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

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 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 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 — 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 — 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 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 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 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 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 3 — 1 and 2

Gucchi (Morchella esculenta) is a rare and expensive wild mushroom fungus found in the Himalayan regions. It grows naturally in temperate forest areas following snowmelt but cannot be commercially cultivated, making statements 1 and 2 correct while statement 3 is incorrect.

✅ Statement 1 – Correct: Gucchi is a fungus (Morchella esculenta) belonging to the Morchellaceae family, known for its distinctive honeycomb-like appearance and prized culinary value.

✅ Statement 2 – Correct: It grows naturally in the temperate conifer forest areas of the Himalayas, particularly in Jammu and Kashmir, Himachal Pradesh, and Uttarakhand during spring after snowmelt.

❌ Statement 3 – Incorrect: Gucchi mushrooms cannot be commercially cultivated due to their complex mycorrhizal associations with trees; they are wild-harvested, and they primarily grow in the Western Himalayas, not the north-eastern foothills.

📝 Short Notes: Gucchi (Morchella Mushroom)

• Scientific Name: Morchella esculenta, belonging to family Morchellaceae
• Appearance: Distinctive honeycomb or sponge-like cap structure, light brown to dark brown color
• Habitat: Temperate conifer forests of Western Himalayas (J&K, Himachal Pradesh, Uttarakhand) at altitudes of 2,500-3,500 meters
• Season: Grows in spring (March-May) following snowmelt in moist, shaded forest floors
• Economic Value: One of the most expensive mushrooms globally, fetching ₹10,000-30,000 per kg; major export item
• Cultivation Status: Cannot be commercially cultivated due to complex symbiotic relationship with tree roots; only wild-harvested by local communities
• Nutritional Value: Rich in protein, vitamins (especially Vitamin D), minerals, and antioxidants
• Conservation Concern: Over-harvesting threatens wild populations; sustainable harvesting practices needed

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements about biofilms are correct. Biofilms are complex microbial communities encased in a self-produced protective matrix that can form on various surfaces, including medical implants, food processing equipment, and biological tissues, exhibiting significant antibiotic resistance.

✅ Statement 1 – Correct: Biofilms readily form on medical implants like catheters, heart valves, and artificial joints within human tissues, leading to chronic infections that are difficult to treat.

✅ Statement 2 – Correct: Biofilms commonly form on food and food processing surfaces, contaminating food products and contributing to spoilage while being resistant to standard cleaning methods.

✅ Statement 3 – Correct: Bacteria within biofilms exhibit 10-1000 times greater antibiotic resistance than planktonic (free-floating) bacteria due to the protective matrix barrier, altered metabolic states, and horizontal gene transfer mechanisms.

📝 Short Notes: Biofilms

• Definition: Biofilms are structured communities of microorganisms encased in a self-produced extracellular polymeric substance (EPS) matrix, adhering to surfaces.
• Medical Implications: Responsible for 65-80% of all microbial infections in humans; form on indwelling medical devices, teeth (dental plaque), and in chronic wounds.
• Resistance Mechanisms: EPS matrix acts as a barrier to antimicrobials; slow growth rate in biofilms reduces antibiotic efficacy; persister cells survive treatment; gene transfer promotes resistance spread.
• Industrial Impact: Contaminate water pipes, ship hulls (biofouling), heat exchangers, and food processing equipment; cause economic losses and efficiency reduction.
• Food Safety: Biofilms in food industry harbor pathogens like Listeria, Salmonella, and E. coli; resistant to standard sanitization procedures.
• Control Strategies: Include mechanical removal, enzymatic disruption of EPS, quorum sensing inhibitors, and combination antimicrobial therapies.

Detailed Explanation:

Answer: Option 3 — 1, 3, 4, 6 and 7 only

Solar storms (solar flares and coronal mass ejections) release charged particles and electromagnetic radiation that interact with Earth's magnetosphere and ionosphere, causing various technological and atmospheric disturbances. The correct effects include disruption to satellite-based navigation, power grid damage, enhanced auroral displays, satellite orbital changes, and radio communication interference.

✅ Statement 1 – Correct: Solar storms disrupt the ionosphere, causing GPS signal delays and navigation system failures.
❌ Statement 2 – Incorrect: Tsunamis are caused by seismic or volcanic activity underwater, not by solar storms which affect electromagnetic and particle environments.
✅ Statement 3 – Correct: Geomagnetically induced currents (GICs) from solar storms can overload transformers and damage power grids, causing blackouts.
✅ Statement 4 – Correct: Enhanced solar wind energizes particles in the magnetosphere, creating intense auroras visible at lower latitudes than normal.
❌ Statement 5 – Incorrect: Solar storms do not directly cause widespread forest fires; they affect electromagnetic systems, not ignition sources on such a scale.
✅ Statement 6 – Correct: Increased atmospheric drag from heating during solar storms can alter satellite orbits, especially in low Earth orbit.
✅ Statement 7 – Correct: Ionospheric disturbances disrupt shortwave (HF) radio communications, particularly affecting polar routes where ionospheric effects are strongest.

📝 Short Notes: Solar Storms and Earth Effects

• Solar Storm Components: Solar flares (electromagnetic radiation) and Coronal Mass Ejections (CME - charged particles) that reach Earth in 1-3 days.
• Magnetosphere Interaction: Charged particles compress Earth's magnetosphere, inducing geomagnetic storms.
• Ionospheric Disruption: Solar radiation alters ionosphere density, affecting radio wave propagation and satellite communications.
• Geomagnetically Induced Currents (GICs): Magnetic field fluctuations induce currents in long conductors like power lines and pipelines.
• Aurora Formation: Charged particles collide with atmospheric gases (oxygen, nitrogen), producing light displays typically at 60-70° latitude, but extending to lower latitudes during major storms.
• Space Weather Monitoring: Organizations like NOAA's Space Weather Prediction Center track solar activity to issue warnings for critical infrastructure protection.
• Historical Events: Carrington Event (1859) caused widespread telegraph failures; Quebec blackout (1989) affected 6 million people for 9 hours.

Detailed Explanation:

Answer: Option 3 — A missile is put into a stable orbit around the Earth and deorbits over a target on the Earth.

The Fractional Orbital Bombardment System (FOBS) is a nuclear weapons delivery system that launches a warhead into a low Earth orbit trajectory instead of a traditional high-arc ballistic path. The key characteristic is that the missile completes only a fraction of an orbit before deorbiting to strike its target, making it harder to detect by early warning systems designed for conventional ballistic missiles. This orbital approach allows the weapon to approach from unexpected directions and reduces warning time significantly.

❌ Option 1 – Incorrect: FOBS is not designed for asteroid defense but for delivering weapons to Earth-based targets via orbital trajectory.
❌ Option 2 – Incorrect: This describes planetary landing maneuvers, not FOBS which is specifically about weapon delivery systems orbiting Earth.
✅ Option 3 – Correct: Accurately describes FOBS as a missile placed in orbit that deorbits over a terrestrial target.
❌ Option 4 – Incorrect: This describes a comet rendezvous mission, unrelated to FOBS weapons systems.

📝 Short Notes: Fractional Orbital Bombardment System (FOBS)

• Concept: A weapons delivery system developed during the Cold War era, primarily by the Soviet Union in the 1960s
• Trajectory: Uses a low Earth orbit (LEO) path rather than a high ballistic arc, completing only a fraction of an orbit before deorbiting
• Strategic Advantage: Can approach targets from unexpected directions (including over the South Pole), bypassing radar systems oriented toward traditional ballistic missile trajectories
• Detection Challenge: Early warning systems designed to detect high-arc ballistic missiles may fail to identify low-orbit FOBS until late in the attack sequence
• Reduced Warning Time: The orbital path and lower altitude mean less time between detection and impact compared to intercontinental ballistic missiles (ICBMs)
• Modern Context: Recent reports suggest renewed interest in FOBS technology by certain nations, making it relevant to contemporary strategic discussions
• Treaty Status: The Outer Space Treaty (1967) prohibits placing weapons of mass destruction in orbit, though FOBS occupies a grey area as it doesn't complete a full orbit

Detailed Explanation:

Answer: Option 4 — They protect the body from the diseases caused by pathogens.

B cells and T cells are both lymphocytes and key components of the adaptive immune system that specifically defend the body against pathogens like viruses, bacteria, fungi, and parasites. B cells produce antibodies that recognize and neutralize specific antigens on pathogens, while T cells either directly kill infected cells (cytotoxic T cells) or help coordinate the immune response (helper T cells).

❌ Option 1 – Incorrect: While immune cells can respond to allergens, the primary role of B and T cells is pathogen defense, not allergen protection.
❌ Option 2 – Incorrect: Pain and inflammation alleviation is not the primary function of B and T cells; they are involved in immune response.
❌ Option 3 – Incorrect: B and T cells are immunoactive, not immunosuppressants; they enhance rather than suppress immune function.
✅ Option 4 – Correct: This accurately describes the primary role of B and T cells in adaptive immunity against pathogenic diseases.

📝 Short Notes: B Cells and T Cells

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

Web 3.0 represents the next generation of the internet built on decentralization, blockchain technology, and user ownership. All three statements correctly describe key features of Web 3.0 technology.

✅ Statement 1 – Correct: Web 3.0 enables users to control their own data through decentralization, eliminating the need for centralized platforms to store and manage personal information.
✅ Statement 2 – Correct: Blockchain technology is fundamental to Web 3.0 and enables the creation of decentralized social networks where users own their content and interactions.
✅ Statement 3 – Correct: Web 3.0 operates on a decentralized model where users collectively maintain and control the network, rather than a single corporate entity.

📝 Short Notes: Web 3.0

• Definition: The third generation of internet services focusing on decentralization, blockchain technology, and semantic web capabilities
• Core Technologies: Blockchain, artificial intelligence, machine learning, and decentralized protocols
• Key Features: User data ownership, permissionless access, trustless interactions, and tokenization
• Differences from Web 2.0: Web 2.0 is centralized (controlled by corporations), while Web 3.0 is decentralized (user-controlled)
• Applications: Decentralized finance (DeFi), NFTs, decentralized autonomous organizations (DAOs), and blockchain-based social networks
• Advantages: Enhanced privacy, data security, censorship resistance, and direct peer-to-peer interactions
• Challenges: Scalability issues, high energy consumption, regulatory uncertainty, and user adoption barriers