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

Detailed Explanation:

Answer: Option 4 — 2 and 3

DNA barcoding is a molecular technique that uses short, standardized gene sequences to identify species. It is particularly effective for distinguishing morphologically similar species and detecting species composition in processed materials, but it cannot determine the age of organisms.

❌ Statement 1 – Incorrect: DNA barcoding identifies species based on genetic sequences but cannot assess the age of a plant or animal, as age determination requires other methods like dendrochronology or carbon dating.

✅ Statement 2 – Correct: DNA barcoding excels at distinguishing among species that look morphologically similar by comparing their unique genetic barcodes (typically COI gene in animals, rbcL or matK in plants).

✅ Statement 3 – Correct: DNA barcoding is extensively used in food safety to identify undeclared or undesirable animal/plant materials in processed foods, helping detect food adulteration and mislabeling.

📝 Short Notes: DNA Barcoding

• Definition: A molecular tool that uses short, standardized DNA sequences to rapidly identify species
• Gene Markers: COI (Cytochrome C Oxidase I) for animals; rbcL, matK, ITS for plants
• Applications: Species identification, biodiversity assessment, food authentication, detection of illegal wildlife trade, identification of medicinal plants
• Advantages: Works with small tissue samples, identifies cryptic species, useful for immature/damaged specimens
• Limitations: Cannot determine age, recent speciation may show similar sequences, requires reference database
• Global Initiative: International Barcode of Life (iBOL) project maintains comprehensive DNA barcode libraries

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three technologies—CCTV, RFID, and WLAN—are classified as short-range communication devices. Short-range technologies typically operate within a few centimeters to a few hundred meters, unlike long-range technologies such as cellular networks or satellite communication.

✅ Closed-Circuit Television (CCTV) – Short-Range: CCTV systems use cables or wireless connections with limited range, typically confined to a building or specific premises, operating within tens to hundreds of meters.

✅ Radio Frequency Identification (RFID) – Short-Range: RFID uses radio waves for identification and tracking, with typical reading ranges from a few centimeters to about 10 meters depending on the tag type (passive, active, or semi-passive).

✅ Wireless Local Area Network (WLAN/Wi-Fi) – Short-Range: WLAN networks typically operate within 20-100 meters indoors and up to 300 meters outdoors, making them short-range compared to wide-area networks like cellular or satellite systems.

📝 Short Notes: Short-Range Communication Technologies

• Short-range vs Long-range: Short-range technologies operate within localized areas (centimeters to hundreds of meters), while long-range technologies like cellular networks (kilometers) and satellite communication (global coverage) serve wider geographical areas.
• Power consumption: Short-range devices typically consume less power, making them suitable for battery-operated applications.
• Data rate: Generally, shorter ranges allow for higher data transfer rates (e.g., Wi-Fi offers Mbps to Gbps speeds).
• Applications: Short-range technologies are ideal for home automation, personal devices, local networking, surveillance, and proximity-based services.

Detailed Explanation:

Answer: Option 4 — 2 and 3

This question tests understanding of nanoparticles, their natural occurrence, applications, and potential safety concerns. Statement 1 is incorrect as nanoparticles occur naturally through various processes, while statements 2 and 3 are correct regarding their use in cosmetics and potential environmental risks.

❌ Statement 1 – Incorrect: Nanoparticles exist naturally in the environment through volcanic eruptions, forest fires, ocean spray, and biological processes (e.g., viruses, protein complexes).

✅ Statement 2 – Correct: Nanoparticles of metallic oxides like zinc oxide (ZnO) and titanium dioxide (TiO₂) are commonly used in sunscreens and cosmetics for UV protection and improved texture.

✅ Statement 3 – Correct: Many nanoparticles from commercial products can enter the environment and may pose health risks due to their ability to penetrate biological barriers and accumulate in organs.

📝 Short Notes: Nanoparticles

• Definition: Particles with at least one dimension between 1-100 nanometers (nm)
• Natural Sources: Volcanic ash, sea spray, forest fires, mineral weathering, and biological entities (viruses, ferritin)
• Cosmetic Applications: Zinc oxide and titanium dioxide nanoparticles in sunscreens provide broad-spectrum UV protection without visible white residue
• Other Applications: Drug delivery, electronics, catalysis, water purification, antibacterial coatings
• Safety Concerns: High surface area-to-volume ratio allows interaction with biological systems; can cross blood-brain barrier and cell membranes; potential for bioaccumulation
• Environmental Impact: Persistence in environment, toxicity to aquatic organisms, unknown long-term effects on ecosystems
• Regulation: Many countries are developing specific guidelines for nanomaterial safety assessment in consumer products

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements correctly describe the characteristics and examples of Software as a Service (SaaS). SaaS is a cloud computing model where software is hosted remotely and accessed via the internet, eliminating the need for local installation.

✅ Statement 1 – Correct: Most SaaS platforms allow users to customize the user interface and modify data fields according to their business requirements, providing flexibility within the hosted environment.

✅ Statement 2 – Correct: A fundamental advantage of SaaS is platform-independent accessibility, enabling users to access their data and applications from any device with internet connectivity, including mobile devices.

✅ Statement 3 – Correct: Outlook (web version), Hotmail, and Yahoo! Mail are classic examples of SaaS applications where email services are delivered over the internet without requiring local software installation.

📝 Short Notes: Software as a Service (SaaS)

• Definition: SaaS is a cloud computing service model where applications are hosted by a service provider and made available to users over the internet.
• Key Characteristics: No local installation required, subscription-based pricing, automatic updates, multi-tenant architecture, and accessibility from anywhere.
• Advantages: Lower upfront costs, scalability, automatic maintenance and updates, cross-platform compatibility, and reduced IT infrastructure burden.
• Common Examples: Google Workspace (Gmail, Docs, Sheets), Microsoft 365, Salesforce, Dropbox, Slack, Zoom, and Adobe Creative Cloud.
• Cloud Service Models: SaaS (Software), PaaS (Platform as a Service), and IaaS (Infrastructure as a Service) form the three main cloud computing service models.
• Security Considerations: Data is stored on third-party servers, requiring trust in the provider's security measures and compliance standards.

Detailed Explanation:

Answer: Option 2 — Quantum Computing

A qubit (quantum bit) is the fundamental unit of information in quantum computing, analogous to the classical bit. Unlike classical bits that exist in either 0 or 1 state, qubits can exist in a superposition of both states simultaneously, enabling quantum computers to perform complex calculations exponentially faster for certain problems.

📝 Short Notes: Quantum Computing Fundamentals

• Qubit (Quantum Bit): The basic unit of quantum information that can exist in superposition of |0⟩ and |1⟩ states simultaneously.
• Superposition: A quantum phenomenon where a qubit exists in multiple states at once until measured, unlike classical bits which are deterministic.
• Quantum Entanglement: Qubits can be entangled such that the state of one instantly affects another, regardless of distance.
• Quantum Gates: Operations that manipulate qubits, analogous to logic gates in classical computing but exploiting quantum properties.
• Decoherence: The main challenge in quantum computing where qubits lose their quantum properties due to environmental interference.
• Applications: Cryptography, drug discovery, optimization problems, artificial intelligence, and financial modeling.
• Major Players: IBM, Google, Microsoft, and various research institutions are developing quantum computers with increasing qubit counts.

Detailed Explanation:

Answer: Option 1 — 1 and 2 only

Non-Fungible Tokens (NFTs) are unique cryptographic tokens on blockchain that enable digital representation of physical or digital assets. However, unlike fungible assets, NFTs cannot be traded at equivalency since each token has a unique value and characteristics, making them unsuitable as a standard medium of commercial transactions.

✅ Statement 1 – Correct: NFTs enable digital representation of physical assets through tokenization, allowing real-world items like real estate, artwork, or luxury goods to be represented on blockchain, facilitating ownership transfer and reducing fraud.

✅ Statement 2 – Correct: NFTs are unique cryptographic tokens that exist on a blockchain with distinct identification codes and metadata that differentiate each token from others, unlike fungible cryptocurrencies like Bitcoin.

❌ Statement 3 – Incorrect: NFTs are non-fungible by definition, meaning they cannot be traded or exchanged at equivalency; each NFT has unique characteristics and value, unlike fungible assets (fiat currency, Bitcoin) that can serve as standard medium of exchange.

📝 Short Notes: Non-Fungible Tokens (NFTs)

• Definition: Unique digital identifiers recorded on blockchain that certify ownership and authenticity of specific digital or physical assets
• Key Characteristic: Non-fungibility means each token is unique and cannot be replaced or exchanged on a one-to-one basis
• Technology: Built on blockchain platforms like Ethereum, using smart contracts to enforce ownership and transfer rules
• Applications: Digital art, collectibles, gaming assets, virtual real estate, music rights, and tokenization of physical assets
• Difference from Cryptocurrency: Cryptocurrencies are fungible (interchangeable), while NFTs are unique with distinct values
• Tokenization: Process of converting rights to an asset into a digital token on blockchain
• Limitations: Cannot function as medium of exchange due to non-fungibility; high energy consumption concerns; speculation and volatility issues

Detailed Explanation:

Answer: Option 2 — 2 and 3 only

This question tests knowledge about different COVID-19 vaccine platforms used in India. Statement 1 is incorrect because Covishield is a viral vector vaccine (using chimpanzee adenovirus), not an mRNA vaccine. Statements 2 and 3 are correct as they accurately describe the platforms used for Sputnik V and COVAXIN respectively.

❌ Statement 1 – Incorrect: Covishield is a viral vector vaccine using chimpanzee adenovirus (ChAdOx1), not an mRNA platform vaccine.
✅ Statement 2 – Correct: Sputnik V uses a vector-based platform with two different human adenovirus vectors (rAd26 and rAd5) in a two-dose regimen.
✅ Statement 3 – Correct: COVAXIN, developed by Bharat Biotech, is an inactivated pathogen-based vaccine using the whole-virion inactivated Vero cell platform.

📝 Short Notes: COVID-19 Vaccine Platforms

Detailed Explanation:

Answer: Option 3 — 1 and 3

This question tests knowledge about probiotics, which are live microorganisms beneficial for gut health. Statements 1 and 3 are correct as probiotics include both bacteria and yeast, and certain strains help digest lactose (milk sugar).

✅ Statement 1 – Correct: Probiotics consist of both bacteria (like Lactobacillus, Bifidobacterium) and yeast (like Saccharomyces boulardii).

❌ Statement 2 – Incorrect: Probiotic organisms naturally occur in our gut as part of the normal gut microbiome; probiotics supplement these beneficial microbes.

✅ Statement 3 – Correct: Some probiotic strains produce lactase enzyme, which helps break down lactose (milk sugar), aiding digestion especially in lactose-intolerant individuals.

📝 Short Notes: Probiotics

• Definition: Live microorganisms that provide health benefits when consumed in adequate amounts, particularly for gut health.
• Common Types: Bacteria (Lactobacillus, Bifidobacterium, Streptococcus thermophilus) and Yeast (Saccharomyces boulardii).
• Natural Sources: Yogurt, kefir, sauerkraut, kimchi, tempeh, miso, pickles, and other fermented foods.
• Benefits: Improve digestive health, enhance immune function, aid lactose digestion, synthesize vitamins (B and K), prevent diarrhea and constipation.
• Gut Microbiome: Human gut naturally contains trillions of microorganisms; probiotics supplement beneficial strains already present.
• vs Prebiotics: Probiotics are live organisms; prebiotics are non-digestible food components that feed beneficial gut bacteria.

Detailed Explanation:

Answer: Option 1 — 1 and 2 Only

Bacteria and fungi can be cultured in artificial/synthetic media as they possess complete cellular machinery for independent growth and reproduction. Viruses, being obligate intracellular parasites, lack cellular machinery and can only replicate inside living host cells, making them incapable of growth in synthetic media.

✅ Statement 1 (Bacteria) – Correct: Bacteria can be cultured in various artificial media like nutrient agar, nutrient broth, and other specialized media as they are self-sufficient organisms with complete metabolic machinery.

✅ Statement 2 (Fungi) – Correct: Fungi can be cultured in artificial media such as Potato Dextrose Agar (PDA), Sabouraud Dextrose Agar, and Czapek Dox Agar, as they can independently utilize nutrients for growth.

❌ Statement 3 (Virus) – Incorrect: Viruses cannot be cultured in artificial/synthetic media as they are acellular and require living host cells (embryonated eggs, cell cultures, or living organisms) for replication.

📝 Short Notes: Microorganism Cultivation Methods

• Artificial Media: Chemically defined or complex media prepared in laboratory without living cells
• Bacterial Culture: Can grow on solid (agar plates) or liquid (broth) media at specific temperature and pH
• Fungal Culture: Require slightly acidic pH and longer incubation periods compared to bacteria
• Viral Culture: Requires tissue culture, embryonated chicken eggs, or experimental animals
• Key Difference: Viruses are acellular and depend entirely on host cell ribosomes, enzymes, and nucleotides for replication

Detailed Explanation:

Answer: Option 1 — it is dipolar in nature

Water is known as the "universal solvent" because of its dipolar (polar) nature. Water molecules have a bent structure with partial positive charges on hydrogen atoms and a partial negative charge on the oxygen atom, creating a dipole. This polarity enables water molecules to surround and interact with ions and other polar molecules through electrostatic attraction, effectively separating and dissolving them. The dipolar nature is the fundamental reason why water can dissolve more substances than any other liquid.

📝 Short Notes: Properties of Water as a Solvent

• Dipolar/Polar Nature: Water has a bent molecular structure (H-O-H angle ~104.5°) with oxygen being more electronegative, creating partial charges (δ+ on H, δ- on O).
• Universal Solvent: Water dissolves ionic compounds (like salts) by surrounding ions with water molecules (hydration) and polar covalent compounds through hydrogen bonding.
• Hydrogen Bonding: The polar nature allows water molecules to form hydrogen bonds with each other and with solute particles, facilitating dissolution.
• High Dielectric Constant: Water has a high dielectric constant (~80), which reduces the electrostatic attraction between dissolved ions, keeping them separated in solution.
• Not Related to Solvent Properties: Good heat conductor, high specific heat, and being an oxide of hydrogen are properties of water but not the primary reasons for its exceptional solvent capabilities.

Detailed Explanation:

Answer: Option 2 — developing genetically modified crop plants.

Bollgard I and Bollgard II are biotechnology products developed for creating genetically modified (GM) cotton plants with insect resistance. These technologies use genes from Bacillus thuringiensis (Bt) bacteria to produce insecticidal proteins that protect cotton plants from bollworm and other lepidopteran pests, thereby reducing the need for chemical pesticides.

📝 Short Notes: Bt Cotton Technologies

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

Recombinant vector vaccines utilize genetic engineering to insert pathogen genes into harmless carrier organisms (vectors), which then deliver these genes into human cells to produce antigens and trigger immunity. Both viruses (like Adenoviruses in Covishield) and bacteria (like attenuated Salmonella or BCG) can serve as vectors in these vaccines.

✅ Statement 1 – Correct: Genetic engineering is essential for developing recombinant vector vaccines, involving the insertion of pathogen antigen genes into a vector's genetic material.
✅ Statement 2 – Correct: Both bacteria (e.g., Salmonella, BCG) and viruses (e.g., Adenovirus, VSV) are used as vectors to deliver antigens.

📝 Short Notes: Recombinant Vector Vaccines

• Technology: Uses genetic engineering to insert genes encoding pathogen antigens into harmless viral or bacterial vectors
• Mechanism: Vectors deliver genetic material into host cells, which then produce antigens triggering immune response
• Viral Vectors: Adenoviruses (Covishield/Sputnik V), Vesicular Stomatitis Virus (Ebola vaccine - Ervebo), Modified Vaccinia Ankara (MVA)
• Bacterial Vectors: Attenuated Salmonella typhimurium, Mycobacterium bovis (BCG), Listeria monocytogenes strains
• Advantages: Strong cellular and humoral immunity, no live pathogen used, scalable production
• Examples: COVID-19 vaccines (AstraZeneca/Covishield, J&J, Sputnik V), Ebola vaccine (Ervebo), experimental TB and malaria vaccines

Detailed Explanation:

Answer: Option 3 — Lemongrass

Lemongrass (also known as Citronella grass) is widely used in preparing natural mosquito repellents due to its strong citrus-like odor. The essential oil extracted from lemongrass contains citronella oil, which is highly effective in repelling mosquitoes. Studies have shown that lemongrass oil can repel or kill up to 95% of certain mosquito species, with effects lasting approximately 2-3 hours.

📝 Short Notes: Natural Mosquito Repellents

• Lemongrass (Cymbopogon): Contains citronella oil, the most commonly used natural mosquito repellent; effective against multiple mosquito species
• Mechanism: The strong citrus odor masks human scent and carbon dioxide, making it difficult for mosquitoes to locate their targets
• Citronella Oil: Extracted from lemongrass leaves; used in candles, sprays, lotions, and incense sticks
• Duration of Effect: Typically lasts 2-3 hours; requires reapplication for extended protection
• Other Natural Repellents: Neem oil, eucalyptus oil, lavender, basil, and marigold also possess mosquito-repelling properties
• Safety: Natural repellents are generally safer than chemical alternatives like DEET, with fewer side effects

Detailed Explanation:

Answer: Option 3 — 1 and 3

This question compares traditional sodium lamps with modern LED lamps used in street lighting. Statement 1 correctly identifies that sodium lamps emit light omnidirectionally (360 degrees), while LEDs are directional, reducing light wastage. Statement 3 correctly notes that sodium lamps produce nearly monochromatic yellow light, whereas LEDs offer better color rendering and spectrum diversity.

✅ Statement 1 – Correct: Sodium lamps emit light in all directions (360 degrees), while LED lamps are directional and focus light where needed, improving efficiency.
❌ Statement 2 – Incorrect: LED lamps have a significantly longer lifespan (50,000-100,000 hours) compared to sodium lamps (15,000-24,000 hours).
✅ Statement 3 – Correct: Sodium lamps produce monochromatic yellow-orange light (narrow spectrum), while LED lamps offer a broad spectrum with better color rendering index (CRI) for street lighting.

📝 Short Notes: Street Lighting Technologies

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

Mitochondrial replacement therapy (MRT) is a reproductive technique designed to prevent the transmission of mitochondrial diseases from mother to child by replacing defective mitochondria with healthy donor mitochondria, either before or after in vitro fertilization. Mitochondrial DNA is inherited exclusively through the maternal line, as mitochondria in sperm are typically destroyed after fertilization, making it impossible for a child to inherit mitochondrial diseases from the father.

✅ Statement 1 – Correct: MRT can be performed either before fertilization (using maternal spindle transfer) or after fertilization (using pronuclear transfer) to prevent mitochondrial disease transmission.
✅ Statement 2 – Correct: Mitochondrial DNA is inherited entirely from the mother, as only the egg contributes mitochondria to the embryo.

📝 Short Notes: Mitochondrial Inheritance and Replacement Therapy