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

Detailed Explanation:

Answer: Option 4 — spread of viral diseases

ACE2 (Angiotensin-Converting Enzyme 2) is a protein receptor found on human cell surfaces that became widely discussed during the COVID-19 pandemic. The SARS-CoV-2 virus uses ACE2 as its primary entry point into human cells, binding to this receptor through its spike protein to infect cells in the lungs, heart, kidneys, and other organs.

📝 Short Notes: ACE2 Receptor

• Full Form: Angiotensin-Converting Enzyme 2
• Normal Function: ACE2 is an enzyme that plays a crucial role in regulating blood pressure and cardiovascular function by converting angiotensin II to angiotensin (1-7)
• Location: Found on cell surfaces in multiple organs including lungs (alveolar cells), heart, kidneys, intestines, and blood vessels
• Role in COVID-19: Acts as the cellular receptor that SARS-CoV-2 spike protein binds to for viral entry into cells
• Research Significance: Target for therapeutic interventions including soluble ACE2, monoclonal antibodies, and small molecule inhibitors to block viral entry
• Previous Connection: The original SARS-CoV virus (2003) also used ACE2 as its receptor, making it a known vulnerability in coronavirus infections

Detailed Explanation:

Answer: Option 4 — Speed of light is always same.

Astronomical distances are measured in light-years because the speed of light in a vacuum is a universal constant (approximately 299,792 km/s). This constant nature makes it a reliable and standardized unit for measuring the vast distances in space. A light-year represents the distance light travels in one year, providing a practical scale for cosmic distances.

❌ Statement A – Incorrect: Distances between stellar bodies do change due to orbital motion, stellar evolution, and galactic movements; this is not why light-years are used as a unit.

❌ Statement B – Incorrect: While gravity is fundamental, the gravitational effects of stellar bodies vary with mass and distance changes; this has no bearing on the choice of light-year as a distance unit.

❌ Statement C – Incorrect: Light does not always travel in a straight line; it bends around massive objects due to gravitational lensing, as predicted by Einstein's General Theory of Relativity.

✅ Statement D – Correct: The speed of light in a vacuum is constant at approximately 3 × 10⁸ m/s, making it an ideal standard for measuring astronomical distances.

📝 Short Notes: Astronomical Distance Measurements

• Light-Year: The distance light travels in one year in a vacuum (approximately 9.46 trillion kilometers or 5.88 trillion miles).
• Astronomical Unit (AU): The average distance from Earth to the Sun (approximately 150 million km); used for measuring distances within the solar system.
• Parsec: Another unit for astronomical distances, equal to about 3.26 light-years; commonly used by professional astronomers.
• Speed of Light (c): A fundamental physical constant equal to 299,792,458 meters per second in vacuum; remains constant regardless of the observer's motion or the source's motion.
• Gravitational Lensing: The bending of light around massive objects due to gravity, predicted by Einstein's General Theory of Relativity and observed around galaxies and black holes.

Detailed Explanation:

Answer: Option 2 — 2 Only

Statement 1 is incorrect because adenoviruses have double-stranded DNA genomes, not single-stranded DNA. Retroviruses have single-stranded RNA genomes (not double-stranded DNA), which they reverse-transcribe into DNA using reverse transcriptase. Statement 2 is correct as adenoviruses are a common cause of the common cold, and AIDS is indeed caused by HIV, a retrovirus.

❌ Statement 1 – Incorrect: Adenoviruses have double-stranded DNA genomes; retroviruses have single-stranded RNA genomes, not double-stranded DNA.
✅ Statement 2 – Correct: The common cold can be caused by adenoviruses, and AIDS is caused by HIV, which is a retrovirus.

📝 Short Notes: Viral Genome Types

• DNA Viruses: Generally replicate in the nucleus using host cell machinery (exceptions: poxviruses replicate in cytoplasm)
• RNA Viruses: Most replicate in the cytoplasm; carry their own RNA polymerase
• Retroviruses: Unique in possessing reverse transcriptase enzyme that synthesizes DNA from RNA template
• Common Cold Causes: Rhinoviruses (most common), coronaviruses, adenoviruses, and others
• HIV Classification: Lentivirus genus of the Retroviridae family; targets CD4+ T cells

Detailed Explanation:

Answer: Option 3 — 1 and 3 Only

In a pressure cooker, the cooking temperature depends on the internal pressure, which determines the boiling point of water. The area of the hole in the lid and the weight of the lid regulate how much pressure builds up inside the cooker, thereby controlling the cooking temperature. The flame temperature only affects the rate of heating, not the maximum temperature achieved.

✅ Statement 1 – Correct: The size of the hole in the lid regulates steam release; a larger hole allows more steam to escape, reducing internal pressure and thus lowering the cooking temperature.

❌ Statement 2 – Incorrect: The temperature of the flame affects only the rate of heating, not the final cooking temperature, which is determined by the internal pressure of the cooker.

✅ Statement 3 – Correct: A heavier weight on the lid requires higher internal pressure to lift it, allowing steam to escape only when higher pressure is reached, which increases the boiling point and thus the cooking temperature.

📝 Short Notes: Pressure Cooker Mechanism

• Principle: Pressure cookers work on the principle that increasing pressure raises the boiling point of water above 100°C.
• Normal Boiling Point: At atmospheric pressure (1 atm), water boils at 100°C.
• In Pressure Cooker: Pressure can reach 15 psi (about 2 atm), raising the boiling point to approximately 121°C.
• Pressure Regulation: The weight (regulator) on the vent controls the maximum pressure by allowing steam to escape when pressure exceeds a threshold.
• Vent Hole Size: The area of the vent hole determines how easily steam can escape, affecting pressure buildup.
• Cooking Time: Higher temperature due to increased pressure reduces cooking time significantly.
• Flame Role: The flame intensity affects how quickly the cooker reaches operating pressure, not the final cooking temperature.

Detailed Explanation:

Answer: Option 4 — 1,2 and 3

All three activities mentioned can be successfully carried out using drones at the current level of technology. Drones have revolutionized various fields by enabling safe, efficient, and cost-effective operations in environments that are hazardous, remote, or difficult to access for humans.

✅ Statement 1 – Correct: Agricultural drones are extensively used for precision spraying of pesticides and fertilizers on crop fields, reducing chemical waste and human exposure to toxins.
✅ Statement 2 – Correct: Drones equipped with thermal cameras and gas sensors are deployed to inspect active volcano craters, allowing scientists to collect critical data from dangerous environments without risking human lives.
✅ Statement 3 – Correct: Specialized drones like 'SnotBot' are used to fly through whale blows (spouting breath) to collect biological samples including DNA, hormones, and microbiomes for non-invasive health monitoring and research.

📝 Short Notes: Applications of Drones (UAVs)

• Agriculture: Precision spraying of pesticides/fertilizers, crop monitoring, soil analysis, and irrigation management
• Environmental Research: Volcano monitoring, wildlife tracking, forest fire detection, and air quality assessment
• Marine Biology: Whale health monitoring through breath sample collection, marine mammal surveys, and coral reef mapping
• Disaster Management: Search and rescue operations, damage assessment, and delivery of emergency supplies
• Infrastructure: Inspection of bridges, power lines, pipelines, and tall structures
• Delivery Services: Medical supplies, e-commerce parcels, and food delivery in remote areas
• Defense & Security: Surveillance, reconnaissance, border patrolling, and tactical operations

Detailed Explanation:

Answer: Option 2 — 1, 3 and 4 only

This question tests the understanding of practical applications of Artificial Intelligence. AI can effectively reduce electricity consumption in industrial units through smart optimization, diagnose diseases through medical image analysis, and convert text to speech using natural language processing. However, creating genuinely meaningful creative content and wireless electrical transmission are not effective AI capabilities.

✅ Statement 1 – Correct: AI-driven automation and smart sensors optimize energy use in industrial units by predicting demand, monitoring equipment health, and adjusting operations in real-time to reduce electricity consumption.
❌ Statement 2 – Incorrect: At the time of this examination, AI could not effectively create truly meaningful short stories and songs with coherent narrative structure, genuine emotional depth, and creative intent beyond pattern recombination.
✅ Statement 3 – Correct: AI is highly effective in disease diagnosis, particularly in analyzing medical imagery such as X-rays, MRIs, and CT scans to detect diseases like cancer, pneumonia, and diabetic retinopathy with high precision.
✅ Statement 4 – Correct: Text-to-Speech (TTS) conversion is a mature and well-established application of AI that utilizes natural language processing and neural networks to synthesize human-like speech from written text.
❌ Statement 5 – Incorrect: Wireless transmission of electrical energy is a physical engineering process based on electromagnetic induction or microwaves, not an AI application. This is a function of physics and hardware design, not Artificial Intelligence.

📝 Short Notes: Applications of Artificial Intelligence

• Industrial Optimization: AI uses machine learning algorithms to analyze real-time data from sensors, predict maintenance needs, optimize production schedules, and reduce energy waste in manufacturing and industrial processes.
• Medical Diagnostics: AI-powered systems, particularly using deep learning and computer vision, assist in disease detection through medical image analysis, pattern recognition in patient data, and early diagnosis of conditions like cancer, cardiovascular diseases, and eye disorders.
• Natural Language Processing (NLP): Text-to-Speech systems use neural networks and deep learning to convert written text into natural-sounding speech, widely used in virtual assistants, accessibility tools, and automated customer service.
• Creative Content Generation: While AI can generate text and music based on patterns learned from training data, creating truly meaningful creative content with genuine emotional depth and narrative coherence remains challenging and was not considered an effective AI capability at the time of this examination.
• Limitations of AI: Physical processes like wireless power transmission depend on electromagnetic principles and hardware engineering, not software-based AI algorithms. AI can optimize such systems but cannot perform the transmission itself.

Detailed Explanation:

Answer: Option 2 — Some use imported uranium and others use domestic supplies

India's nuclear reactors are divided into civilian and strategic facilities under the 2005 Indo-US Civil Nuclear Deal. Reactors using imported uranium are placed under IAEA safeguards to ensure peaceful use, as mandated by international agreements for nuclear fuel supply. Reactors using domestic uranium remain outside IAEA safeguards, allowing India to maintain its strategic nuclear weapons program independently.

📝 Short Notes: India's Nuclear Programme and IAEA Safeguards

• Indo-US Civil Nuclear Deal (2008): Separated India's nuclear facilities into civilian (under IAEA safeguards) and military (outside safeguards) categories, ending India's nuclear isolation despite not signing the NPT.
• IAEA Safeguards: International inspection regime to verify that nuclear materials are used only for peaceful purposes and not diverted to weapons programs.
• Separation Plan: India voluntarily placed 14 of its 22 power reactors under IAEA safeguards, while keeping 8 reactors and other facilities outside for strategic purposes.
• Imported Uranium Condition: Any reactor using imported uranium or fuel must be under IAEA safeguards as per bilateral agreements with supplier countries (USA, Russia, France, etc.).
• Domestic Uranium: Reactors using indigenous uranium from Indian mines (Jharkhand, Andhra Pradesh) remain outside safeguards, preserving India's three-stage nuclear program and weapons capability.
• Three-Stage Programme: India's unique nuclear strategy using natural uranium (Stage I), plutonium breeder reactors (Stage II), and thorium-U233 cycle (Stage III) to achieve energy security.
• Strategic Autonomy: The separation allows India to maintain its minimum credible nuclear deterrent while accessing international nuclear commerce and technology.

Detailed Explanation:

Answer: Option 4 — 1 and 3 only

Blockchain is a decentralized, distributed ledger technology where data is transparent and publicly inspectable, yet no single entity controls the network. While blockchain gained prominence through cryptocurrencies, its applications extend far beyond digital currencies to supply chain management, smart contracts, healthcare records, and more.

✅ Statement 1 – Correct: Blockchain functions as a public, distributed ledger that anyone can inspect, but which operates without centralized control, being maintained by a network of nodes.
❌ Statement 2 – Incorrect: Blockchain's architecture is not limited to cryptocurrency data; it can record and verify any type of digital information including contracts, identity records, supply chain data, and voting records.
✅ Statement 3 – Correct: The open-source and decentralized nature of blockchain allows developers to build applications (DApps) leveraging its core features—transparency, immutability, and decentralization—without requiring permission from any central authority.

📝 Short Notes: Blockchain Technology

• Definition: A distributed, decentralized ledger that records transactions across multiple computers in a way that makes records immutable and transparent.
• Key Features: Decentralization (no single point of control), Transparency (public inspection), Immutability (records cannot be altered retroactively), Security (cryptographic hashing).
• Structure: Data is stored in blocks, each containing transaction data, timestamp, and cryptographic hash of the previous block, forming a chain.
• Applications Beyond Cryptocurrency: Supply chain tracking, smart contracts, digital identity verification, healthcare records management, voting systems, land registry, and intellectual property protection.
• Types: Public blockchains (permissionless, like Bitcoin), Private blockchains (permissioned, restricted access), and Hybrid blockchains (combination of both).
• Consensus Mechanisms: Proof of Work (PoW), Proof of Stake (PoS), Practical Byzantine Fault Tolerance (PBFT), and others ensure network agreement on transaction validity.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements regarding genome editing and stem cell technologies are scientifically correct and represent current capabilities in biotechnology.

✅ Statement 1 – Correct: Germline gene editing using technologies like CRISPR-Cas9 can introduce genetic changes in germ cells (eggs or sperm), making these modifications heritable and transmissible to future generations.

✅ Statement 2 – Correct: Genome editing can be performed at the early embryonic stage (zygote or blastocyst stage) before birth, allowing for correction of genetic mutations that cause hereditary diseases.

✅ Statement 3 – Correct: Human induced pluripotent stem cells (hiPSCs) can be injected into pig embryos to create human-animal chimeras, a technique used in research for studying organ development and exploring potential for human organ transplantation.

📝 Short Notes: Genome Editing and Stem Cell Technologies

• CRISPR-Cas9: A revolutionary gene-editing tool that allows precise modifications to DNA sequences in living organisms, enabling targeted correction of genetic defects.
• Germline Editing: Modifications made to germ cells (eggs, sperm) or early embryos that are heritable and passed to future generations, raising significant ethical concerns.
• Somatic Gene Editing: Changes made to non-reproductive cells that affect only the individual and are not passed to offspring.
• Induced Pluripotent Stem Cells (iPSCs): Adult cells reprogrammed to an embryonic-like pluripotent state, capable of differentiating into any cell type in the body.
• Chimeras: Organisms containing cells from two different species; human-animal chimeras are used in research to study disease mechanisms and organ development.
• Ethical Concerns: Germline editing and chimera research raise questions about human dignity, unintended consequences, equity in access, and the creation of designer babies.
• Regulatory Status: Many countries have banned or strictly regulate germline editing in humans, though research continues in controlled settings for therapeutic purposes.

Detailed Explanation:

Answer: Option 4 — prevention of mitochondrial diseases in offspring

Pronuclear transfer is a mitochondrial replacement therapy technique used to prevent the transmission of mitochondrial diseases from mother to child. The technique involves transferring the pronuclei (nuclei from both egg and sperm before fusion) from a fertilized egg with defective mitochondria into a donor egg with healthy mitochondria but whose own pronuclei have been removed. This allows the child to inherit nuclear DNA from the biological parents while receiving healthy mitochondrial DNA from the donor, thereby preventing mitochondrial diseases.

📝 Short Notes: Mitochondrial Replacement Therapy

• Mitochondria: Cellular organelles with their own DNA (mtDNA) separate from nuclear DNA; mutations in mtDNA cause inherited mitochondrial diseases affecting muscles, nerves, brain, and other organs.
• Pronuclear Transfer (PNT): One of two main mitochondrial replacement techniques; involves transferring pronuclei from fertilized egg to donor egg with healthy mitochondria.
• Maternal Spindle Transfer (MST): Alternative technique performed before fertilization; nuclear DNA from mother's egg transferred to donor egg with healthy mitochondria.
• Three-Parent Baby: Resulting child has nuclear DNA from biological parents and mitochondrial DNA from donor (contributes <0.1% of total DNA).
• Ethical and Legal Status: First approved in UK (2015); performed in limited countries; raises ethical debates about genetic modification and germline editing.
• Applications: Prevents severe mitochondrial diseases like Leigh syndrome, MELAS, and Kearns-Sayre syndrome from being passed to offspring.

Detailed Explanation:

Answer: Option 3 — 1 and 3 only

This question tests the fundamental structural differences between plant and animal cells. Statement 2 is incorrect because both plant and animal cells possess a plasma membrane, which is a universal feature of all cells.

✅ Statement 1 – Correct: Plant cells have rigid cellulose cell walls for structural support and protection, while animal cells lack cell walls and only have a flexible plasma membrane.

❌ Statement 2 – Incorrect: Both plant and animal cells have plasma membranes (cell membranes); this is a fundamental feature present in all living cells, controlling the movement of substances in and out of the cell.

✅ Statement 3 – Correct: Mature plant cells typically contain one large central vacuole for storage of water, nutrients, and waste, whereas animal cells have multiple small vacuoles that are less prominent.

📝 Short Notes: Plant vs Animal Cells

Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Visible Light Communication (VLC) is an optical wireless communication technology that uses visible light spectrum for data transmission. Statements 1, 3, and 4 correctly describe VLC's characteristics, while statement 2 incorrectly classifies it as long-range communication.

✅ Statement 1 – Correct: VLC operates in the visible light spectrum range of 375 nm (violet) to 780 nm (red), which falls within the electromagnetic spectrum.

❌ Statement 2 – Incorrect: VLC is a short-range optical wireless communication technology, typically limited to distances within a room or line-of-sight areas, not long-range communication.

✅ Statement 3 – Correct: VLC can achieve data transmission speeds significantly faster than Bluetooth, with potential speeds reaching several Gbps compared to Bluetooth's maximum of around 50 Mbps.

✅ Statement 4 – Correct: Since VLC uses light waves instead of radio frequencies, it does not cause or suffer from electromagnetic interference (EMI), making it suitable for sensitive environments like hospitals and aircraft.

📝 Short Notes: Visible Light Communication (VLC)

• Technology Basis: Uses LED bulbs to transmit data through rapid light intensity modulation imperceptible to the human eye
• Spectrum Range: Operates in 375-780 nm wavelength (visible light spectrum)
• Speed: Can achieve data rates from 100 Mbps to several Gbps, much faster than WiFi and Bluetooth
• Range: Short-range technology, typically effective within 10 meters in line-of-sight conditions
• Advantages: No electromagnetic interference, high security (light cannot penetrate walls), energy efficient, uses existing LED infrastructure
• Limitations: Requires line-of-sight, affected by ambient light, cannot work through opaque objects
• Applications: Indoor navigation, underwater communication, secure data transfer in sensitive areas, vehicle-to-vehicle communication
• Li-Fi: A related technology that uses VLC for high-speed wireless internet connectivity

Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Carbon nanotubes (CNTs) are cylindrical nanostructures with unique properties that make them suitable for biomedical applications including drug delivery, biosensing, and under certain conditions, biodegradation. Statement 2 is incorrect as CNTs cannot be reliably made into functional artificial blood capillaries—this application remains experimental and lacks validated clinical use.

✅ Statement 1 – Correct: CNTs can be functionalized with drugs and antigens, making them effective carriers for targeted delivery in the human body due to their ability to cross biological membranes.

❌ Statement 2 – Incorrect: While CNTs have been explored in tissue engineering scaffolds, they cannot be made into functional artificial blood capillaries as these require precise biological compatibility, flexibility, and permeability that CNTs alone cannot replicate.

✅ Statement 3 – Correct: CNTs possess high surface-to-volume ratio and unique electrical properties, making them ideal for biochemical sensors that detect biomolecules like glucose, proteins, and DNA with high sensitivity.

✅ Statement 4 – Correct: Research has shown that CNTs can be biodegraded by oxidative enzymes such as myeloperoxidase (MPO) found in human neutrophils, though biodegradability depends on CNT type, structure, and surface functionalization.

📝 Short Notes: Carbon Nanotubes

• Structure: Cylindrical nanostructures composed of rolled-up sheets of graphene, with diameters in nanometers and lengths up to micrometers.
• Types: Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).
• Properties: Exceptional mechanical strength, high electrical and thermal conductivity, high surface area, and ability to be functionalized.
• Biomedical Applications: Drug delivery systems, gene therapy carriers, biosensors, tissue engineering scaffolds, and imaging contrast agents.
• Drug Delivery: Can be functionalized to carry therapeutic agents and target specific cells, improving drug efficacy and reducing side effects.
• Biosensors: Used in electrochemical and optical sensors for detecting glucose, cholesterol, DNA, proteins, and pathogens with high sensitivity.
• Biodegradability Debate: Some studies show enzymatic degradation by peroxidases, but biodegradability varies with CNT structure, functionalization, and environmental conditions; persistence in biological systems remains a concern.
• Challenges: Potential toxicity, biocompatibility issues, aggregation in biological fluids, and lack of standardized methods for large-scale production and functionalization.

Detailed Explanation:

Answer: Option 1 — Digital security infrastructure

Public Key Infrastructure (PKI) is a comprehensive framework used specifically for digital security infrastructure in India. It enables secure electronic communication and transactions through digital certificates, certificate authorities, and cryptographic key pairs (public and private keys), ensuring authentication, confidentiality, integrity, and non-repudiation of digital data.

📝 Short Notes: Public Key Infrastructure (PKI)

• Definition: PKI is a set of roles, policies, hardware, software, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates and manage public-key encryption.
• Components: Includes Certificate Authority (CA), Registration Authority (RA), digital certificates, certificate repositories, and certificate revocation lists (CRL).
• Function: Uses asymmetric cryptography with a pair of keys - public key (shared openly) and private key (kept secret) for encryption and digital signatures.
• Applications in India: Used in e-governance initiatives, digital signatures, secure email, online banking, e-commerce, and Aadhaar-based authentication.
• Controller of Certifying Authorities (CCA): Under the IT Act 2000, CCA is the authority to license and regulate Certifying Authorities in India.
• Benefits: Ensures data confidentiality, integrity, authentication, and non-repudiation in digital communications and transactions.

Detailed Explanation:

Answer: Option 4 — Evolved LISA

The description of three spacecraft flying in an equilateral triangle formation with sides one million kilometres long, using lasers for measurement, uniquely identifies the Evolved Laser Interferometer Space Antenna (eLISA) mission. This is a proposed space-based gravitational wave observatory designed to detect low-frequency gravitational waves by measuring tiny distance changes between the spacecraft using laser interferometry. Voyager and New Horizons are single-spacecraft exploration missions, while LISA Pathfinder was only a technology demonstrator for testing eLISA components, not the full mission itself.

📝 Short Notes: Gravitational Wave Detection Missions

• LISA (Laser Interferometer Space Antenna): Original concept for space-based gravitational wave detection proposed by ESA and NASA.
• Evolved LISA (eLISA): Redesigned version with three spacecraft in equilateral triangle formation, each separated by ~1 million km, using laser interferometry to detect gravitational waves.
• LISA Pathfinder (2015-2017): Technology demonstration mission that successfully tested drag-free flight and precision measurement technologies required for eLISA.
• Configuration: Three identical spacecraft maintain precise formation while measuring distance changes of picometers (10⁻¹² meters) caused by passing gravitational waves.
• Target: Detection of low-frequency gravitational waves (0.1 mHz to 1 Hz) from sources like merging supermassive black holes, binary star systems, and early universe events.
• Ground-based counterpart: LIGO (Laser Interferometer Gravitational-Wave Observatory) detects high-frequency gravitational waves on Earth.