Physics
1. Units & Measurement
Every physical quantity is expressed as a number multiplied by a unit. The International System of Units (SI), adopted by the General Conference on Weights and Measures (CGPM), provides a coherent set of units used worldwide in science, commerce, and industry.
Seven SI Base Units
| Physical Quantity | SI Unit | Symbol | Definition Basis |
|---|---|---|---|
| Length | metre | m | Distance light travels in 1/299,792,458 s |
| Mass | kilogram | kg | International Prototype of the Kilogram (Planck constant) |
| Time | second | s | 9,192,631,770 periods of Cs-133 radiation |
| Electric Current | ampere | A | Fixed value of elementary charge e |
| Temperature | kelvin | K | Fixed value of Boltzmann constant kB |
| Amount of Substance | mole | mol | 6.022×10²³ elementary entities (Avogadro number fixed) |
| Luminous Intensity | candela | cd | Fixed value of luminous efficacy of 540 THz radiation |
Derived Units (selected)
| Quantity | Unit | Symbol | In Base Units |
|---|---|---|---|
| Force | newton | N | kg m s⁻² |
| Energy/Work | joule | J | kg m² s⁻² |
| Power | watt | W | kg m² s⁻³ |
| Pressure | pascal | Pa | kg m⁻¹ s⁻² |
| Electric Charge | coulomb | C | A s |
| Voltage | volt | V | kg m² s⁻³ A⁻¹ |
| Resistance | ohm | Ω | kg m² s⁻³ A⁻² |
| Frequency | hertz | Hz | s⁻¹ |
| Magnetic Flux | weber | Wb | kg m² s⁻² A⁻¹ |
Dimensional Analysis
Every physical quantity can be expressed in terms of fundamental dimensions: Mass [M], Length [L], Time [T], Electric Current [A], Temperature [θ], Luminous Intensity [cd], Amount of Substance [mol]. Dimensional analysis is used to check correctness of equations, convert units, and derive relations.
[Force] = [M L T⁻²] (F = ma, dimensions: kg × m/s²)
[Energy] = [M L² T⁻²] (E = ½mv², dimensions: kg × m² × s⁻²)
[Power] = [M L² T⁻³] (P = W/t)
[Pressure] = [M L⁻¹ T⁻²] (P = F/A)
[Momentum] = [M L T⁻¹] (p = mv)
Errors in Measurement
Absolute Error: The magnitude of difference between the measured value and the true value. Δa = |a_true - a_measured|
Relative Error: Ratio of absolute error to true value = Δa / a_true
Percentage Error: Relative error × 100 = (Δa / a_true) × 100%
Significant figures indicate the precision of a measurement. All non-zero digits, zeros between non-zero digits, and trailing zeros after a decimal point are significant. Leading zeros are never significant.
Measuring Instruments
Vernier Calliper: Least Count = 1 Main Scale Division (MSD) − 1 Vernier Scale Division (VSD). Typically LC = 0.1 mm = 0.01 cm. Reading = MSR + (VC × LC), where VC is the vernier coincidence.
Screw Gauge (Micrometer): Least Count = Pitch / Number of divisions on circular scale. Pitch = distance moved per full rotation. Common LC = 0.5 mm / 50 = 0.01 mm. Reading = MSR + (CSR × LC).
2. Motion
Motion is change in position with time. It is described by scalars (magnitude only — distance, speed) and vectors (magnitude + direction — displacement, velocity, acceleration).
Equations of Motion (uniform acceleration)
v = u + at (velocity-time relation)
s = ut + ½at² (displacement-time relation)
v² = u² + 2as (velocity-displacement relation)
s_n = u + a(2n-1)/2 (displacement in nth second)
where: u = initial velocity, v = final velocity,
a = acceleration, s = displacement, t = time
Distance-Time and Velocity-Time Graphs
Distance-Time Graph: Slope = velocity. Horizontal line → body at rest. Straight oblique line → uniform velocity. Curve (concave up) → acceleration. Curve (concave down) → deceleration.
Velocity-Time Graph: Slope = acceleration. Area under the graph = displacement. Horizontal line → uniform velocity (a = 0). Straight oblique line → uniform acceleration.
Velocity-Time Graph: Slope = acceleration. Area under the graph = displacement. Horizontal line → uniform velocity (a = 0). Straight oblique line → uniform acceleration.
Projectile Motion
When a body is projected at an angle θ to the horizontal with initial speed u, horizontal velocity (u cosθ) remains constant (no horizontal force) while vertical velocity changes due to gravity.
Horizontal Range: R = u² sin2θ / g (maximum at θ = 45°)
Maximum Height: H = u² sin²θ / (2g)
Time of Flight: T = 2u sinθ / g
At θ = 45°: R_max = u² / g
For complementary angles (θ and 90°−θ): Ranges are equal
🎯 BPSC Fact: Range is maximum at θ = 45°. Complementary angles (e.g., 30° and 60°) give the same range. A projectile at angle θ has the same horizontal range as one at (90°−θ). At the highest point, only horizontal velocity remains; vertical velocity = 0.
3. Laws of Motion
Newton's First Law (Law of Inertia): A body at rest stays at rest, and a body in uniform motion stays in uniform motion unless acted upon by an external unbalanced force. Inertia is the tendency of a body to resist any change in its state of motion. Greater the mass, greater the inertia.
Newton's Second Law (Law of Force): The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of force.
F = ma (force = mass × acceleration)
p = mv (momentum = mass × velocity)
F = Δp/Δt (force = rate of change of momentum)
Impulse = F·Δt = Δp = change in momentum [unit: N·s or kg·m/s]
Newton's Third Law: For every action there is an equal and opposite reaction. Forces always occur in pairs — but they act on different bodies, so they do not cancel each other.
Friction
Friction is a contact force opposing relative motion between surfaces. It arises due to irregularities at the molecular level.
Types: Static friction (f_s ≤ μ_s N) — body at rest; Kinetic/Sliding friction (f_k = μ_k N) — body in motion; Rolling friction — least (f_r < f_k < f_s).
Angle of Repose (θ): The maximum angle of an incline at which a body remains just on the verge of sliding. tan θ = μ_s (coefficient of static friction).
Laws of Friction: (1) Friction ∝ normal force (2) Independent of area of contact (3) Independent of velocity for kinetic friction.
Angle of Repose (θ): The maximum angle of an incline at which a body remains just on the verge of sliding. tan θ = μ_s (coefficient of static friction).
Laws of Friction: (1) Friction ∝ normal force (2) Independent of area of contact (3) Independent of velocity for kinetic friction.
f_s(max) = μ_s × N (maximum static friction)
f_k = μ_k × N (kinetic friction)
tan θ = μ_s (angle of repose)
μ_k < μ_s (kinetic always less than static)
4. Work, Energy & Power
Work is done when a force causes displacement. Energy is the capacity to do work. Power is the rate of doing work.
Work: W = F × s × cosθ [unit: joule J = N·m]
(θ = angle between F and displacement)
W = 0 when θ = 90° (e.g., centripetal force)
W < 0 when θ > 90° (opposing motion, e.g., friction)
Kinetic Energy: KE = ½mv² [unit: J]
Potential Energy: PE = mgh (gravitational) [unit: J]
Elastic PE: U = ½kx² (spring)
Work-Energy Theorem: W_net = ΔKE = KE_final − KE_initial
Power: P = W/t = F·v [unit: watt W = J/s]
1 horsepower = 746 W
Efficiency: η = (Useful Output / Total Input) × 100%
Conservation of Mechanical Energy
In the absence of non-conservative forces (like friction), the total mechanical energy (KE + PE) of a system remains constant. At the top of a swing: all PE; at the bottom: all KE. This principle underlies pendulum motion, roller coasters, and ball rolling down inclines.
Simple Machines
| Machine | Mechanical Advantage (MA) | Principle | Examples |
|---|---|---|---|
| Lever (Class I) | Effort Arm / Load Arm | Pivot between effort and load | Scissors, seesaw, pliers |
| Lever (Class II) | >1 | Load between pivot and effort | Wheelbarrow, nutcracker |
| Lever (Class III) | <1 (speed multiplier) | Effort between pivot and load | Tweezers, forearm |
| Pulley (fixed) | 1 (changes direction only) | Tension in rope | Well pulley |
| Pulley (movable) | 2 | Weight supported by 2 rope segments | Block and tackle |
| Inclined Plane | Length / Height | Force × distance constant | Ramps, screws, wedges |
5. Gravitation
Newton's Universal Law of Gravitation: Every particle in the universe attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
F = G × m₁ × m₂ / r²
G = 6.674 × 10⁻¹¹ N m² kg⁻² (Universal Gravitational Constant)
Acceleration due to gravity at Earth's surface:
g = GM/R² ≈ 9.8 m/s²
(M = 6×10²⁴ kg, R = 6.4×10⁶ m)
Variation with altitude h (h << R):
g' = g(1 − 2h/R) (g decreases with altitude)
Variation with depth d:
g' = g(1 − d/R) (g decreases with depth, g = 0 at centre)
At poles: g is maximum (Earth is oblate, closer to centre)
At equator: g is minimum (farthest from centre + centrifugal effect)
g_poles > g_equator by ≈ 0.052 m/s²
Escape Velocity: v_e = √(2gR) = √(2GM/R) ≈ 11.2 km/s (from Earth)
(Minimum velocity to escape Earth's gravity permanently)
Orbital Velocity (near Earth): v_o = √(gR) = √(GM/R) ≈ 7.9 km/s
Relation: v_e = √2 × v_o
Kepler's Laws of Planetary Motion
First Law (Law of Ellipses): Every planet revolves around the Sun in an elliptical orbit with the Sun at one of the two foci.
Second Law (Law of Equal Areas): A line joining a planet to the Sun sweeps equal areas in equal intervals of time. This implies a planet moves fastest at perihelion (closest to Sun) and slowest at aphelion (farthest). This is a consequence of conservation of angular momentum.
Third Law (Law of Periods): The square of the orbital period of a planet is proportional to the cube of its semi-major axis (average distance from Sun). T² ∝ a³, or T²/a³ = constant for all planets in a solar system.
Second Law (Law of Equal Areas): A line joining a planet to the Sun sweeps equal areas in equal intervals of time. This implies a planet moves fastest at perihelion (closest to Sun) and slowest at aphelion (farthest). This is a consequence of conservation of angular momentum.
Third Law (Law of Periods): The square of the orbital period of a planet is proportional to the cube of its semi-major axis (average distance from Sun). T² ∝ a³, or T²/a³ = constant for all planets in a solar system.
🎯 BPSC Fact: g decreases both as you go up (altitude) and as you go down (depth). g = 0 at Earth's centre. Escape velocity from Earth = 11.2 km/s; from Moon ≈ 2.4 km/s (hence Moon has no atmosphere). Geostationary orbit is at ~36,000 km altitude; orbital period = 24 hours.
6. Properties of Matter
Elasticity
Elasticity: The property of a material to regain its original shape and size after the deforming force is removed. The elastic limit is the maximum stress beyond which permanent deformation occurs.
Stress = Force / Area [unit: Pa = N/m²]
Strain = Change in dimension / Original dimension (dimensionless)
Young's Modulus (E) = Longitudinal Stress / Longitudinal Strain
= (F/A) / (ΔL/L) [unit: Pa]
Bulk Modulus (B): for volume change — liquids and gases
Modulus of Rigidity (G): for shear deformation
Hooke's Law: Stress ∝ Strain (valid within elastic limit)
F = −kx (restoring force in spring, k = spring constant)
Fluid Mechanics
Fluid Pressure: P = ρgh, where ρ = fluid density, g = gravity, h = depth. Pressure in a fluid acts equally in all directions (Pascal's Law).
Pascal's Law: Pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid and the walls of the container. Application: Hydraulic lift — small force applied to small piston creates large force at large piston (F₁/A₁ = F₂/A₂, so F₂ = F₁ × A₂/A₁).
Archimedes' Principle: When a body is wholly or partially immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced. Buoyant Force = ρ_fluid × V_displaced × g.
Law of Floatation: A body floats if the weight of fluid displaced equals the body's weight, i.e., its average density ≤ density of the fluid. Ice (ρ ≈ 917 kg/m³) floats in water (1000 kg/m³) with 9/10 submerged.
Archimedes' Principle: When a body is wholly or partially immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced. Buoyant Force = ρ_fluid × V_displaced × g.
Law of Floatation: A body floats if the weight of fluid displaced equals the body's weight, i.e., its average density ≤ density of the fluid. Ice (ρ ≈ 917 kg/m³) floats in water (1000 kg/m³) with 9/10 submerged.
Surface Tension: T = F/L [unit: N/m]
Capillary Rise: h = 2T cosθ / (ρgr)
(Water rises in narrow tubes — wetting liquid; mercury falls — non-wetting)
Bernoulli's Theorem (conservation of energy in fluid flow):
P + ½ρv² + ρgh = constant (along a streamline)
(Higher velocity → lower pressure — explains airplane lift, atomiser,
venturimeter, Bunsen burner, roof being blown off in storms)
Viscosity: F = ηA(dv/dy) (Newton's law of viscosity)
η = coefficient of dynamic viscosity [unit: Pa·s]
Stokes' Law: F_drag = 6πηrv (for sphere of radius r in fluid)
7. Thermal Physics
Temperature Scales
Celsius ↔ Fahrenheit: °F = (9/5 × °C) + 32
°C = (°F − 32) × 5/9
Kelvin ↔ Celsius: K = °C + 273.15
Absolute zero: 0 K = −273.15°C (lowest possible temperature)
Thermal Expansion
Linear: ΔL = α × L₀ × ΔT (α = linear expansion coefficient)
Area: ΔA = 2α × A₀ × ΔT
Volume: ΔV = 3α × V₀ × ΔT (γ = 3α = volume expansion coefficient)
Liquids have volume expansion only (γ_liquid >> α_solid)
Water: anomalous expansion — density maximum at 4°C
(expands on freezing — pipes burst, ice floats)
Heat Transfer
Conduction: Transfer of heat through a medium by molecular collisions without bulk movement of the medium. Rate Q/t = kA(T₁−T₂)/d (Fourier's law). Best conductors: silver, copper, aluminium. Insulators: wood, glass, air.
Convection: Transfer through bulk movement of the fluid itself. Hot fluid rises (less dense), cool fluid sinks — convection currents. Responsible for sea breeze/land breeze, trade winds, heating systems, ocean currents.
Radiation: Transfer without any medium through electromagnetic waves (infrared). All bodies above 0 K radiate. Stefan's Law: P = σεAT⁴ (σ = 5.67×10⁻⁸ W m⁻² K⁻⁴). Black body: perfect absorber and emitter (ε = 1). Newton's Law of Cooling: rate of cooling ∝ excess temperature above surroundings.
Convection: Transfer through bulk movement of the fluid itself. Hot fluid rises (less dense), cool fluid sinks — convection currents. Responsible for sea breeze/land breeze, trade winds, heating systems, ocean currents.
Radiation: Transfer without any medium through electromagnetic waves (infrared). All bodies above 0 K radiate. Stefan's Law: P = σεAT⁴ (σ = 5.67×10⁻⁸ W m⁻² K⁻⁴). Black body: perfect absorber and emitter (ε = 1). Newton's Law of Cooling: rate of cooling ∝ excess temperature above surroundings.
Specific Heat Capacity: Q = mcΔT
c_water = 4186 J/(kg·K) = 1 cal/(g·°C) [highest among common liquids]
c_ice = 2090 J/(kg·K), c_steam = 2010 J/(kg·K)
Latent Heat: Q = mL (no temperature change during phase transition)
Latent heat of fusion of ice: L_f = 80 cal/g = 3.35 × 10⁵ J/kg
Latent heat of vaporisation of water: L_v = 540 cal/g = 2.26 × 10⁶ J/kg
(Steam has more energy than water at 100°C — hence steam burns are worse)
Laws of Thermodynamics
Zeroth Law: If A is in thermal equilibrium with C, and B is in equilibrium
with C, then A and B are in thermal equilibrium with each other.
(Basis of temperature measurement)
First Law: ΔU = Q − W
(Energy is conserved: heat added − work done by system = change in internal energy)
Second Law: Heat flows spontaneously from hot to cold body only.
Entropy of the universe always increases (Clausius).
No heat engine can convert all heat to work (Kelvin-Planck).
Carnot Engine Efficiency: η = 1 − T_cold/T_hot = (T_hot − T_cold)/T_hot
(Maximum possible efficiency; real engines are always less efficient)
8. Waves and Sound
A wave is a disturbance that transfers energy without transferring matter. Mechanical waves require a medium (sound); electromagnetic waves do not (light).
Classification
Transverse waves: Particles vibrate perpendicular to wave direction (light, electromagnetic, waves on a string, S-waves in earthquakes).
Longitudinal waves: Particles vibrate parallel to wave direction — compressions and rarefactions (sound, P-waves in earthquakes, spring oscillations).
Longitudinal waves: Particles vibrate parallel to wave direction — compressions and rarefactions (sound, P-waves in earthquakes, spring oscillations).
Wave equation: v = fλ (v = wave speed, f = frequency, λ = wavelength)
Period: T = 1/f
Angular frequency: ω = 2πf
Wave number: k = 2π/λ
Speed of sound in a medium: v = √(E/ρ)
(E = elastic modulus, ρ = density)
In air (at 0°C): ~331 m/s; at 25°C: ~346 m/s
In water: ~1480 m/s (denser + more elastic)
In steel: ~5100 m/s (very high elasticity)
Sound speed increases with temperature: v ∝ √T
Properties of Sound
Pitch: Perceived frequency — higher frequency = higher pitch. Loudness: Depends on amplitude and measured in decibels (dB). Quality/Timbre: Depends on the waveform shape — distinguishes same note on different instruments.
Important Sound Phenomena
Echo: Reflection of sound heard distinctly after original. Minimum distance from reflecting surface = 17 m (sound travels 34 m in 0.1 s — minimum time the human ear needs to distinguish the echo from the original sound at 340 m/s).
Resonance: When the natural frequency of a body matches the driving frequency — large amplitude oscillations. Examples: Tacoma Narrows Bridge collapse, shattering a glass with the right sound frequency, tuning of radio/TV receivers.
Beats: When two sounds of slightly different frequencies (f₁ and f₂) are heard simultaneously, the intensity waxes and wanes at a rate equal to |f₁ − f₂|. Beat frequency = |f₁ − f₂|. Used for tuning musical instruments.
Doppler Effect: Apparent change in frequency when source or observer moves. If source approaches observer: apparent frequency increases (blue shift). If source moves away: frequency decreases (red shift). Applications: RADAR speed guns, sonar, medical ultrasound, astronomy (measuring speed of stars).
Resonance: When the natural frequency of a body matches the driving frequency — large amplitude oscillations. Examples: Tacoma Narrows Bridge collapse, shattering a glass with the right sound frequency, tuning of radio/TV receivers.
Beats: When two sounds of slightly different frequencies (f₁ and f₂) are heard simultaneously, the intensity waxes and wanes at a rate equal to |f₁ − f₂|. Beat frequency = |f₁ − f₂|. Used for tuning musical instruments.
Doppler Effect: Apparent change in frequency when source or observer moves. If source approaches observer: apparent frequency increases (blue shift). If source moves away: frequency decreases (red shift). Applications: RADAR speed guns, sonar, medical ultrasound, astronomy (measuring speed of stars).
Doppler effect (source moving, observer stationary):
f' = f × [v / (v ± v_s)]
Use − when source approaches (f' > f)
Use + when source recedes (f' < f)
Beat frequency: f_beat = |f₁ − f₂|
Ultrasound and Infrasound
| Type | Frequency Range | Examples/Applications |
|---|---|---|
| Infrasound | <20 Hz | Earthquakes, volcanic eruptions, elephant communication, whales |
| Audible (Human) | 20 Hz – 20,000 Hz | Human speech (300–3000 Hz), music |
| Ultrasound | >20,000 Hz | Medical sonography (1–20 MHz), SONAR, bat echolocation (20–200 kHz), industrial cleaning, welding, NDT |
9. Light — Reflection
Laws of Reflection
1. The angle of incidence equals the angle of reflection (both measured from the normal). 2. The incident ray, reflected ray, and normal all lie in the same plane.
Plane Mirror
Image in a plane mirror: virtual, erect, same size as object, laterally inverted. Distance of image behind mirror = distance of object in front. If mirror rotates by angle θ, reflected ray rotates by 2θ. Number of images formed by two mirrors at angle θ = 360°/θ − 1 (when 360/θ is an integer).
Spherical Mirrors — Mirror Formula
Mirror Formula: 1/v + 1/u = 1/f = 2/R
Magnification: m = −v/u = h_image / h_object
Sign Convention (New Cartesian):
Distance measured from pole (centre of mirror)
Along incident ray direction = positive
Against incident ray direction = negative
Heights above principal axis = positive, below = negative
For concave mirror: f is negative (−), R is negative
For convex mirror: f is positive (+), R is positive
Image Formation by Concave Mirror
| Object Position | Image Position | Nature | Size | Use |
|---|---|---|---|---|
| At infinity | At F | Real, inverted | Point-sized | Solar furnace |
| Beyond C (u>2f) | Between F and C | Real, inverted | Diminished | — |
| At C (u=2f) | At C | Real, inverted | Same size | — |
| Between F and C | Beyond C | Real, inverted | Magnified | Projectors |
| At F | At infinity | Real, inverted | Highly enlarged | Search lights |
| Between F and P (u<f) | Behind mirror | Virtual, erect | Magnified | Shaving/makeup mirror |
Convex mirror: Always forms a virtual, erect, diminished image for any real object position. Used as rear-view mirrors in vehicles (wide field of view).
🎯 BPSC Key: Concave mirror uses: torch/headlights (object at F), shaving/dentist's mirror (object between F and P). Convex mirror uses: rear-view mirrors, security mirrors in shops. Concave mirror is converging; convex is diverging.
10. Light — Refraction, Lenses & Optical Instruments
Refraction and Snell's Law
Snell's Law: n₁ sinθ₁ = n₂ sinθ₂
Refractive index: n = c/v = sin(θ_i)/sin(θ_r)
(where c = speed of light in vacuum = 3×10⁸ m/s, v = speed in medium)
n_glass ≈ 1.5, n_water ≈ 1.33, n_diamond ≈ 2.42, n_air ≈ 1.0003
Total Internal Reflection (TIR): occurs when light goes from denser to rarer
medium AND angle of incidence > critical angle (C)
sin C = 1/n (n = refractive index of denser medium w.r.t. rarer)
For glass: C ≈ 42°; For diamond: C ≈ 24° (very small → brilliant sparkle)
For water: C ≈ 49°
Applications of TIR: optical fibre cables (telecommunications, endoscopy), mirage (hot air near road surface — total internal reflection of sky light), sparkling of diamonds, prism binoculars.
Lenses — Lens Formula
Lens Formula: 1/v − 1/u = 1/f
Power: P = 1/f [unit: dioptre D, when f is in metres]
Convex lens: f positive, P positive
Concave lens: f negative, P negative
Magnification: m = v/u
Lens Maker's Formula: 1/f = (n−1)[1/R₁ − 1/R₂]
Combination of lenses (thin lenses in contact):
1/f = 1/f₁ + 1/f₂ + ... or P = P₁ + P₂ + ...
Human Eye and Defects of Vision
| Defect | Problem | Cause | Correction |
|---|---|---|---|
| Myopia (near-sightedness) | Cannot see distant objects | Image forms in front of retina; eyeball too long or lens too converging | Concave (diverging) lens |
| Hypermetropia (far-sightedness) | Cannot see near objects | Image forms behind retina; eyeball too short or lens too weak | Convex (converging) lens |
| Presbyopia | Cannot focus both near and far (age-related) | Loss of accommodation due to hardening of lens | Bifocal lens |
| Astigmatism | Blurred/distorted vision | Non-spherical cornea — different focal lengths in different planes | Cylindrical lens |
| Colour blindness | Cannot distinguish red/green | Absence of cone cells for those colours (genetic, X-linked) | No optical correction |
Normal near point of human eye = 25 cm (least distance of distinct vision). Far point = infinity (for normal eye).
Optical Instruments
Simple Microscope (Magnifier): A single convex lens. Object placed within focal length. M = 1 + D/f (D = 25 cm, near point). Image is virtual, erect, magnified.
Compound Microscope: Two convex lenses (objective + eyepiece). Objective has very short focal length; forms real, magnified, inverted image. Eyepiece acts as magnifier for this image. Net magnification M = m_o × m_e.
Astronomical Telescope (Normal Adjustment): Objective has large focal length and aperture; eyepiece has short focal length. M = f_o/f_e. Image is virtual, inverted, at infinity. Large aperture → more light gathered → fainter stars visible.
Compound Microscope: Two convex lenses (objective + eyepiece). Objective has very short focal length; forms real, magnified, inverted image. Eyepiece acts as magnifier for this image. Net magnification M = m_o × m_e.
Astronomical Telescope (Normal Adjustment): Objective has large focal length and aperture; eyepiece has short focal length. M = f_o/f_e. Image is virtual, inverted, at infinity. Large aperture → more light gathered → fainter stars visible.
11. Dispersion and Scattering of Light
Dispersion
When white light passes through a glass prism, it splits into its constituent colours — VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red). This is dispersion. It occurs because different colours have different refractive indices in the glass — violet light is deviated most (highest refractive index, shortest wavelength) and red is deviated least (lowest refractive index, longest wavelength).
Dispersion is the phenomenon of splitting of white light into its component colours on passing through a medium with wavelength-dependent refractive index. The collection of colours is called a spectrum.
Rainbow: Formed when sunlight enters raindrops (refraction + dispersion + total internal reflection + refraction). Primary rainbow: red on outside, violet inside. Secondary rainbow (fainter, reversed colours): formed by two internal reflections inside droplet.
Scattering of Light (Rayleigh Scattering)
Rayleigh's Law: Intensity of scattered light ∝ 1/λ⁴. Shorter wavelengths scatter much more than longer wavelengths.
Blue Sky: Nitrogen and oxygen molecules in the atmosphere scatter blue light (shorter wavelength, λ ≈ 450 nm) about 5–6 times more than red light (λ ≈ 650 nm). So sky appears blue.
Red Sunrise/Sunset: At sunrise/sunset, sunlight travels through a much thicker layer of atmosphere to reach the observer. Blue light is scattered away; only the longer-wavelength red and orange light reaches our eyes.
White Clouds: Water droplets in clouds are much larger than light wavelengths — they scatter all wavelengths equally (Mie scattering), so clouds appear white.
Danger signals are red: Red light scatters least — can be seen from greater distances even in fog or rain.
Blue Sky: Nitrogen and oxygen molecules in the atmosphere scatter blue light (shorter wavelength, λ ≈ 450 nm) about 5–6 times more than red light (λ ≈ 650 nm). So sky appears blue.
Red Sunrise/Sunset: At sunrise/sunset, sunlight travels through a much thicker layer of atmosphere to reach the observer. Blue light is scattered away; only the longer-wavelength red and orange light reaches our eyes.
White Clouds: Water droplets in clouds are much larger than light wavelengths — they scatter all wavelengths equally (Mie scattering), so clouds appear white.
Danger signals are red: Red light scatters least — can be seen from greater distances even in fog or rain.
12. Electricity & Magnetism
Electrostatics
Coulomb's Law: F = k q₁q₂ / r²
k = 1/(4πε₀) = 9 × 10⁹ N m² C⁻²
ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²
Electric Field: E = F/q = kq/r² [unit: N/C or V/m]
Electric Potential: V = W/q = kq/r [unit: volt V = J/C]
Potential Energy: U = kq₁q₂/r
Capacitance: C = Q/V [unit: farad F]
Energy stored: U = ½CV² = Q²/2C
Series combination: 1/C = 1/C₁ + 1/C₂ + ... (C_eff < smallest)
Parallel combination: C = C₁ + C₂ + ... (C_eff > largest)
Current Electricity
Ohm's Law: V = IR (R = resistance, V = voltage, I = current)
Resistance: R = ρL/A (ρ = resistivity, L = length, A = cross-section)
Temperature dependence: R_T = R₀(1 + αT)
(resistance of metals increases with temperature;
semiconductors and electrolytes: resistance decreases with temperature)
Series connection: R_eff = R₁ + R₂ + R₃ + ...
(same current through all; voltages add)
Parallel connection: 1/R_eff = 1/R₁ + 1/R₂ + 1/R₃ + ...
(same voltage across all; currents add; R_eff < smallest)
Kirchhoff's Current Law (KCL): ΣI_in = ΣI_out at any junction
Kirchhoff's Voltage Law (KVL): ΣV = 0 around any closed loop
Heating Effect (Joule's Law): H = I²Rt = V²t/R = VIt
Power: P = VI = I²R = V²/R [unit: watt W]
Electrical energy: E = Pt = VIt [unit: J; commercial unit: kWh]
1 kWh = 3.6 × 10⁶ J (1 unit on electricity bill)
🎯 BPSC Fact: In a series circuit, the element with highest resistance dissipates most power. In a parallel circuit, the element with lowest resistance dissipates most power. Fuse wire has high resistivity and low melting point — placed in series; melts when current exceeds safe value, breaking the circuit.
Magnetism
Like magnetic poles repel, unlike poles attract. Earth behaves as a huge bar magnet with its magnetic south pole near the geographic North Pole (so that a compass needle's north points geographically north). Magnetic field lines emerge from N and enter S pole; never intersect; closer together where field is stronger.
Oersted (1820) discovered that a current-carrying conductor produces a magnetic field around it. Ampere established that every magnetic phenomenon is due to moving electric charges. The force on a current-carrying conductor in a magnetic field: F = BIL sinθ (Fleming's left-hand rule: thumb = force, index = field, middle = current). Electric motor uses this principle.
13. Electromagnetic Induction
Faraday's Law: EMF = −dΦ/dt (Φ = magnetic flux = BAcosθ)
Magnitude: EMF = N × ΔΦ/Δt (N = number of turns)
Lenz's Law: The induced current is in a direction such that it opposes the
change in magnetic flux that caused it (consequence of conservation of energy)
Self-Inductance: EMF = −L × dI/dt (L = self-inductance, unit: henry H)
Mutual Inductance: EMF₂ = −M × dI₁/dt (M = mutual inductance)
Transformer (ideal):
V_s/V_p = N_s/N_p = I_p/I_s
Step-up: N_s > N_p → V_s > V_p (high voltage, low current — used in power transmission)
Step-down: N_s < N_p → V_s < V_p (household supply)
Efficiency: η = P_output/P_input × 100%
AC Generator: EMF = NBAω sin(ωt) = E₀ sin(ωt)
Peak EMF: E₀ = NBAω
RMS values: V_rms = V₀/√2 ≈ 0.707 V₀ ; I_rms = I₀/√2
Power: P = V_rms × I_rms × cosφ (φ = phase difference)
14. Electromagnetic Spectrum
All electromagnetic waves travel at the speed of light in vacuum (c = 3×10⁸ m/s) and obey c = fλ. They differ only in wavelength and frequency. The complete range is called the electromagnetic spectrum.
| Type | Wavelength | Frequency (Hz) | Source | Uses |
|---|---|---|---|---|
| Gamma Rays (γ) | <0.01 nm | >3×10¹⁹ | Nuclear decay, supernovae | Cancer radiotherapy (γ-knife), sterilisation of food/instruments, nuclear medicine (PET scan) |
| X-Rays | 0.01–10 nm | 3×10¹⁶–3×10¹⁹ | X-ray tubes (decelerated electrons) | Medical imaging (bone fractures), airport security, crystallography (DNA structure by X-ray diffraction) |
| Ultraviolet (UV) | 10–400 nm | 7.5×10¹⁴–3×10¹⁶ | Sun, UV lamps, mercury vapour lamp | Germicidal lamps (kills bacteria), sterilisation of water, phototherapy, fluorescence, detecting counterfeit notes, vitamin D synthesis in skin |
| Visible Light | 400–700 nm | 4.3–7.5×10¹⁴ | Sun, incandescent/LED/fluorescent lamps | Vision, photography, optical instruments |
| Infrared (IR) | 700 nm–1 mm | 3×10¹¹–4.3×10¹⁴ | Hot objects, IR LEDs, sun | Thermal imaging (night vision), remote controls, heat therapy, cooking (IR oven), greenhouse effect, fibre-optic communication |
| Microwaves | 1 mm–30 cm | 10⁹–3×10¹¹ | Magnetron, Klystron tube | Microwave cooking (water molecule resonance at 2.45 GHz), RADAR (aircraft/ship detection), satellite communication, mobile telephony (3G/4G) |
| Radio Waves | >30 cm | <10⁹ | Oscillating electric circuits/antenna | AM radio (0.5–1.7 MHz), FM radio (88–108 MHz), TV, long-distance communication (ionospheric reflection for AM), Wi-Fi, Bluetooth |
🎯 BPSC Fact: Going from radio → gamma: wavelength decreases, frequency and energy increase. Ozone layer absorbs harmful UV from the Sun. Greenhouse gases absorb IR (Earth's emitted radiation), causing global warming. Microwaves and radio waves both penetrate clouds — used in satellite communication.
15. Modern Physics
Photoelectric Effect and Quantum Nature of Light
Einstein's Photoelectric Equation:
hν = φ + KE_max = hν₀ + ½mv²_max
φ = Work function = hν₀ (minimum energy to eject electron)
ν₀ = Threshold frequency (below which no emission however intense the light)
h = Planck's constant = 6.626 × 10⁻³⁴ J·s
Photon Energy: E = hν = hc/λ
de Broglie Wavelength (wave-particle duality): λ = h/mv = h/p
(particles have wave-like properties; electrons in atom behave as standing waves)
Bohr's Atomic Model (for hydrogen-like atoms)
Radius of nth orbit: rₙ = 0.529 × n² Å = 0.529 × n² × 10⁻¹⁰ m
(r₁ = 0.529 Å for n=1 — Bohr radius)
Energy of nth level: Eₙ = −13.6/n² eV
(E₁ = −13.6 eV, E₂ = −3.4 eV, E₃ = −1.51 eV, E∞ = 0 — ionised)
Negative energy → electron bound to nucleus
Spectral series (hydrogen):
Lyman series: transitions to n=1 (UV region)
Balmer series: transitions to n=2 (visible — H_α at 656 nm red)
Paschen series: transitions to n=3 (IR)
Brackett series: to n=4 (IR)
Pfund series: to n=5 (far IR)
Radioactivity
α decay: Nucleus emits α particle (₂⁴He nucleus — 2 protons + 2 neutrons). Mass number decreases by 4, atomic number decreases by 2. Example: ²³⁸U → ²³⁴Th + ⁴He. Alpha particles are stopped by a sheet of paper or skin; dangerous if ingested.
β decay: Neutron converts to proton (β⁻: emits electron and antineutrino) OR proton converts to neutron (β⁺: emits positron and neutrino). Mass number unchanged; atomic number changes by ±1. Beta particles stopped by a few mm of aluminium.
γ decay: Nucleus in excited state releases energy as γ photons (no change in A or Z). Gamma rays are most penetrating — need several cm of lead or meters of concrete to stop.
β decay: Neutron converts to proton (β⁻: emits electron and antineutrino) OR proton converts to neutron (β⁺: emits positron and neutrino). Mass number unchanged; atomic number changes by ±1. Beta particles stopped by a few mm of aluminium.
γ decay: Nucleus in excited state releases energy as γ photons (no change in A or Z). Gamma rays are most penetrating — need several cm of lead or meters of concrete to stop.
Radioactive Decay Law: N = N₀ × e^(−λt) = N₀ × (½)^(t/T₁/₂)
Half-life: T₁/₂ = 0.693/λ
(λ = decay constant; T₁/₂ = time for half the nuclei to decay)
After n half-lives: N = N₀/2ⁿ ; Activity A = A₀/2ⁿ
Important half-lives:
C-14: 5730 years (radiocarbon dating of organic material)
U-238: 4.5 × 10⁹ years (geological dating)
Ra-226: 1600 years (used in early cancer treatment)
I-131: 8 days (thyroid disorders treatment)
Nuclear Fission and Fusion
Nuclear Fission:
²³⁵₉₂U + ¹₀n → ⁹⁴₃₆Kr + ¹³⁹₅₆Ba + 3¹₀n + ~200 MeV energy
(1 atomic mass unit = 931.5 MeV)
Chain reaction: 3 neutrons released → each can cause more fissions
Critical mass: minimum mass for sustained chain reaction (U-235 ≈ 52 kg unmoderated)
Nuclear Fusion:
²₁H + ³₁H → ⁴₂He + ¹₀n + 17.6 MeV
(Deuterium + Tritium → Helium + neutron + energy)
Powers the Sun; hydrogen bomb; ITER (International Thermonuclear Experimental Reactor)
Energy per kg of fuel: Fusion >> Fission >> Chemical
🎯 BPSC Comparison — Fission vs Fusion: Fission: heavy nucleus (U-235, Pu-239) splits; requires critical mass; produces radioactive waste; used in current nuclear reactors and atomic bomb. Fusion: light nuclei (H isotopes) merge; requires extremely high temperature (≈10⁷ K); produces less radioactive waste; powers stars and H-bomb; not yet achieved commercially.
Chemistry
1. Matter & Classification
States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite | Indefinite (takes container shape) | Indefinite |
| Volume | Definite | Definite | Indefinite |
| Compressibility | Negligible | Very low | High |
| Intermolecular force | Very strong | Moderate | Very weak |
| Particle arrangement | Close-packed, ordered | Close but disordered | Far apart, random |
| Kinetic energy | Lowest | Intermediate | Highest |
| Diffusion | Negligible | Slow | Rapid |
Physical vs Chemical Change
Physical Change: No new substance formed; original substance recoverable. Change in physical state or shape. Examples: melting, freezing, dissolving sugar in water, cutting paper, boiling water.
Chemical Change: New substances formed with different properties; generally irreversible. Energy change occurs. Examples: burning wood, rusting iron, cooking food, milk souring, photosynthesis, neutralisation.
Chemical Change: New substances formed with different properties; generally irreversible. Energy change occurs. Examples: burning wood, rusting iron, cooking food, milk souring, photosynthesis, neutralisation.
Laws of Chemical Combination
| Law | Scientist | Statement |
|---|---|---|
| Law of Conservation of Mass | Lavoisier (1774) | Mass of reactants = mass of products in a chemical reaction (matter is neither created nor destroyed) |
| Law of Definite Proportions | Proust (1799) | A pure chemical compound always contains the same elements combined in the same fixed proportion by mass |
| Law of Multiple Proportions | Dalton (1803) | When two elements combine to form more than one compound, masses of one element that combine with a fixed mass of the other are in simple whole-number ratios (e.g., CO and CO₂) |
| Gay-Lussac's Law of Volumes | Gay-Lussac (1808) | Gases react in volumes that bear simple whole-number ratios to each other and to volumes of gaseous products at same T and P |
| Avogadro's Law | Avogadro (1811) | Equal volumes of all gases under same temperature and pressure contain equal numbers of molecules |
2. Atomic Structure
Subatomic Particles
| Particle | Discoverer / Year | Charge | Mass | Location |
|---|---|---|---|---|
| Electron (e⁻) | J.J. Thomson, 1897 (cathode ray experiment) | −1.6×10⁻¹⁹ C (−1) | 9.11×10⁻³¹ kg ≈ 1/1836 u | Outside nucleus (orbitals) |
| Proton (p⁺) | Rutherford 1919 (Goldstein 1886 — canal rays) | +1.6×10⁻¹⁹ C (+1) | 1.67×10⁻²⁷ kg ≈ 1 u | Inside nucleus |
| Neutron (n⁰) | James Chadwick, 1932 | 0 (neutral) | 1.675×10⁻²⁷ kg ≈ 1 u | Inside nucleus |
Atomic Models — Evolution
Dalton's Atomic Theory (1803): Matter is made of indivisible, indestructible atoms. All atoms of an element are identical. Atoms of different elements have different masses. Atoms combine in simple whole-number ratios. Limitations: could not explain subatomic particles, isotopes, or isobars.
Thomson's Plum Pudding Model (1904): Atom is a sphere of positive charge with electrons (like plums) embedded in it. Explained electrical neutrality but could not explain Rutherford's results.
Rutherford's Nuclear Model (1911): Alpha particle scattering experiment with gold foil. Most alpha particles passed straight through → atom is mostly empty space. A few deflected at large angles → a tiny, massive, positively charged nucleus. Electrons revolve around the nucleus. Limitation: could not explain atomic stability (accelerating electron should radiate energy and spiral into nucleus) or atomic spectra.
Bohr's Model (1913): Electrons revolve in fixed circular orbits (shells: K, L, M, N...) without radiating energy. Energy is absorbed or emitted only when electrons jump between orbits. Explained hydrogen spectrum (line spectra). Limitation: could not explain spectra of multi-electron atoms or fine structure.
Quantum Numbers and Electron Configuration
Principal quantum number (n): Shell number (1, 2, 3...), determines energy and size. Maximum electrons in shell = 2n².
Azimuthal quantum number (l): Subshell (0, 1, 2, 3 → s, p, d, f). Determines orbital shape. l ranges from 0 to n−1.
Magnetic quantum number (m_l): Orientation of orbital in space. Ranges from −l to +l, giving (2l+1) orbitals in each subshell.
Spin quantum number (m_s): Electron spin, +½ or −½. Each orbital holds max 2 electrons (with opposite spins — Pauli exclusion principle).
Aufbau principle: Fill lowest energy subshells first. Energy order: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d...
Pauli Exclusion Principle: No two electrons in an atom can have the same set of all four quantum numbers.
Hund's Rule: In degenerate orbitals (same energy), electrons first occupy each orbital singly with parallel spins before pairing.
Azimuthal quantum number (l): Subshell (0, 1, 2, 3 → s, p, d, f). Determines orbital shape. l ranges from 0 to n−1.
Magnetic quantum number (m_l): Orientation of orbital in space. Ranges from −l to +l, giving (2l+1) orbitals in each subshell.
Spin quantum number (m_s): Electron spin, +½ or −½. Each orbital holds max 2 electrons (with opposite spins — Pauli exclusion principle).
Aufbau principle: Fill lowest energy subshells first. Energy order: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d...
Pauli Exclusion Principle: No two electrons in an atom can have the same set of all four quantum numbers.
Hund's Rule: In degenerate orbitals (same energy), electrons first occupy each orbital singly with parallel spins before pairing.
Isotopes, Isobars, Isotones
| Term | Same | Different | Examples |
|---|---|---|---|
| Isotopes | Atomic number (Z) — same element, same chemical properties | Mass number (A) — different number of neutrons | ¹H (protium), ²H (deuterium), ³H (tritium); ¹²C, ¹³C, ¹⁴C |
| Isobars | Mass number (A) | Atomic number (Z) — different elements | ⁴⁰Ca and ⁴⁰Ar; ¹⁴C and ¹⁴N |
| Isotones | Number of neutrons (N = A−Z) | Atomic number (Z) and Mass number (A) | ¹⁴C (N=8) and ¹⁵N (N=8); ³H and ⁴He |
3. Periodic Table
Historical Development
Döbereiner's Triads (1829): Groups of three elements with similar properties where the atomic weight of the middle element ≈ average of the other two. (Li-Na-K, Ca-Sr-Ba, Cl-Br-I). Too few triads to be general.
Newlands' Law of Octaves (1866): When arranged in increasing atomic weight, every eighth element has properties similar to the first. Failed for heavier elements.
Mendeleev's Periodic Law (1869): Properties of elements are periodic functions of their atomic weights. Left gaps for undiscovered elements — correctly predicted Gallium (eka-aluminium) and Germanium (eka-silicon). Limitation: could not explain position of hydrogen, isotopes, or anomalous pairs (Ar/K, Co/Ni, Te/I).
Modern Periodic Law (Moseley, 1913): Properties of elements are periodic functions of their atomic numbers (nuclear charge). Resolved all anomalies of Mendeleev's table.
Newlands' Law of Octaves (1866): When arranged in increasing atomic weight, every eighth element has properties similar to the first. Failed for heavier elements.
Mendeleev's Periodic Law (1869): Properties of elements are periodic functions of their atomic weights. Left gaps for undiscovered elements — correctly predicted Gallium (eka-aluminium) and Germanium (eka-silicon). Limitation: could not explain position of hydrogen, isotopes, or anomalous pairs (Ar/K, Co/Ni, Te/I).
Modern Periodic Law (Moseley, 1913): Properties of elements are periodic functions of their atomic numbers (nuclear charge). Resolved all anomalies of Mendeleev's table.
Structure of the Modern Periodic Table
The modern periodic table has 7 periods (horizontal rows) and 18 groups (vertical columns). Elements in the same group have the same number of valence electrons and similar chemical properties.
| Block | Groups | Filling Orbital | Notable Members |
|---|---|---|---|
| s-block | 1 and 2 | s orbital (1–2 electrons) | Alkali metals (Group 1: Li, Na, K, Rb, Cs, Fr), Alkaline earth metals (Group 2: Be, Mg, Ca, Sr, Ba, Ra); H and He also s-block |
| p-block | 13–18 | p orbital (1–6 electrons) | Non-metals, metalloids, noble gases; includes halogens (Group 17), noble gases (Group 18) |
| d-block | 3–12 | d orbital (1–10 electrons) | Transition metals: Fe, Cu, Zn, Mn, Cr, Ni, Co, Ti, V, Mo, W; variable valency, coloured compounds, catalytic activity |
| f-block | — (inner transition) | f orbital (1–14 electrons) | Lanthanides (Ce-Lu) and Actinides (Th-Lr); all actinides are radioactive |
Periodic Trends
Atomic Radius: Decreases left→right across period (increasing nuclear charge pulls electrons closer); increases top→bottom in group (new shells added). Na > Mg > Al > Si > P > S > Cl > Ar (across period 3).
Ionisation Energy (IE): Energy needed to remove the outermost electron. Increases left→right (electron harder to remove as nuclear charge increases, radius decreases). Decreases top→bottom (electron farther from nucleus, shielded by inner shells). Noble gases have highest IE; alkali metals have lowest IE. Exception: IE(N) > IE(O) because N has half-filled 2p (extra stability).
Electron Affinity: Energy released when an electron is added. Generally increases (more exothermic) left→right. Halogens have highest electron affinity (Cl highest, not F — F too small, strong repulsion). Noble gases have nearly zero (stable configuration).
Electronegativity (Pauling Scale): Tendency to attract bonding electrons. F = 4.0 (highest); Cs = 0.7 (lowest); O = 3.5; N = 3.0; Cl = 3.0; H = 2.1; C = 2.5. Increases across period, decreases down group.
Ionisation Energy (IE): Energy needed to remove the outermost electron. Increases left→right (electron harder to remove as nuclear charge increases, radius decreases). Decreases top→bottom (electron farther from nucleus, shielded by inner shells). Noble gases have highest IE; alkali metals have lowest IE. Exception: IE(N) > IE(O) because N has half-filled 2p (extra stability).
Electron Affinity: Energy released when an electron is added. Generally increases (more exothermic) left→right. Halogens have highest electron affinity (Cl highest, not F — F too small, strong repulsion). Noble gases have nearly zero (stable configuration).
Electronegativity (Pauling Scale): Tendency to attract bonding electrons. F = 4.0 (highest); Cs = 0.7 (lowest); O = 3.5; N = 3.0; Cl = 3.0; H = 2.1; C = 2.5. Increases across period, decreases down group.
4. Chemical Bonding
Types of Bonds
| Bond Type | Formation | Examples | Properties |
|---|---|---|---|
| Ionic (electrovalent) | Complete electron transfer from metal to non-metal (electronegativity difference >1.7) | NaCl, MgO, CaF₂, KBr, Al₂O₃ | High MP/BP, crystalline solid, brittle, conducts electricity when molten or dissolved, not in solid state |
| Covalent | Electron sharing between non-metals (electronegative atoms) | H₂, O₂, N₂, CO₂, H₂O, CH₄, NH₃, HCl | Low MP/BP, usually non-conductor (except graphite), can be solid/liquid/gas |
| Polar Covalent | Unequal electron sharing (partial charges δ+/δ−) | HCl, H₂O, NH₃, HF | Soluble in polar solvents; possess dipole moment |
| Metallic | Sea of delocalised electrons in lattice of positive ions | Na, Cu, Fe, Al, Au | Electrical and thermal conductivity, malleability, ductility, lustre, high MP (W), low MP (Hg liquid) |
| Hydrogen Bond | Electrostatic attraction between H (bonded to F, O, or N) and lone pair on F, O, or N | H₂O, HF, NH₃, DNA double helix, proteins | Responsible for anomalously high BP of H₂O, HF; ice less dense than water; protein secondary structure |
VSEPR Theory — Molecular Shapes
| Molecule | Central Atom | BP | LP | Shape | Bond Angle |
|---|---|---|---|---|---|
| BeCl₂, CO₂ | Be, C | 2 | 0 | Linear | 180° |
| BF₃, AlCl₃ | B, Al | 3 | 0 | Trigonal planar | 120° |
| CH₄, CCl₄, NH₄⁺ | C, N | 4 | 0 | Tetrahedral | 109.5° |
| NH₃, PCl₃ | N | 3 | 1 | Trigonal pyramidal | 107° |
| H₂O, H₂S | O | 2 | 2 | V-shaped (bent) | 104.5° |
| PCl₅ | P | 5 | 0 | Trigonal bipyramidal | 90°/120° |
| SF₆ | S | 6 | 0 | Octahedral | 90° |
5. Acids, Bases and Salts
Concepts of Acids and Bases
Arrhenius Concept: Acid produces H⁺ (or H₃O⁺) in water; base produces OH⁻. Limitation: applies only to aqueous solutions.
Brønsted-Lowry Concept: Acid = proton (H⁺) donor; Base = proton acceptor. Conjugate acid-base pairs. Applies to non-aqueous systems also. NH₃ acts as base (accepts H⁺); HCl acts as acid (donates H⁺).
Lewis Concept (broadest): Acid = electron-pair acceptor (e.g., BF₃, AlCl₃, Fe³⁺); Base = electron-pair donor (e.g., NH₃, H₂O, F⁻). Explains reactions where no proton transfer occurs.
Brønsted-Lowry Concept: Acid = proton (H⁺) donor; Base = proton acceptor. Conjugate acid-base pairs. Applies to non-aqueous systems also. NH₃ acts as base (accepts H⁺); HCl acts as acid (donates H⁺).
Lewis Concept (broadest): Acid = electron-pair acceptor (e.g., BF₃, AlCl₃, Fe³⁺); Base = electron-pair donor (e.g., NH₃, H₂O, F⁻). Explains reactions where no proton transfer occurs.
pH Scale
pH = −log₁₀[H⁺] (concentration of hydrogen ions)
pOH = −log₁₀[OH⁻]
pH + pOH = 14 (at 25°C)
pH 0-6.9 = acidic; pH 7 = neutral; pH 7.1-14 = basic/alkaline
Strong acids (fully ionise): HCl, H₂SO₄, HNO₃, HClO₄, HBr, HI
Weak acids (partially ionise): CH₃COOH, H₂CO₃, H₃PO₄, HF
Strong bases: NaOH, KOH, Ca(OH)₂, Ba(OH)₂
Weak bases: NH₄OH, Mg(OH)₂
Important Acids
| Acid | Formula | Common Name | Key Uses/Notes |
|---|---|---|---|
| Hydrochloric acid | HCl | Muriatic acid | Digestive system (gastric juice, 0.1M HCl), metal pickling, chemical synthesis; pH of stomach ≈ 1.5–2 |
| Sulphuric acid | H₂SO₄ | King of Chemicals / Oil of vitriol | Fertilisers (superphosphate), car batteries, petroleum refining, dyes; concentrated H₂SO₄ is hygroscopic and oxidising |
| Nitric acid | HNO₃ | Aqua fortis | Fertilisers (ammonium nitrate), explosives (TNT, RDX, nitroglycerin), Aqua regia (HNO₃ + 3HCl — dissolves gold and platinum) |
| Acetic acid | CH₃COOH | Ethanoic acid / Vinegar | Vinegar (5–8% solution), food preservative, making plastics, pharmaceuticals; freezes at 16.6°C (glacial acetic acid) |
| Carbonic acid | H₂CO₃ | — | Formed when CO₂ dissolves in water; responsible for carbonation of drinks; dissolved in rain (pH ≈ 5.6 — slightly acidic) |
| Phosphoric acid | H₃PO₄ | Orthophosphoric acid | Fertilisers, food additive (cola drinks — pH ≈ 2.5), rust removal, dental cements |
| Tartaric acid | C₄H₆O₆ | — | Baking powder (with NaHCO₃), wine, tamarind, cream of tartar |
| Citric acid | C₆H₈O₇ | — | Citrus fruits, food preservative, cleaning agent (descaler) |
Indicators
| Indicator | In Acid | At Neutral | In Base | Range |
|---|---|---|---|---|
| Litmus (natural — from lichens) | Red | Purple | Blue | pH 4.5–8.3 |
| Phenolphthalein (synthetic) | Colourless | Colourless | Pink/Magenta | pH 8.2–10 |
| Methyl orange (synthetic) | Red | Orange | Yellow | pH 3.1–4.4 |
| Universal indicator | Red | Green | Violet | Full pH range |
6. Redox Reactions and Electrochemistry
Oxidation: Loss of electrons; increase in oxidation number; gain of oxygen; loss of hydrogen. Reduction: Gain of electrons; decrease in oxidation number; loss of oxygen; gain of hydrogen. These always occur together (redox).
Rules for Oxidation Number: Pure element = 0; Monatomic ion = charge; H = +1 (usually; −1 in metal hydrides like NaH); O = −2 (usually; −1 in peroxides H₂O₂, Na₂O₂; −½ in superoxides; 0 in O₂; +2 in OF₂); F = −1 always; sum of oxidation numbers = 0 for neutral compound; = charge for polyatomic ion.
🎯 Electrochemical Activity Series (Reactivity Series) — BPSC Essential:
K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Pt > Au
Metals above H: displace H₂ from dilute acids. Metals above each other: displace lower metals from their salt solutions. More reactive metal undergoes oxidation (anode in a cell). Gold and platinum do not react with any single acid — only aqua regia (1:3 HNO₃:HCl) dissolves them.
K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Pt > Au
Metals above H: displace H₂ from dilute acids. Metals above each other: displace lower metals from their salt solutions. More reactive metal undergoes oxidation (anode in a cell). Gold and platinum do not react with any single acid — only aqua regia (1:3 HNO₃:HCl) dissolves them.
Electrochemical Cells
Galvanic/Voltaic Cell (Daniel Cell — Zn-Cu): Zn rod in ZnSO₄ solution (anode compartment) + Cu rod in CuSO₄ solution (cathode compartment) + salt bridge (KNO₃ or KCl in agar — maintains electrical neutrality).
Anode (−): Zn → Zn²⁺ + 2e⁻ (oxidation) [negative electrode in galvanic cell]
Cathode (+): Cu²⁺ + 2e⁻ → Cu (reduction) [positive electrode]
EMF ≈ 1.1 V. Converts chemical energy to electrical energy.
Electrolytic Cell: External electric source drives non-spontaneous reaction. Anode connected to positive terminal of battery (oxidation). Cathode connected to negative terminal (reduction). Applications: electroplating (coating base metal with precious metal), electrolysis of water (2H₂O → 2H₂ + O₂), refining of copper, Hall-Héroult process for aluminium extraction.
Anode (−): Zn → Zn²⁺ + 2e⁻ (oxidation) [negative electrode in galvanic cell]
Cathode (+): Cu²⁺ + 2e⁻ → Cu (reduction) [positive electrode]
EMF ≈ 1.1 V. Converts chemical energy to electrical energy.
Electrolytic Cell: External electric source drives non-spontaneous reaction. Anode connected to positive terminal of battery (oxidation). Cathode connected to negative terminal (reduction). Applications: electroplating (coating base metal with precious metal), electrolysis of water (2H₂O → 2H₂ + O₂), refining of copper, Hall-Héroult process for aluminium extraction.
Faraday's First Law: m = ZQ = ZIt
(m = mass deposited, Z = electrochemical equivalent, Q = charge, I = current, t = time)
Faraday's Second Law: masses deposited by same charge ∝ equivalent weights
m₁/m₂ = E₁/E₂ (E = atomic mass / valency)
Faraday constant: F = 96,485 C/mol ≈ 96,500 C/mol
(charge of 1 mole of electrons)
7. Important Chemical Compounds
| Common Name | Chemical Name | Formula | Key Uses / Notes |
|---|---|---|---|
| Common salt / Table salt | Sodium chloride | NaCl | Food seasoning, food preservation, raw material for Na, Cl₂, NaOH; maintained blood osmolarity |
| Caustic soda / Lye | Sodium hydroxide | NaOH | Soap and detergent manufacture, paper industry, textile (mercerising cotton), petroleum refining |
| Washing soda | Sodium carbonate decahydrate | Na₂CO₃·10H₂O | Laundering, softening hard water, glass, paper; loses water on heating (efflorescence) → Na₂CO₃ (anhydrous, soda ash) |
| Baking soda | Sodium bicarbonate | NaHCO₃ | Baking (releases CO₂ when heated: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂), antacid (neutralises stomach acid), fire extinguisher (CO₂ gas), soda-acid fire extinguisher |
| Quick lime / Burnt lime | Calcium oxide | CaO | Cement manufacture, glass, bleaching powder, removing acidity from soil; slakes violently with water: CaO + H₂O → Ca(OH)₂ + heat |
| Slaked lime / Hydrated lime | Calcium hydroxide | Ca(OH)₂ | Whitewash (dilute suspension = milk of lime), mortar (Ca(OH)₂ + CO₂ → CaCO₃), water treatment, making bleaching powder, cement |
| Limestone / Chalk / Marble | Calcium carbonate | CaCO₃ | Construction, lime kiln (CaCO₃ → CaO + CO₂ above 840°C), antacid tablets, blackboard chalk, marble — metamorphic rock; forms stalactites/stalagmites |
| Bleaching powder / Chloride of lime | Calcium hypochlorite chloride | Ca(OCl)Cl | Bleaching cotton, linen, wood pulp; water disinfection; made by passing Cl₂ over slaked lime; bleaching due to nascent oxygen: Ca(OCl)Cl + H₂O → CaCl₂ + 2[O] + H₂O |
| Plaster of Paris | Calcium sulphate hemihydrate | CaSO₄·½H₂O | Orthopaedic casts, statues, dentistry, chalk board (gypsum board), fire-resistant structures; made by heating gypsum (CaSO₄·2H₂O) at 120–130°C; hardens by reabsorbing water |
| Alum / Fitkari | Potassium aluminium sulphate | KAl(SO₄)₂·12H₂O | Water purification (coagulant — Al³⁺ makes colloidal impurities coagulate), mordant in dyeing, styptic pencil (stops bleeding), baking powder |
| Green vitriol | Ferrous sulphate heptahydrate | FeSO₄·7H₂O | Making inks, fertiliser, reducing agent; turns reddish-brown on oxidation (Fe²⁺→ Fe³⁺) |
| Blue vitriol | Copper sulphate pentahydrate | CuSO₄·5H₂O | Bordeaux mixture (fungicide for grapes/potatoes), electroplating, analytical reagent; loses water on heating → white anhydrous CuSO₄ (used as water test) |
| White vitriol | Zinc sulphate heptahydrate | ZnSO₄·7H₂O | Fertiliser (zinc micronutrient), eye drops, medicine |
| Potassium permanganate / Lal dawa | Potassium permanganate | KMnO₄ | Powerful oxidising agent, disinfectant (water purification), antiseptic (dilute solution for wound washing), bleaching, analytical chemistry |
| Hypo (photography) | Sodium thiosulphate pentahydrate | Na₂S₂O₃·5H₂O | Photography fixer (dissolves unexposed silver halide), de-chlorination of water, antidote for cyanide poisoning, analytical chemistry |
| Heavy water | Deuterium oxide | D₂O | Moderator in nuclear reactors (slows neutrons without absorbing them), NMR spectroscopy, tracing reactions; density 1.1 g/cm³, BP = 101.4°C, FP = 3.82°C |
| Laughing gas | Nitrous oxide | N₂O | Anaesthetic (dental procedures), propellant in whipped cream cans; causes euphoria hence 'laughing gas' |
| Aqua regia | Mixture of acids | 1 HNO₃ + 3 HCl (freshly prepared) | Dissolves gold and platinum; used to assay gold purity; HNO₃ oxidises, HCl provides Cl⁻ to form complex chloroaurate [AuCl₄]⁻ |
| Dry ice | Solid carbon dioxide | CO₂ (s) | Refrigerant (sublimes directly at −78.5°C), food preservation during transport, special effects (fog), fire extinguisher (CO₂ gas from cylinders) |
| Marsh gas | Methane | CH₄ | Main component of natural gas (CNG), biogas; produced in marshes/paddy fields by anaerobic bacteria; greenhouse gas (25× more potent than CO₂ per molecule) |
8. Carbon and Organic Chemistry
Unique Properties of Carbon
Tetravalency: Carbon has 4 valence electrons and forms 4 bonds (single, double, or triple). Catenation: Carbon uniquely forms long chains, branched chains, and rings with itself — giving rise to millions of organic compounds. Small size: Carbon forms strong, stable bonds with H, O, N, S, halogens.
Allotropes of Carbon
🎯 Allotropes of Carbon — BPSC Critical:
Diamond: Each carbon bonded to 4 other carbons in a 3D tetrahedral network. Hardest natural substance (10 on Mohs scale). Non-conductor (no free electrons). Very high melting point. Used in cutting, drilling, abrasives, jewellery.
Graphite: Each carbon bonded to 3 others in flat hexagonal layers; 4th electron is delocalised between layers. Soft (layers slide over each other); good conductor of electricity. Used as lubricant, pencil lead, electrode in electrolytic cells, moderator in nuclear reactors.
Fullerene (Buckminsterfullerene, C₆₀): Discovered in 1985 by Kroto, Curl, Smalley (Nobel Prize 1996). Football-shaped molecule with 60 carbon atoms — 20 hexagons and 12 pentagons. Superconducting when doped with alkali metals. Potential drug delivery systems, nanotubes.
Graphite: Each carbon bonded to 3 others in flat hexagonal layers; 4th electron is delocalised between layers. Soft (layers slide over each other); good conductor of electricity. Used as lubricant, pencil lead, electrode in electrolytic cells, moderator in nuclear reactors.
Fullerene (Buckminsterfullerene, C₆₀): Discovered in 1985 by Kroto, Curl, Smalley (Nobel Prize 1996). Football-shaped molecule with 60 carbon atoms — 20 hexagons and 12 pentagons. Superconducting when doped with alkali metals. Potential drug delivery systems, nanotubes.
Hybridisation
| Hybridisation | Shape | Bond Angle | Example Compounds | Bond Type |
|---|---|---|---|---|
| sp³ | Tetrahedral | 109.5° | CH₄, C₂H₆, CCl₄, diamond | All single bonds (σ) |
| sp² | Trigonal planar | 120° | C₂H₄ (ethylene), benzene (C₆H₆), graphite | One double bond (σ + π) |
| sp | Linear | 180° | C₂H₂ (acetylene), CO₂, HCN | One triple bond (σ + 2π) |
Functional Groups
| Functional Group | Name | General Formula | Example |
|---|---|---|---|
| -OH | Hydroxyl (Alcohol) | R-OH | CH₃OH (methanol), C₂H₅OH (ethanol) |
| -CHO | Aldehyde | R-CHO | HCHO (formaldehyde/methanal), CH₃CHO (acetaldehyde) |
| -CO- (C=O between C atoms) | Ketone | R-CO-R' | CH₃COCH₃ (acetone/propanone) |
| -COOH | Carboxylic Acid | R-COOH | CH₃COOH (acetic acid), C₆H₅COOH (benzoic acid) |
| -COO- | Ester | R-COO-R' | CH₃COOC₂H₅ (ethyl acetate, fruity smell) |
| -NH₂ | Amine | R-NH₂ | CH₃NH₂ (methylamine), C₆H₅NH₂ (aniline) |
| -X (F, Cl, Br, I) | Halide (Haloalkane) | R-X | CHCl₃ (chloroform), CCl₄ (carbon tetrachloride) |
| -NO₂ | Nitro | R-NO₂ | C₆H₅NO₂ (nitrobenzene) — precursor to aniline |
Important Polymers
| Polymer | Type | Monomer | Key Uses |
|---|---|---|---|
| Polyethylene (PE) | Synthetic, thermoplastic | Ethylene (CH₂=CH₂) | Plastic bags, bottles, films, pipes |
| Polypropylene (PP) | Synthetic, thermoplastic | Propylene (CH₂=CHCH₃) | Woven sacks, fibres, medical equipment |
| PVC (Polyvinyl chloride) | Synthetic, thermoplastic | Vinyl chloride (CH₂=CHCl) | Pipes, electrical insulation, flooring, clothing |
| Polystyrene (PS) | Synthetic, thermoplastic | Styrene (C₆H₅CH=CH₂) | Packaging (Styrofoam), disposable cups, insulation |
| Nylon-6,6 | Synthetic, thermoplastic (polyamide) | Hexamethylenediamine + Adipic acid | Fibres (stockings, ropes, parachutes), gears |
| Nylon-6 | Synthetic, thermoplastic (polyamide) | Caprolactam | Toothbrush bristles, fishing nets, tyre cords |
| Teflon (PTFE) | Synthetic, thermoplastic | Tetrafluoroethylene (CF₂=CF₂) | Non-stick cookware, gaskets, lubricants; most chemically inert polymer |
| Bakelite | Synthetic, thermosetting | Phenol + Formaldehyde | First synthetic plastic; electrical switches, handles, billiard balls; cannot be remoulded |
| Urea-formaldehyde resin | Synthetic, thermosetting | Urea + Formaldehyde | Adhesives, laminates (Formica), foam insulation |
| Natural rubber (polyisoprene) | Natural, elastomer | Isoprene (C₅H₈) | Tyres, gloves, balloons; vulcanised with sulphur (Goodyear, 1839) to improve strength |
| Buna-S (SBR) | Synthetic, elastomer | Butadiene + Styrene | Automobile tyres, footwear (most widely used synthetic rubber) |
| Buna-N (Nitrile rubber) | Synthetic, elastomer | Butadiene + Acrylonitrile | Oil-resistant hoses, seals, gloves (resistant to oils and fuels) |
Important Organic Reactions
Saponification: Ester + NaOH (aqueous) → Soap (sodium salt of fatty acid) + Glycerol. This is how soap is made (cooking fat/oil with concentrated NaOH). Soap cleans because it has hydrophilic (-COONa) and hydrophobic (hydrocarbon tail) ends — forms micelles around grease.
Esterification: Carboxylic acid + Alcohol ⇌ Ester + Water (reversible, acid catalyst like conc. H₂SO₄). Esters have fruity smell — used in perfumes, food flavourings. This is the reverse of saponification.
Combustion: Alkane + O₂ → CO₂ + H₂O + heat. Complete combustion: blue flame, CO₂; incomplete: yellow/orange flame, CO (toxic) + soot.
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (catalysed by yeast enzyme zymase, anaerobic). Used to produce ethanol (alcohol), beer, wine, bread (CO₂ causes rising).
Esterification: Carboxylic acid + Alcohol ⇌ Ester + Water (reversible, acid catalyst like conc. H₂SO₄). Esters have fruity smell — used in perfumes, food flavourings. This is the reverse of saponification.
Combustion: Alkane + O₂ → CO₂ + H₂O + heat. Complete combustion: blue flame, CO₂; incomplete: yellow/orange flame, CO (toxic) + soot.
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (catalysed by yeast enzyme zymase, anaerobic). Used to produce ethanol (alcohol), beer, wine, bread (CO₂ causes rising).
Biology
1. Cell Biology — The Fundamental Unit of Life
Cell Theory
Schleiden (1838): All plants are made of cells.
Schwann (1839): All animals are made of cells; cells are the basic unit of life.
Virchow (1858): Omnis cellula e cellula — all cells arise from pre-existing cells.
Modern Cell Theory: Cell is the basic structural and functional unit of all living organisms; all cells arise from pre-existing cells; cells contain hereditary information (DNA) that is passed on during division.
Schwann (1839): All animals are made of cells; cells are the basic unit of life.
Virchow (1858): Omnis cellula e cellula — all cells arise from pre-existing cells.
Modern Cell Theory: Cell is the basic structural and functional unit of all living organisms; all cells arise from pre-existing cells; cells contain hereditary information (DNA) that is passed on during division.
Prokaryotes vs Eukaryotes
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Nuclear envelope | Absent — nucleoid region | Present — true nucleus with membrane |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi, etc.) |
| DNA form | Circular, naked (no histone) | Linear, associated with histone proteins (chromatin) |
| Ribosome | 70S (50S + 30S subunits) | 80S (60S + 40S); 70S in mitochondria/chloroplasts |
| Cell wall | Peptidoglycan (bacteria), no cell wall (mycoplasma) | Plants: cellulose; fungi: chitin; animals: absent |
| Reproduction | Binary fission | Mitosis and meiosis |
| Size | 1–10 μm | 10–100 μm (typically) |
| Examples | Bacteria, Archaea, Cyanobacteria | Fungi, Plants, Animals, Protists |
Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present (cellulose, pectin, lignin) | Absent |
| Chloroplasts | Present (in green parts) | Absent |
| Vacuole | Large central vacuole (maintains turgor) | Small or absent |
| Centrioles | Absent (except lower plants) | Present (forms spindle in cell division) |
| Lysosomes | Rare | Prominent (intracellular digestion) |
| Plastids | Present (chloroplast, chromoplast, leucoplast) | Absent |
| Glyoxysomes | Present (fat seed germination) | Absent |
| Shape | Regular (due to rigid wall) | Irregular, flexible |
Cell Organelles — Detailed
Nucleus — Control centre of the cell. Bounded by double nuclear membrane (nuclear envelope) with pores that allow mRNA and ribosomes to pass through. Nucleolus (inside nucleus) — site of rRNA synthesis and ribosome assembly. DNA is organised with histone proteins into chromatin; during cell division it condenses into visible chromosomes. Human somatic cells: 46 chromosomes (23 pairs — 22 autosomes + 1 sex chromosome pair). Human gametes: 23 chromosomes (haploid).
Mitochondria — "Powerhouse of the cell." Double membrane: smooth outer membrane and inner membrane folded into cristae (greatly increases surface area for ATP synthesis). Matrix (inside inner membrane): contains Krebs cycle enzymes, mtDNA (circular, maternal inheritance), and 70S ribosomes. ATP produced by oxidative phosphorylation on inner membrane (electron transport chain + ATP synthase). Number: highly active cells have thousands (e.g., liver, muscle); red blood cells have none.
Chloroplast — "Kitchen of the cell." Found in green parts of plants. Double outer membrane + inner thylakoid system. Thylakoids stacked into grana (granum = stack) — site of light-dependent reactions (photosystems I and II, electron transport chain, ATP synthesis, NADPH production). Stroma (fluid surrounding thylakoids) — site of Calvin cycle (CO₂ fixation). Contains own circular DNA and 70S ribosomes — evidence of endosymbiotic origin (from cyanobacteria).
Endoplasmic Reticulum (ER) — Network of membrane-bound channels and sacs. Rough ER: studded with ribosomes on cytoplasmic face; synthesises secretory proteins, membrane proteins; packages them in vesicles for Golgi. Smooth ER: no ribosomes; synthesises lipids (including steroids), detoxifies drugs and poisons (liver), stores Ca²⁺ (muscle cells — sarcoplasmic reticulum releases Ca²⁺ for contraction).
Golgi Apparatus (Golgi Complex) — Stack of flattened membrane sacs (cisternae). cis face (forming face) receives vesicles from ER; trans face (maturing face) dispatches vesicles to cell membrane/secretion. Functions: protein modification (glycosylation — adding sugar groups, phosphorylation), packaging in vesicles, sorting of proteins to correct destinations, forms lysosomes. Discovered by Camillo Golgi (1898) in nerve cells.
Lysosomes — "Suicidal bags." Membrane-bound sacs containing ~50 hydrolytic enzymes (lipases, proteases, nucleases, glycosidases) capable of digesting all biological macromolecules. Functions: intracellular digestion of worn-out organelles (autophagy), digestion of phagocytosed bacteria (in macrophages and neutrophils), apoptosis (programmed cell death). Deficiency of lysosomal enzymes causes lysosomal storage diseases (Tay-Sachs, Gaucher's disease). Formed by Golgi apparatus.
Cell Membrane (Plasma Membrane) — Fluid Mosaic Model (Singer and Nicolson, 1972). Phospholipid bilayer: hydrophilic phosphate heads face outward (toward water), hydrophobic fatty acid tails face inward. Embedded proteins: integral proteins (span the bilayer — channels, pumps, receptors) and peripheral proteins (on the surface). Cholesterol interspersed — regulates fluidity (prevents too rigid at low T, too fluid at high T). Selective permeability: O₂, CO₂, small non-polar molecules diffuse freely; ions and large polar molecules need protein carriers or pumps.
Biomolecules
| Biomolecule | Monomer | Key Types / Examples | Function |
|---|---|---|---|
| Carbohydrates | Monosaccharides (sugars) | Glucose (blood sugar), fructose (fruit), galactose; Sucrose, lactose, maltose; Starch, glycogen, cellulose, chitin | Primary energy source; structural (cellulose — plant wall, chitin — exoskeleton); energy storage (starch in plants, glycogen in animals) |
| Proteins | Amino acids (20 standard) | Enzymes, antibodies, haemoglobin, insulin, collagen, keratin, actin, myosin | Catalysis (enzymes), structure (collagen), transport (haemoglobin), immunity (antibodies), signalling (hormones), movement (actin-myosin) |
| Lipids | Fatty acids + glycerol | Saturated fats, unsaturated fats, phospholipids, cholesterol, waxes | Energy storage (9 kcal/g), cell membrane structure (phospholipids), insulation, hormone precursors (steroids), vitamins A/D/E/K |
| Nucleic Acids | Nucleotides (base + sugar + phosphate) | DNA (deoxyribose + A/T/G/C), RNA (ribose + A/U/G/C) | Genetic information storage and expression; ATP (adenosine triphosphate) — energy currency |
2. Cell Division
Mitosis (Somatic Cell Division)
Mitosis is the type of cell division where one parent cell produces two genetically identical daughter cells, each with the same chromosome number as the parent (2n → 2n). It is the basis of growth, repair, and asexual reproduction.
| Phase | Key Events | Duration (relative) |
|---|---|---|
| Interphase (G1, S, G2) | G1: cell growth, protein synthesis; S: DNA replication (2n → 4 copies of DNA); G2: preparation for division, organelle duplication | 90–95% of cell cycle |
| Prophase | Chromatin condenses into visible chromosomes (each consisting of 2 sister chromatids joined at centromere); spindle apparatus forms; nuclear envelope breaks down; nucleolus disappears | ~ |
| Metaphase | Chromosomes align at equatorial plate (cell's equator); kinetochores (on centromeres) attach to spindle fibres from both poles — this is used for karyotyping | ~ |
| Anaphase | Centromeres split; sister chromatids (now called daughter chromosomes) pulled to opposite poles by spindle contraction; cell elongates; if non-disjunction occurs here → aneuploidy (Down syndrome if chr 21) | ~ |
| Telophase | Nuclear envelopes reform around each set of chromosomes; chromosomes decondense; spindle breaks down; nucleoli reappear | ~ |
| Cytokinesis | Animal cell: cleavage furrow (actin-myosin ring pinches cell in two); Plant cell: cell plate forms (from Golgi vesicles) at equator → becomes new cell wall | ~ |
Meiosis (Reduction Division)
Meiosis produces 4 haploid (n) cells from one diploid (2n) cell. It occurs in reproductive organs (gonads — testes/ovaries) to produce gametes (sperm, egg). It consists of two successive divisions:
Meiosis I (Reductional division): Homologous chromosomes separate (2n → n). Most important events in Prophase I: (1) Synapsis — homologous chromosomes pair up (form bivalents); (2) Crossing over — exchange of segments between non-sister chromatids of homologous chromosomes at points called chiasmata. Crossing over is the molecular basis of genetic recombination and is the major source of genetic variation.
Meiosis II (Equational division): Similar to mitosis — sister chromatids separate (n → n). Final result: 4 haploid cells (in males: 4 spermatocytes; in females: 1 large egg + 3 polar bodies).
Meiosis I (Reductional division): Homologous chromosomes separate (2n → n). Most important events in Prophase I: (1) Synapsis — homologous chromosomes pair up (form bivalents); (2) Crossing over — exchange of segments between non-sister chromatids of homologous chromosomes at points called chiasmata. Crossing over is the molecular basis of genetic recombination and is the major source of genetic variation.
Meiosis II (Equational division): Similar to mitosis — sister chromatids separate (n → n). Final result: 4 haploid cells (in males: 4 spermatocytes; in females: 1 large egg + 3 polar bodies).
3. Genetics — Heredity and Variation
Mendel's Experiments
Gregor Mendel (1822–1884) studied 7 pairs of contrasting traits in pea plants (Pisum sativum) over 8 years and analysed the results statistically. He chose pea plants because they have: distinct traits, short generation time, large number of offspring, self-pollination normally, and can be artificially cross-pollinated.
Law of Segregation (First Law / Law of Purity of Gametes): The two alleles of a character segregate (separate) during gamete formation so each gamete receives only one allele of each gene.
Law of Independent Assortment (Second Law): Alleles of different genes assort independently during gamete formation (genes on different chromosomes segregate independently). Basis of dihybrid cross 9:3:3:1 ratio.
Law of Independent Assortment (Second Law): Alleles of different genes assort independently during gamete formation (genes on different chromosomes segregate independently). Basis of dihybrid cross 9:3:3:1 ratio.
Monohybrid and Dihybrid Crosses
Monohybrid Cross (Tall × Dwarf):
P: TT × tt
F1: Tt (all Tall — phenotypic ratio 1:0; T is dominant over t)
F1 × F1: Tt × Tt
F2 genotypes: 1 TT : 2 Tt : 1 tt (1:2:1 genotypic ratio)
F2 phenotypes: 3 Tall : 1 Dwarf (3:1 phenotypic ratio)
Dihybrid Cross (TTRR × ttrr):
F1: TtRr (Round Yellow — all like dominant parent)
F1 × F1: TtRr × TtRr
F2 phenotypic ratio: 9 T_R_ : 3 T_rr : 3 ttR_ : 1 ttrr
= 9 Round Yellow : 3 Wrinkled Yellow : 3 Round Green : 1 Wrinkled Green
Incomplete Dominance (1:2:1 phenotypic ratio):
Red (RR) × White (rr) → Pink (Rr) — snapdragon, four o'clock
F2 of Rr × Rr: 1 Red : 2 Pink : 1 White (phenotypic ratio same as genotypic)
Codominance: Both alleles expressed equally in heterozygote.
Example: AB blood group — both A and B antigens expressed (IA IB genotype)
Blood groups: IA IA or IA i = A; IB IB or IB i = B; IA IB = AB; ii = O
Universal donor: O (no A or B antigens); Universal recipient: AB (both A and B antibodies absent)
Sex Determination and Sex-Linked Traits
Human sex determination: XX (female), XY (male). Father's sperm determines sex of offspring — Y-bearing sperm → son; X-bearing sperm → daughter. Sex ratio at fertilisation: 1:1.
Sex-linked (X-linked) traits: Genes located on X chromosome. Males (XY) are hemizygous — a single recessive allele on X is expressed (no masking by second X allele). Examples: Haemophilia A (clotting factor VIII deficiency), red-green colour blindness, Duchenne muscular dystrophy, glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Haemophilia: Affected males (X_h Y); carrier females (X_H X_h); affected females (X_h X_h) — very rare. Queen Victoria of England was a carrier — spread haemophilia to European royal families through her daughters.
Sex-linked (X-linked) traits: Genes located on X chromosome. Males (XY) are hemizygous — a single recessive allele on X is expressed (no masking by second X allele). Examples: Haemophilia A (clotting factor VIII deficiency), red-green colour blindness, Duchenne muscular dystrophy, glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Haemophilia: Affected males (X_h Y); carrier females (X_H X_h); affected females (X_h X_h) — very rare. Queen Victoria of England was a carrier — spread haemophilia to European royal families through her daughters.
DNA and Molecular Genetics
DNA (Deoxyribonucleic Acid): Double-stranded helical polymer of deoxyribonucleotides. Each nucleotide = deoxyribose sugar + phosphate group + nitrogenous base. Bases: purines (Adenine, Guanine) and pyrimidines (Thymine, Cytosine). Watson-Crick model (1953): A pairs with T (2 hydrogen bonds); G pairs with C (3 hydrogen bonds). Two strands are antiparallel (one 5'→3', other 3'→5'). Human DNA: ~3 billion base pairs per haploid genome; if stretched, would be ~2 metres long.
Central Dogma of Molecular Biology (Crick, 1958): DNA → RNA → Protein
Transcription: DNA → mRNA (in nucleus; enzyme: RNA polymerase)
Translation: mRNA → Protein (at ribosomes; amino acid sequence determined by codons — triplets of bases)
Genetic code: 64 codons (4³) for 20 amino acids + 3 stop codons. Code is degenerate (multiple codons for same amino acid), universal (same in nearly all organisms), non-overlapping, comma-less.
DNA Replication: Semi-conservative (each new DNA molecule has one old strand + one new strand — shown by Meselson-Stahl experiment, 1958). Enzyme: DNA polymerase (adds nucleotides only in 5'→3' direction). Also requires: helicase (unwinds helix), primase (makes RNA primer), ligase (joins Okazaki fragments on lagging strand).
Transcription: DNA → mRNA (in nucleus; enzyme: RNA polymerase)
Translation: mRNA → Protein (at ribosomes; amino acid sequence determined by codons — triplets of bases)
Genetic code: 64 codons (4³) for 20 amino acids + 3 stop codons. Code is degenerate (multiple codons for same amino acid), universal (same in nearly all organisms), non-overlapping, comma-less.
DNA Replication: Semi-conservative (each new DNA molecule has one old strand + one new strand — shown by Meselson-Stahl experiment, 1958). Enzyme: DNA polymerase (adds nucleotides only in 5'→3' direction). Also requires: helicase (unwinds helix), primase (makes RNA primer), ligase (joins Okazaki fragments on lagging strand).
🎯 BPSC Genetics Facts: Down syndrome (Trisomy 21) — extra chromosome 21, 47 chromosomes total; Turner syndrome (45, XO) — female with single X; Klinefelter syndrome (47, XXY) — male features with two X chromosomes. Mutation = permanent heritable change in DNA sequence. Frameshift mutations (insertion/deletion) are most harmful. PCR (Polymerase Chain Reaction) — invented by Kary Mullis (Nobel 1993) — amplifies DNA fragments; used in forensics, diagnosis, paternity testing.
4. Human Physiology
4a. Digestive System
The human digestive system converts food into small absorbable molecules through mechanical and chemical digestion. The alimentary canal runs from mouth to anus, accompanied by accessory organs (salivary glands, liver, pancreas, gallbladder).
| Organ | Secretion / Enzyme | Substrate → Product | pH |
|---|---|---|---|
| Mouth (salivary glands) | Salivary amylase (ptyalin) | Starch → Maltose | 6.5–7.0 |
| Stomach | HCl + Pepsinogen → Pepsin; Gastric lipase; Rennin (infants) | Proteins → Peptides; Fat → Fatty acids; Milk casein → Paracasein | 1.5–2.0 |
| Small intestine (Pancreatic juice) | Trypsin, chymotrypsin, carboxypeptidase; Pancreatic amylase; Pancreatic lipase; Nucleases | Proteins → Amino acids; Starch → Maltose; Fat → Glycerol + fatty acids; DNA/RNA → nucleotides | 7–8 |
| Small intestine (Intestinal juice / Succus entericus) | Peptidases; Maltase, sucrase, lactase; Intestinal lipase | Peptides → Amino acids; Disaccharides → Monosaccharides; Fat → Fatty acids | 7.5–8.0 |
| Liver (via bile) | Bile salts (not enzymes) | Emulsification of fats (breaks large fat globules into tiny droplets → increases surface area for lipase) | 7.8–8.0 |
Absorption: Occurs mainly in small intestine (jejunum and ileum). Villi and microvilli (brush border) enormously increase absorptive surface area. Glucose, amino acids, water-soluble vitamins → portal blood → liver. Fatty acids, glycerol, fat-soluble vitamins (A, D, E, K) → lacteals (lymphatics) → thoracic duct → blood.
Large intestine (colon): Absorbs water and electrolytes from undigested material. Gut flora (E. coli, Lactobacillus) synthesise Vitamin K and some B vitamins. Cellulose not digested — forms dietary fibre, helps peristalsis.
Large intestine (colon): Absorbs water and electrolytes from undigested material. Gut flora (E. coli, Lactobacillus) synthesise Vitamin K and some B vitamins. Cellulose not digested — forms dietary fibre, helps peristalsis.
4b. Circulatory System
Double circulation: Blood passes through the heart twice for each complete circuit. Pulmonary circuit: right heart → lungs → left heart (oxygenation). Systemic circuit: left heart → body → right heart (oxygen delivery). Ensures oxygenated blood does not mix with deoxygenated blood — efficient oxygen delivery.
Heart structure: 4 chambers — 2 atria (upper, receive blood) + 2 ventricles (lower, pump blood). Right side: deoxygenated blood; Left side: oxygenated blood. Valves prevent backflow: tricuspid (right AV), bicuspid/mitral (left AV), pulmonary semilunar (right ventricle exit), aortic semilunar (left ventricle exit). "Lubb" = AV valves closing; "Dubb" = semilunar valves closing.
Cardiac cycle: Systole (contraction, 0.3 s) → Diastole (relaxation, 0.5 s). Heart rate: ~72 beats/min at rest. Cardiac output = heart rate × stroke volume = 72 × 70 mL ≈ 5 L/min (entire blood volume/minute). SA node (sinoatrial node) in right atrium wall = natural pacemaker — sets heart rhythm; if damaged → artificial pacemaker required.
Blood pressure: Normal = 120/80 mmHg (systolic/diastolic). Hypertension >140/90 (silent killer — damages kidneys, heart, brain). Hypotension <90/60. Measured by sphygmomanometer.
Cardiac cycle: Systole (contraction, 0.3 s) → Diastole (relaxation, 0.5 s). Heart rate: ~72 beats/min at rest. Cardiac output = heart rate × stroke volume = 72 × 70 mL ≈ 5 L/min (entire blood volume/minute). SA node (sinoatrial node) in right atrium wall = natural pacemaker — sets heart rhythm; if damaged → artificial pacemaker required.
Blood pressure: Normal = 120/80 mmHg (systolic/diastolic). Hypertension >140/90 (silent killer — damages kidneys, heart, brain). Hypotension <90/60. Measured by sphygmomanometer.
Blood Components
| Component | Normal Count | Function | Lifetime |
|---|---|---|---|
| Red Blood Cells (Erythrocytes) | 4.5–5.5 million/μL (males); 4.0–5.0 million (females) | Carry O₂ (haemoglobin) and CO₂; biconcave disc, no nucleus, no mitochondria in mammals | 120 days; destroyed in spleen |
| White Blood Cells (Leukocytes) | 5,000–10,000/μL | Immunity: neutrophils (phagocytosis), lymphocytes (antibody production / cell-mediated immunity), monocytes (become macrophages), eosinophils (allergy/parasites), basophils (heparin/histamine) | Hours to years (memory cells) |
| Platelets (Thrombocytes) | 150,000–400,000/μL | Blood clotting (form platelet plug; release clotting factors); abnormally low → thrombocytopenia (dengue fever) | 8–10 days |
| Plasma (55% of blood) | — | Transports nutrients, hormones, antibodies, waste; contains plasma proteins (albumin, globulins, fibrinogen) | — |
🎯 BPSC Blood Facts: ABO blood group system: O negative is universal donor (no A, B, or Rh antigens); AB positive is universal recipient. Rh factor (Rh positive or negative): if Rh-negative mother carries Rh-positive fetus — erythroblastosis fetalis (haemolytic disease of newborn) in second pregnancy. Anti-D injection given during first pregnancy to prevent sensitisation. Iron-deficiency anaemia (most common type): low haemoglobin; treated with iron supplements. Sickle-cell anaemia: genetic; malformed haemoglobin (Glu→Val mutation in β-chain) — RBCs become sickle-shaped; common in malaria-endemic regions (heterozygotes protected against malaria).
4c. Respiratory System
Respiration: Process of gas exchange between the organism and its environment (external respiration) and the cellular process of ATP production using oxygen (cellular/internal respiration). In humans: breathing (ventilation) → gas exchange in alveoli → gas transport in blood → cellular respiration in mitochondria.
Pathway of air: Nostrils → nasal cavity (filters, warms, humidifies air) → pharynx → larynx (voice box; epiglottis prevents aspiration) → trachea (C-shaped cartilage rings, lined with cilia and mucus) → bronchi (right and left) → bronchioles → alveoli.
Alveoli: ~300 million in lungs; total surface area ~70 m² (tennis court size). Walls one cell thick; surrounded by dense capillary network. O₂ diffuses from alveolar air into blood; CO₂ diffuses from blood into alveoli. Surfactant (dipalmitoylphosphatidylcholine) coats alveoli — prevents collapse.
Breathing mechanism: Inspiration (active): diaphragm contracts and flattens, external intercostals contract → thoracic volume increases → lung volume increases → pressure drops below atmospheric → air flows in. Expiration (passive at rest): diaphragm and intercostals relax → thoracic volume decreases → pressure rises → air flows out. Rate: ~15–20 breaths/min; tidal volume ~500 mL; vital capacity ~4500 mL.
Gas transport in blood: O₂: 97% as oxyhaemoglobin (HbO₂); 3% dissolved in plasma. CO₂: ~70% as bicarbonate ions (HCO₃⁻) in plasma; 23% bound to haemoglobin (carbaminohaemoglobin); 7% dissolved. CO is ~250 times more strongly bound to Hb than O₂ — causes CO poisoning.
Alveoli: ~300 million in lungs; total surface area ~70 m² (tennis court size). Walls one cell thick; surrounded by dense capillary network. O₂ diffuses from alveolar air into blood; CO₂ diffuses from blood into alveoli. Surfactant (dipalmitoylphosphatidylcholine) coats alveoli — prevents collapse.
Breathing mechanism: Inspiration (active): diaphragm contracts and flattens, external intercostals contract → thoracic volume increases → lung volume increases → pressure drops below atmospheric → air flows in. Expiration (passive at rest): diaphragm and intercostals relax → thoracic volume decreases → pressure rises → air flows out. Rate: ~15–20 breaths/min; tidal volume ~500 mL; vital capacity ~4500 mL.
Gas transport in blood: O₂: 97% as oxyhaemoglobin (HbO₂); 3% dissolved in plasma. CO₂: ~70% as bicarbonate ions (HCO₃⁻) in plasma; 23% bound to haemoglobin (carbaminohaemoglobin); 7% dissolved. CO is ~250 times more strongly bound to Hb than O₂ — causes CO poisoning.
4d. Excretory System
| Organ | Waste Eliminated | Notes |
|---|---|---|
| Kidneys | Urea, uric acid, creatinine, excess salts, water | ~1–2 L urine/day; maintain osmoregulation, acid-base balance, blood pressure (renin-angiotensin) |
| Lungs | CO₂, water vapour | ~200 mL CO₂/min at rest |
| Skin | NaCl, urea, water (sweat) | Eccrine glands: thermoregulation; apocrine glands: odour (armpits) |
| Liver | Bilirubin (from Hb breakdown) → bile → intestine | Detoxification of drugs, alcohol; converts ammonia → urea (urea cycle) |
Nephron (functional unit of kidney): ~1 million nephrons per kidney. Glomerulus (tangle of capillaries in Bowman's capsule) → Proximal Convoluted Tubule (PCT) → Loop of Henle → Distal Convoluted Tubule (DCT) → Collecting duct → renal pelvis → ureter → bladder → urethra.
Filtration (in glomerulus) → Selective reabsorption (glucose, amino acids, most water and salts in PCT and DCT; water in collecting duct under ADH control) → Secretion (H⁺, K⁺, drugs) → Urine formation. Normal urine: 95% water, urea, uric acid, creatinine, salts; pH 5–8 (avg 6); no glucose (glucosuria → diabetes mellitus), no protein (proteinuria → kidney disease).
Filtration (in glomerulus) → Selective reabsorption (glucose, amino acids, most water and salts in PCT and DCT; water in collecting duct under ADH control) → Secretion (H⁺, K⁺, drugs) → Urine formation. Normal urine: 95% water, urea, uric acid, creatinine, salts; pH 5–8 (avg 6); no glucose (glucosuria → diabetes mellitus), no protein (proteinuria → kidney disease).
4e. Nervous System
Organisation:
Central NS (CNS): Brain + Spinal cord
Peripheral NS (PNS): Cranial nerves (12 pairs from brain) + Spinal nerves (31 pairs from spinal cord)
Autonomic NS: Sympathetic (fight-or-flight: increases heart rate, dilates pupils, inhibits digestion) and Parasympathetic (rest-and-digest: decreases heart rate, constricts pupils, stimulates digestion).
Neuron (nerve cell): Functional unit of nervous system. Parts: Cell body (soma, contains nucleus) → Dendrites (receive signals) → Axon (conducts impulse away from cell body) → Synaptic knobs (release neurotransmitters). Myelin sheath (Schwann cells) insulates axon, speeds conduction (up to 120 m/s in myelinated fibres; 0.5 m/s in unmyelinated). Nodes of Ranvier: gaps in myelin — saltatory conduction.
Synapse: Junction between two neurons. Presynaptic neuron releases neurotransmitter into synaptic cleft → binds to receptor on postsynaptic neuron → generates or inhibits new impulse. Neurotransmitters: Acetylcholine (voluntary muscle, parasympathetic); Noradrenaline (sympathetic); Dopamine (reward, movement — deficient in Parkinson's disease); Serotonin (mood — low in depression); GABA (inhibitory).
Reflex arc: Receptor → Sensory neuron → Spinal cord (integration centre) → Motor neuron → Effector. Knee jerk reflex: monosynaptic (no interneuron). Withdrawal reflex (from heat/pain): polysynaptic.
Central NS (CNS): Brain + Spinal cord
Peripheral NS (PNS): Cranial nerves (12 pairs from brain) + Spinal nerves (31 pairs from spinal cord)
Autonomic NS: Sympathetic (fight-or-flight: increases heart rate, dilates pupils, inhibits digestion) and Parasympathetic (rest-and-digest: decreases heart rate, constricts pupils, stimulates digestion).
Neuron (nerve cell): Functional unit of nervous system. Parts: Cell body (soma, contains nucleus) → Dendrites (receive signals) → Axon (conducts impulse away from cell body) → Synaptic knobs (release neurotransmitters). Myelin sheath (Schwann cells) insulates axon, speeds conduction (up to 120 m/s in myelinated fibres; 0.5 m/s in unmyelinated). Nodes of Ranvier: gaps in myelin — saltatory conduction.
Synapse: Junction between two neurons. Presynaptic neuron releases neurotransmitter into synaptic cleft → binds to receptor on postsynaptic neuron → generates or inhibits new impulse. Neurotransmitters: Acetylcholine (voluntary muscle, parasympathetic); Noradrenaline (sympathetic); Dopamine (reward, movement — deficient in Parkinson's disease); Serotonin (mood — low in depression); GABA (inhibitory).
Reflex arc: Receptor → Sensory neuron → Spinal cord (integration centre) → Motor neuron → Effector. Knee jerk reflex: monosynaptic (no interneuron). Withdrawal reflex (from heat/pain): polysynaptic.
| Brain Region | Function |
|---|---|
| Cerebrum (largest, 2 hemispheres) | Consciousness, intelligence, memory, language, voluntary movement, sensory perception; left hemisphere: language, logic; right hemisphere: creativity, spatial reasoning |
| Cerebellum (hind-brain) | Coordination of movement, balance, fine motor control; damage → ataxia (unsteady gait) |
| Medulla oblongata | Vital autonomic functions: breathing, heart rate, blood pressure, swallowing, vomiting; connects brain to spinal cord |
| Hypothalamus | Temperature regulation, hunger, thirst, sleep-wake cycle, emotional responses; controls pituitary gland (master endocrine gland) via releasing hormones |
| Thalamus | Relay station for sensory signals to cerebral cortex; pain perception |
| Limbic system | Emotion, memory formation, motivation; includes hippocampus (memory), amygdala (fear/emotion) |
4f. Endocrine System
Endocrine glands secrete hormones directly into the blood (ductless). Hormones act on target organs/cells. They are chemical messengers that regulate growth, metabolism, reproduction, and homeostasis.
| Gland | Hormone(s) | Function | Disorder if Abnormal |
|---|---|---|---|
| Pituitary (master gland) | GH, TSH, ACTH, FSH, LH, Prolactin, ADH, Oxytocin | Growth, stimulates other glands, water balance, labour/lactation | Dwarfism/Gigantism (GH↓/↑), Diabetes insipidus (ADH↓) |
| Thyroid | Thyroxine (T4), Triiodothyronine (T3), Calcitonin | Metabolic rate, growth, development; calcitonin lowers blood Ca²⁺ | Hypothyroidism (cretinism in children; myxoedema in adults); Hyperthyroidism (Graves' disease); Goitre (iodine deficiency) |
| Parathyroid (4 tiny glands behind thyroid) | Parathyroid hormone (PTH) | Increases blood Ca²⁺ (opposite of calcitonin) | Hypoparathyroidism → tetany (muscle spasms) |
| Adrenal (two zones) | Cortex: Cortisol (stress), Aldosterone (salt balance); Medulla: Adrenaline, Noradrenaline (fight-or-flight) | Stress response, inflammation, electrolyte balance, blood pressure | Addison's disease (adrenal insufficiency); Cushing's syndrome (excess cortisol) |
| Pancreas (islets of Langerhans) | Insulin (β cells), Glucagon (α cells) | Insulin: lowers blood glucose (promotes uptake/storage); Glucagon: raises blood glucose (promotes glycogenolysis) | Diabetes mellitus (Type 1: no insulin production; Type 2: insulin resistance) |
| Gonads (testes/ovaries) | Testosterone (male); Oestrogen, Progesterone (female) | Secondary sexual characteristics, reproduction, menstrual cycle | Hypogonadism; PCOS (excess androgens in females) |
| Pineal gland | Melatonin | Regulates sleep-wake cycle (circadian rhythm); decreases with light exposure | Sleep disorders, jet lag |
4g. Immune System
Immunity: The ability of the body to resist disease-causing organisms and substances. Non-specific (innate) immunity: skin barrier, mucus, fever, phagocytes, inflammation — present from birth. Specific (adaptive) immunity: targets particular antigens; involves lymphocytes; has immunological memory — basis of vaccination.
Types of specific immunity:
Humoral (antibody-mediated) immunity: B lymphocytes → differentiate into plasma cells → produce antibodies (immunoglobulins: IgG, IgA, IgM, IgD, IgE). Antibodies neutralise pathogens, activate complement system, mark pathogens for phagocytosis (opsonisation).
Cell-mediated immunity (CMI): T lymphocytes (T cells). Helper T cells (CD4⁺): coordinate immune response, activate B cells and cytotoxic T cells. Cytotoxic T cells (CD8⁺): kill virus-infected cells and cancer cells directly. Memory T and B cells: persist long-term → rapid response on re-exposure (basis of immunological memory and vaccination).
Vaccination: Introduces weakened/killed pathogen or antigen → body mounts primary immune response → memory cells formed → future exposure triggers rapid, stronger secondary response → protection. Types: Live attenuated (BCG — TB, oral polio), Killed (rabies, influenza), Toxoid (tetanus, diphtheria), Subunit (Hepatitis B), mRNA (COVID-19 — Pfizer/Moderna).
HIV/AIDS: HIV (Human Immunodeficiency Virus) targets Helper T cells (CD4⁺) → progressive destruction → AIDS (Acquired Immunodeficiency Syndrome) when CD4⁺ count <200/μL (normal >500/μL). Transmitted via blood, sexual contact, mother-to-child. HAART (Highly Active Antiretroviral Therapy): does not cure but suppresses viral load.
Humoral (antibody-mediated) immunity: B lymphocytes → differentiate into plasma cells → produce antibodies (immunoglobulins: IgG, IgA, IgM, IgD, IgE). Antibodies neutralise pathogens, activate complement system, mark pathogens for phagocytosis (opsonisation).
Cell-mediated immunity (CMI): T lymphocytes (T cells). Helper T cells (CD4⁺): coordinate immune response, activate B cells and cytotoxic T cells. Cytotoxic T cells (CD8⁺): kill virus-infected cells and cancer cells directly. Memory T and B cells: persist long-term → rapid response on re-exposure (basis of immunological memory and vaccination).
Vaccination: Introduces weakened/killed pathogen or antigen → body mounts primary immune response → memory cells formed → future exposure triggers rapid, stronger secondary response → protection. Types: Live attenuated (BCG — TB, oral polio), Killed (rabies, influenza), Toxoid (tetanus, diphtheria), Subunit (Hepatitis B), mRNA (COVID-19 — Pfizer/Moderna).
HIV/AIDS: HIV (Human Immunodeficiency Virus) targets Helper T cells (CD4⁺) → progressive destruction → AIDS (Acquired Immunodeficiency Syndrome) when CD4⁺ count <200/μL (normal >500/μL). Transmitted via blood, sexual contact, mother-to-child. HAART (Highly Active Antiretroviral Therapy): does not cure but suppresses viral load.
5. Plant Biology
Photosynthesis
Photosynthesis: Process by which green plants, algae, and cyanobacteria use light energy (from sun), water, and CO₂ to produce glucose (food) and oxygen. Occurs in chloroplasts. Overall equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
| Stage | Location | Reactions | Products |
|---|---|---|---|
| Light-dependent reactions (Light reactions) | Thylakoid membranes (grana) | Absorption of light by chlorophyll; photolysis of water (2H₂O → O₂ + 4H⁺ + 4e⁻); electron transport chain; photophosphorylation | ATP, NADPH, O₂ (released as byproduct) |
| Light-independent reactions (Calvin cycle / Dark reactions) | Stroma | CO₂ fixation by RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase); reduction using ATP and NADPH; regeneration of RuBP | Glucose (G3P → eventually sucrose, starch) |
Chlorophyll pigments: Chlorophyll a (main; blue-green; absorbs red and blue light best) — universal in all photosynthetic organisms. Chlorophyll b (accessory; yellow-green). Carotenoids (carotene — orange; xanthophyll — yellow): accessory pigments; protect chlorophyll from photo-oxidation; responsible for autumn colours when chlorophyll breaks down.
C3 vs C4 plants: C3 plants (most plants: wheat, rice, soybean): first stable product of CO₂ fixation is 3-carbon compound (3-PGA). Less efficient in high temperature/light — lose carbon through photorespiration. C4 plants (sugarcane, maize/corn, sorghum): CO₂ first fixed in mesophyll cells as 4-carbon compound (oxaloacetate) → transferred to bundle sheath cells where Calvin cycle occurs. More efficient, less photorespiration. CAM plants (cacti, pineapple, agave): open stomata only at night to reduce water loss.
C3 vs C4 plants: C3 plants (most plants: wheat, rice, soybean): first stable product of CO₂ fixation is 3-carbon compound (3-PGA). Less efficient in high temperature/light — lose carbon through photorespiration. C4 plants (sugarcane, maize/corn, sorghum): CO₂ first fixed in mesophyll cells as 4-carbon compound (oxaloacetate) → transferred to bundle sheath cells where Calvin cycle occurs. More efficient, less photorespiration. CAM plants (cacti, pineapple, agave): open stomata only at night to reduce water loss.
Plant Hormones (Phytohormones)
| Hormone | Site of Production | Functions | Application |
|---|---|---|---|
| Auxins (IAA — Indole-3-Acetic Acid) | Shoot apex, young leaves, developing seeds | Cell elongation (phototropism, gravitropism); apical dominance (inhibits lateral buds); root initiation; fruit development | Rooting powder for cuttings; herbicides (2,4-D kills dicots); prevents premature fruit drop |
| Gibberellins (GA) | Young leaves, seeds, roots | Stem elongation (internode elongation); breaks dormancy of seeds/buds; promotes germination; fruit development without fertilisation (parthenocarpy) | Malting industry (promotes amylase in barley); seedless grapes; treating dwarf plants |
| Cytokinins | Root apex, developing seeds | Promotes cell division (cytokinesis); delays senescence (leaf yellowing); promotes lateral bud growth (antagonises apical dominance of auxin) | Tissue culture (with auxin controls organogenesis); preserving freshness of cut flowers |
| Abscisic Acid (ABA) | Leaves, roots, seeds | Inhibits growth; promotes dormancy of seeds and buds; promotes leaf/fruit abscission; closes stomata in water stress (drought — signals guard cells) | "Stress hormone"; seed dormancy; post-harvest storage |
| Ethylene (gaseous) | Ripening fruits, nodes, aging tissues | Promotes fruit ripening; promotes abscission; senescence; inhibits elongation; promotes lateral growth | Artificial ripening of bananas/tomatoes (calcium carbide produces acetylene which converts to ethylene); storage in CO₂-rich atmosphere slows ripening |
Transpiration and Water Movement
Transpiration: Loss of water vapour from aerial parts of plant (mainly through stomata on leaves). Necessary for: (a) creates negative pressure (transpiration pull) that draws water up from roots through xylem — cohesion-tension theory; (b) cooling of leaf surface; (c) mineral absorption (water carries dissolved minerals). Stomata open in light (guard cells become turgid via K⁺ uptake → swell → pore opens) and close in dark or drought (ABA triggers K⁺ efflux → guard cells lose turgor).
Ascent of sap (water transport in xylem): Cohesion-Tension-Transpiration pull theory: evaporation at leaf surface → tension (negative pressure) in xylem → cohesion (water molecules stick together by H-bonds) → adhesion (water sticks to xylem walls) → continuous water column pulled up. Osmosis at root hair cells: soil water (high water potential) → root hair cells (lower water potential due to dissolved solutes) by osmosis. Root pressure (active — some contribution especially at night).
Phloem transport: Organic solutes (sucrose mainly) transported from source (leaves where photosynthesis occurs) to sink (roots, fruits, seeds where storage/utilisation occurs) through sieve tubes by pressure-flow hypothesis. Active loading of sucrose into phloem at source creates high osmotic pressure → water enters by osmosis → pressure pushes contents to sink where sucrose is unloaded.
Ascent of sap (water transport in xylem): Cohesion-Tension-Transpiration pull theory: evaporation at leaf surface → tension (negative pressure) in xylem → cohesion (water molecules stick together by H-bonds) → adhesion (water sticks to xylem walls) → continuous water column pulled up. Osmosis at root hair cells: soil water (high water potential) → root hair cells (lower water potential due to dissolved solutes) by osmosis. Root pressure (active — some contribution especially at night).
Phloem transport: Organic solutes (sucrose mainly) transported from source (leaves where photosynthesis occurs) to sink (roots, fruits, seeds where storage/utilisation occurs) through sieve tubes by pressure-flow hypothesis. Active loading of sucrose into phloem at source creates high osmotic pressure → water enters by osmosis → pressure pushes contents to sink where sucrose is unloaded.
Nitrogen Fixation and Plant Nutrition
Essential minerals: Macronutrients (needed in large amounts): N (proteins, nucleic acids), P (ATP, DNA, cell membrane), K (stomatal regulation, enzyme cofactor), Ca (cell wall, spindle fibres), Mg (chlorophyll centre), S (amino acids cysteine/methionine). Micronutrients (needed in trace amounts): Fe (haemoglobin-like compounds, cytochromes), Mn, Zn, Cu, Mo, B, Cl.
Nitrogen fixation: Conversion of atmospheric N₂ (inert) to NH₃ (usable form) by nitrogen-fixing bacteria. Free-living: Azotobacter (aerobic), Clostridium (anaerobic), Anabaena (cyanobacterium in rice fields). Symbiotic: Rhizobium in root nodules of legumes (soybean, pea, bean, groundnut) — most efficient (up to 200 kg N/ha/year). Enzyme: nitrogenase (requires 16 ATP per N₂ fixed, functions only under low O₂). This is why legumes improve soil fertility and are used in crop rotation with cereals.
Nitrification: NH₄⁺ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter) — makes nitrogen available for plant uptake.
Denitrification: NO₃⁻ → N₂ by anaerobic bacteria (Pseudomonas denitrificans) — returns N to atmosphere; happens in waterlogged soils (reduces soil fertility).
Nitrogen fixation: Conversion of atmospheric N₂ (inert) to NH₃ (usable form) by nitrogen-fixing bacteria. Free-living: Azotobacter (aerobic), Clostridium (anaerobic), Anabaena (cyanobacterium in rice fields). Symbiotic: Rhizobium in root nodules of legumes (soybean, pea, bean, groundnut) — most efficient (up to 200 kg N/ha/year). Enzyme: nitrogenase (requires 16 ATP per N₂ fixed, functions only under low O₂). This is why legumes improve soil fertility and are used in crop rotation with cereals.
Nitrification: NH₄⁺ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter) — makes nitrogen available for plant uptake.
Denitrification: NO₃⁻ → N₂ by anaerobic bacteria (Pseudomonas denitrificans) — returns N to atmosphere; happens in waterlogged soils (reduces soil fertility).
6. Diseases and Human Health
Infectious (Communicable) Diseases
| Disease | Causative Agent | Mode of Transmission | Key Features / Prevention |
|---|---|---|---|
| Malaria | Plasmodium (P. falciparum most severe) — protozoan | Female Anopheles mosquito bite | Periodic fever (48h cycle for P. vivax, 72h for P. malariae); chills; Drug: chloroquine, artemisinin; prevention: mosquito nets, DDT |
| Dengue Fever | Dengue virus (Flavivirus, 4 serotypes) | Aedes aegypti mosquito (daytime biting) | High fever, severe headache, joint pain ("breakbone fever"), rash, thrombocytopenia; No specific antiviral; supportive treatment; Vaccine: Dengvaxia |
| Chikungunya | Chikungunya virus (Alphavirus) | Aedes aegypti / A. albopictus | Fever + severe joint pain (can persist for months-years); rash; no fatalities usually; no specific treatment |
| Tuberculosis (TB) | Mycobacterium tuberculosis (bacterium) | Airborne droplets (coughing, sneezing) | Affects lungs mainly; persistent cough, blood in sputum, weight loss, night sweats. Treatment: DOTS (Directly Observed Treatment, Short-course) — 6 months of multiple antibiotics (rifampicin, isoniazid, pyrazinamide, ethambutol). Vaccine: BCG. Drug-resistant TB (MDR-TB, XDR-TB) major concern |
| Typhoid | Salmonella typhi (bacterium) | Contaminated food and water (faecal-oral) | Sustained high fever, rose spots on abdomen, relative bradycardia. Widal test (agglutination test) for diagnosis. Treatment: antibiotics (ciprofloxacin, azithromycin) |
| Cholera | Vibrio cholerae (bacterium) | Contaminated water/food (faecal-oral) | Profuse watery diarrhoea ("rice water stools"), dehydration, electrolyte imbalance. Treatment: ORS (Oral Rehydration Solution), antibiotics. Vaccine available |
| Hepatitis B | Hepatitis B virus (HBV) | Blood, sexual contact, mother-to-child | Liver inflammation, jaundice; can progress to cirrhosis, liver cancer. Vaccine available (universal immunisation in India). Treatment: tenofovir, lamivudine |
| COVID-19 | SARS-CoV-2 (Coronavirus) | Respiratory droplets and aerosols | Fever, cough, breathlessness, loss of taste/smell; can cause severe pneumonia, ARDS. Vaccines: Covishield (AstraZeneca), Covaxin (Bharat Biotech), Corbevax, mRNA vaccines (Pfizer/Moderna) |
| Rabies | Rabies virus (Rhabdovirus) | Bite of infected animal (dog, bat) | Attacks nervous system; hydrophobia; nearly 100% fatal once symptoms appear. Prevention: post-exposure prophylaxis (PEP) — immediate wound washing + anti-rabies vaccine + immunoglobulin |
| Poliomyelitis | Poliovirus (Picornavirus, 3 serotypes) | Faecal-oral (contaminated water/food) | Irreversible flaccid paralysis of limbs; mainly affects children under 5. India declared polio-free (2014). Vaccines: OPV (oral, live attenuated, used in India's Pulse Polio Programme) and IPV (inactivated, injectable) |
| Filariasis (elephantiasis) | Wuchereria bancrofti (filarial worm — nematode) | Culex mosquito | Blockage of lymphatic vessels → lymphedema → swelling of legs/genitals. Drug: DEC (diethylcarbamazine) |
| Ringworm | Trichophyton, Microsporum (fungi) | Direct contact, contaminated towels/clothes | Circular itchy patches; treated with antifungal creams (clotrimazole, miconazole) |
Non-Communicable Diseases (NCDs)
Cardiovascular diseases: Leading cause of death globally. Atherosclerosis: plaque (cholesterol + calcium) deposits in artery walls → narrows and hardens arteries → reduced blood flow. Coronary artery disease (CAD) → angina, myocardial infarction (heart attack). Risk factors: hypertension, smoking, diabetes, obesity, sedentary lifestyle, high LDL cholesterol. Treatment: lifestyle changes, statins, angioplasty, bypass surgery.
Diabetes mellitus: Type 1 (insulin-dependent, autoimmune destruction of beta cells); Type 2 (insulin resistance, most common, lifestyle-related). Complications: retinopathy, nephropathy, neuropathy, cardiovascular disease. Management: diet, exercise, oral hypoglycaemics (metformin), insulin injections.
Cancer: Uncontrolled cell proliferation due to mutations in proto-oncogenes (become oncogenes) and tumour-suppressor genes (p53, Rb). Carcinogens: tobacco (lung, oral, bladder cancer), UV radiation (skin cancer), ionising radiation, certain viruses (HPV → cervical cancer; HBV/HCV → liver cancer). Diagnosis: biopsy, CT scan, MRI, PET scan. Treatment: surgery, chemotherapy (kills rapidly dividing cells — also affects normal cells → hair loss, nausea), radiotherapy, immunotherapy.
Diabetes mellitus: Type 1 (insulin-dependent, autoimmune destruction of beta cells); Type 2 (insulin resistance, most common, lifestyle-related). Complications: retinopathy, nephropathy, neuropathy, cardiovascular disease. Management: diet, exercise, oral hypoglycaemics (metformin), insulin injections.
Cancer: Uncontrolled cell proliferation due to mutations in proto-oncogenes (become oncogenes) and tumour-suppressor genes (p53, Rb). Carcinogens: tobacco (lung, oral, bladder cancer), UV radiation (skin cancer), ionising radiation, certain viruses (HPV → cervical cancer; HBV/HCV → liver cancer). Diagnosis: biopsy, CT scan, MRI, PET scan. Treatment: surgery, chemotherapy (kills rapidly dividing cells — also affects normal cells → hair loss, nausea), radiotherapy, immunotherapy.
Deficiency Diseases
| Vitamin/Mineral | Deficiency Disease | Symptoms | Food Sources |
|---|---|---|---|
| Vitamin A (Retinol) | Night blindness; Xerophthalmia | Poor vision in dim light; dry cornea; complete blindness in severe cases | Carrot, sweet potato, papaya, liver, egg, dairy |
| Vitamin B₁ (Thiamine) | Beriberi | Peripheral neuropathy, muscle weakness, cardiac failure (wet beriberi) | Whole grains, legumes, nuts, yeast |
| Vitamin B₃ (Niacin) | Pellagra | 3 Ds: Dermatitis, Diarrhoea, Dementia | Meat, fish, groundnuts, whole grains |
| Vitamin B₁₂ (Cobalamin) | Pernicious anaemia | Megaloblastic anaemia, nerve damage; requires intrinsic factor for absorption | Meat, fish, dairy, eggs (absent in plants → vegan deficiency risk) |
| Vitamin C (Ascorbic acid) | Scurvy | Bleeding gums, poor wound healing, joint pain; collagen synthesis impaired | Citrus fruits, amla (Indian gooseberry — highest Vit C), guava, tomato, bell pepper |
| Vitamin D (Calciferol) | Rickets (children); Osteomalacia (adults) | Soft/deformed bones, bowed legs; bones lack calcium mineralisation | Sunlight (UV converts 7-dehydrocholesterol to Vit D in skin), fish oil, fortified milk |
| Vitamin K | Haemorrhagic disease; excess bleeding | Impaired blood clotting (needed for prothrombin synthesis) | Green leafy vegetables, soybean; also synthesised by gut bacteria |
| Iron | Iron-deficiency anaemia | Fatigue, pallor, pica; most common nutritional deficiency globally | Spinach, lentils, liver, red meat, jaggery |
| Iodine | Goitre; Cretinism (in infants) | Enlarged thyroid gland; mental retardation + dwarfism if deficiency in foetus/infant | Iodised salt, seafood, dairy; common in Himalayan regions (iodine-poor soil) — hence iodine added to table salt |
| Calcium | Osteoporosis; Tetany | Bone loss, fracture risk; muscle cramps and spasms | Dairy, leafy greens, sesame, tofu |
Environment & Ecology
1. Ecology — Basic Concepts
Ecology: Scientific study of the interactions between living organisms (biotic factors) and their non-living environment (abiotic factors). Coined by Ernst Haeckel (1866). Ecosystem: A self-sustaining unit comprising all living organisms (biotic community) and non-living components (abiotic environment) in a given area interacting with each other.
Ecological Organisation (Levels)
Organism → Population (same species, same area) → Community (all populations in an area) → Ecosystem → Biome (major ecosystem type, e.g., tropical rainforest) → Biosphere (all ecosystems on Earth — thin layer from ~10 km below sea surface to ~10 km altitude; only zone where life exists).
Biotic and Abiotic Factors
| Category | Examples | Ecological Role |
|---|---|---|
| Biotic | Plants, animals, bacteria, fungi, viruses | Producers, consumers, decomposers, competitors, symbionts |
| Temperature (abiotic) | Varies by latitude and altitude | Determines distribution of species; most organisms active 10–40°C; Bergmann's rule: larger body size in colder climates |
| Water (abiotic) | Rainfall, humidity, availability | Key limiting factor; determines biome type; xeric (dry) → hydric (wet) species |
| Light (abiotic) | Solar radiation intensity, photoperiod | Drives photosynthesis; controls flowering (photoperiodism), breeding seasons; affects diurnal activity patterns |
| Soil (abiotic) | pH, texture, minerals, organic matter | Determines plant species composition; laterite soil (tropical, leached) vs black cotton soil (regur, Deccan, good for cotton) |
2. Food Chains, Food Webs and Ecological Pyramids
Food chain: Linear sequence of organisms where each organism eats the one below it, transferring energy from one trophic level to the next. Example: Grass → Grasshopper → Frog → Snake → Hawk
Trophic levels:
Producers (T1): Green plants, phytoplankton, cyanobacteria — fix solar energy by photosynthesis; support all other trophic levels.
Primary consumers (T2): Herbivores — eat producers directly (grasshopper, rabbit, cow, deer).
Secondary consumers (T3): Carnivores/omnivores — eat herbivores (frog, snake, fox).
Tertiary consumers (T4): Top carnivores — eat secondary consumers (hawk, tiger, crocodile).
Decomposers: Bacteria and fungi — break down dead organic matter into inorganic substances, recycling nutrients back into soil/water.
10% Law (Lindeman's rule, 1942): Only ~10% of energy at one trophic level is transferred to the next; ~90% is lost as heat (respiration), dead material, waste. This limits food chains to 4–5 levels and explains why carnivores are always rarer than herbivores.
Food web: Complex, interconnected network of multiple food chains in an ecosystem. More realistic than a single food chain. More trophic connections → greater stability of ecosystem (one species lost → less impact because predators/prey have alternatives).
Producers (T1): Green plants, phytoplankton, cyanobacteria — fix solar energy by photosynthesis; support all other trophic levels.
Primary consumers (T2): Herbivores — eat producers directly (grasshopper, rabbit, cow, deer).
Secondary consumers (T3): Carnivores/omnivores — eat herbivores (frog, snake, fox).
Tertiary consumers (T4): Top carnivores — eat secondary consumers (hawk, tiger, crocodile).
Decomposers: Bacteria and fungi — break down dead organic matter into inorganic substances, recycling nutrients back into soil/water.
10% Law (Lindeman's rule, 1942): Only ~10% of energy at one trophic level is transferred to the next; ~90% is lost as heat (respiration), dead material, waste. This limits food chains to 4–5 levels and explains why carnivores are always rarer than herbivores.
Food web: Complex, interconnected network of multiple food chains in an ecosystem. More realistic than a single food chain. More trophic connections → greater stability of ecosystem (one species lost → less impact because predators/prey have alternatives).
Ecological Pyramids
| Pyramid Type | What is Represented | Shape (usually) | Exceptions |
|---|---|---|---|
| Pyramid of Numbers | Number of organisms at each trophic level | Upright (in grass ecosystem) | Inverted in tree ecosystem (1 tree supports many insects → many birds) |
| Pyramid of Biomass | Total dry weight of organisms at each level | Upright (in terrestrial) | Inverted in aquatic (phytoplankton biomass < zooplankton at a given time — phytoplankton reproduce rapidly) |
| Pyramid of Energy | Energy (kcal/m²/year) at each level | Always upright (never inverted) | None — 10% law ensures energy always decreases up the pyramid |
3. Biogeochemical Cycles
Biogeochemical cycles: The cyclic movement of chemical elements between living organisms (biotic) and the non-living environment (abiotic — atmosphere, hydrosphere, lithosphere). Also called nutrient cycles.
Carbon Cycle
Carbon in atmosphere as CO₂: Photosynthesis removes CO₂ (plants fix ~120 billion tonnes C/year). Respiration (all organisms) releases CO₂. Decomposition releases CO₂ from dead matter. Combustion of fossil fuels (coal, oil, gas) releases stored carbon → increases atmospheric CO₂ → greenhouse effect → global warming. Ocean acts as carbon sink (CO₂ dissolves, forms carbonates). Deforestation reduces carbon fixation capacity.
Human impact: Pre-industrial CO₂ ≈ 280 ppm; current (2024) ≈ 420 ppm (highest in 800,000 years based on ice cores). Rate of increase: ~3 ppm/year.
Human impact: Pre-industrial CO₂ ≈ 280 ppm; current (2024) ≈ 420 ppm (highest in 800,000 years based on ice cores). Rate of increase: ~3 ppm/year.
Nitrogen Cycle
Atmospheric N₂ (78%) → Nitrogen fixation (Rhizobium, Azotobacter, lightning, Haber-Bosch industrial process) → NH₃/NH₄⁺ → Nitrification (Nitrosomonas: NH₄⁺ → NO₂⁻; Nitrobacter: NO₂⁻ → NO₃⁻) → plant uptake → proteins → decomposition (ammonification: Bacillus) → NH₄⁺ → Denitrification (Pseudomonas: NO₃⁻ → N₂) → atmosphere. Nitrogen is the most common limiting nutrient in agriculture → hence nitrogen fertilisers (urea, ammonium nitrate) are widely used.
Water Cycle (Hydrological Cycle)
Evaporation (from oceans, lakes, rivers) + Transpiration (from plants) → Water vapour in atmosphere → Condensation (cloud formation) → Precipitation (rain, snow, sleet, hail) → Surface runoff (rivers, streams) + Infiltration (groundwater recharge) → back to oceans/lakes. Total water on Earth ≈ 1.4 billion km³; fresh water ≈ 2.5% (of which 68.7% in glaciers; 30.1% groundwater; only 0.3% in rivers/lakes/accessible surface water).
4. Types of Ecosystems and Biodiversity
Major Biomes
| Biome | Climate | Characteristic Vegetation | Location Examples |
|---|---|---|---|
| Tropical Rainforest | Hot, humid, high rainfall (>200 cm/year), no dry season | Dense multi-layered canopy; highest biodiversity; epiphytes, lianas | Amazon (South America), Congo (Africa), Western Ghats/Andaman (India) |
| Tropical Savanna | Distinct wet and dry seasons; moderate rainfall | Grassland with scattered trees (acacia, baobab) | African grasslands, Deccan Plateau parts |
| Desert | Very low rainfall (<25 cm/year); extreme temperatures | CAM plants (cacti), xerophytes; sparse vegetation; high animal diversity adapted to heat | Sahara, Arabian, Thar (India), Atacama |
| Temperate Deciduous Forest | Moderate rainfall, cold winters (leaves shed) | Oak, maple, beech, birch; rich humus soil | Eastern USA, Europe, East Asia |
| Boreal Forest (Taiga) | Cold, long winters; short summers; moderate precipitation as snow | Coniferous trees (pine, spruce, fir) — adapted to snow load, frost | Canada, Siberia, Scandinavia |
| Tundra | Arctic; permafrost; very cold, low precipitation | No trees; low shrubs, mosses, lichens; seasonal flowering plants | Arctic regions, alpine zones (high altitude tundra) |
| Grassland / Steppe | Semi-arid; seasonal | Grasses, few trees; rich organic soil (mollisols) | Great Plains (USA), Pampas (S. America), Steppes (Central Asia) |
Aquatic Ecosystems
Freshwater ecosystems: Lakes (lentic — standing water), rivers/streams (lotic — flowing water), wetlands (highest productivity per unit area; carbon sinks; nursery habitats), swamps, bogs.
Marine ecosystems: Open ocean (oligotrophic — low nutrients); coastal zones and continental shelf (productive — upwelling brings nutrients); coral reefs ("rainforests of the sea" — highest marine biodiversity; formed by coral polyps — cnidarians with symbiotic zooxanthellae — threatened by bleaching due to warming oceans); estuaries (mixing of fresh and salt water — highly productive, nurseries for fish; mangroves stabilise coastline, protect from cyclones/tsunami); deep sea (chemosynthetic ecosystems near hydrothermal vents).
Mangroves in India: Sundarbans (West Bengal — largest mangrove forest in world; UNESCO World Heritage Site; Bengal Tiger habitat), Bhitarkanika (Odisha), Pichavaram (Tamil Nadu), Mahanadi delta. Mangroves provide: coastal protection, nursery habitat for fish/shrimp, carbon sequestration (blue carbon).
Marine ecosystems: Open ocean (oligotrophic — low nutrients); coastal zones and continental shelf (productive — upwelling brings nutrients); coral reefs ("rainforests of the sea" — highest marine biodiversity; formed by coral polyps — cnidarians with symbiotic zooxanthellae — threatened by bleaching due to warming oceans); estuaries (mixing of fresh and salt water — highly productive, nurseries for fish; mangroves stabilise coastline, protect from cyclones/tsunami); deep sea (chemosynthetic ecosystems near hydrothermal vents).
Mangroves in India: Sundarbans (West Bengal — largest mangrove forest in world; UNESCO World Heritage Site; Bengal Tiger habitat), Bhitarkanika (Odisha), Pichavaram (Tamil Nadu), Mahanadi delta. Mangroves provide: coastal protection, nursery habitat for fish/shrimp, carbon sequestration (blue carbon).
Biodiversity
Biodiversity: Variety of life on Earth at all levels — genetic diversity (variation within species), species diversity (number of different species), ecosystem diversity (variety of habitats and ecological processes). Coined by E.O. Wilson.
India's Biodiversity: India is a megadiverse country (one of 17 megadiverse countries with >70% of world's biodiversity). 2.4% of world's land area but 7–8% of world's species: 45,000 plant species, 90,000 animal species. Hotspots in India: Western Ghats + Sri Lanka; Eastern Himalayas; Indo-Burma (NE India); Sundaland. Total global biodiversity hotspots: 36 (Norman Myers concept — areas with high endemism and high habitat loss).
Endemism: Species found nowhere else on Earth. Western Ghats: Lion-tailed macaque, Nilgiri tahr, Malabar pied hornbill. Andaman-Nicobar: Andaman wild pig, Nicobar megapode.
Wildlife Protection Act, 1972: Protects wildlife; provides for national parks, sanctuaries, biosphere reserves; Schedule I animals (highest protection, e.g., tiger, elephant, lion, rhinoceros).
Project Tiger (1973): Launched by PM Indira Gandhi; 50+ Tiger Reserves; tiger population has recovered (from ~1827 in 2014 to ~3167 in 2022 — India has 75% of world's wild tigers). Project Elephant (1992); Project Snow Leopard; Operation Crocodile.
Endemism: Species found nowhere else on Earth. Western Ghats: Lion-tailed macaque, Nilgiri tahr, Malabar pied hornbill. Andaman-Nicobar: Andaman wild pig, Nicobar megapode.
Wildlife Protection Act, 1972: Protects wildlife; provides for national parks, sanctuaries, biosphere reserves; Schedule I animals (highest protection, e.g., tiger, elephant, lion, rhinoceros).
Project Tiger (1973): Launched by PM Indira Gandhi; 50+ Tiger Reserves; tiger population has recovered (from ~1827 in 2014 to ~3167 in 2022 — India has 75% of world's wild tigers). Project Elephant (1992); Project Snow Leopard; Operation Crocodile.
5. Environmental Issues and Conservation
Air Pollution
| Pollutant | Source | Effects |
|---|---|---|
| SO₂ (Sulphur dioxide) | Coal burning, smelting of sulphide ores | Acid rain (H₂SO₄); respiratory irritation; corrosion of buildings (marble cancer) |
| NOₓ (Nitrogen oxides) | Vehicle exhaust, thermal power plants | Acid rain (HNO₃); photochemical smog; ozone depletion |
| CO (Carbon monoxide) | Incomplete combustion; vehicle exhaust | Binds Hb (250× more than O₂) → asphyxiation; odourless, colourless, silent killer |
| Particulate Matter (PM2.5, PM10) | Vehicle exhaust, construction, crop burning, industrial dust | Respiratory diseases (asthma, COPD); PM2.5 most dangerous (enters blood); Delhi's major air quality issue |
| Ozone (ground level) | Photochemical reaction: NOₓ + VOCs + sunlight | Photochemical smog (Los Angeles type); respiratory damage; crop damage |
| Lead (Pb) | Leaded petrol (eliminated in India 2000), paint, batteries | Neurotoxic (impairs brain development in children); plumbism |
| Hydrocarbons / VOCs | Vehicle fuel evaporation, industrial solvents, natural (isoprene from plants) | Precursors to photochemical smog; many are carcinogens (benzene) |
Greenhouse Effect and Global Warming
Greenhouse gases (GHGs): CO₂ (most important — 76%); CH₄ (methane — 16%, 25× more potent than CO₂ over 100 years; from livestock, rice paddies, landfills, wetlands); N₂O (nitrous oxide — 6%, 298× more potent; from fertilisers, combustion); Fluorinated gases (HFCs, CFCs, SF₆ — most potent per molecule; from refrigerants, industry). Water vapour is actually the most abundant GHG but not directly controllable (feedback amplifier).
Consequences of global warming: Sea level rise (thermal expansion + glacial melt — threatens low-lying areas like Bangladesh, Maldives, Pacific islands); more frequent and intense extreme weather (floods, droughts, cyclones, heat waves); coral bleaching; species extinction; altered monsoon pattern; crop yield changes; spread of vector-borne diseases (malaria to higher altitudes and latitudes).
Paris Agreement (2015): Legally binding international treaty; goal: limit global temperature rise to well below 2°C above pre-industrial levels, ideally 1.5°C. NDCs (Nationally Determined Contributions) submitted by each country. India's NDC: 45% reduction in emissions intensity of GDP by 2030 (vs 2005); 50% cumulative electric power capacity from non-fossil fuels by 2030; net zero by 2070.
Consequences of global warming: Sea level rise (thermal expansion + glacial melt — threatens low-lying areas like Bangladesh, Maldives, Pacific islands); more frequent and intense extreme weather (floods, droughts, cyclones, heat waves); coral bleaching; species extinction; altered monsoon pattern; crop yield changes; spread of vector-borne diseases (malaria to higher altitudes and latitudes).
Paris Agreement (2015): Legally binding international treaty; goal: limit global temperature rise to well below 2°C above pre-industrial levels, ideally 1.5°C. NDCs (Nationally Determined Contributions) submitted by each country. India's NDC: 45% reduction in emissions intensity of GDP by 2030 (vs 2005); 50% cumulative electric power capacity from non-fossil fuels by 2030; net zero by 2070.
Ozone Layer Depletion
Ozone layer is in the stratosphere (15–35 km altitude). Ozone (O₃) absorbs harmful UV-B and UV-C radiation from the sun, protecting life on Earth.
Depletion mechanism: CFCs (chlorofluorocarbons — Freons; used in refrigerators, air conditioners, aerosol propellants) released in lower atmosphere → reach stratosphere → UV breaks C-Cl bond → chlorine radical (Cl•) catalytically destroys ozone: Cl• + O₃ → ClO + O₂; ClO + O → Cl• + O₂. One Cl atom destroys up to 100,000 ozone molecules.
Antarctic ozone hole: Observed since 1985 (Farman et al.); most severe in September–October (Southern spring); polar stratospheric clouds catalyse reactions; related to Antarctic vortex (cold, isolated air mass).
Montreal Protocol (1987): Most successful international environmental treaty — phased out CFCs and other ODSs (Ozone Depleting Substances). Ozone layer expected to recover by 2065–2070. HFCs (replacements for CFCs) are potent GHGs → addressed by Kigali Amendment (2016) to phase down HFCs.
Depletion mechanism: CFCs (chlorofluorocarbons — Freons; used in refrigerators, air conditioners, aerosol propellants) released in lower atmosphere → reach stratosphere → UV breaks C-Cl bond → chlorine radical (Cl•) catalytically destroys ozone: Cl• + O₃ → ClO + O₂; ClO + O → Cl• + O₂. One Cl atom destroys up to 100,000 ozone molecules.
Antarctic ozone hole: Observed since 1985 (Farman et al.); most severe in September–October (Southern spring); polar stratospheric clouds catalyse reactions; related to Antarctic vortex (cold, isolated air mass).
Montreal Protocol (1987): Most successful international environmental treaty — phased out CFCs and other ODSs (Ozone Depleting Substances). Ozone layer expected to recover by 2065–2070. HFCs (replacements for CFCs) are potent GHGs → addressed by Kigali Amendment (2016) to phase down HFCs.
Water and Soil Pollution
Eutrophication: Excessive nutrient (N and P from agricultural runoff, sewage) loading into water bodies → algal bloom → oxygen depletion as algae decompose → hypoxia → fish/aquatic life death. Creates "dead zones" (e.g., Baltic Sea, Gulf of Mexico).
Biological Oxygen Demand (BOD): Amount of oxygen needed by microorganisms to decompose organic matter in water. High BOD = highly polluted water. Clean water: BOD <1 mg/L; moderately polluted: 2–8 mg/L; heavily polluted: >8 mg/L. Sewage BOD ≈ 200 mg/L.
Biomagnification (bioaccumulation): Concentration of persistent pollutants (DDT, mercury, PCBs) increases at each trophic level. Example: DDT in water → plankton → small fish → large fish → birds of prey → humans. Pelicans, ospreys had eggshell thinning due to DDT (Ca metabolism disrupted) — nearly led to extinction; banned in India 2008.
Soil pollution: Industrial effluents, heavy metals (Cd, Pb, Hg, As — toxic, non-biodegradable), pesticide residues, plastic waste. Remediation: phytoremediation (plants like sunflower, mustard absorb heavy metals), bioremediation (bacteria/fungi degrade organic pollutants).
Biological Oxygen Demand (BOD): Amount of oxygen needed by microorganisms to decompose organic matter in water. High BOD = highly polluted water. Clean water: BOD <1 mg/L; moderately polluted: 2–8 mg/L; heavily polluted: >8 mg/L. Sewage BOD ≈ 200 mg/L.
Biomagnification (bioaccumulation): Concentration of persistent pollutants (DDT, mercury, PCBs) increases at each trophic level. Example: DDT in water → plankton → small fish → large fish → birds of prey → humans. Pelicans, ospreys had eggshell thinning due to DDT (Ca metabolism disrupted) — nearly led to extinction; banned in India 2008.
Soil pollution: Industrial effluents, heavy metals (Cd, Pb, Hg, As — toxic, non-biodegradable), pesticide residues, plastic waste. Remediation: phytoremediation (plants like sunflower, mustard absorb heavy metals), bioremediation (bacteria/fungi degrade organic pollutants).
Key Environmental Laws and Initiatives (India)
| Act / Initiative | Year | Key Provisions |
|---|---|---|
| Environment Protection Act | 1986 | Umbrella legislation; empowers central government to protect and improve environment; enacted after Bhopal gas tragedy (1984) |
| Wildlife Protection Act | 1972 | Protects wildlife; establishes national parks, sanctuaries; bans hunting of Schedule I species; CITES implementation |
| Forest Conservation Act | 1980 | Requires central government approval for diversion of forest land for non-forest purposes |
| Biological Diversity Act | 2002 | Implements CBD (Convention on Biological Diversity); establishes National Biodiversity Authority; access and benefit sharing |
| National Action Plan on Climate Change (NAPCC) | 2008 | 8 national missions: Solar Mission (JNNSM), Enhanced Energy Efficiency, Sustainable Habitat, Water, Himalayan Ecosystem, Green India, Sustainable Agriculture, Strategic Knowledge for Climate Change |
| National Green Tribunal (NGT) | 2010 | Specialised court for environmental cases; speedy disposal; can impose penalties; covers air, water, soil pollution |
| International Solar Alliance (ISA) | 2015 | India + France initiative at COP21; promotes solar energy in countries between Tropics of Cancer and Capricorn; 120+ member countries |
Science & Technology
1. Space Technology — ISRO Achievements
The Indian Space Research Organisation (ISRO), established in 1969 under Dr Vikram Sarabhai, has made India a major spacefaring nation. ISRO headquarters: Bengaluru. Chairman (as of 2024): Dr V. Narayanan.
| Mission / Programme | Year | Achievement / Significance |
|---|---|---|
| Aryabhata | 1975 | India's first satellite; launched by Soviet Kosmos-3M rocket |
| SLV-3 (Satellite Launch Vehicle) | 1980 | India's first successful satellite launch vehicle; placed Rohini satellite in orbit; led by APJ Abdul Kalam |
| ASLV (Augmented SLV) | 1994 | Augmented capability; paved way for PSLV |
| PSLV (Polar Satellite Launch Vehicle) | 1993 (first; 1994 success) | Workhorse of ISRO; 4-stage alternating solid/liquid; 60+ launches; launched Chandrayaan-1, MOM, Astrosat, navigation and EO satellites; PSLV-C37 (2017): 104 satellites in one launch — world record |
| GSLV (Geosynchronous SLV) | 2001 (first); 2014 (indigenous cryo) | Heavy-lift; uses cryogenic upper stage (India developed indigenous cryogenic engine after technology denial by USA/Russia); places satellites in GTO |
| GSLV Mk III / LVM3 | 2017 | India's heaviest rocket (640 tonnes); 4-tonne class to GTO; used for Chandrayaan-2, Chandrayaan-3, commercial OneWeb launches |
| Chandrayaan-1 | 2008 | India's first lunar mission; MIP (Moon Impact Probe) crashed at south pole; Moon Mineralogy Mapper confirmed water molecules in lunar soil (in permanently shadowed craters); discovered hydroxyl on Moon |
| Mangalyaan (MOM) | 2013–2014 | Mars Orbiter Mission; India first Asian nation and fourth globally to reach Mars; cheapest Mars mission ($73 million); studied Martian atmosphere and surface |
| Chandrayaan-2 | 2019 | Orbiter (operational, providing high-resolution lunar maps), Vikram lander (hard-landed due to braking software issue — 2.1 km from target), Pragyan rover (not deployed) |
| Chandrayaan-3 | 2023 | India first country to land near lunar south pole (23 August 2023); Vikram lander + Pragyan rover operated for ~14 days (one lunar day); measured surface temperature (top: +50°C; 8 cm below: −10°C); detected sulphur on south polar surface; registered moonquake |
| Aditya-L1 | 2023 | India's first solar observatory; placed at Sun-Earth Lagrange Point 1 (L1, ~1.5 million km from Earth); studies solar corona, solar wind, CMEs, UV and X-ray emissions; operational from January 2024 |
| NavIC (Navigation with Indian Constellation) | 2016–2018 | India's own regional navigation satellite system (like GPS); 8 satellites; covers India + ~1500 km surrounding region; accuracy <20 m; used in transport, fishing boats, disaster management |
| Gaganyaan | Expected 2025–2026 | India's first human spaceflight mission; crew of 3 Indian astronauts (Vyomanauts) for 3-day orbit; CM capsule recovery from Bay of Bengal |
🎯 BPSC Space Facts: ISRO launch centres: Satish Dhawan Space Centre (SDSC), Sriharikota, Andhra Pradesh — primary launch site; Thumba Equatorial Rocket Launching Station (TERLS), Kerala — first sounding rocket site. Remote sensing: Cartosat, Resourcesat series. Communication: INSAT, GSAT series. ISRO's commercial arm: NewSpace India Limited (NSIL). Antrix Corporation: older commercial arm. VSSC (Vikram Sarabhai Space Centre), Thiruvananthapuram: designs and develops launch vehicles. SAC (Space Applications Centre), Ahmedabad: develops satellite payloads.
2. Defence Technology
Missile Programme (DRDO and BrahMos Aerospace)
| Missile | Type | Range | Key Features |
|---|---|---|---|
| Prithvi | Surface-to-Surface (ballistic) | 150–350 km | India's first indigenously developed ballistic missile; liquid-fuelled; nuclear capable; variants: Prithvi I (army), II (air force), III (naval, Dhanush) |
| Agni | Surface-to-Surface (ballistic, ICBM class) | 700–5000+ km | Agni-I (700 km), Agni-II (2000 km), Agni-III (3500 km), Agni-IV (4000 km), Agni-V (5000+ km, ICBM, MIRV capable); solid-fuelled; nuclear capable |
| BrahMos | Supersonic cruise missile | 290–500+ km | Joint India (DRDO) + Russia (NPO Mashinostroyenia); fastest operational cruise missile (~Mach 2.8–3.0); can be launched from land, sea, air, submarine; named after Brahmaputra and Moskva rivers |
| Akash | Surface-to-Air (SAM) | 25–30 km | Indigenous air defence missile system; Mach 2.5; guided by phased array radar (Rajendra); protects against aircraft, helicopters, drones, cruise missiles; exported to Philippines |
| Trishul | Short-range Surface-to-Air | 9 km | Low-level quick reaction SAM; ship-borne and land-based; part of IGMDP |
| Nag | Anti-tank guided missile | 4–7 km | Fire-and-forget; imaging infrared seeker; helicopter-launched (Helina) and ground-launched (Namica) |
| Astra | Beyond Visual Range Air-to-Air | 80–110 km | India's first indigenously developed air-to-air missile; carried by Sukhoi-30MKI, Tejas; active radar homing |
IGMDP (Integrated Guided Missile Development Programme, 1983–2008): Launched by Dr APJ Abdul Kalam; developed Prithvi, Agni, Akash, Trishul, and Nag missiles. Now succeeded by mission-specific programmes.
Tejas (LCA): Light Combat Aircraft; first indigenous supersonic fighter; operated by IAF; Mark 1A has upgraded radar (AESA), IRST, better avionics; DRDO/ADA/HAL collaboration.
INS Vikrant: India's first indigenous aircraft carrier (commissioned 2022); 45,000 tonnes; MiG-29K and LCA naval variant operate from it; built at Cochin Shipyard.
Tejas (LCA): Light Combat Aircraft; first indigenous supersonic fighter; operated by IAF; Mark 1A has upgraded radar (AESA), IRST, better avionics; DRDO/ADA/HAL collaboration.
INS Vikrant: India's first indigenous aircraft carrier (commissioned 2022); 45,000 tonnes; MiG-29K and LCA naval variant operate from it; built at Cochin Shipyard.
3. Nuclear Technology
Nuclear Power in India: Regulated by Atomic Energy Commission (AEC); operated by Nuclear Power Corporation of India (NPCIL). Installed capacity: ~7.5 GW (2024); target 22 GW by 2031. Major plants: Tarapur (Maharashtra, oldest — 1969), Kakrapar (Gujarat), Rajasthan (Rawatbhata), Madras (Kalpakkam), Kaiga (Karnataka), Kudankulam (Tamil Nadu — Russia collaboration, largest plant in India).
Nuclear fuel cycle in India: Stage 1: Pressurised Heavy Water Reactors (PHWRs) using natural uranium (U-238/U-235); produce Pu-239. Stage 2: Fast Breeder Reactors (FBRs) using Pu-239 as fuel; breed U-238 → Pu-239 AND thorium-232 → U-233. Stage 3: Advanced Heavy Water Reactors (AHWRs) using U-233 (from Th-232). India has world's largest thorium reserves (Kerala/Tamil Nadu beach sands — monazite) → strategic 3-stage programme.
Pokhran Tests: 1974 (Pokhran I, Operation Smiling Buddha) — India became 6th nuclear power. 1998 (Pokhran II, Operation Shakti) — 5 tests under PM Atal Bihari Vajpayee; India declared itself a nuclear weapons state.
Nuclear fuel cycle in India: Stage 1: Pressurised Heavy Water Reactors (PHWRs) using natural uranium (U-238/U-235); produce Pu-239. Stage 2: Fast Breeder Reactors (FBRs) using Pu-239 as fuel; breed U-238 → Pu-239 AND thorium-232 → U-233. Stage 3: Advanced Heavy Water Reactors (AHWRs) using U-233 (from Th-232). India has world's largest thorium reserves (Kerala/Tamil Nadu beach sands — monazite) → strategic 3-stage programme.
Pokhran Tests: 1974 (Pokhran I, Operation Smiling Buddha) — India became 6th nuclear power. 1998 (Pokhran II, Operation Shakti) — 5 tests under PM Atal Bihari Vajpayee; India declared itself a nuclear weapons state.
4. Information Technology and Biotechnology
Key IT Developments
Artificial Intelligence (AI): Machine simulation of human intelligence. Machine Learning (ML): algorithms that learn from data. Deep Learning: neural networks with many layers (GPT models, image recognition). India's National AI Strategy (NITI Aayog); National Supercomputing Mission (NSM): PARAM series supercomputers (PARAM Siddhi — ranks in global Top500; built by C-DAC, Pune).
Digital India Programme (2015): Transforms India into digitally empowered society. Key pillars: BharatNet (broadband connectivity to gram panchayats), digital literacy, e-governance (DigiLocker, MyGov, UMANG app), UPI (Unified Payments Interface — India's fastest-growing digital payment system; over 10 billion transactions/month; available in multiple countries).
PARAM Supercomputers (C-DAC): PARAM 8000 (1991 — India's first indigenously designed supercomputer after USA denied Cray supercomputer); PARAM Siddhi-AI (2020 — 210 PFLOPS — National Supercomputer Mission, IIT Kharagpur). Used for weather forecasting, drug discovery, seismic analysis.
5G in India: Launched October 2022; Jio and Airtel offering 5G; India has two 5G bands — mid-band (3.3 GHz) and mmWave (26 GHz). BIS (Bureau of Indian Standards) 5G standards; BSNL developing its own 4G/5G stack with TCS (made-in-India 4G core).
Digital India Programme (2015): Transforms India into digitally empowered society. Key pillars: BharatNet (broadband connectivity to gram panchayats), digital literacy, e-governance (DigiLocker, MyGov, UMANG app), UPI (Unified Payments Interface — India's fastest-growing digital payment system; over 10 billion transactions/month; available in multiple countries).
PARAM Supercomputers (C-DAC): PARAM 8000 (1991 — India's first indigenously designed supercomputer after USA denied Cray supercomputer); PARAM Siddhi-AI (2020 — 210 PFLOPS — National Supercomputer Mission, IIT Kharagpur). Used for weather forecasting, drug discovery, seismic analysis.
5G in India: Launched October 2022; Jio and Airtel offering 5G; India has two 5G bands — mid-band (3.3 GHz) and mmWave (26 GHz). BIS (Bureau of Indian Standards) 5G standards; BSNL developing its own 4G/5G stack with TCS (made-in-India 4G core).
Biotechnology Advances
Recombinant DNA Technology / Genetic Engineering: Manipulation of DNA to produce recombinant proteins or genetically modified organisms. Key tools: Restriction endonucleases (molecular scissors — cut DNA at specific sequences); DNA ligase (joins DNA fragments); vectors (plasmids, viruses — carry foreign DNA); host cells (bacteria, yeast). Applications: Insulin production (Humulin — human insulin gene in E. coli; replaced pig/cow insulin); Human Growth Hormone; Hepatitis B vaccine (recombinant); erythropoietin (for anaemia); tissue plasminogen activator (tPA — for heart attack treatment).
CRISPR-Cas9 (Gene Editing): Clustered Regularly Interspaced Short Palindromic Repeats + Cas9 nuclease. Discovered in bacteria (bacterial immune system). Jennifer Doudna and Emmanuelle Charpentier — Nobel Prize in Chemistry, 2020. Allows precise, efficient editing of any gene at any location. Applications: potential cure for sickle-cell anaemia (done — first patient cured 2023), cancer immunotherapy (CAR-T cells), agricultural crop improvement, gene drives to eliminate malaria-carrying mosquitoes. Ethical concerns: germline editing, designer babies.
Bt crops: Bacillus thuringiensis produces Bt toxin (Cry proteins) — insecticidal protein. Bt gene inserted into crops → plants produce their own insecticide. Bt cotton (approved in India 2002) — controls bollworm; dramatically reduced insecticide use; India now one of world's largest cotton producers. Bt Brinjal (Bt eggplant) — approved but moratorium maintained due to controversy. GM mustard (DMH-11) — herbicide tolerant and hybrid seed production; approved by GEAC 2022.
Vaccines — Novel platforms: mRNA vaccines (COVID-19 — Pfizer-BioNTech, Moderna): synthetic mRNA encoding spike protein → body produces spike protein → immune response. No live virus; cannot cause infection; rapidly designed. Vector vaccines (Covishield/AstraZeneca — adenovirus vector; Russia's Sputnik V). Protein subunit vaccines (Novavax, Corbevax). VLP (Virus-Like Particle) vaccines. India's Covaxin: inactivated whole-virus vaccine; developed by Bharat Biotech with ICMR; BBV152 strain.
CRISPR-Cas9 (Gene Editing): Clustered Regularly Interspaced Short Palindromic Repeats + Cas9 nuclease. Discovered in bacteria (bacterial immune system). Jennifer Doudna and Emmanuelle Charpentier — Nobel Prize in Chemistry, 2020. Allows precise, efficient editing of any gene at any location. Applications: potential cure for sickle-cell anaemia (done — first patient cured 2023), cancer immunotherapy (CAR-T cells), agricultural crop improvement, gene drives to eliminate malaria-carrying mosquitoes. Ethical concerns: germline editing, designer babies.
Bt crops: Bacillus thuringiensis produces Bt toxin (Cry proteins) — insecticidal protein. Bt gene inserted into crops → plants produce their own insecticide. Bt cotton (approved in India 2002) — controls bollworm; dramatically reduced insecticide use; India now one of world's largest cotton producers. Bt Brinjal (Bt eggplant) — approved but moratorium maintained due to controversy. GM mustard (DMH-11) — herbicide tolerant and hybrid seed production; approved by GEAC 2022.
Vaccines — Novel platforms: mRNA vaccines (COVID-19 — Pfizer-BioNTech, Moderna): synthetic mRNA encoding spike protein → body produces spike protein → immune response. No live virus; cannot cause infection; rapidly designed. Vector vaccines (Covishield/AstraZeneca — adenovirus vector; Russia's Sputnik V). Protein subunit vaccines (Novavax, Corbevax). VLP (Virus-Like Particle) vaccines. India's Covaxin: inactivated whole-virus vaccine; developed by Bharat Biotech with ICMR; BBV152 strain.
Nanotechnology
Nanotechnology: Science and engineering at the nanoscale (1–100 nm = 10⁻⁹ m). Properties at nanoscale differ from bulk — quantum effects, high surface-area-to-volume ratio, unique optical/electrical/catalytic properties. Examples: Gold nanoparticles (appear red/purple — used in pregnancy test kits — lateral flow assays); Carbon nanotubes (stronger than steel, electrically conductive — future electronics, drug delivery); Quantum dots (semiconductor nanocrystals — coloured by size — LED displays, medical imaging); Nano-silver (antimicrobial — antibacterial socks, wound dressings).
Applications: Drug delivery (nanoparticles encapsulate drugs → targeted delivery to tumour cells → less side effects); Diagnostic imaging (iron oxide NPs for MRI contrast); Water purification (nano-membranes); Sunscreen (nano-TiO₂ and ZnO particles absorb UV); Nano-composites (stronger, lighter materials for aerospace, automobiles).
India's nano initiatives: Nano Science and Technology Initiative (NSTI); Mission Nano Science and Technology (Nano Mission) under DST; National Nanofabrication Centre (NNfC), IISc Bengaluru.
Applications: Drug delivery (nanoparticles encapsulate drugs → targeted delivery to tumour cells → less side effects); Diagnostic imaging (iron oxide NPs for MRI contrast); Water purification (nano-membranes); Sunscreen (nano-TiO₂ and ZnO particles absorb UV); Nano-composites (stronger, lighter materials for aerospace, automobiles).
India's nano initiatives: Nano Science and Technology Initiative (NSTI); Mission Nano Science and Technology (Nano Mission) under DST; National Nanofabrication Centre (NNfC), IISc Bengaluru.
5. Important Scientific Institutions in India
| Institution | Location | Area of Work |
|---|---|---|
| ISRO (Indian Space Research Organisation) | Bengaluru, Karnataka | Space research, launch vehicles, satellites, lunar/planetary missions |
| DRDO (Defence Research and Development Organisation) | New Delhi (HQ); 50+ labs across India | Defence technology — missiles, aircraft, armoured vehicles, electronics, chemical/bio defence |
| BARC (Bhabha Atomic Research Centre) | Trombay, Mumbai, Maharashtra | Nuclear research, reactor design, isotope production, radiation applications; India's primary nuclear research facility |
| CSIR (Council of Scientific and Industrial Research) | New Delhi (HQ); 37 labs | Applied research; labs include: NCL (National Chemical Laboratory, Pune), CCMB (Centre for Cellular and Molecular Biology, Hyderabad), CDRI (Central Drug Research Institute, Lucknow), NIO (National Institute of Oceanography, Goa) |
| ICAR (Indian Council of Agricultural Research) | New Delhi (HQ) | Agricultural research; Green Revolution; crop varieties; IARI (Indian Agricultural Research Institute, New Delhi — "Pusa Institute"); NRSA; IVRI (Izatnagar) |
| ICMR (Indian Council of Medical Research) | New Delhi (HQ) | Medical and biomedical research; developed Covaxin with Bharat Biotech; monitors disease burden, drug trials |
| IITs (Indian Institutes of Technology) | 23 IITs across India (oldest: IIT Kharagpur, 1951) | Science, engineering, research, innovation; produce world-class engineers and scientists |
| IISc (Indian Institute of Science) | Bengaluru, Karnataka (est. 1909) | Basic and applied research across all science disciplines; consistently ranked India's top research university |
| GSI (Geological Survey of India) | Kolkata, West Bengal (est. 1851) | Geological mapping, mineral exploration, seismic monitoring, offshore surveys; oldest scientific organisation in India |
| IMD (India Meteorological Department) | New Delhi (HQ) | Weather forecasting, cyclone warning, monsoon prediction; established 1875 |
| NITI Aayog | New Delhi | Policy think tank (replaced Planning Commission in 2015); drives innovation and AI policy; operates Atal Innovation Mission (AIM) |
| DST (Department of Science and Technology) | New Delhi | Promotes science and technology; funds research through SERB (Science and Engineering Research Board), various national missions |
Nobel Prizes — Indian Scientists
| Scientist | Year | Prize | Contribution |
|---|---|---|---|
| C.V. Raman | 1930 | Physics | Discovery of Raman Effect (inelastic scattering of light — frequency change when light passes through a transparent medium; used in Raman spectroscopy) |
| Hargobind Khorana | 1968 | Medicine | Interpretation of the genetic code and its function in protein synthesis (Indian-American) |
| Subramanyan Chandrasekhar | 1983 | Physics | Chandrasekhar limit (~1.4 solar masses — maximum mass of a stable white dwarf star; beyond this → neutron star or black hole); Indian-American |
| Amartya Sen | 1998 | Economics | Welfare economics; famine analysis (famines occur not from food shortage but from distribution failure); Human Development Index |
| Venkatraman Ramakrishnan | 2009 | Chemistry | Structure and function of the ribosome (along with Thomas Steitz and Ada Yonath); Indian-American |
| Abhijit Banerjee | 2019 | Economics | Experimental approach to alleviating global poverty (randomised controlled trials in development economics); Indian-American |
6. Recent Science & Technology (Current Affairs Context)
Quantum Computing: Uses quantum bits (qubits) that exist in superposition (both 0 and 1 simultaneously) and entanglement. Vastly outperforms classical computers for specific problems: factorisation of large numbers (breaking RSA encryption), drug molecule simulation, optimisation. Google's Sycamore processor (2019): 53 qubits, solved specific problem in 200 seconds that would take classical supercomputer 10,000 years. IBM, IonQ, Quantinuum, Rigetti are key players. India's National Quantum Mission (2023): ₹6,000 crore over 8 years; targets 1000-qubit quantum computer by 2031.
ChatGPT and Large Language Models (LLMs): GPT-4 (OpenAI), Gemini (Google), Llama (Meta), Claude (Anthropic) — transformer-based neural networks trained on vast text data; can understand and generate human-like text. India developing BharatGPT (consortium of IITs) for Indian languages. Concerns: misinformation, bias, job displacement, privacy.
Electric Vehicles (EVs) in India: FAME (Faster Adoption and Manufacturing of EVs) scheme; PLI (Production-Linked Incentive) for advanced chemistry cell batteries; Tata Nexon EV, Ola Electric S1, Ather 450 prominent examples. NITI Aayog target: 30% EV penetration by 2030. Lithium-ion battery: cathode (LiCoO₂ or LFP), anode (graphite), electrolyte (lithium salt in organic solvent). India's Li-ion supply chain: imports from China/Japan; domestic lithium reserves found in J&K Reasi district (2023 — ~5.9 million tonnes potential — largest in world).
Green Hydrogen: Produced by electrolysis of water using renewable energy (solar/wind). Zero-carbon fuel; can replace fossil fuels in steel production, fertilisers, shipping, aviation. India's National Green Hydrogen Mission (2023): target 5 million tonnes/year production by 2030; ₹19,744 crore budget. ISRO and NTPC have demonstrated hydrogen fuel cells.
ChatGPT and Large Language Models (LLMs): GPT-4 (OpenAI), Gemini (Google), Llama (Meta), Claude (Anthropic) — transformer-based neural networks trained on vast text data; can understand and generate human-like text. India developing BharatGPT (consortium of IITs) for Indian languages. Concerns: misinformation, bias, job displacement, privacy.
Electric Vehicles (EVs) in India: FAME (Faster Adoption and Manufacturing of EVs) scheme; PLI (Production-Linked Incentive) for advanced chemistry cell batteries; Tata Nexon EV, Ola Electric S1, Ather 450 prominent examples. NITI Aayog target: 30% EV penetration by 2030. Lithium-ion battery: cathode (LiCoO₂ or LFP), anode (graphite), electrolyte (lithium salt in organic solvent). India's Li-ion supply chain: imports from China/Japan; domestic lithium reserves found in J&K Reasi district (2023 — ~5.9 million tonnes potential — largest in world).
Green Hydrogen: Produced by electrolysis of water using renewable energy (solar/wind). Zero-carbon fuel; can replace fossil fuels in steel production, fertilisers, shipping, aviation. India's National Green Hydrogen Mission (2023): target 5 million tonnes/year production by 2030; ₹19,744 crore budget. ISRO and NTPC have demonstrated hydrogen fuel cells.
7. Applied Chemistry — Everyday Science
Common Chemicals in Daily Life
| Common Name | Chemical Name | Formula | Use / Significance |
|---|---|---|---|
| Table salt | Sodium chloride | NaCl | Food seasoning, preservation, electrolyte; iodised to prevent goitre |
| Washing soda | Sodium carbonate decahydrate | Na₂CO₃·10H₂O | Laundry, softening hard water, glass manufacturing |
| Baking soda | Sodium bicarbonate | NaHCO₃ | Leavening agent in baking, antacid, fire extinguisher (releases CO₂) |
| Bleaching powder | Calcium hypochlorite (mixed) | Ca(ClO)Cl | Water treatment, disinfectant, bleaching agent; active chlorine kills bacteria |
| Plaster of Paris | Calcium sulphate hemihydrate | CaSO₄·½H₂O | Casts, moulds, broken bone immobilisation; sets hard by reabsorbing water |
| Alum | Potassium aluminium sulphate | KAl(SO₄)₂·12H₂O | Water purification (flocculates suspended particles), styptic pencil (stops bleeding), pickling |
| Limestone | Calcium carbonate | CaCO₃ | Construction, glass, cement manufacturing; caves (stalactites/stalagmites) |
| Caustic soda | Sodium hydroxide | NaOH | Strong base; soap making (saponification), paper industry, drain cleaners |
| Vinegar | Dilute acetic acid (5–8%) | CH₃COOH | Food preservative, condiment; produced by acetic acid fermentation by Acetobacter bacteria |
| Dry ice | Solid carbon dioxide | CO₂ (solid) | Refrigerant for biological samples, stage fog effects; sublimes directly (−78.5°C) without liquid phase |
| Heavy water | Deuterium oxide | D₂O | Moderator in CANDU nuclear reactors (slows neutrons without absorbing them); freezes at 3.8°C (vs 0°C for H₂O) |
| Acetylene | Ethyne | C₂H₂ | Oxyacetylene welding/cutting (hottest flame ~3500°C); calcium carbide + water → C₂H₂ |
| Chloroform | Trichloromethane | CHCl₃ | Historic anaesthetic; now solvent; reacts with air → phosgene (toxic) so stored dark |
| CFC (Freon) | Chlorofluorocarbons (various) | CCl₂F₂ (Freon-12) | Former refrigerants/aerosol propellants; cause ozone depletion; phased out under Montreal Protocol |
| TNT | 2,4,6-Trinitrotoluene | C₇H₅N₃O₆ | Military explosive; reference for explosion energy (1 tonne TNT = 4.184 GJ) |
Metals and Alloys — Properties and Uses
| Alloy | Composition | Properties | Uses |
|---|---|---|---|
| Steel | Iron + Carbon (0.2–2.1%) | Hard, strong, malleable | Construction, machinery, railway tracks, automobiles |
| Stainless steel | Iron + 10.5–18% Chromium + Nickel | Corrosion resistant, hard, lustrous | Cutlery, kitchen equipment, surgical instruments, architecture |
| Brass | Copper + Zinc (30%) | Yellow, corrosion resistant, acoustic | Musical instruments, fittings, coins, valves |
| Bronze | Copper + Tin (5–25%) | Hard, corrosion resistant, historically important | Statues, bells, bearings, coins; Bronze Age (3300–1200 BCE) |
| Duralumin | Aluminium + Copper (4%) + Mn + Mg | Light, strong, age hardens | Aircraft, spacecraft structural parts; density ~2.8 g/cm³ |
| Solder | Lead + Tin (60:40 or 50:50) | Low melting point (~180°C), good electrical conductivity | Electronics joining; lead-free solder (Sn-Ag-Cu) now preferred for health/environment |
| Nichrome | Nickel + Chromium (80:20) | High resistance, high melting point, doesn't oxidise | Heating elements in toasters, electric irons, furnaces |
| Amalgam | Mercury + other metal (Ag, Sn, Hg) | Sets hard, mercury causes toxicity concerns | Dental fillings (being phased out due to mercury content); thermometers |
pH and Its Importance
pH scale (0–14): pH = −log₁₀[H⁺]. pH < 7: acidic; pH = 7: neutral (pure water at 25°C); pH > 7: alkaline/basic.
Biological importance: Blood pH: 7.35–7.45 (must be maintained precisely — acidosis <7.35; alkalosis >7.45 both life-threatening). Gastric juice: pH 1.5–2 (kills most bacteria). Saliva: 6.5–7.4 (amylase works). Urine: 4.5–8.5 (normally ~6). Soil pH: affects nutrient availability — most crops grow best at pH 6–7; acidic soils amended with lime (CaCO₃) or slaked lime (Ca(OH)₂).
Buffer solutions: Resist pH change on addition of acid or base. Blood buffer: carbonic acid/bicarbonate system (H₂CO₃/HCO₃⁻); haemoglobin also acts as buffer. Bicarbonate buffer: H₂CO₃ ⇌ H⁺ + HCO₃⁻ — if H⁺ added, bicarbonate neutralises it; if H⁺ removed, carbonic acid dissociates to replenish.
Biological importance: Blood pH: 7.35–7.45 (must be maintained precisely — acidosis <7.35; alkalosis >7.45 both life-threatening). Gastric juice: pH 1.5–2 (kills most bacteria). Saliva: 6.5–7.4 (amylase works). Urine: 4.5–8.5 (normally ~6). Soil pH: affects nutrient availability — most crops grow best at pH 6–7; acidic soils amended with lime (CaCO₃) or slaked lime (Ca(OH)₂).
Buffer solutions: Resist pH change on addition of acid or base. Blood buffer: carbonic acid/bicarbonate system (H₂CO₃/HCO₃⁻); haemoglobin also acts as buffer. Bicarbonate buffer: H₂CO₃ ⇌ H⁺ + HCO₃⁻ — if H⁺ added, bicarbonate neutralises it; if H⁺ removed, carbonic acid dissociates to replenish.
8. Human Nutrition and Food Science
Macronutrients
| Nutrient | Caloric Value | Functions | Sources | Recommended Daily Intake (adult) |
|---|---|---|---|---|
| Carbohydrates | 4 kcal/g | Primary energy source; glucose → ATP via glycolysis → Krebs cycle; brain exclusively uses glucose (120 g/day); fibre supports gut health | Cereals (rice, wheat, maize), potato, sugar, fruits, legumes | 45–65% of total calorie intake (~250–350 g for 2000 kcal diet) |
| Proteins | 4 kcal/g | Building and repair of tissues; enzymes, antibodies, hormones; haemoglobin; growth | Meat, fish, eggs, dairy, legumes (dal, rajma, soya — incomplete protein), tofu, nuts | 0.8 g/kg body weight; athletes 1.2–2.0 g/kg; India: 60 g/day (adult male) |
| Fats | 9 kcal/g | Energy storage (9 kcal/g — most energy-dense); fat-soluble vitamin absorption (A, D, E, K); cell membrane component; insulation; hormone synthesis | Oils, butter, ghee, nuts, seeds, fatty fish, meat, dairy | 20–35% of calorie intake; limit saturated fat <10%; avoid trans fat |
Essential amino acids (9): Cannot be synthesised by the human body; must come from diet. Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine (mnemonic: "His Ile Leu Lys Met Phe Thr Trp Val"). Lysine deficient in cereals; methionine deficient in legumes — hence combining cereal + legume gives complete protein (e.g., rice + dal).
Essential fatty acids: Omega-3 (alpha-linolenic acid — ALA → EPA → DHA): found in flaxseed, walnuts, fatty fish; important for brain, heart, anti-inflammatory. Omega-6 (linoleic acid): sunflower oil, corn oil; important for skin, reproduction. Both are polyunsaturated fatty acids (PUFAs) that the body cannot synthesise.
Trans fats: Artificially hydrogenated vegetable oils (vanaspati, margarine); raise LDL, lower HDL — strongest dietary predictor of cardiovascular disease. WHO target: global elimination by 2023 (ongoing). India: mandatory trans fat declaration on labels; max 2% in foods from 2022.
Essential fatty acids: Omega-3 (alpha-linolenic acid — ALA → EPA → DHA): found in flaxseed, walnuts, fatty fish; important for brain, heart, anti-inflammatory. Omega-6 (linoleic acid): sunflower oil, corn oil; important for skin, reproduction. Both are polyunsaturated fatty acids (PUFAs) that the body cannot synthesise.
Trans fats: Artificially hydrogenated vegetable oils (vanaspati, margarine); raise LDL, lower HDL — strongest dietary predictor of cardiovascular disease. WHO target: global elimination by 2023 (ongoing). India: mandatory trans fat declaration on labels; max 2% in foods from 2022.
Food Preservation Methods
| Method | Principle | Foods Preserved |
|---|---|---|
| Refrigeration (4°C) | Slows microbial growth and enzyme activity | Dairy, meat, vegetables, cooked food (short-term) |
| Freezing (−18°C) | Stops microbial growth; ice crystals inhibit enzymes | Meat, fish, vegetables, fruits, ice cream (long-term) |
| Pasteurisation | 72°C for 15 seconds (HTST) kills pathogens without changing taste significantly; some spoilage bacteria survive — still needs refrigeration | Milk, fruit juices, beer, wine |
| Sterilisation/UHT | 135°C for 2–4 seconds kills all microorganisms including spores; aseptic packaging → shelf stable | UHT milk (Tetra Pak), canned foods (115°C for 30 min in autoclave) |
| Drying/Dehydration | Removes water (aw <0.6) — microbes cannot grow; reduces weight | Pulses, cereals, dried fruits, fish (sun-dried), milk powder, instant noodles |
| Salting/Pickling | High salt/acid (low pH) creates osmotic pressure or inhibits enzymes; acetic acid/lactic acid are antimicrobial | Pickles (achar), salt fish, sauerkraut, kimchi, cured meat |
| Sugaring | High sugar (jams, jellies): high osmotic pressure inhibits microbial growth | Jams, jellies, marmalade, candied fruits |
| Fermentation | Beneficial microorganisms produce alcohol or acid that inhibit pathogens; enhances nutrition (B vitamins) | Idli/dosa (lactic acid bacteria), yoghurt (Lactobacillus), cheese, bread (yeast), beer/wine |
| Irradiation | Ionising radiation (gamma rays from Co-60 or Cs-137) kills bacteria, insects, delays ripening; no radioactivity retained in food | Spices, onions, potatoes, strawberries; WHO/FAO approved as safe |
| Chemical preservatives | Antimicrobial or antioxidant action | Sodium benzoate (soft drinks, jams); potassium sorbate (cheese, wine); BHA/BHT (fats and oils — antioxidant); SO₂/sulphites (dried fruit, wine) |
9. Physics Applications — Instruments and Measurements
Scientific Instruments and Their Uses
| Instrument | Measures / Detects | Principle |
|---|---|---|
| Barometer | Atmospheric pressure | Mercury column supported by air pressure; Torricelli (1643); 1 atm = 760 mmHg = 101.325 kPa |
| Hygrometer | Relative humidity | Hair hygrometer: hair length changes with humidity; dew point hygrometer; digital capacitive sensors |
| Anemometer | Wind speed | Cup anemometer: cups rotate with wind, counts rotations; Beaufort scale (0–12) for wind force |
| Seismograph | Seismic waves/earthquakes | Inertia of hanging mass vs moving Earth; records P, S, and surface waves; Richter scale (logarithmic): each unit = 10× greater amplitude, ~31× more energy |
| Spectrometer | Light spectrum / wavelengths | Prism or diffraction grating disperses light; identifies elements (emission spectra — unique fingerprints) and molecules (absorption spectra); used in astronomy, chemistry |
| Oscilloscope | Voltage vs time waveforms | Electron beam deflected by electric field traces waveform on phosphor screen; diagnoses electrical signals, measures frequency |
| Galvanometer | Small electric current | Moving coil in magnetic field; torque proportional to current; basis for ammeter (shunt resistor) and voltmeter (high series resistor) |
| Geiger-Muller counter | Ionising radiation (α, β, γ) | Radiation ionises gas in tube → electric pulse → count; does not distinguish radiation type; measured in counts per second (cps) |
| Electroencephalograph (EEG) | Brain electrical activity | Electrodes on scalp detect microvolt-level potentials from synchronised neuronal activity; diagnoses epilepsy, sleep disorders |
| Electrocardiograph (ECG/EKG) | Heart electrical activity | Records P, QRS, T waves representing atrial depolarisation, ventricular depolarisation, ventricular repolarisation; diagnoses arrhythmias, MI |
| Spirometer | Lung volume and capacity | Water-sealed or digital; measures tidal volume, vital capacity, FEV₁ (forced expiratory volume in 1 second); diagnoses asthma, COPD |
| Pyrometer | High temperature (without contact) | Optical/radiation pyrometer: measures thermal radiation emitted by hot body (Stefan-Boltzmann law: P = εσAT⁴); range 600–3000°C+; foundry, glass-making |
| Sonar | Distance/depth using sound | Sound Navigation and Ranging; emits ultrasound (40 kHz), measures echo time; used for submarine detection, ocean depth mapping (echolocation principle) |
| Radar | Distance, speed, direction of objects | Radio waves reflected from objects; Doppler radar (frequency shift) measures speed; weather forecasting, air traffic control, speed guns |
| MRI (Magnetic Resonance Imaging) | Soft tissue internal structure | Strong magnetic field aligns proton spins; radiofrequency pulse disrupts alignment; protons emit signals as they realign — computer reconstructs cross-sectional image; no ionising radiation |
| CT scan | Cross-sectional X-ray images | X-ray source rotates around patient; detectors measure attenuation from different angles; computer reconstructs 3D image (Hounsfield units); uses more radiation than plain X-ray |
| Ultrasound (USG) | Internal organs, foetus | High-frequency sound (1–20 MHz) reflects off tissue boundaries; depth from echo delay; no ionising radiation; safe in pregnancy |
Semiconductor Physics and Electronics
Conductors, semiconductors, insulators: Conductors (metals: Cu, Al, Ag): many free electrons, resistivity 10⁻⁸ Ω·m; increases with temperature. Insulators (glass, rubber, diamond): no free electrons, resistivity >10¹⁰ Ω·m; unaffected by temperature. Semiconductors (Si, Ge, GaAs): intermediate resistivity (10⁻⁴ to 10³ Ω·m); resistivity decreases with temperature (negative temperature coefficient). Intrinsic semiconductors have equal electron and hole concentrations. Extrinsic semiconductors: doped to shift balance.
p-n junction diode: p-type (B-doped Si — excess holes) + n-type (P-doped Si — excess electrons) → depletion region at junction (contact potential ≈ 0.7 V for Si, 0.3 V for Ge). Forward bias: reduces depletion, current flows easily. Reverse bias: widens depletion, only tiny leakage current. Uses: rectifier (AC → DC), LED, photodiode, solar cell, Zener diode (voltage regulator).
Transistor (BJT): Three layers: n-p-n or p-n-p. Emitter-base-collector. Acts as amplifier (small base current controls large collector current, current gain hFE = 50–300) or switch (saturated = ON, cut-off = OFF). Foundation of all digital electronics. MOSFET (field-effect transistor): voltage-controlled — basis of CMOS chips; VLSI (Very Large Scale Integration) allows billions of transistors on one chip.
Moore's Law (Gordon Moore, 1965): Number of transistors on a microchip doubles approximately every 2 years (cost stays roughly the same). Has held roughly true for 50+ years; now slowing as transistor size approaches atomic limits (2–3 nm). Apple M4 (2024): ~28 billion transistors.
p-n junction diode: p-type (B-doped Si — excess holes) + n-type (P-doped Si — excess electrons) → depletion region at junction (contact potential ≈ 0.7 V for Si, 0.3 V for Ge). Forward bias: reduces depletion, current flows easily. Reverse bias: widens depletion, only tiny leakage current. Uses: rectifier (AC → DC), LED, photodiode, solar cell, Zener diode (voltage regulator).
Transistor (BJT): Three layers: n-p-n or p-n-p. Emitter-base-collector. Acts as amplifier (small base current controls large collector current, current gain hFE = 50–300) or switch (saturated = ON, cut-off = OFF). Foundation of all digital electronics. MOSFET (field-effect transistor): voltage-controlled — basis of CMOS chips; VLSI (Very Large Scale Integration) allows billions of transistors on one chip.
Moore's Law (Gordon Moore, 1965): Number of transistors on a microchip doubles approximately every 2 years (cost stays roughly the same). Has held roughly true for 50+ years; now slowing as transistor size approaches atomic limits (2–3 nm). Apple M4 (2024): ~28 billion transistors.
10. BPSC Science Quick Reference — Important Facts
Speed Reference Values
| Phenomenon | Speed | Notes |
|---|---|---|
| Speed of light in vacuum | 3 × 10⁸ m/s (299,792,458 m/s exactly) | Universal constant c; defines the metre; nothing with mass can reach it |
| Speed of sound in air (20°C) | ~343 m/s (1,235 km/h) | Increases with temperature; Mach 1 = speed of sound; Mach 2+ = supersonic |
| Speed of sound in water | ~1480 m/s | ~4.3× faster than in air (denser medium) |
| Speed of sound in steel | ~5960 m/s | ~17× faster than in air |
| Escape velocity (Earth) | 11.2 km/s | Minimum speed to escape Earth's gravity; used by rockets and space probes |
| First cosmic velocity (orbital) | 7.9 km/s | Minimum speed for circular orbit at Earth's surface (satellites orbit at this speed) |
| Nerve impulse speed | 0.5–120 m/s | Myelinated fibres: fast (120 m/s); unmyelinated: slow (0.5 m/s) |
Temperature Reference Points
| Scale | Water freezes | Water boils | Absolute zero | Body temperature |
|---|---|---|---|---|
| Celsius (°C) | 0 | 100 | −273.15 | 37 |
| Fahrenheit (°F) | 32 | 212 | −459.67 | 98.6 |
| Kelvin (K) — SI unit | 273.15 | 373.15 | 0 | 310.15 |
Conversions:
°C = (°F − 32) × 5/9
°F = (°C × 9/5) + 32
K = °C + 273.15
Electromagnetic Spectrum — Memory Table
| Region | Wavelength | Frequency | Key Applications |
|---|---|---|---|
| Radio waves | >1 mm (up to km) | <300 GHz | AM/FM radio, TV, mobile phones, MRI, radar, WiFi, Bluetooth |
| Microwaves | 1 mm – 30 cm | 1–300 GHz | Microwave ovens (2.45 GHz), satellite communication, radar, 5G |
| Infrared (IR) | 700 nm – 1 mm | 0.3–430 THz | Thermal imaging (FLIR), night vision, remote controls, heat lamps, fibre optics |
| Visible light | 380–700 nm | 430–790 THz | Human vision; VIBGYOR (violet 380–450 nm to red 620–700 nm); photography |
| Ultraviolet (UV) | 10–380 nm | 0.79–30 PHz | Vitamin D synthesis, sterilisation, fluorescence, ozone absorption (UV-B & UV-C), black lights |
| X-rays | 0.01–10 nm | 30 PHz – 30 EHz | Medical imaging (bone, CT), airport security, crystallography (Bragg's law — determines crystal structure) |
| Gamma rays | <0.01 nm | >30 EHz | Cancer radiotherapy, sterilisation, nuclear reactions, PET scanning, Gamma-ray bursts (most energetic events in universe) |
Nobel Prizes Relevant to Science Syllabus
| Discovery / Theory | Scientist(s) | Year | Field |
|---|---|---|---|
| Special and General Relativity | Albert Einstein | 1921 (Photo-electric effect) | Physics |
| Quantum mechanics (uncertainty principle) | Werner Heisenberg | 1932 | Physics |
| Penicillin discovery | Fleming, Chain, Florey | 1945 | Medicine |
| DNA double helix structure | Watson, Crick, Wilkins | 1962 | Medicine |
| Green Revolution / wheat varieties | Norman Borlaug | 1970 | Peace (for ending hunger) |
| Restriction enzymes (molecular scissors) | Smith, Arber, Nathans | 1978 | Medicine |
| PCR technique | Kary Mullis | 1993 | Chemistry |
| Ozone depletion chemistry (CFCs) | Molina, Rowland, Crutzen | 1995 | Chemistry |
| GFP (Green Fluorescent Protein) — biological imaging | Shimomura, Chalfie, Tsien | 2008 | Chemistry |
| Ribosome structure | Steitz, Yonath, Ramakrishnan | 2009 | Chemistry |
| CRISPR-Cas9 gene editing | Doudna, Charpentier | 2020 | Chemistry |
| mRNA vaccine technology (COVID) | Karikó, Weissman | 2023 | Medicine |
BPSC Science — Frequently Tested One-Liners
1. SI unit of force: Newton (N = kg·m/s²); of pressure: Pascal (Pa = N/m²); of energy: Joule (J); of power: Watt (W = J/s).
2. Photosynthesis equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Cellular respiration (reverse): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP.
3. Ohm's Law: V = IR. Power: P = VI = I²R = V²/R. Series: R_total = R₁ + R₂ + ... Parallel: 1/R_total = 1/R₁ + 1/R₂ + ...
4. Atomic number = number of protons. Mass number = protons + neutrons. Isotopes: same atomic number, different mass numbers (e.g., ¹²C and ¹⁴C).
5. Mole = 6.022 × 10²³ particles (Avogadro's number); molar mass in grams = atomic/molecular weight numerically.
6. pH of pure water at 25°C = 7 (neutral). Acids pH < 7; bases pH > 7. Strong acids: HCl, H₂SO₄, HNO₃. Strong bases: NaOH, KOH.
7. Vitamins: water-soluble (B-complex, C) — not stored, need daily intake; fat-soluble (A, D, E, K) — stored in liver/fat, can accumulate to toxicity.
8. Largest organelle: nucleus. Largest cell in human body: ovum (egg cell, ~100 μm). Smallest cell: platelet (2–3 μm) or mycoplasma. Longest cell: neuron (up to 1 m).
9. Blood composition: 55% plasma + 45% formed elements (RBC 99.9%, WBC, platelets). Blood clotting: platelet plug → fibrin clot (prothrombin → thrombin → fibrinogen → fibrin); requires Ca²⁺ and Vitamin K.
10. Fleming's rules: Left hand rule (motor — force on current-carrying conductor in magnetic field); Right hand rule / Right-hand thumb rule (generator — direction of induced current).
11. Newton's Law of Gravitation: F = Gm₁m₂/r²; G = 6.67 × 10⁻¹¹ N·m²/kg². g = GM/R² (surface); g decreases with altitude and depth (zero at Earth's centre).
12. Doppler effect: source approaching observer → apparent frequency increases (blue shift); source moving away → apparent frequency decreases (red shift). Used in radar speed guns, astronomy (Hubble's expansion), echolocation.
13. Valence electrons determine chemical properties. Elements in same group have same valence electrons; same period have same number of shells. Electronegativity: F > O > N > Cl > Br (highest to lowest, top right to bottom left on periodic table).
14. Entropy (S): measure of disorder. Second law of thermodynamics: entropy of universe always increases. Absolute zero (0 K): zero entropy (perfect crystal, third law).
15. Radioactive decay law: N(t) = N₀e^(−λt); half-life t½ = 0.693/λ. Carbon-14 dating (t½ = 5730 years) for archaeological samples <50,000 years; Uranium-238 dating (t½ = 4.5 billion years) for geological samples.
2. Photosynthesis equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Cellular respiration (reverse): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP.
3. Ohm's Law: V = IR. Power: P = VI = I²R = V²/R. Series: R_total = R₁ + R₂ + ... Parallel: 1/R_total = 1/R₁ + 1/R₂ + ...
4. Atomic number = number of protons. Mass number = protons + neutrons. Isotopes: same atomic number, different mass numbers (e.g., ¹²C and ¹⁴C).
5. Mole = 6.022 × 10²³ particles (Avogadro's number); molar mass in grams = atomic/molecular weight numerically.
6. pH of pure water at 25°C = 7 (neutral). Acids pH < 7; bases pH > 7. Strong acids: HCl, H₂SO₄, HNO₃. Strong bases: NaOH, KOH.
7. Vitamins: water-soluble (B-complex, C) — not stored, need daily intake; fat-soluble (A, D, E, K) — stored in liver/fat, can accumulate to toxicity.
8. Largest organelle: nucleus. Largest cell in human body: ovum (egg cell, ~100 μm). Smallest cell: platelet (2–3 μm) or mycoplasma. Longest cell: neuron (up to 1 m).
9. Blood composition: 55% plasma + 45% formed elements (RBC 99.9%, WBC, platelets). Blood clotting: platelet plug → fibrin clot (prothrombin → thrombin → fibrinogen → fibrin); requires Ca²⁺ and Vitamin K.
10. Fleming's rules: Left hand rule (motor — force on current-carrying conductor in magnetic field); Right hand rule / Right-hand thumb rule (generator — direction of induced current).
11. Newton's Law of Gravitation: F = Gm₁m₂/r²; G = 6.67 × 10⁻¹¹ N·m²/kg². g = GM/R² (surface); g decreases with altitude and depth (zero at Earth's centre).
12. Doppler effect: source approaching observer → apparent frequency increases (blue shift); source moving away → apparent frequency decreases (red shift). Used in radar speed guns, astronomy (Hubble's expansion), echolocation.
13. Valence electrons determine chemical properties. Elements in same group have same valence electrons; same period have same number of shells. Electronegativity: F > O > N > Cl > Br (highest to lowest, top right to bottom left on periodic table).
14. Entropy (S): measure of disorder. Second law of thermodynamics: entropy of universe always increases. Absolute zero (0 K): zero entropy (perfect crystal, third law).
15. Radioactive decay law: N(t) = N₀e^(−λt); half-life t½ = 0.693/λ. Carbon-14 dating (t½ = 5730 years) for archaeological samples <50,000 years; Uranium-238 dating (t½ = 4.5 billion years) for geological samples.
Indian Science and Technology Milestones
Ancient Indian contributions to science:
Mathematics: Aryabhata (499 CE) — value of π (3.1416), concept of zero as a number and positional notation, heliocentric model of solar system (before Copernicus), calculated Earth's circumference. Brahmagupta (628 CE) — rules for arithmetic operations with zero, negative numbers, quadratic equations. Madhava of Sangamagrama (1350–1425 CE) — infinite series for π and trigonometric functions (centuries before Newton/Leibniz). Srinivasa Ramanujan (1887–1920) — highly composite numbers, mock theta functions, Ramanujan prime, Hardy-Ramanujan number 1729 (taxicab number).
Surgery: Sushruta Samhita (6th century BCE) — described over 300 surgical procedures including rhinoplasty (nose reconstruction), cataract surgery, caesarean section; 120 surgical instruments; antiseptic practices using turmeric and wine.
Metallurgy: Iron Pillar of Delhi (400 CE) — 7.2 metres tall, 98% wrought iron; corrosion-resistant due to misawite (iron hydrogen phosphate hydrate) layer formed by hammer welding; remarkable evidence of ancient Indian metallurgical skill. Wootz (Damascus) steel — produced in South India; high carbon content (1–2%), cementite nanowires; famous for pattern and sharpness; sought worldwide in ancient/medieval times.
Mathematics: Aryabhata (499 CE) — value of π (3.1416), concept of zero as a number and positional notation, heliocentric model of solar system (before Copernicus), calculated Earth's circumference. Brahmagupta (628 CE) — rules for arithmetic operations with zero, negative numbers, quadratic equations. Madhava of Sangamagrama (1350–1425 CE) — infinite series for π and trigonometric functions (centuries before Newton/Leibniz). Srinivasa Ramanujan (1887–1920) — highly composite numbers, mock theta functions, Ramanujan prime, Hardy-Ramanujan number 1729 (taxicab number).
Surgery: Sushruta Samhita (6th century BCE) — described over 300 surgical procedures including rhinoplasty (nose reconstruction), cataract surgery, caesarean section; 120 surgical instruments; antiseptic practices using turmeric and wine.
Metallurgy: Iron Pillar of Delhi (400 CE) — 7.2 metres tall, 98% wrought iron; corrosion-resistant due to misawite (iron hydrogen phosphate hydrate) layer formed by hammer welding; remarkable evidence of ancient Indian metallurgical skill. Wootz (Damascus) steel — produced in South India; high carbon content (1–2%), cementite nanowires; famous for pattern and sharpness; sought worldwide in ancient/medieval times.
Key Inventions and Discoverers
| Invention / Discovery | Inventor / Discoverer | Year | Significance |
|---|---|---|---|
| Printing press (movable type) | Johannes Gutenberg | 1440 | Democratised knowledge; enabled Reformation, Scientific Revolution, literacy spread |
| Steam engine (practical) | James Watt | 1769 | Powered Industrial Revolution; unit of power named Watt |
| Vaccine (smallpox) | Edward Jenner | 1796 | First vaccine; used cowpox (Vaccinia); led to global smallpox eradication (1980) |
| Electric battery (voltaic pile) | Alessandro Volta | 1800 | First steady electric current source; Volt unit named after him |
| Electromagnetic induction | Michael Faraday | 1831 | Foundation of electric generator and transformer; Faraday's laws; Farad unit named after him |
| Periodic table | Dmitri Mendeleev | 1869 | Organised 63 known elements; predicted properties of undiscovered elements (Ge, Ga, Sc) |
| Telephone | Alexander Graham Bell | 1876 | Converted sound to electrical signals; Bel (unit of sound intensity) named after him |
| Pasteurisation | Louis Pasteur | 1864 | Disproved spontaneous generation; germ theory of disease; microbiological food safety |
| X-rays | Wilhelm Röntgen | 1895 | First Nobel Prize in Physics (1901); medical imaging; crystallography |
| Electron | J.J. Thomson | 1897 | First subatomic particle discovered; plum-pudding model; cathode ray tube experiments |
| Radioactivity | Henri Becquerel; Curie (Marie, Pierre) | 1896–1898 | Natural radioactivity; discovered polonium and radium; Marie Curie — only person to win Nobel in two different sciences (Physics 1903, Chemistry 1911) |
| Penicillin | Alexander Fleming | 1928 | First antibiotic; moulds (Penicillium notatum) inhibit bacteria; mass production in WWII saved millions of lives |
| Nuclear fission | Hahn, Strassmann (1938); Meitner, Frisch (explanation) | 1938 | Uranium nucleus splits → chain reaction → nuclear weapons (Manhattan Project) and nuclear power |
| Transistor | Bardeen, Brattain, Shockley (Bell Labs) | 1947 | Nobel 1956; replaced vacuum tubes; enabled miniaturisation of electronics; foundation of modern computing |
| Internet (ARPANET) | US DoD/DARPA | 1969 | Packet-switching network; TCP/IP protocols (1974); World Wide Web (Tim Berners-Lee, 1989) built on top; transformed communication and commerce |
11. Animal Kingdom — Key Classification Points for BPSC
Kingdom Animalia characteristics: Multicellular, eukaryotic, heterotrophic (ingestion of food), no cell wall, most sexually reproduce. Classified by: symmetry, coelom, segmentation, notochord presence.
Non-chordates (Phyla):
Porifera (sponges): No true tissues; ostia (pores); spongocoel; Leucosolenia, Spongilla.
Cnidaria (coelenterates): Radial symmetry; cnidoblasts (stinging cells); polyp and medusa forms; Hydra, Obelia, Aurelia (jellyfish), Adamsia (sea anemone), coral.
Platyhelminthes (flatworms): Bilaterally symmetrical; acoelomate; parasitic or free-living; Taenia (tapeworm), Fasciola (liver fluke), Planaria (regeneration experiments).
Nematoda: Cylindrical body; pseudocoelom; dioecious; Ascaris (roundworm — most common intestinal parasite in humans), Wuchereria (filariasis), hookworm.
Annelida (segmented worms): True coelom; metamerism (segments); closed circulatory system; Earthworm (Pheretima — ecological importance: soil fertility); Nereis; Hirudinaria (leech — anticoagulant hirudin).
Arthropoda (largest phylum by species count): Jointed appendages; exoskeleton (chitin); open circulatory system; Insects (six legs: bee, butterfly, mosquito, cockroach), Arachnida (eight legs: spider, scorpion), Crustacea (Prawn, Crab), Myriapoda (Centipede, Millipede). Insects = most abundant animals on Earth.
Mollusca: Soft body, mantle, shell (CaCO₃); Pila (apple snail), Octopus (most intelligent invertebrate), Pearl oyster (Pinctada — pearl formation: nacre around irritant), Sepia (cuttlefish), Loligo (squid).
Echinodermata: Radial symmetry (adults); water vascular system; tube feet; regeneration; Starfish (Asterias), Sea cucumber (Holothuria), Sea urchin, Brittle star. All marine.
Chordates — key features: Notochord, dorsal hollow nerve cord, pharyngeal gill slits at some life stage, post-anal tail.
Subphylum Vertebrata — five classes:
1. Pisces (Fish): Cold-blooded; two-chambered heart; gills throughout life; lateral line system; Labeo (rohu), Catla, Clarias (catfish), Exocoetus (flying fish), Hippocampus (seahorse — male carries young).
2. Amphibia: Cold-blooded; three-chambered heart; gills in larva, lungs in adult; moist skin (cutaneous respiration); Rana (frog), Bufo (toad), Salamandra, Ichthyophis. First truly terrestrial vertebrates evolutionarily.
3. Reptilia: Cold-blooded; three-chambered heart (crocodile: four-chambered); dry, scaly skin; internal fertilisation; amniotic egg (water-independent reproduction); Turtle, Lizard, Snake, Crocodile. Boids (pythons, boas) largest snakes.
4. Aves (Birds): Warm-blooded (homeothermic); four-chambered heart; feathers; flight adaptations (hollow bones, keeled sternum, air sacs); Columba (pigeon), Pavo (peacock — national bird of India), Psittacula (parrot), Struthio (ostrich — largest living bird; cannot fly). Penguin (flightless; Antarctica).
5. Mammalia: Warm-blooded; four-chambered heart; mammary glands (milk); hair/fur; diaphragm; external ear (pinnae); three middle ear ossicles (malleus, incus, stapes). Prototheria (egg-laying: Platypus, Echidna), Metatheria (marsupials: Kangaroo, Koala — pouches), Eutheria (placental mammals — most, including humans). Blue whale (Balaenoptera musculus) — largest animal ever; Shrew (Suncus) — smallest mammal; Bat — only flying mammal.
Non-chordates (Phyla):
Porifera (sponges): No true tissues; ostia (pores); spongocoel; Leucosolenia, Spongilla.
Cnidaria (coelenterates): Radial symmetry; cnidoblasts (stinging cells); polyp and medusa forms; Hydra, Obelia, Aurelia (jellyfish), Adamsia (sea anemone), coral.
Platyhelminthes (flatworms): Bilaterally symmetrical; acoelomate; parasitic or free-living; Taenia (tapeworm), Fasciola (liver fluke), Planaria (regeneration experiments).
Nematoda: Cylindrical body; pseudocoelom; dioecious; Ascaris (roundworm — most common intestinal parasite in humans), Wuchereria (filariasis), hookworm.
Annelida (segmented worms): True coelom; metamerism (segments); closed circulatory system; Earthworm (Pheretima — ecological importance: soil fertility); Nereis; Hirudinaria (leech — anticoagulant hirudin).
Arthropoda (largest phylum by species count): Jointed appendages; exoskeleton (chitin); open circulatory system; Insects (six legs: bee, butterfly, mosquito, cockroach), Arachnida (eight legs: spider, scorpion), Crustacea (Prawn, Crab), Myriapoda (Centipede, Millipede). Insects = most abundant animals on Earth.
Mollusca: Soft body, mantle, shell (CaCO₃); Pila (apple snail), Octopus (most intelligent invertebrate), Pearl oyster (Pinctada — pearl formation: nacre around irritant), Sepia (cuttlefish), Loligo (squid).
Echinodermata: Radial symmetry (adults); water vascular system; tube feet; regeneration; Starfish (Asterias), Sea cucumber (Holothuria), Sea urchin, Brittle star. All marine.
Chordates — key features: Notochord, dorsal hollow nerve cord, pharyngeal gill slits at some life stage, post-anal tail.
Subphylum Vertebrata — five classes:
1. Pisces (Fish): Cold-blooded; two-chambered heart; gills throughout life; lateral line system; Labeo (rohu), Catla, Clarias (catfish), Exocoetus (flying fish), Hippocampus (seahorse — male carries young).
2. Amphibia: Cold-blooded; three-chambered heart; gills in larva, lungs in adult; moist skin (cutaneous respiration); Rana (frog), Bufo (toad), Salamandra, Ichthyophis. First truly terrestrial vertebrates evolutionarily.
3. Reptilia: Cold-blooded; three-chambered heart (crocodile: four-chambered); dry, scaly skin; internal fertilisation; amniotic egg (water-independent reproduction); Turtle, Lizard, Snake, Crocodile. Boids (pythons, boas) largest snakes.
4. Aves (Birds): Warm-blooded (homeothermic); four-chambered heart; feathers; flight adaptations (hollow bones, keeled sternum, air sacs); Columba (pigeon), Pavo (peacock — national bird of India), Psittacula (parrot), Struthio (ostrich — largest living bird; cannot fly). Penguin (flightless; Antarctica).
5. Mammalia: Warm-blooded; four-chambered heart; mammary glands (milk); hair/fur; diaphragm; external ear (pinnae); three middle ear ossicles (malleus, incus, stapes). Prototheria (egg-laying: Platypus, Echidna), Metatheria (marsupials: Kangaroo, Koala — pouches), Eutheria (placental mammals — most, including humans). Blue whale (Balaenoptera musculus) — largest animal ever; Shrew (Suncus) — smallest mammal; Bat — only flying mammal.
Plant Kingdom — Key Divisions
Algae (Thallophyta): Aquatic, no vascular tissue, no embryo; Spirogyra (conjugation), Chara, Volvox, Ulva, Sargassum (brown algae), Porphyra (red algae — nori). Economic: agar (Gelidium, Gracilaria), alginates (Laminaria), Chlorella and Spirulina (food supplement/space food). Biological oxygen production: marine algae produce 50% of global O₂.
Bryophyta (Amphibians of plant kingdom): Non-vascular; depend on water for fertilisation; Marchantia (liverwort), Funaria, Sphagnum (peat moss — forms peat, used as fuel and in horticulture). Dominant gametophyte; sporophyte dependent on gametophyte.
Pteridophyta (first vascular land plants): Vascular but no seeds; dominant sporophyte; Fern (Pteris), Horsetail (Equisetum), Club moss (Selaginella). Coal formation: ancient tree ferns and pteridophytes formed coal (Carboniferous period 358–299 million years ago).
Gymnosperms ("naked seeds"): Seeds on open cone scales (no fruit); mostly evergreen conifers; Pinus (pine), Cycas (sago palm — living fossil), Ginkgo biloba (oldest living tree species; maidenhair tree; used in medicine), Sequoia (tallest living tree — up to 115 m). Pollen cones (male) + ovule cones (female). Conifers dominate boreal (taiga) biome.
Angiosperms ("enclosed seeds" = flowering plants): Most diverse (300,000+ species); seeds enclosed in fruit (from ovary wall); double fertilisation (triple fusion → endosperm; syngamy → embryo). Monocots: one cotyledon; parallel venation; fibrous root; flowers in 3s (grass, maize, wheat, rice, bamboo, banana, onion, lily). Dicots: two cotyledons; reticulate venation; tap root; flowers in 4s or 5s (mango, pea, rose, sunflower, tomato, potato, neem). Largest flower: Rafflesia arnoldii (~1 metre diameter, parasitic, smells of rotting flesh). Smallest flowering plant: Wolffia (watermeal — 1 mm).
Bryophyta (Amphibians of plant kingdom): Non-vascular; depend on water for fertilisation; Marchantia (liverwort), Funaria, Sphagnum (peat moss — forms peat, used as fuel and in horticulture). Dominant gametophyte; sporophyte dependent on gametophyte.
Pteridophyta (first vascular land plants): Vascular but no seeds; dominant sporophyte; Fern (Pteris), Horsetail (Equisetum), Club moss (Selaginella). Coal formation: ancient tree ferns and pteridophytes formed coal (Carboniferous period 358–299 million years ago).
Gymnosperms ("naked seeds"): Seeds on open cone scales (no fruit); mostly evergreen conifers; Pinus (pine), Cycas (sago palm — living fossil), Ginkgo biloba (oldest living tree species; maidenhair tree; used in medicine), Sequoia (tallest living tree — up to 115 m). Pollen cones (male) + ovule cones (female). Conifers dominate boreal (taiga) biome.
Angiosperms ("enclosed seeds" = flowering plants): Most diverse (300,000+ species); seeds enclosed in fruit (from ovary wall); double fertilisation (triple fusion → endosperm; syngamy → embryo). Monocots: one cotyledon; parallel venation; fibrous root; flowers in 3s (grass, maize, wheat, rice, bamboo, banana, onion, lily). Dicots: two cotyledons; reticulate venation; tap root; flowers in 4s or 5s (mango, pea, rose, sunflower, tomato, potato, neem). Largest flower: Rafflesia arnoldii (~1 metre diameter, parasitic, smells of rotting flesh). Smallest flowering plant: Wolffia (watermeal — 1 mm).
🎯 Last-Minute BPSC Reminders: Always check the unit in calculation questions. In genetics, Mendel worked with garden pea (Pisum sativum) — 7 pairs of contrasting traits. Human genome has ~20,000–25,000 protein-coding genes. India signed the Paris Agreement on 2 October 2016 (Gandhi Jayanti). The Convention on Biological Diversity (CBD) was signed at Rio Earth Summit, 1992. India's first Five-Year Plan (1951–56) focused on agriculture; currently India is on 15th Finance Commission cycle. National Science Day: 28 February (Raman Effect discovery, 1928). Technology Day: 11 May (Pokhran-II, 1998). Earth Day: 22 April. World Environment Day: 5 June. Ozone Day: 16 September (Montreal Protocol signing date, 1987).