) – first product. It is carried to bundle-sheath cells, releases CO₂, and the Calvin cycle runs there.
• C₄ plants tolerate high light and temperature, use water well and show no photorespiration, so they are more productive.

6. Photorespiration and limiting factors

• Photorespiration: at high O₂ and temperature, RuBisCO binds O₂ instead of CO₂; no sugar or ATP is made – a wasteful process in C₃ plants.
• Blackman’s law of limiting factors: when many factors affect a process, the rate depends on the one closest to its minimum value.
• Factors: light, CO₂ concentration (a major limiting factor), temperature and water.

Important questions and answers

1. Respiration in plants

• Breaking down of food (mainly glucose) to release energy stored as ATP.
• Plants have no special respiratory organs: gases are exchanged through stomata and lenticels, and each part takes care of its own needs.

2. Glycolysis (EMP pathway)

• In the cytoplasm, in both aerobic and anaerobic respiration.
• Glucose → 2 pyruvic acid; net gain of 2 ATP and 2 NADH.

3. Aerobic respiration

• Link reaction (mitochondrial matrix): pyruvate → acetyl CoA + CO₂ + NADH (pyruvate dehydrogenase).
• Krebs (citric acid) cycle: acetyl CoA + oxaloacetate → citrate … back to oxaloacetate. Per acetyl CoA: 2 CO₂, 3 NADH, 1 FADH₂, 1 ATP (GTP).
• Electron transport system (inner mitochondrial membrane): electrons from NADH and FADH₂ pass along carriers; oxygen is the final acceptor, forming water.
• Oxidative phosphorylation: 1 NADH → 3 ATP, 1 FADH₂ → 2 ATP (older count). Net about 38 ATP per glucose (theoretical).

4. Anaerobic respiration (fermentation)

• Without oxygen, only glycolysis gives energy: net 2 ATP per glucose.
• Alcoholic fermentation (yeast): pyruvate → ethanol + CO₂.
• Lactic acid fermentation (muscles during heavy exercise, some bacteria): pyruvate → lactic acid (causes muscle fatigue).

5. Respiratory quotient (RQ)

• RQ = volume of CO₂ released ÷ volume of O₂ used.
• Carbohydrates: 1. Fats: less than 1 (tripalmitin ≈ 0.7). Proteins: about 0.9. Organic acids: more than 1. Anaerobic respiration: infinity (no O₂ used).
• Respiration is amphibolic – it breaks down molecules and also gives building blocks for making new ones.

Important questions and answers

1. Growth and germination

• Growth: an irreversible, permanent increase in size.
• Epigeal germination: cotyledons come above the soil (bean, castor, cotton). Hypogeal: cotyledons stay below (pea, maize, gram). Vivipary: seed germinates while still on the parent plant (mangroves like Rhizophora).

2. Where and how plants grow

• Growth occurs at meristems (apical, intercalary, lateral) – plants show open, indefinite growth.
• Phases: meristematic (dividing), elongation, maturation.
• Growth rates: arithmetic (L_t = L₀ + rt, straight line) and geometric (W₁ = W₀e^rt). A population shows a sigmoid (S-shaped) curve: lag, log (exponential) and stationary phases.
• Factors: water, oxygen, nutrients, temperature and light.
• Differentiation, dedifferentiation and redifferentiation produce different cell types.

3. Auxins

• Discovered from Charles and Francis Darwin’s studies of canary grass bending towards light (phototropism); F.W. Went isolated auxin from oat coleoptile tips.
• Avena curvature test: a bioassay (using a living plant part to measure a hormone) for auxin.
• Roles: apical dominance, rooting of stem cuttings, parthenocarpy (seedless fruits, e.g. tomato), preventing early fruit drop. 2,4-D is a weedicide that kills broad-leaved weeds.
• Anti-auxins oppose auxin action.

4. Gibberellins and cytokinins

• Gibberellins: discovered from the ‘bakanae’ (foolish seedling) disease of rice caused by the fungus Gibberella fujikuroi. Increase stem length (bolting in cabbage), increase sugarcane yield, speed up malting in brewing, delay senescence.
• Cytokinins: kinetin (from DNA of herring sperm), zeatin (from maize). Promote cell division, new leaves and shoots, overcome apical dominance, delay leaf ageing.

5. Ethylene and abscisic acid

• Ethylene: a gaseous hormone; ripens fruits (climacteric), promotes leaf and fruit fall (abscission) and senescence; causes the ‘triple response’ in seedlings. Ethephon is used to ripen fruits.
• Abscisic acid (ABA): the ‘stress hormone’; closes stomata in drought, causes seed and bud dormancy, promotes abscission. It often opposes gibberellins.

Important questions and answers

1. Respiratory organs in animals

• Body surface (earthworm), tracheal tubes (insects), gills (fish, most aquatic animals), lungs (terrestrial vertebrates).

2. Human respiratory system

• Nostrils → nasal chamber → pharynx → larynx (voice box; epiglottis prevents food entry) → trachea → bronchi → bronchioles → alveoli.
• Lungs are covered by a double pleural membrane with pleural fluid (reduces friction).
• The part up to the terminal bronchioles is the conducting part; the alveoli are the exchange part.

3. Mechanism of breathing

• Inspiration: diaphragm contracts and flattens, external intercostal muscles lift the ribs → chest volume increases → pressure falls → air enters.
• Expiration: muscles relax → volume decreases → air is pushed out (normally passive).
• Normal breathing rate: 12–16 times per minute. Measured with a spirometer.

4. Volumes and capacities

• Tidal volume (TV) ≈ 500 mL; inspiratory reserve volume (IRV) ≈ 2500–3000 mL; expiratory reserve volume (ERV) ≈ 1000–1100 mL; residual volume (RV) ≈ 1100–1200 mL.
• Vital capacity = TV + IRV + ERV. Total lung capacity = VC + RV.

5. Exchange and transport of gases

• Exchange occurs by diffusion across the very thin alveolar and capillary walls, due to differences in partial pressure.
• pO₂ (mm Hg): alveoli 104, deoxygenated blood 40, tissues 40. pCO₂: alveoli 40, deoxygenated blood 45, tissues 45. CO₂ is about 20–25 times more soluble than O₂.
• O₂ transport: about 97% as oxyhaemoglobin, 3% dissolved in plasma. The oxygen dissociation curve is sigmoid; high pCO₂, H⁺ and temperature shift it right (more O₂ released in tissues).
• CO₂ transport: 20–25% as carbamino-haemoglobin, about 70% as bicarbonate (helped by carbonic anhydrase in RBCs), about 7% dissolved.

6. Regulation and disorders

• Respiratory rhythm centre in the medulla; pneumotaxic centre in the pons adjusts it; a chemosensitive area responds to CO₂ and H⁺.
• Asthma: inflammation of bronchi and bronchioles, difficulty breathing. Emphysema: alveolar walls damaged (mainly smoking), less surface area. Occupational lung disorders: dust causes fibrosis (silicosis, asbestosis) – workers should wear masks.

Important questions and answers

1. Blood

• Plasma (about 55%): 90–92% water; proteins – fibrinogen (clotting), globulins (defence), albumins (osmotic balance); plus nutrients, hormones and wastes.
• RBCs: 5–5.5 million/mm³; no nucleus, biconcave; carry haemoglobin (12–16 g/100 mL); live about 120 days and are destroyed in the spleen.
• WBCs: 6000–8000/mm³. Neutrophils (60–65%, most, phagocytic), eosinophils (allergy), basophils (release histamine), lymphocytes (20–25%, B and T cells – immunity), monocytes (6–8%, phagocytic).
• Platelets: 1.5–3.5 lakh/mm³; fragments of megakaryocytes; help clotting.

2. Blood groups and clotting

• ABO: A (antigen A, anti-B), B (antigen B, anti-A), AB (both antigens, no antibodies – universal recipient), O (no antigens, both antibodies – universal donor).
• Rh factor: an Rh⁻ mother carrying an Rh⁺ baby may make antibodies that harm a later Rh⁺ baby – erythroblastosis fetalis.
• Clotting: injured tissue and platelets release factors → prothrombin → thrombin (needs Ca²⁺) → fibrinogen → fibrin threads trap cells to form a clot.

3. Lymph

• Tissue fluid collected by lymph vessels; colourless, has lymphocytes; returns fluid to blood; lacteals absorb fats from the intestine.

4. Circulatory systems

• Open (arthropods, molluscs – blood in open spaces) vs closed (annelids, vertebrates – blood in vessels).
• Fish: 2-chambered heart (single circulation). Amphibians and most reptiles: 3 chambers (mixing of blood). Birds and mammals: 4 chambers (double circulation, no mixing).

5. Human heart

• In the chest, covered by the pericardium; two atria and two ventricles. Valves: tricuspid (right), bicuspid/mitral (left), semilunar valves at the aorta and pulmonary artery.
• Myogenic heart: the beat starts in heart muscle itself. SA node (pacemaker, 70–75 per minute) → AV node → bundle of His → Purkinje fibres. (A neurogenic heart, seen in some invertebrates, is started by nerves.)
• Cardiac cycle ≈ 0.8 s. Stroke volume ≈ 70 mL; cardiac output ≈ 5 L/min.
• Heart sounds: ‘lub’ (closure of AV valves) and ‘dub’ (closure of semilunar valves).
• ECG: P wave – atrial depolarisation; QRS – ventricular depolarisation (contraction); T wave – ventricular repolarisation.

6. Circulation, blood vessels and regulation

• Double circulation: pulmonary (heart → lungs → heart) and systemic (heart → body → heart). Hepatic portal system carries blood from the intestine to the liver.
• Arteries: thick-walled, carry blood away from the heart (all oxygenated except the pulmonary artery). Veins: thin-walled with valves. Capillaries: exchange with tissues.
• Normal blood pressure ≈ 120/80 mm Hg.
• Regulation: sympathetic nerves and adrenal medulla hormones increase heart rate; parasympathetic nerves decrease it.

7. Disorders

• Hypertension: BP repeatedly 140/90 or higher. Coronary artery disease (atherosclerosis – fat deposits narrow heart arteries). Angina: chest pain from too little oxygen to heart muscle. Heart failure: heart can’t pump enough blood.

Important questions and answers

1. Types of nitrogenous waste

• Ammonotelic (ammonia – very toxic, needs lots of water): bony fish, aquatic amphibians.
• Ureotelic (urea): mammals, terrestrial amphibians, marine fish.
• Uricotelic (uric acid – least water loss): birds, reptiles, insects, land snails.

2. Excretory organs in animals

• Protonephridia / flame cells (flatworms), nephridia (earthworm), Malpighian tubules (insects), antennal/green glands (crustaceans), kidneys (vertebrates).

3. Human excretory system and nephron

• Two kidneys, two ureters, urinary bladder, urethra. Kidney: outer cortex, inner medulla (pyramids), hilum, renal pelvis with calyces.
• About one million nephrons per kidney. Parts: glomerulus + Bowman’s capsule (together the Malpighian body), proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), collecting duct.
• Cortical nephrons (short loops) and juxtamedullary nephrons (long loops); vasa recta run beside the loops.

4. Urine formation

• Glomerular filtration: blood is filtered under pressure; GFR ≈ 125 mL/min (about 180 L/day).
• Reabsorption: about 99% of the filtrate is reabsorbed; PCT reabsorbs most glucose, amino acids, Na⁺ and water.
• Tubular secretion: H⁺, K⁺ and NH₃ are secreted into the filtrate, helping keep blood pH and ion balance.

5. Counter-current mechanism

• Opposite flows in the loop of Henle and the vasa recta build a rising osmotic gradient in the medulla (about 300 to 1200 mOsm/L).
• This lets water leave the collecting duct, so mammals can make concentrated urine.

6. Regulation of kidney function

• ADH (vasopressin) from the hypothalamus/posterior pituitary increases water reabsorption when the body loses water.
• Juxtaglomerular apparatus (JGA) releases renin when blood pressure falls → angiotensin II → raises BP and releases aldosterone (more Na⁺ and water reabsorbed) – the RAAS.
• ANF (atrial natriuretic factor) from the heart widens blood vessels and checks RAAS.
• Micturition: a reflex emptying of the bladder. Adults pass 1–1.5 L urine per day with 25–30 g urea.

7. Other excretory organs and disorders

• Lungs (CO₂, water), liver (bile pigments, cholesterol, drugs), skin (sweat, sebum), saliva.
• Uraemia: urea builds up in blood due to kidney failure – treated by haemodialysis (artificial kidney; heparin prevents clotting; dialysing fluid removes wastes) or kidney transplant (preferably from a close relative).
• Renal calculi (kidney stones); glomerulonephritis (inflammation of glomeruli).

Important questions and answers

1. Types of movement and muscles

• Amoeboid (pseudopodia; macrophages, WBCs), ciliary (lining of trachea, fallopian tubes), muscular (limbs, jaws, tongue).
• Muscles: skeletal (striated, voluntary), visceral/smooth (non-striated, involuntary; gut, blood vessels), cardiac (striated, involuntary, branched; heart).

2. Structure of skeletal muscle

• Muscle → fascicles → muscle fibres (cells) covered by sarcolemma, with sarcoplasm and sarcoplasmic reticulum (stores Ca²⁺).
• Each fibre has myofibrils with alternate light (I band, actin) and dark (A band, myosin) bands.
• Sarcomere – the functional unit, between two Z lines; H zone in the middle of the A band, with the M line.
• Thin filaments: F-actin with tropomyosin and troponin. Thick filaments: myosin with heads that have ATPase activity.

3. Mechanism of contraction – sliding filament theory

• A nerve impulse releases acetylcholine at the neuromuscular junction → action potential in the fibre.
• Ca²⁺ is released from the sarcoplasmic reticulum and binds troponin, exposing binding sites on actin.
• Myosin heads (energised by ATP hydrolysis) attach to actin, forming cross-bridges, and pull actin towards the M line.
• The sarcomere shortens: I band and H zone shorten, A band stays the same length. Relaxation happens when Ca²⁺ is pumped back.
• Repeated contraction builds up lactic acid, causing fatigue.
• Red fibres: much myoglobin and mitochondria, aerobic, slow to tire. White fibres: less myoglobin, fast, anaerobic.

4. Human skeleton (206 bones)

• Axial skeleton (80): skull 29 (8 cranial + 14 facial + hyoid + 6 ear ossicles), vertebral column 26 (cervical 7, thoracic 12, lumbar 5, sacrum 1, coccyx 1), sternum 1, ribs 12 pairs (true 1–7, false 8–10, floating 11–12).
• Appendicular skeleton (126): each limb has 30 bones. Forelimb: humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges. Hindlimb: femur, tibia, fibula, patella, 7 tarsals, 5 metatarsals, 14 phalanges. Pectoral girdle: clavicle and scapula. Pelvic girdle: two coxal bones.

5. Joints

• Fibrous (immovable – skull sutures), cartilaginous (slightly movable – between vertebrae), synovial (freely movable, fluid-filled cavity).
• Synovial types: ball and socket (shoulder, hip), hinge (knee, elbow), pivot (atlas–axis), gliding (between carpals), saddle (carpal–metacarpal of thumb).

6. Disorders

• Myasthenia gravis: autoimmune disorder of the neuromuscular junction; weakness.
• Muscular dystrophy: genetic, progressive muscle degeneration.
• Tetany: rapid spasms due to low Ca²⁺ in body fluid.
• Arthritis: joint inflammation. Osteoporosis: bones become weak with age, often linked to low oestrogen. Gout: uric acid crystals in joints.

Important questions and answers

1. Neuron

• Parts: cell body (with Nissl granules), dendrites (carry impulses towards the cell body), axon (carries impulses away).
• Myelinated fibres have a myelin sheath from Schwann cells with gaps called nodes of Ranvier; non-myelinated fibres lack it.
• Types: multipolar (brain cortex), bipolar (retina), unipolar (embryo).

2. Nerve impulse

• Resting potential: the membrane is polarised – outside positive, inside negative (about −70 mV). The Na⁺/K⁺ pump sends 3 Na⁺ out and 2 K⁺ in, keeping more K⁺ inside and more Na⁺ outside.
• Action potential: a stimulus opens Na⁺ channels, Na⁺ rushes in and the inside becomes positive (depolarisation). K⁺ then moves out (repolarisation).
• The impulse travels along the axon; in myelinated fibres it jumps from node to node – saltatory conduction – which is much faster.

3. Synapse

• Junction between two neurons. Electrical synapse: direct, very fast. Chemical synapse: the impulse releases neurotransmitters (e.g. acetylcholine) from synaptic vesicles; they cross the cleft and bind receptors, starting a new impulse.

4. Divisions of the nervous system

• CNS: brain and spinal cord. PNS: cranial and spinal nerves – somatic (to skeletal muscles) and autonomic (to internal organs).
• Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves.

5. Human brain

• Protected by the skull and three meninges (dura mater, arachnoid, pia mater).
• Forebrain: cerebrum – two hemispheres joined by the corpus callosum; outer grey matter (cortex) with sensory, motor and association areas (thinking, memory, speech); thalamus – relay centre; hypothalamus – controls temperature, hunger, thirst and makes hormones; limbic system – emotions.
• Midbrain: corpora quadrigemina (visual and auditory reflexes).
• Hindbrain: pons (helps regulate breathing), cerebellum (balance, posture, coordination), medulla oblongata (breathing, heartbeat, blood pressure; reflexes like swallowing, coughing, vomiting).
• Brainstem = midbrain + pons + medulla.

6. Spinal cord and autonomic nervous system

• Spinal cord: white matter outside, H-shaped grey matter inside; carries messages to and from the brain.
• Sympathetic system: ‘fight or flight’ – increases heart rate, dilates pupils and bronchi, slows digestion.
• Parasympathetic system: ‘rest and digest’ – slows heart rate, constricts pupils, increases digestion. The two work in opposition.

Important questions and answers

1. Endocrine system and hormones

• Endocrine glands are ductless and release hormones directly into the blood.
• Hormones: non-nutrient chemicals that act as messengers and work in tiny amounts on target organs.

2. Hypothalamus and pituitary

• Hypothalamus: makes releasing and inhibiting hormones (e.g. GnRH, somatostatin) that control the anterior pituitary through a portal system. It also makes oxytocin and ADH, which are stored in the posterior pituitary.
• Pituitary (‘master gland’), in the sella turcica. Anterior (adenohypophysis): GH (excess → gigantism in children, acromegaly in adults; deficiency → dwarfism), prolactin (milk production), TSH, ACTH, LH, FSH; MSH from the pars intermedia.
• Posterior (neurohypophysis): oxytocin (uterine contraction at birth, milk ejection) and ADH/vasopressin (water reabsorption; deficiency → diabetes insipidus).

3. Pineal, thyroid, parathyroid, thymus

• Pineal: melatonin – sleep–wake (24-hour) rhythm.
• Thyroid: T₄ (thyroxine) and T₃ – control basal metabolic rate and RBC formation. Iodine deficiency → goitre; hypothyroidism in pregnancy → cretinism in the child; in adults → myxoedema; hyperthyroidism → exophthalmic goitre (Graves’ disease). Thyrocalcitonin lowers blood Ca²⁺.
• Parathyroid: PTH raises blood Ca²⁺ (hypercalcaemic hormone).
• Thymus: thymosins help T-lymphocytes mature; the gland shrinks with age.

4. Adrenal gland

• Medulla: adrenaline and noradrenaline (catecholamines) – ‘emergency hormones’: raise heart rate, BP, alertness and blood sugar.
• Cortex: glucocorticoids (cortisol – makes glucose, reduces inflammation), mineralocorticoids (aldosterone – Na⁺ and water reabsorption), small amounts of androgens. Deficiency → Addison’s disease.

5. Pancreas and gonads

• Islets of Langerhans: α cells → glucagon (raises blood sugar), β cells → insulin (lowers blood sugar). Lack of insulin → diabetes mellitus.
• Testes: Leydig cells make androgens (testosterone) – male features and sperm formation. Ovaries: oestrogen and progesterone – female features, menstrual cycle, pregnancy.

6. Other hormone sources

• Heart atria: ANF (lowers BP). Kidneys: erythropoietin (RBC formation). Stomach and intestine: gastrin, secretin, CCK, GIP. Placenta: hCG, hPL, oestrogen, progesterone.

7. How hormones act and are controlled

• Protein/peptide hormones (water-soluble, e.g. insulin) bind to receptors on the cell membrane and act through second messengers (cAMP, Ca²⁺).
• Steroid and iodothyronine hormones (lipid-soluble) enter the cell, bind intracellular receptors and change gene expression.
• Negative feedback: a high level of a hormone reduces its own production, e.g. high thyroxine lowers TRH and TSH.

Important questions and answers

1. What is directed writing?

• You are given a situation, a purpose and some points. You must write in the correct format, for the right audience, and cover every point given.
• Marks are for content (all points), format, organisation and language.

2. Feature article

• A detailed, interesting piece on a topic for a newspaper or magazine.
• Format: catchy headline, optional sub-heading, ‘By [name]’, an engaging opening (anecdote, question, striking fact), well-developed paragraphs, and a thoughtful ending.
• Tone: informative but lively; use examples and quotes from people.

3. Book review

• Start with title, author, genre and publisher.
• Give a short summary without revealing the ending; discuss characters, themes, style and what you liked or disliked.
• End with a clear recommendation (who should read it, rating).

4. Newspaper report

• Headline → byline (By a Staff Reporter) → place and date line → first paragraph answering who, what, when, where, why and how → details in order of importance → quotes from witnesses or officials.
• Written in the third person and mostly in the past tense; formal and factual, no personal opinions.

5. Statement of purpose (SOP)

• Written for college or scholarship applications.
• Cover: your background, interest in the subject, achievements, why this course or institution, and future goals.
• First person, formal, honest and specific; avoid exaggeration.

6. Blog

• Informal and personal, like talking to readers. Give a title, date, a friendly opening, clear short paragraphs, and end by inviting comments or questions.
• Can use headings, lists and a conversational style, but keep grammar correct.

Important questions and answers

1. What is a proposal?

• A formal plan suggesting a project or change (e.g. a school garden, an anti-plastic drive), written to convince an authority to approve it.

2. Format

• Title of the proposal.
• Introduction / background: the problem or need.
• Objectives: what you want to achieve.
• Plan of action: step-by-step activities, who will do what.
• Resources / budget needed.
• Timeline.
• Expected outcomes / benefits.
• Conclusion: a short, convincing closing request.

3. Tips

• Use headings and short paragraphs; points can be numbered.
• Formal, clear and practical language; show the plan is realistic.
• Use every point given in the question.

Important questions and answers

1. Steps to solve comprehension

• Read the passage once for the general idea, then read the questions, then read again carefully.
• Underline key lines that answer each question.
• Answer in your own words unless asked to quote; keep answers to the point.

2. Vocabulary questions

• Find the meaning from context – the sentences around the word.
• Replace the word with your answer; it should fit grammatically and in meaning.

3. Summary writing

• Pick only main ideas; leave out examples, repetitions and figures of speech.
• Write in complete, connected sentences within the word limit.

Important questions and answers

1. Subject–verb agreement

• Singular subject → singular verb; plural → plural. The list of items is on the desk.
• Each, every, either, neither → singular. Two subjects joined by and → plural. With or/nor, the verb agrees with the nearer subject.
• Collective nouns take a singular verb when acting as one unit.

2. Tenses and sequence of tenses

• Present, past and future, each in simple, continuous, perfect and perfect continuous forms.
• If the main verb is in the past, the verb in the subordinate clause is usually also past: He said that he was tired. Exception: universal truths stay present: She said that the sun rises in the east.

3. Active and passive voice

• Object becomes subject; use a form of be + past participle. They built the bridge → The bridge was built (by them).

4. Direct and indirect speech

• Change pronouns, tense (one step back), and words like now → then, today → that day, tomorrow → the next day, here → there.
• Questions: He asked, “Where are you going?” → He asked where I was going. Commands: use told/ordered + to-infinitive.

5. Degrees of comparison

• Positive, comparative, superlative: tall, taller, tallest; good, better, best.
• Transform: No other boy is as tall as Ram → Ram is taller than any other boy → Ram is the tallest boy.

6. Conditional sentences

• Zero (facts): If you heat ice, it melts. First (likely): If it rains, I will stay home. Second (unlikely): If I were rich, I would travel. Third (past, impossible): If I had studied, I would have passed.

7. Transformation, prepositions and phrasal verbs

• Common transformations: too…to ↔ so…that, no sooner…than, hardly…when, unless = if…not, although ↔ in spite of.
• Prepositions: in (months, years), on (days, dates), at (clock time).
• Phrasal verbs: look after (take care of), put off (postpone), give up (stop), carry on (continue), turn down (reject).

Important questions and answers

1. Listening (aural)

• Read the questions before the audio starts, if allowed.
• Note key words, numbers and names while listening; listen for the speaker’s main idea and attitude.

2. Speaking (oral)

• Plan a quick outline: opening, 2–3 points with examples, conclusion.
• Speak clearly, at a steady pace, with correct pronunciation; keep eye contact and good posture.
• In discussions, listen to others, respond politely and support your view with reasons.

Important questions and answers

1. About the poem

• By Rabindranath Tagore; based on a Buddhist legend. ‘Abhisara’ means a tryst or secret meeting with a lover.

2. Summary

• Upagupta, a young Buddhist monk, sleeps in the dust by the city wall of Mathura.
• Vasavadatta, a beautiful dancing girl, going to meet a lover, trips over him. Struck by his handsome young face, she invites him to her home, saying the dusty ground is no bed for him.
• He gently replies that the time has not yet come; he will visit her when it does.
• Later, Vasavadatta is struck by a terrible pestilence (plague with sores). The townspeople throw her outside the city wall to avoid infection.
• Upagupta finds her, lays her head on his lap, gives her water and applies balm to her sores. When she asks who he is, he says the time has now come to visit her – and he is there.

3. Themes and devices

• True love is compassion, not physical attraction: Upagupta comes when she needs care, not when she offers pleasure.
• Spiritual vs physical beauty; the transience of youth and beauty; the cruelty of society to the sick.
• Contrast: the first scene (night, beauty, desire) and the second (disease, abandonment, service). The line about the ‘time’ coming frames the poem.

Important questions and answers

1. About the poem

• By William Shakespeare; a Shakespearean sonnet: 14 lines – three quatrains and a couplet, rhyme scheme ABAB CDCD EFEF GG, in iambic pentameter.

2. Meaning

• Quatrain 1: The speaker won’t accept obstacles to the union of true minds. Love that changes when circumstances change, or ends when the loved one leaves, is not true love.
• Quatrain 2: True love is a fixed mark that faces storms without shaking, and like the star that guides lost ships – its worth can’t be measured, even if its height can.
• Quatrain 3: Love is not the fool of Time. Time’s curved sickle cuts away youthful beauty (rosy lips and cheeks), but love does not change with the brief hours and weeks; it lasts to the edge of doom.
• Couplet: If this is proved wrong, then the poet never wrote and no one ever loved – showing complete confidence in his claim.

3. Themes and devices

• Themes: constancy, the eternal nature of true love, love vs time.
• Imagery: the fixed sea-mark, the guiding star, Time with a sickle (personification). Metaphors from navigation.

Important questions and answers

1. About the poem

• By Seamus Heaney, Irish poet; the title poem of his first collection. Written in blank verse in two stanzas.

2. Summary

• Stanza 1: The flax-dam in the townland is rotting in the sun, full of bubbles and bluebottle flies. Every spring the child fills jam jars with frogspawn, watches the tadpoles grow, and learns from his teacher, Miss Walls, a simple, cosy version of how frogs are born. Nature is a source of wonder.
• Stanza 2: One hot day, the flax-dam is invaded by angry, gross-bellied frogs croaking loudly. The child is sickened and afraid; he feels the frogs have gathered for revenge and that the spawn would grab his hand if he dipped it in. He runs away.

3. Themes and devices

• Loss of innocence: the child’s romantic view of nature ends – the ‘death’ of the young naturalist.
• Nature has an ugly, frightening side too.
• Rich sensory imagery and onomatopoeia (sounds of croaking, slapping), strong contrast between the two stanzas, and childlike language in the first stanza.

Important questions and answers

1. About the poem

• By Wilfred Owen, a British soldier-poet of World War I, killed a week before the war ended. Published after his death.

2. Summary

• The speaker seems to escape from battle down a deep, dark tunnel, where sleeping soldiers lie. One springs up and stares at him with pity – the speaker realises he is in Hell, yet there are no sounds of guns there.
• The dead soldier speaks of the ‘undone years’ – the life, hope and beauty he lost. He wanted to tell the truth about war, the ‘pity of war’, which now will remain untold; nations will keep marching into more bloodshed.
• He wanted to use his mind and courage to heal the world, not to kill.
• He finally reveals: he is the enemy the speaker killed the day before, calling him ‘my friend’, and invites him to sleep now.

3. Themes and devices

• Futility and horror of war; the enemy is also a human being; the loss of young potential; reconciliation in death.
• Dream-like, ghostly setting. Pararhyme (half-rhyme, e.g. similar consonants with different vowels) creates an uneasy, haunting effect. Irony in calling the enemy ‘friend’.

Important questions and answers

1. About the story

• By Lafcadio Hearn, a writer who lived in Japan and wrote about its culture. Set in a Japanese coastal village.

2. Summary

• Hamaguchi Gohei, an old, wealthy and respected farmer, lives in a house on a hill above the village. The villagers below are busy with a harvest festival.
• After a long, slow earthquake he sees the sea suddenly moving away from the shore – a sign of a coming tsunami. There is no time to go down and warn everyone.
• He asks his grandson Tada to bring a torch and sets fire to his own rice-stacks – his whole harvest and wealth. The temple bell rings and the villagers rush up the hill to put out the fire.
• As they reach the top, the huge wave strikes and destroys the village below. Everyone realises he burned his rice to save their lives.
• The grateful villagers call him a living god and build a shrine to his spirit while he is still alive.

3. Themes

• Self-sacrifice and wisdom; presence of mind in a crisis; gratitude and respect; Japanese culture of honouring great souls.

Important questions and answers

1. About the text

• A humorous speech by Mark Twain (1882). It uses satire and irony – saying the opposite of what is meant to make fun of usual moral advice.

2. The ‘advice’

• Obey your parents – when they are present; it is wise, because they think they know better.
• Respect your superiors and strangers too; if someone offends you, don’t take revenge immediately – wait for a chance to hit them with a brick (a joke on revenge).
• Go to bed early and get up early – with a joke about the lark and the worm.
• Lying: learn to lie well and with care; don’t lie clumsily – a mock lesson on how common lying is.
• Firearms: never handle them carelessly – with a comic story about a boy who aimed an ‘unloaded’ gun at his grandmother, and how badly people aim.
• Read good books – he names serious religious books and adds his own, The Innocents Abroad, as a joke.

3. Purpose

• He mocks preachy, conventional advice and the hypocrisy of adults, while slyly suggesting real lessons: think for yourself, be careful, value good books.

Important questions and answers

1. About the story

• By Ken Liu (2011); a fantasy-tinged story that won major awards. Themes of immigration, identity and a mother’s love.

2. Summary

• Jack is the son of an American father and a Chinese mother whom the father met through a catalogue. His mother folds origami animals that come to life when she breathes into them – especially the tiger Laohu.
• As Jack grows up, neighbours and classmates mock his Chinese looks and his paper toys. He starts rejecting his mother’s language, food and culture, demanding she speak only English, and puts the paper animals away.
• His mother becomes sad and silent. She develops cancer and dies when Jack is at college, asking him to keep the paper animals.
• Years later, on Qingming (the festival for remembering the dead), Laohu comes alive and unfolds, showing a letter written in Chinese. Jack has it translated by a stranger.
• The letter tells her story: her family died in hardship in China; she survived, was trafficked to Hong Kong, and married to escape. She was lonely in America, and her son was her only joy – his rejection broke her heart. Jack is filled with regret and love.

3. Themes

• Cultural identity and racism; the pain of rejection; language as connection; a mother’s unconditional love; regret that comes too late.

Important questions and answers

1. About the story

• By Roald Dahl; a satirical, darkly funny story written in the 1950s that now seems prophetic about AI writing.

2. Summary

• Adolph Knipe, a brilliant engineer at Mr Bohlen’s computer firm, wants to be a writer but is unsuccessful.
• He realises that English grammar follows mathematical rules and builds the Great Automatic Grammatizator, a machine that produces stories and novels in minutes.
• With his employer Mr Bohlen, he floods magazines and publishers with machine-written works. They then make famous authors sign contracts to stop writing and allow their names to be used, paying them well.
• Soon a huge share of all novels and stories is produced by the machine.
• The narrator, a struggling writer, refuses to sign – even though his children are hungry – and prays for strength to hold out.

3. Themes

• Satire on mechanisation and commercialisation of art; loss of originality; greed; the dignity of the true artist.

Important questions and answers

1. About the story

• By Langston Hughes, an African-American writer of the Harlem Renaissance (1958).

2. Summary

• Late at night, a teenage boy, Roger, tries to snatch the purse of a large woman, Mrs Luella Bates Washington Jones. The heavy purse makes him fall.
• She grabs him, scolds him, and instead of calling the police, drags him to her home.
• She makes him wash his face, shares her simple dinner with him and talks about her own mistakes. She leaves her purse where he could take it and run, but he chooses to stay – she trusts him.
• He wanted money for blue suede shoes. She gives him ten dollars and advises him not to steal again.
• At the door, Roger wants to say more than ‘Thank you, ma’am’ but can’t – and never sees her again.

3. Themes

• Kindness and empathy can change people more than punishment; trust and respect; poverty and dignity.

Important questions and answers

1. About the play

• A tragedy by William Shakespeare, set in Scotland. (Check with your teacher which acts are in your Class 11 portion.)

2. Plot by acts

• Act I: Three witches prophesy that Macbeth will become Thane of Cawdor and then king, and that Banquo’s descendants will be kings. Macbeth is made Thane of Cawdor. Lady Macbeth, reading his letter, pushes him to kill King Duncan, who visits their castle.
• Act II: Macbeth sees an imaginary dagger and murders Duncan in his sleep; Lady Macbeth plants the daggers on the guards. Duncan’s sons Malcolm and Donalbain flee. Macbeth becomes king.
• Act III: Fearing the prophecy about Banquo, Macbeth has him murdered, but Banquo’s son Fleance escapes. At a banquet, Banquo’s ghost appears to Macbeth, who loses control.
• Act IV: The witches show apparitions: beware Macduff; no man ‘born of woman’ can harm Macbeth; he is safe until Birnam Wood comes to Dunsinane. Macbeth has Macduff’s wife and children killed. Macduff joins Malcolm in England.
• Act V: Lady Macbeth sleepwalks, trying to wash imaginary blood off her hands, and later dies. The army carries branches from Birnam Wood. Macduff reveals he was born by caesarean (‘untimely ripped’) and kills Macbeth. Malcolm becomes king.

3. Characters

• Macbeth: brave but ambitious; his ambition, guilt and fear turn him into a tyrant.
• Lady Macbeth: strong-willed and manipulative at first; later destroyed by guilt.
• Banquo: loyal, cautious, a contrast to Macbeth. Macduff: loyal to Scotland, avenges his family. Duncan: kind, trusting king. The witches: symbols of evil and temptation.

4. Themes and devices

• Unchecked ambition; guilt and conscience (blood imagery, sleeplessness); fate vs free will; appearance vs reality (‘fair is foul, and foul is fair’); order and disorder in nature.
• Dramatic irony, soliloquies, supernatural elements and recurring imagery of blood, darkness and sleep.

Important questions and answers