🔬 SCIENCE & TECHNOLOGY · Complete Topic-by-Topic Explainer

Weightage: Prelims 7–12 questions · Mains GS-III (S&T developments, indigenization, IPR, biotech, space, defence). Why it matters: S&T in Prelims is ~80–90% current affairs — but the concept behind each news item is static and comes from NCERT Class 6–10. Learn the concept once here, then track the news.

═══ PART A: FUNDAMENTAL SCIENCE (NCERT core) ═══

1. PHYSICS — concepts with everyday applications

Mechanics

• Newton's laws: (1) inertia — a body continues in its state unless acted on by a force (why you lurch forward when a bus brakes); (2) F = ma; (3) action–reaction (rocket propulsion, recoil of a gun).
• Momentum = mass × velocity; conserved in collisions. Work = force × displacement; Power = work/time. Energy: kinetic (½mv²) and potential (mgh); conservation of energy.
• Gravitation: weight = mg; weightlessness in orbit is free fall, not absence of gravity. Escape velocity from Earth ≈ 11.2 km/s.
• Pressure: P = F/A (why a sharp knife cuts better). Archimedes' principle (buoyancy — why ships float, why you feel lighter in water). Pascal's law (hydraulic brakes/lifts). Bernoulli's principle (aeroplane lift, spin of a ball).
• Surface tension (water droplets spherical, capillary rise in plants), viscosity.

Heat

• Transfer: conduction (solids), convection (fluids — land/sea breeze, boiling), radiation (no medium needed — sun's heat, thermos flask blocks all three).
• Specific heat: water's is very high → moderates coastal climate; used as a coolant.
• Latent heat: heat absorbed/released during a phase change at constant temperature (why steam burns worse than boiling water; why sweating cools you).

Light & optics

• Reflection (mirrors — concave used in headlights/shaving; convex in rear-view mirrors for a wider field).
• Refraction (bending in a different medium): mirage, apparent bending of a stick in water, twinkling of stars (atmospheric refraction), advance sunrise/delayed sunset.
• Dispersion: splitting into VIBGYOR — rainbow (refraction + internal reflection + dispersion in raindrops).
• Scattering (Rayleigh): shorter wavelengths scatter more → blue sky; at sunrise/sunset light travels a longer path so blue is scattered away → red sun. Danger signals are red because red scatters least and travels farthest.
• Total internal reflection: optical fibres (communication, endoscopy), diamond's sparkle, mirage.
• Defects of vision: myopia (short sight — concave lens), hypermetropia (long sight — convex lens), presbyopia, astigmatism, cataract.

Sound

• Mechanical wave — needs a medium (no sound in vacuum). Speed: solids > liquids > gases; ~343 m/s in air.
• Audible range 20 Hz–20 kHz; infrasound (<20 Hz, elephants, earthquakes) and ultrasound (>20 kHz — SONAR, medical imaging, cleaning). Echo, reverberation, Doppler effect (pitch change of a passing siren).

Electricity & magnetism

• Ohm's law V = IR; series (same current) vs parallel (same voltage — used in household wiring).
• Safety: fuse melts on excess current; earthing provides a low-resistance path to the ground; MCB.
• Electromagnetic induction (Faraday): basis of the generator, transformer, induction stove. Motor converts electrical → mechanical.
• AC vs DC: AC is transmitted over long distances (easily stepped up/down by transformers, lower losses).
• Electromagnetic spectrum (increasing frequency/energy):

 RADIO → MICROWAVE → INFRARED → VISIBLE → ULTRAVIOLET → X-RAY → GAMMA
 (broadcast) (oven,   (heat,     (light)   (sterilize, (imaging) (cancer
             radar)   remote)              vit-D)                therapy)

Modern physics

• Radioactivity: alpha, beta, gamma; half-life; carbon dating.
• Nuclear fission = splitting a heavy nucleus (uranium/plutonium) → reactors and atom bombs. Nuclear fusion = combining light nuclei (hydrogen → helium) → the Sun, hydrogen bomb, ITER. Fusion releases more energy per unit mass and is cleaner but needs extreme temperature/pressure.
• Semiconductors, superconductors (zero resistance below a critical temperature), LEDs, lasers.

2. CHEMISTRY

• Atomic structure: protons/neutrons/electrons; atomic number vs mass number; isotopes (same Z, different A — U-235/U-238, C-14) vs isobars.
• Periodic table trends: across a period → atomic size decreases, electronegativity increases; down a group → the reverse.
• Bonding: ionic (electron transfer — NaCl), covalent (sharing — water, CO₂), metallic, hydrogen bonding (water's high boiling point, ice floating).
• Acids, bases, salts: pH scale 0–14 (7 neutral; <7 acidic; >7 basic). Applications: antacids for acidity, lime to correct acidic soil, tooth decay below pH 5.5, baking soda, washing soda, bleaching powder, plaster of Paris.
• Metals & non-metals: reactivity series; corrosion/rusting (needs oxygen + moisture; prevented by galvanising, painting, alloying); alloys (steel = Fe+C; stainless steel adds Cr/Ni; brass = Cu+Zn; bronze = Cu+Sn).
• Carbon: catenation; allotropes — diamond (hardest, 3-D network), graphite (conducts, layers slide — lubricant), fullerene, graphene (single layer, exceptional strength/conductivity), carbon nanotubes.
• Hydrocarbons & polymers: petroleum fractions, plastics (thermoplastic vs thermosetting), biodegradable vs non-biodegradable.
• Soaps & detergents: micelle formation — the hydrophobic tail traps grease, the hydrophilic head faces water. Detergents work in hard water; soaps form scum.

3. BIOLOGY

Cell & molecular basis

• Organelles: nucleus (DNA), mitochondria ("powerhouse", ATP), chloroplast (photosynthesis, contains magnesium-based chlorophyll), ribosome (protein synthesis), lysosome ("suicide bag"), Golgi, ER, vacuole.
• Prokaryote (no true nucleus — bacteria) vs eukaryote.
• Central dogma:

   DNA ──transcription──▶ RNA ──translation──▶ PROTEIN
   Gene editing (CRISPR-Cas9) cuts DNA at a targeted site

• Photosynthesis: 6CO₂ + 6H₂O --light/chlorophyll--> C₆H₁₂O₆ + 6O₂ (releases oxygen). Respiration is essentially the reverse (releases energy/ATP).
• Cell division: mitosis (growth, identical cells) vs meiosis (gametes, halves chromosome number, creates variation).

Human physiology (high-yield)

• Digestive: enzymes (amylase, pepsin, trypsin), liver (bile), pancreas.
• Circulatory: double circulation, four-chambered heart, arteries (away, oxygenated except pulmonary) vs veins; blood groups A/B/AB/O + Rh (O⁻ universal donor, AB⁺ universal recipient); haemoglobin contains iron.
• Respiratory: alveoli, gas exchange.
• Excretory: kidney → nephron (filtration unit); dialysis.
• Nervous: neuron, reflex arc (spinal cord, involuntary), brain parts (cerebrum — thinking; cerebellum — balance; medulla — involuntary functions).
• Endocrine (hormone → gland → deficiency): insulin → pancreas → diabetes; thyroxine → thyroid → goitre (iodine); adrenaline ("fight or flight"); growth hormone → pituitary ("master gland").
• Nutrition & deficiency diseases:

 Vitamin A  → night blindness, xerophthalmia
 Vitamin B1 → beriberi     B3 (niacin) → pellagra   B12 → anaemia
 Vitamin C  → SCURVY       Vitamin D → RICKETS (adults: osteomalacia)
 Vitamin K  → poor blood clotting
 Iron → anaemia   Iodine → goitre   Calcium → weak bones
 Protein deficiency → KWASHIORKOR ; Protein+calorie → MARASMUS

• Genetics: Mendel's laws (dominance, segregation, independent assortment); XY sex determination (the father's sperm determines the child's sex); mutations; genetic disorders (haemophilia, colour blindness — X-linked; sickle-cell anaemia; thalassaemia).

Diseases & immunity

• Immunity: innate vs acquired; active (vaccination/infection — long lasting) vs passive (antibodies given directly — immediate but short). Vaccine types: live attenuated, inactivated, subunit, toxoid, mRNA, viral vector.
• Antibiotics work on bacteria, NOT viruses; misuse drives antimicrobial resistance (AMR) — a major current-affairs theme.

═══ PART B: TECHNOLOGY & CURRENT S&T ═══

4. SPACE TECHNOLOGY

• ISRO milestones: Aryabhata (1975 — first Indian satellite) · INSAT & IRS series · Chandrayaan (lunar; Chandrayaan-1 confirmed water molecules) · Mangalyaan/MOM (Mars — success on the first attempt) · Aditya-L1 (solar observation at Lagrange point L1) · Gaganyaan (human spaceflight) · NavIC (regional navigation).
• Launch vehicles: PSLV (reliable workhorse, polar/sun-synchronous orbits) · GSLV (heavier, cryogenic upper stage) · LVM3/GSLV Mk-III (heaviest) · SSLV (small satellites).
• Orbits:

   ● Earth
     ├─ LEO (~200–2000 km): ISS, earth observation, Starlink
     ├─ SUN-SYNCHRONOUS (polar, ~600–800 km): remote sensing —
     │    passes over a location at the same local time daily
     ├─ MEO: navigation satellites (GPS)
     └─ GEO (~36,000 km, equatorial): communication & weather —
          appears STATIONARY relative to earth (period = 24 h)
   LAGRANGE POINTS (L1–L5): gravitational equilibrium points;
     L1 (Sun-Earth) → Aditya-L1 ; L2 → James Webb Telescope

• Applications: telecommunication, weather forecasting, disaster warning, navigation, resource mapping, agriculture, defence.
• Space policy: IN-SPACe, NSIL, private-sector participation; space debris and Kessler syndrome as emerging issues.

5. DEFENCE TECHNOLOGY

• Missiles: ballistic (Agni series — parabolic trajectory, long range; Prithvi) vs cruise (BrahMos — supersonic, low-altitude, self-navigating). Surface-to-air: Akash, QRSAM; anti-tank: Nag; Astra (air-to-air); Pinaka (rocket system).
• Nuclear: India's three-stage programme (PHWR → fast breeder → thorium-based, exploiting India's large thorium reserves); no-first-use doctrine; nuclear triad (land, air, sea — INS Arihant SSBN).
• Other: Tejas LCA, AMCA, Rafale, indigenous aircraft carrier INS Vikrant, DRDO labs, defence indigenisation, Agnipath, hypersonic vehicles (HSTDV), drones/UAVs, directed-energy weapons.

6. INFORMATION TECHNOLOGY & EMERGING TECH

• Cyber security: malware, ransomware, phishing, DDoS; CERT-In, National Cyber Security Policy, critical infrastructure protection (NCIIPC). Digital Personal Data Protection Act — privacy after Puttaswamy.
• Digital India: Aadhaar, UPI, DBT, DigiLocker, ONDC, BharatNet.

7. BIOTECHNOLOGY

• Genetic engineering / recombinant DNA: inserting a desired gene into an organism. Bt cotton (gene from Bacillus thuringiensis, resists bollworm) — India's only commercially approved GM food/fibre crop; Bt brinjal under moratorium; GM mustard DMH-11 (barnase–barstar system) contested.
• CRISPR-Cas9: precise "molecular scissors" for gene editing — therapy, crops, ethical concerns.
• Applications: vaccines (recombinant, mRNA), insulin production, gene therapy, DNA fingerprinting (forensics, paternity), tissue culture, biofertilizers, biopesticides, biofuels (ethanol blending), stem cells, golden rice (vitamin A).
• Regulation & IPR: GEAC (approves GM release), Biological Diversity Act, TRIPS, patents (product vs process), Geographical Indications, plant variety protection; biosafety under the Cartagena Protocol.

8. ENERGY TECHNOLOGY

• Conventional: coal (dominant), oil & gas, large hydro, nuclear.
• Renewables: solar (PV vs solar thermal; International Solar Alliance headquartered in India), wind (onshore/offshore), small hydro, biomass, tidal/wave, geothermal.
• Green hydrogen: produced by electrolysis of water using renewable electricity (vs grey = from natural gas, blue = grey + carbon capture). National Green Hydrogen Mission.
• Storage & grid: lithium-ion batteries, pumped storage, smart grids; critical minerals (lithium, cobalt) supply-chain concerns.
• Efficiency: PAT scheme, BEE star labelling, LED (UJALA), electric vehicles (FAME).

9. HEALTH TECHNOLOGY (current affairs anchor)

• Vaccine platforms, genome sequencing, telemedicine (eSanjeevani), Ayushman Bharat Digital Mission, drug regulation (CDSCO), clinical trials, One Health approach, AMR, universal immunisation.

HOW UPSC ASKS SCIENCE & TECHNOLOGY (pattern notes)

1. "What is X and what is it used for" — where X is a technology in the news (a mission, a device, a technique).
2. Statement-based questions on applications — e.g., "Consider the following statements about CRISPR…"
3. Concept discrimination — fission vs fusion, active vs passive immunity, GEO vs sun-synchronous, FDI-style pairings.
4. Disease–pathogen–vector matching.
5. Institution/mission mapping — which agency runs what.

Revision rule: maintain a monthly "S&T in news" page — every ISRO/DRDO test, health breakthrough, and new technology, with one line on what it is and why it matters. Pair each with the underlying concept from Part A above. That pairing is exactly how UPSC frames the question.

📖 SOURCE & CHAPTER MAP — NCERT VI–X Science + current affairs

Modern reality: UPSC S&T is now ~70% current affairs. The NCERT base makes news comprehensible; the marks come from tracking missions, breakthroughs, and regulations through the year.

DEEPER COVERAGE — the static base + the current frontier

Biology & health (highest static yield)

• Cell: nucleus (DNA), mitochondria (ATP powerhouse), chloroplast (photosynthesis, magnesium in chlorophyll), ribosome (protein). Central dogma: DNA→RNA→protein.
• Human systems: insulin (pancreas → diabetes), haemoglobin (iron), thyroid (iodine → goitre). Vitamin deficiencies: A→night blindness, B1→beriberi, B3→pellagra, C→scurvy, D→rickets, protein→kwashiorkor.
• Diseases: bacterial (TB, cholera, typhoid), viral (dengue, COVID, hepatitis, polio), protozoan (malaria — Plasmodium), vector-borne. Immunity — active (vaccine) vs passive; herd immunity.
• Genetics & biotech: DNA, genes, mutation; CRISPR-Cas9 gene editing; GM crops (Bt cotton — bollworm resistance), stem cells, gene therapy, mRNA vaccines.

Physics & chemistry essentials

• Optics: blue sky & red sunset = Rayleigh scattering; rainbow = dispersion; optical fibre = total internal reflection.
• Conservation laws (energy, momentum, charge); entropy/2nd law (no 100% efficiency).
• EM spectrum: radio → microwave → IR → visible → UV → X-ray → gamma (rising energy).
• Nuclear: fission (splits heavy nucleus — reactors, bombs) vs fusion (Sun); radioactivity, half-life, isotopes.

Space technology

• ISRO milestones: Aryabhata (1st satellite), Chandrayaan (Moon; Chandrayaan-3 south-pole landing), Mangalyaan (Mars), Aditya-L1 (Sun, L1 point), Gaganyaan (human spaceflight). Launch vehicles: PSLV (workhorse), GSLV, LVM3. Orbits: LEO, geostationary (~36,000 km), polar/sun-synchronous, Lagrange points.

Defence & nuclear

• Missiles: ballistic (Agni, Prithvi) vs cruise (BrahMos); Akash (SAM), Nag (anti-tank). Nuclear triad; India's "No First Use" doctrine; NPT/CTBT (India non-signatory), NSG.

Digital & emerging tech

• AI/ML, blockchain (distributed immutable ledger), quantum computing/communication, 5G/6G, IoT, cloud, semiconductors.
• Digital Public Infrastructure: Aadhaar, UPI, DigiLocker, ONDC, CoWIN. Data protection (DPDP Act), cyber security.
• Green tech: green hydrogen (electrolysis via renewables), solar/wind, batteries, EVs, carbon capture.

Rapid-file

 • Geostationary ~36,000 km; sun-synchronous polar for remote sensing
 • CRISPR = gene editing; PCR = DNA amplification; ELISA = antibody test
 • Bt = Bacillus thuringiensis (pest resistance); Golden Rice = vitamin A
 • Boson/fermion, Higgs; nanotech (10⁻⁹ m); graphene
 • Vaccines: live-attenuated, inactivated, subunit, mRNA, viral-vector