UPSC CSE Prelims
Science & Technology Previous Year Questions (PYQs)
Solved Previous Year Questions (PYQs) for Science & Technology in UPSC CSE Prelims in English & Hindi Medium.
Chapter Breakdown: Scroll →
Which of the following statements is/are correct?
- Viruses lack enzymes necessary for the generation of energy.
- Viruses can be cultured in any synthetic medium.
- Viruses are transmitted from one organism to another by biological vectors only.
Select the correct answer using the codes given below.
Detailed Explanation:
✅ Statement 1 – Correct: Viruses lack metabolic machinery and enzymes for ATP generation; they depend entirely on host cells for energy production.
❌ Statement 2 – Incorrect: Viruses cannot be cultured in synthetic or artificial media; they require living host cells (bacteria, plants, animals, or cell cultures) for replication.
❌ Statement 3 – Incorrect: Viral transmission occurs through multiple routes – direct contact, respiratory droplets, contaminated water/food, airborne particles, fomites, and biological vectors (mosquitoes, ticks); vectors are not the only mode.
The known forces of nature can be divided into four classes, viz, gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?
Detailed Explanation:
❌ Statement 1 – Incorrect: Gravity is the weakest of the four fundamental forces, not the strongest.
✅ Statement 2 – Correct: Electromagnetism acts only on particles with electric charge (positive or negative).
✅ Statement 3 – Correct: Weak nuclear force is responsible for radioactivity and beta decay.
✅ Statement 4 – Correct: Strong nuclear force holds protons and neutrons together inside the atomic nucleus.
What is the role of ultraviolet (UV) radiation in the water purification systems?
- It inactivates /kills the harmful microorganisms in water.
- It removes all the undesirable odours from the water.
- It quickens the sedimentation of solid particles, removes turbidity and improves the clarity of the water.
Detailed Explanation:
✅ Statement 1 – Correct: UV radiation damages the DNA/RNA of microorganisms (bacteria, viruses, protozoa), effectively inactivating or killing them and making it a powerful disinfection method in water purification.
❌ Statement 2 – Incorrect: UV radiation does not remove odours from water; odour removal requires activated carbon filtration, aeration, or chemical treatment.
❌ Statement 3 – Incorrect: UV radiation does not affect sedimentation, turbidity removal, or water clarity; these processes require coagulation, flocculation, and filtration.
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With reference to ‘stem cells’, frequently in the news, which of the following statements is/are correct?
- Stem cells can be derived from mammals only
- Stem cells can be used for screening new drugs
- Stem cells can be used for medical therapies
Detailed Explanation:
❌ Statement 1 – Incorrect: Stem cells are found in all multicellular organisms, not just mammals—including plants, vertebrates, and invertebrates.
✅ Statement 2 – Correct: Stem cells are used for drug screening by generating specific cell types to test safety and efficacy of new pharmaceutical compounds before clinical trials.
✅ Statement 3 – Correct: Stem cells have applications in regenerative medicine including bone marrow transplants for blood disorders and tissue/organ repair.
Consider the following kinds of organisms :
- Bacteria
- Fungi
- Flowering plants
Some species of which of the above kinds of organisms are employed as biopesticides?
Detailed Explanation:
Bacteria (e.g., Bacillus thuringiensis) produce toxins that kill specific insects and are widely used as biopesticides.
Fungi (e.g., Beauveria bassiana, Metarhizium anisopliae) infect and kill pests through parasitism.
Flowering plants (e.g., Chrysanthemum producing pyrethrin, Neem with azadirachtin) contain natural insecticidal compounds used as biopesticides.
All three organism types are employed as biopesticides.
Other than resistance to pests, what are the prospects for which genetically engineered plants have been created?
- To enable them to withstand drought
- To increase the nutritive value of the produce
- To enable them to grow and do photosynthesis in spaceships and space stations
- To increase their shelf life
Select the correct answer using the codes given below:
Detailed Explanation:
✅ Statement 1 – Correct: Drought-resistant crops like drought-tolerant maize and water-efficient rice have been developed by introducing genes that enable water conservation and stress tolerance.
✅ Statement 2 – Correct: Golden Rice (fortified with Vitamin A), iron-biofortified crops, and protein-enhanced legumes demonstrate increased nutritive value through genetic engineering.
❌ Statement 3 – Incorrect: Growing plants in spaceships and space stations relies on controlled environment agriculture, not genetic engineering; NASA experiments use conventional plant varieties adapted through breeding, not GM technology.
✅ Statement 4 – Correct: Flavr Savr tomato (first GM food approved in 1994) and other crops have been engineered with delayed ripening genes to increase shelf life and reduce post-harvest losses.
What are the reasons for the people’s resistance to the introduction of Bt brinjal in India?
- Bt brinjal has been created by inserting a gene from a soil fungus into its genome.
- The seeds of Bt brinjal are terminator seeds and therefore, the farmers have to buy the seeds before every season from the seed companies.
- There is an apprehension that the consumption of Bt brinjal may have an adverse impact on health.
- There is some concern that the introduction of Bt brinjal may have an adverse effect on biodiversity.
Select the correct answer using the codes given below:
Detailed Explanation:
❌ Statement 1 – Incorrect: Bt brinjal is created by inserting the Cry1Ac gene from Bacillus thuringiensis, a soil bacterium, not a fungus, to provide resistance against the Brinjal Fruit and Shoot Borer (BFSB).
❌ Statement 2 – Incorrect: Bt brinjal seeds are not terminator seeds; they do not contain Genetic Use Restriction Technology (GURT) that prevents seed saving and reuse.
✅ Statement 3 – Correct: Major resistance stems from apprehensions about adverse health impacts, including concerns about allergenicity, toxicity, and lack of long-term independent safety studies on human consumption.
✅ Statement 4 – Correct: India is a center of origin and diversity for brinjal; concerns exist that cross-pollination with wild and local varieties could lead to genetic contamination and loss of indigenous biodiversity.
To meet its rapidly growing energy demand, some opine that India should pursue research and development on thorium as the future fuel of nuclear energy. In this context, what advantage does thorium hold over uranium?
Detailed Explanation:
✅ Statement 1 – Correct: Thorium is approximately 3-4 times more abundant in nature than uranium, found widely in Earth's crust including monazite sands.
✅ Statement 2 – Correct: Thorium-232 can generate approximately 30 times more energy per unit mass than natural uranium when bred into fissile U-233.
✅ Statement 3 – Correct: Thorium fuel cycle produces significantly less long-lived radioactive waste and minimal plutonium, making waste management easier than uranium fuel cycle.
Which of the following is /are cited by the scientists as evidence/evidences for the continued expansion of the universe?
- Detection of microwaves in space
- Observation of the redshift phenomenon in space
- Movement of asteroids in space
- The occurrence of supernova explosions in space
Detailed Explanation:
✅ Statement 1 – Correct: Cosmic Microwave Background (CMB) radiation is relic radiation from the Big Bang, discovered by Penzias and Wilson, providing strong evidence for the expanding universe model.
✅ Statement 2 – Correct: Redshift phenomenon shows that light from distant galaxies is stretched as they move away, demonstrating universal expansion as per Hubble's Law.
❌ Statement 3 – Incorrect: Asteroid movement is governed by local gravitational forces within solar systems and has no relevance to large-scale cosmic expansion.
✅ Statement 4 – Correct: Type Ia supernovae serve as standard candles for measuring cosmic distances, providing evidence for the universe's accelerated expansion and leading to the discovery of dark energy.
A team of scientists at Brookhaven National Laboratory including those from India created the heaviest antimatter (anti-helium nucleus). What is/are the implication/implications of the creation of antimatter?
- It will make mineral prospecting and oil exploration easier and cheaper.
- It will help probe the possibility of the existence of stars and galaxies made of antimatter.
- It will help understand the evolution of the universe.
Select the correct answer using the code given below:
Detailed Explanation:
❌ Statement 1 – Incorrect: Antimatter production is extremely costly and impractical; it has no application in mineral prospecting or oil exploration, which rely on seismic surveys and remote sensing.
✅ Statement 2 – Correct: Discovery of anti-helium-4 nucleus provides a reference for space-based experiments like Alpha Magnetic Spectrometer (AMS) to search for antimatter in cosmic rays, helping probe the existence of antimatter stars and galaxies.
✅ Statement 3 – Correct: Studying heavy antimatter nuclei helps understand the matter-antimatter asymmetry puzzle—why the Big Bang produced a matter-dominated universe despite equal creation of both—crucial for understanding early universe evolution.
Consider the following statements - If there were no phenomenon of capillarity
- It would be difficult to use a kerosene lamp
- One would not be able to use a straw to consume a soft drink
- The blotting paper would fail to function
- The big trees that we see around would not have grown on the earth
Detailed Explanation:
✅ Statement 1 – Correct: Kerosene lamps rely on capillary action to draw kerosene up the wick from the reservoir for combustion.
❌ Statement 2 – Incorrect: Drinking through a straw works by air pressure difference, not capillarity; sucking removes air, allowing atmospheric pressure to push liquid up.
✅ Statement 3 – Correct: Blotting paper absorbs ink/liquid through capillary action in its porous structure and fine fibres.
✅ Statement 4 – Correct: Tall trees depend on capillary action to transport water from roots to leaves against gravity through xylem vessels.
Graphene is frequently in the news recently. What is its importance?
- It is a two-dimensional material and has good electrical conductivity
- It is one of the thinnest but strongest materials tested so far
- It is entirely made of silicon and has high optical transparency
- It can be used as ‘conducting electrodes’ required for touch screens, LCDs and organic LEDs
Detailed Explanation:
✅ Statement 1 – Correct: Graphene is a two-dimensional material consisting of a single layer of carbon atoms arranged in a hexagonal lattice, and it exhibits excellent electrical conductivity due to the mobility of electrons in its structure.
✅ Statement 2 – Correct: Graphene is one of the thinnest materials (only one atom thick) yet possesses extraordinary tensile strength — approximately 200 times stronger than steel — making it one of the strongest materials tested.
❌ Statement 3 – Incorrect: Graphene is composed entirely of carbon atoms, not silicon. However, it does possess high optical transparency (absorbs only ~2.3% of visible light).
✅ Statement 4 – Correct: Due to its combination of electrical conductivity, optical transparency, and flexibility, graphene is highly suitable for use as conducting electrodes in touch screens, LCDs, and organic LEDs.