UPSC Prelims 2023
Science & Technology Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 1 — 1 only

Carbon fibres are extensively used in manufacturing components for automobiles and aircraft due to their exceptional strength-to-weight ratio, high stiffness, and lightweight properties. Statement 1 is correct as these materials are crucial in aerospace and automotive industries for reducing weight and improving fuel efficiency.

✅ Statement 1 – Correct: Carbon fibres are indeed used in manufacturing automobile and aircraft components due to their superior mechanical properties and lightweight nature.

❌ Statement 2 – Incorrect: Carbon fibres can be recycled through various methods including mechanical recycling (breaking down into smaller pieces), chemical recycling (dissolving resin to extract fibres), and thermal recycling (pyrolysis to recover fibres), though the technology is still evolving.

📝 Short Notes: Carbon Fibres

• Composition: Made from organic polymers consisting of long strings of carbon atoms bonded together in crystalline alignment
• Key Properties: High tensile strength, low weight (5 times lighter than steel), high stiffness, high temperature tolerance, low thermal expansion, and chemical resistance
• Manufacturing Process: Produced through carbonization of precursor materials like polyacrylonitrile (PAN), pitch, or rayon at high temperatures (1000-3000°C)
• Applications: Aerospace (aircraft fuselage, wings), automotive (racing cars, luxury vehicles), sports equipment (bicycles, tennis rackets), wind turbine blades, and medical devices
• Recycling Methods: Mechanical (chopping/milling), thermal/pyrolysis (burning off resin at 450-700°C), chemical (solvolysis using solvents), and electrochemical processes
• Challenges: High production cost, brittleness (low impact resistance), difficulty in recycling compared to metals, and specialized manufacturing requirements
• Environmental Consideration: While recyclability was limited earlier, modern recycling technologies are making carbon fibre composites more sustainable with recovered fibres retaining 90-95% of original properties

Detailed Explanation:

Answer: Option 4 — Neither 1 nor 2

Both statements incorrectly describe the fundamental characteristics of ballistic and cruise missiles, as well as the specific types of Agni-V and BrahMos missiles. Let us evaluate each statement:

❌ Statement 1 – Incorrect: The statement incorrectly swaps the propulsion characteristics. Ballistic missiles are rocket-powered and follow a high, arcing ballistic trajectory at supersonic or hypersonic speeds, while cruise missiles are jet-propelled, fly at lower altitudes using aerodynamic lift, and can be subsonic, supersonic, or hypersonic.

❌ Statement 2 – Incorrect: The statement incorrectly describes both missiles. Agni-V is a solid-fuelled Intercontinental Ballistic Missile (ICBM) with a range exceeding 5,000 km, capable of striking targets across continents. BrahMos is a supersonic cruise missile (not a ballistic missile) developed jointly by India and Russia, with a range of around 450-600 km.

📝 Short Notes: Ballistic vs Cruise Missiles

• Agni-V: India's longest-range ICBM with a strike range of over 5,000 km, three-stage solid-fuelled missile, capable of carrying nuclear warheads, enhances India's strategic deterrence.
• BrahMos: World's fastest supersonic cruise missile (Mach 2.8-3), joint venture between India (DRDO) and Russia (NPO Mashinostroyeniya), available in land, sea, air, and submarine-launched variants.
• Detection Difficulty: Cruise missiles fly low and are harder to detect by radar, while ballistic missiles have predictable trajectories once launched but are harder to intercept due to high speeds.

Detailed Explanation:

Answer: Option 4 — All four

All four statements about mushroom properties are scientifically accurate. Mushrooms exhibit a remarkable diversity of biological properties that have been documented and utilized across medicinal, recreational, agricultural, and ecological contexts.

✅ Statement 1 – Correct: Medicinal mushrooms like Reishi (Ganoderma lucidum), Turkey Tail (Trametes versicolor), and Lion's Mane (Hericium erinaceus) contain bioactive compounds with immune-modulating, anti-inflammatory, and neuroprotective properties.

✅ Statement 2 – Correct: Psychoactive mushrooms containing psilocybin (such as Psilocybe cubensis) produce hallucinogenic effects and are being researched for therapeutic applications in treating depression and PTSD.

✅ Statement 3 – Correct: Insecticidal mushrooms like Metarhizium anisopliae and Beauveria bassiana produce compounds toxic to insects and are used as biological pest control agents in agriculture.

✅ Statement 4 – Correct: Bioluminescent mushrooms such as Mycena chlorophos and Panellus stipticus produce light through enzymatic reactions involving luciferin and luciferase, creating a natural glow in dark forest environments.

📝 Short Notes: Properties of Mushrooms

Detailed Explanation:

Answer: Option 3 — All three

An accelerometer is a sensor that measures acceleration forces, including changes in velocity, sudden movements, and changes in orientation (tilt). All three actions described in the question require the detection of acceleration changes or orientation shifts, making the accelerometer essential for their functioning.

✅ Action 1 – Car Crash Detection: Accelerometers detect the rapid deceleration during a collision, triggering immediate airbag deployment through the crash detection system.

✅ Action 2 – Laptop Free Fall Detection: Accelerometers sense the characteristic acceleration pattern of free fall (near-zero resistance), immediately parking the hard drive heads to prevent damage upon impact.

✅ Action 3 – Smartphone Tilt Detection: Accelerometers continuously monitor the device's orientation relative to gravity, enabling automatic display rotation between portrait and landscape modes.

📝 Short Notes: Accelerometer Applications

• Definition: An accelerometer is an electromechanical device that measures acceleration forces, both static (gravity) and dynamic (movement, vibration, shock).
• Working Principle: It detects changes in velocity, tilt, rotation, and vibration by measuring the displacement of a proof mass on springs when subjected to acceleration.
• Types: MEMS (Micro-Electro-Mechanical Systems) accelerometers are most commonly used in consumer electronics due to their small size and low power consumption.
• Automotive Safety: Used in airbag deployment systems, electronic stability control (ESC), anti-lock braking systems (ABS), and rollover detection.
• Consumer Electronics: Smartphones (screen rotation, step counting, gesture recognition), laptops (hard drive protection), gaming controllers (motion sensing), and fitness trackers.
• Industrial Applications: Vibration monitoring in machinery, structural health monitoring of buildings and bridges, and seismic activity detection.
• Aviation and Navigation: Inertial navigation systems, flight stabilization, and drone orientation control.

Detailed Explanation:

Answer: Option 1 — Controlling the viral diseases spread by mosquitoes

The Wolbachia method is a biological intervention that uses Wolbachia bacteria to control mosquito-borne viral diseases, particularly dengue, Zika, chikungunya, and yellow fever. When Wolbachia is introduced into Aedes aegypti mosquitoes (which don't naturally carry it), it reduces the mosquito's ability to transmit these viruses to humans. Additionally, Wolbachia spreads through mosquito populations via maternal transmission, making it a self-sustaining and environmentally friendly approach to disease control.

📝 Short Notes: Wolbachia Method for Vector Control

• What is Wolbachia: A naturally occurring bacterium found in approximately 60% of insect species, but not in Aedes aegypti or Aedes albopictus mosquitoes.
• Mechanism: When introduced into Aedes mosquitoes, Wolbachia interferes with virus replication, reducing vector competence for dengue, Zika, chikungunya, and yellow fever viruses.
• Self-sustaining: Wolbachia is maternally inherited; infected females pass the bacteria to their offspring, ensuring its persistence in mosquito populations.
• Cytoplasmic Incompatibility: Eggs produced by uninfected females mating with Wolbachia-infected males do not hatch, giving Wolbachia-carrying mosquitoes a reproductive advantage.
• Implementation: Successfully deployed by the World Mosquito Program in countries like Australia, Indonesia, Brazil, Colombia, and India (pilot projects in Pune and Delhi).
• Advantages: Safe for humans and environment, cost-effective in the long term, does not involve genetic modification, and targets multiple diseases simultaneously.

Detailed Explanation:

Answer: Option 1 — Studying the evolutionary relationships among various species of fauna

Microsatellite DNA, also known as Short Tandem Repeats (STRs), are highly polymorphic DNA sequences that show significant variation among individuals and populations. These variations make them excellent genetic markers for studying evolutionary relationships, population genetics, and phylogenetic studies among different species of fauna. The high mutation rate and variability in the number of repeated sequences allow researchers to trace genetic lineages and understand evolutionary divergence patterns.

📝 Short Notes: Microsatellite DNA (Short Tandem Repeats)

• Definition: Microsatellites are short repetitive DNA sequences (typically 1-6 base pairs) repeated in tandem arrays throughout the genome.
• Polymorphism: Highly variable in repeat number between individuals, making them useful genetic markers for identification and diversity studies.
• Applications in Evolutionary Biology: Used to study genetic diversity, population structure, gene flow, and phylogenetic relationships among species.
• Other Applications: DNA fingerprinting, paternity testing, forensic analysis, conservation genetics, and breeding programs.
• Advantages: Co-dominant inheritance, high mutation rates, abundance in genomes, and ease of amplification using PCR.
• Not Related to: Stem cell transformation, clonal propagation techniques, or direct drug efficacy testing (these involve different molecular techniques).

Detailed Explanation:

Answer: Option 1 — Only one

This question tests the knowledge of celestial objects and their correct definitions. Out of the three pairs given, only the third pair (Pulsars) is correctly matched, while the first two pairs have their descriptions reversed.

❌ Pair 1 – Incorrect: Cepheids are not giant clouds of dust and gas; they are actually pulsating stars that brighten and dim periodically, making them important distance markers in astronomy.

❌ Pair 2 – Incorrect: Nebulae are not stars that brighten and dim periodically; they are giant clouds of dust and gas in space where stars are born or remnants of dead stars.

✅ Pair 3 – Correct: Pulsars are indeed rapidly rotating neutron stars formed when massive stars exhaust their nuclear fuel and collapse in supernova explosions, emitting regular pulses of radiation.

📝 Short Notes: Celestial Objects

Detailed Explanation:

Answer: Option 1 — Collecting DNA samples from air in a habitat at one go

Aerial metagenomics is a cutting-edge technique that involves collecting environmental DNA (e-DNA) directly from the air using specialized filters or vacuum systems. Organisms constantly shed genetic material into their surroundings through breath, skin cells, fur, pollen, spores, and other biological particles, which can be captured from air samples. This method allows researchers to simultaneously identify and monitor multiple species—including animals, plants, fungi, and microorganisms—in a specific habitat without physical intrusion, making it a powerful non-invasive tool for biodiversity assessment.

📝 Short Notes: Metagenomics & Environmental DNA

• Metagenomics: The study of genetic material recovered directly from environmental samples (soil, water, air) without isolating individual organisms in laboratory cultures.
• Environmental DNA (e-DNA): Genetic material shed by organisms into their environment through skin cells, mucus, feces, gametes, and other biological materials.
• Aerial Metagenomics: Specifically focuses on capturing DNA from airborne particles using air filtration systems to assess biodiversity in a habitat.
• Applications: Non-invasive biodiversity monitoring, detecting rare or elusive species, tracking disease vectors, and studying ecosystem health.
• Advantages: Simultaneous detection of multiple taxa, no need for visual observation or physical capture, time and cost-efficient for large-scale surveys.

Detailed Explanation:

Answer: Option 4 — Japan

Japan operates the QZSS (Quasi-Zenith Satellite System), which is a regional satellite navigation system designed to enhance GPS coverage and accuracy in the Asia-Oceania region, particularly over Japan. Among the given options, only Japan has its own satellite navigation system.

📝 Short Notes: Satellite Navigation Systems Worldwide

• Global Navigation Satellite Systems (GNSS): Four operational systems - GPS (USA), GLONASS (Russia), Galileo (European Union), and BeiDou (China) - provide worldwide coverage.
• Regional Navigation Satellite Systems: NavIC/IRNSS (India) covers Indian subcontinent and surrounding region up to 1,500 km; QZSS (Japan) enhances GPS signals in Asia-Oceania region.
• GPS (USA): First operational GNSS with 24+ satellites, launched in 1978, fully operational since 1995.
• GLONASS (Russia): Developed during Soviet era, fully operational since 2011 with 24+ satellites.
• Galileo (EU): European system providing high-precision positioning, became operational in 2016.
• BeiDou (China): Completed global coverage in 2020 with 35 satellites, serves both regional and global users.
• NavIC (India): Indian Regional Navigation Satellite System with 7 satellites, operational since 2018, provides positioning accuracy better than 20 meters.
• QZSS (Japan): Quasi-Zenith Satellite System with satellites in quasi-zenith orbits, providing enhanced positioning over Japan and neighboring regions.

Detailed Explanation:

Answer: Option 3 — All three

All three statements are correct as extremophiles (microorganisms adapted to extreme conditions) can survive and thrive in environments that would be lethal to most life forms. These include extreme temperatures both above boiling and below freezing, as well as highly acidic conditions.

✅ Statement 1 – Correct: Hyperthermophiles like Pyrolobus fumarii can thrive in temperatures above 100°C (boiling point of water), often found in hydrothermal vents at temperatures up to 113°C.

✅ Statement 2 – Correct: Psychrophiles (cryophiles) are cold-loving microorganisms capable of growth in temperatures ranging from -20°C to +10°C, well below the freezing point of water (0°C).

✅ Statement 3 – Correct: Acidophiles such as Picrophilus oshimae thrive in highly acidic environments with pH below 3, with some species surviving at pH levels near 0.

📝 Short Notes: Extremophiles

Detailed Explanation:

Answer: Option 4 — None

All three statements regarding coal-based thermal power plants in India are incorrect. Some plants use seawater for cooling (like Mundra), many are located in water-stressed districts, and a significant number are privately owned.

❌ Statement 1 – Incorrect: The Mundra Thermal Power Plant uses seawater from the Gulf of Kutch in a closed-cycle cooling system, and also employs purified seawater from reverse osmosis plants for auxiliary systems.

❌ Statement 2 – Incorrect: According to WRI research, 40% of India's thermal power plants are situated in water-stressed regions, with 14 out of 20 largest thermal utilities experiencing shutdowns between 2013-2016 due to water shortages.

❌ Statement 3 – Incorrect: Out of India's 269 thermal power plants, 138 are publicly owned while 131 are privately owned, demonstrating significant private sector participation.

📝 Short Notes: Coal-Based Thermal Power Plants in India

• Cooling Water Sources: While most plants use freshwater from rivers or reservoirs, coastal plants like Mundra (Gujarat) utilize seawater cooling systems to conserve freshwater resources.
• Water Stress Challenge: 40% of thermal plants are in water-stressed regions, leading to operational disruptions and forced shutdowns during water scarcity periods.
• Ownership Structure: Total 269 plants - 138 public sector (Central/State utilities like NTPC, State Gencos) and 131 private sector (Adani Power, Tata Power, Reliance Power, etc.).
• Capacity Distribution: Thermal power contributes approximately 50-55% of India's total installed electricity generation capacity.
• Environmental Concerns: High water consumption (3-5 liters per kWh), thermal pollution, and emissions make water management critical for sustainability.

Detailed Explanation:

Answer: Option 3 — Statement-I is correct but Statement-II is incorrect

India indeed has domestic uranium deposits but relies heavily on coal for electricity generation (around 70% of total capacity). However, Statement-II is factually wrong because commercial nuclear power plants do not require uranium enriched to 60%.

✅ Statement-I – Correct: India has uranium deposits in Jharkhand (Singhbhum), Andhra Pradesh (Tummalapalle), and other regions, yet coal remains the dominant source for electricity production due to its abundance, lower cost, and established infrastructure.

❌ Statement-II – Incorrect: Uranium enriched to 60% or more is classified as Highly Enriched Uranium (HEU) and is used for research reactors or nuclear weapons, not commercial electricity production. India's PHWRs use natural uranium (0.7% U-235), while most commercial Light Water Reactors worldwide use Low Enriched Uranium (LEU) enriched to only 3-5% U-235.

📝 Short Notes: Nuclear Fuel Enrichment Levels

• India's Nuclear Program: Uses indigenous three-stage program starting with natural uranium in PHWRs
• Coal Dominance: India's coal reserves (4th largest globally) and lower capital costs make it preferred despite environmental concerns
• Uranium Sources: Jharkhand (Jaduguda), Andhra Pradesh (Tummalapalle - one of world's largest), Meghalaya, Rajasthan
• Nuclear Capacity: Only ~3% of India's total electricity comes from nuclear power (as of 2023)