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 →
Consider the following pairs :
| Vitamin | Deficiency disease |
|---|---|
| 1. Vitamin C | Scurvy |
| 2. Vitamin D | Rickets |
| 3. Vitamin E | Night blindness |
Which of the pairs given above is/are correctly matched?
Detailed Explanation:
✅ Pair 1 – Correct: Vitamin C deficiency causes Scurvy, characterized by bleeding gums, weakness, and poor wound healing.
✅ Pair 2 – Correct: Vitamin D deficiency causes Rickets in children, leading to soft and weak bones.
❌ Pair 3 – Incorrect: Vitamin E deficiency causes neurological problems and muscle weakness, not Night blindness. Night blindness is caused by Vitamin A deficiency.
Which one of the following is the process involved in photosynthesis?
Detailed Explanation:
Photosynthesis converts light energy (free energy) from the sun into chemical energy (potential energy) and stores it in the bonds of glucose molecules.
The process uses carbon dioxide and water as raw materials and releases oxygen as a byproduct, while the stored energy in glucose can later be used by plants and other organisms.
In addition to fingerprint scanning, which of the following can be used in the biometric identification of a person?
- Iris scanning
- Retinal scanning
- Voice recognition
Select the correct answer using the code given below.
Detailed Explanation:
✅ Statement 1 – Correct: Iris scanning captures unique patterns in the colored ring around the pupil, which remain stable throughout life and are highly distinctive for each individual.
✅ Statement 2 – Correct: Retinal scanning maps the unique pattern of blood vessels at the back of the eye, providing one of the most accurate biometric identification methods.
✅ Statement 3 – Correct: Voice recognition analyzes unique vocal characteristics including pitch, tone, cadence, and physical features of the vocal tract for identification.
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Which of the following is/are the example/examples of chemical change?
- Crystallization of sodium chloride
- Melting of ice
- Souring of milk
Select the correct answer using the code given below.
Detailed Explanation:
✅ Statement 1 – Incorrect: Crystallization of sodium chloride is a physical change; NaCl changes from dissolved to solid state without altering its chemical composition.
✅ Statement 2 – Incorrect: Melting of ice is a physical change; H₂O molecules transition from solid to liquid state while maintaining the same chemical structure.
✅ Statement 3 – Correct: Souring of milk is a chemical change; bacteria convert lactose into lactic acid, creating new substances and irreversibly altering the chemical composition.
Which of the following pair is/are correctly matched?
| Spacecraft | Purpose |
|---|---|
| 1. Cassini-Huygens | Orbiting Venus and transmitting data to the Earth |
| 2. Messenger | Mapping and investigating the Mercury |
| 3. Voyager 1 and 2 | Exploring the outer solar system |
Select the correct answer using the code given below.
Detailed Explanation:
❌ Pair 1 – Incorrect: Cassini-Huygens was a mission to study Saturn and its moons (not Venus). The Huygens probe landed on Titan (Saturn's largest moon) in 2005.
✅ Pair 2 – Correct: MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) orbited Mercury from 2011 to 2015, mapping and studying its surface, composition, and magnetic field.
✅ Pair 3 – Correct: Voyager 1 and 2 were launched by NASA in 1977 to explore the outer solar system, providing data on Jupiter, Saturn, Uranus, and Neptune before entering interstellar space.
Which of the following statements is/are correct regarding vegetative propagation of plants?
- Vegetative propagation produces clonal population.
- Vegetative propagation helps in eliminating the virus.
- Vegetative propagation can be practised most of the year.
Select the correct answer using the code given below.
Detailed Explanation:
✅ Statement 1 – Correct: Vegetative propagation is an asexual reproduction method where new plants grow from vegetative parts (roots, stems, leaves) without gamete fusion, producing genetically identical offspring—a clonal population.
❌ Statement 2 – Incorrect: Vegetative propagation does not eliminate viruses; instead, it propagates them. If the parent plant is virus-infected, the pathogen transmits to offspring through infected tissues.
✅ Statement 3 – Correct: Unlike sexual reproduction dependent on seasonal flowering cycles, vegetative propagation can be practiced year-round as it relies on mature vegetative organs available regardless of reproductive phase.
The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is /are the importance/importances of discovering this particle?
- It will enable us to understand as to why elementary particles have mass.
- It will enable us in the near future to develop the technology to transferring matter from one point to another without traversing the physical space between them.
- It will enable us to create better fuels for nuclear fission.
Select the correct answer using the codes given below:
Detailed Explanation:
✅ Statement 1 – Correct: The Higgs boson discovery confirms the Higgs field mechanism that explains why elementary particles acquire mass through interaction with this field.
❌ Statement 2 – Incorrect: Matter teleportation (transferring matter without traversing physical space) is not related to the Higgs boson; this particle explains mass, not quantum teleportation or matter transport technologies.
❌ Statement 3 – Incorrect: The Higgs boson is a fundamental particle in the Standard Model of physics unrelated to nuclear fission fuels; it does not improve fuel efficiency or reactor technology.
Many transplanted seedlings do not grow because -
Detailed Explanation:
Root hairs are delicate, thin-walled extensions of the root epidermis responsible for water and mineral absorption.
During transplantation, these fragile root hairs are easily broken or damaged, severely reducing the seedling's ability to absorb water and causing transplant failure.
Improper handling and storage of cereal grains and oilseeds result in the production of toxins known as aflatoxins which are not generally destroyed by normal cooking process. Aflatoxins are produced by
Detailed Explanation:
Aflatoxins are poisonous carcinogens produced by certain moulds, specifically Aspergillus flavus and Aspergillus parasiticus.
These moulds grow in soil, decaying vegetation, hay, and improperly stored grains and are not destroyed by normal cooking temperatures.
Consider the following phenomena:
- Size of the sun at dusk
- Colour of the sun at dawn
- Moon being visible at dawn
- The twinkle of stars in the sky
- Polestar being visible in the sky
Which of the above are optical illusions?
Detailed Explanation:
1. Size of the sun at dusk – Optical illusion: The sun appears larger near the horizon due to the moon illusion, a psychological effect where our brain misinterprets distance cues, though its actual angular size remains constant.
2. Colour of the sun at dawn – Optical illusion: The sun appears red/orange because its light travels through more atmosphere, causing Rayleigh scattering that removes blue light, creating a perceived color change.
3. Moon being visible at dawn – NOT an illusion: This is a real astronomical event where the moon's orbital position allows it to be visible during daylight hours.
4. Twinkle of stars – Optical illusion: Stars don't actually twinkle; their light is refracted by turbulent atmospheric layers, causing rapid brightness fluctuations.
5. Polestar being visible – NOT an illusion: The Pole Star (Polaris) is genuinely visible due to its alignment with Earth's rotational axis, making it appear stationary.
Answer: Option 3 (1, 2 and 4) are optical illusions.
Consider the following minerals -
- Calcium
- Iron
- Sodium
Which of the minerals given above is/are required by the human body for the contraction of muscles?
Detailed Explanation:
Calcium triggers muscle contraction by binding to troponin, which allows actin-myosin interaction.
Iron enables oxygen transport via myoglobin and supports ATP production in mitochondria for sustained muscle contraction.
Sodium maintains membrane potential and initiates action potentials that trigger muscle fiber contraction.
All three minerals (Calcium, Iron, Sodium) are essential for muscle contraction. Hence, option 4 is correct.
Recombinant DNA technology (Genetic Engineering) allows genes to be transferred
- Across different species of plants.
- From animals to plants.
- From microorganisms to higher organisms.
Select the correct Solution using the codes given below.
Detailed Explanation:
✅ Statement 1 – Correct: Recombinant DNA technology enables gene transfer across different plant species to introduce desirable traits like disease resistance.
✅ Statement 2 – Correct: Animal genes can be transferred to plants; for example, antifreeze protein genes from cold-water fish have been introduced into tomatoes and strawberries for frost tolerance.
✅ Statement 3 – Correct: Genes from microorganisms are routinely transferred to higher organisms; Bacillus thuringiensis (Bt) genes from soil bacteria are transferred to crops like cotton and corn for pest resistance.
Ball bearings are used in bicycles, cars, etc., because
Detailed Explanation:
Ball bearings reduce the effective area of contact between the wheel and axle, replacing sliding friction with rolling friction.
Reduced contact area means lower friction and higher efficiency, as rolling balls have a much lower coefficient of friction than flat surfaces sliding against each other.
Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this?
- Dispersion
- Refraction
- Internal reflection
Select the correct Solution using the codes given below.
Detailed Explanation:
Refraction occurs when sunlight enters and exits the raindrop, bending light at air-water boundaries.
Dispersion separates white light into constituent colours as different wavelengths refract at different angles inside the droplet.
Internal reflection bounces the dispersed light off the rear inner surface of the raindrop back toward the observer, creating the visible rainbow arc.
All three phenomena—Dispersion, Refraction, and Internal Reflection—work together to form a rainbow.
Which of the following diseases can be transmitted from one person to another through tattooing?
- Chikungunya
- Hepatitis B
- HIV-AIDS
Select the correct answer using the codes given below.
Detailed Explanation:
❌ Statement 1 – Incorrect: Chikungunya is a mosquito-borne viral disease transmitted by Aedes mosquitoes, not through blood contact or tattooing.
✅ Statement 2 – Correct: Hepatitis B is a bloodborne viral infection that can be transmitted through contaminated tattooing needles and equipment.
✅ Statement 3 – Correct: HIV-AIDS spreads through contact with infected blood, making transmission possible via unsterilized tattooing equipment.