Science & Technology (UPSC Prelims) [2013-2022] – Previous Year Questions

• This statement is correct. Probiotics are live microorganisms that are intended to have health benefits when consumed or applied to the body. They can be found in yogurt and other fermented foods, dietary supplements, and beauty products. Probiotics are live bacteria and yeasts that are thought to be beneficial in preventing several health conditions.

• This statement is incorrect. Probiotics live naturally in your body. L. acidophilus is a probiotic bacteria that naturally occur in the human gut. The most common place linked to beneficial microbes in your gut (mostly large intestines), but there are other places like the mouth, urinary tract, skin, lungs, etc where these probiotics are found.

• This statement is correct. Certain strains of bacteria in yogurt have ß-D-galactosidase, which is an enzyme that helps break down lactose in dairy products into the sugars glucose and galactose. Thus Probiotics help in the digestion of milk sugars.

GPS and navigation systems could fail:

• Solar storms can interfere with GPS signals, causing them to fail. This is because the solar storm’s charged particles can cause fluctuations in the Earth’s magnetic field, which can interfere with radio signals, including those used by GPS systems.

Tsunamis could occur at equatorial regions:

• Solar storms do not cause tsunamis. Tsunamis are caused by undersea earthquakes or other seismic activity. Solar storms and tsunamis are unrelated phenomena.

Power grids could be damaged:

• Solar storms can disrupt power grids and cause power outages. The charged particles from a solar storm can induce currents in power lines, which can overload the system and cause power outages.

Intense auroras could occur over much of the Earth:

• Solar storms can cause intense auroras, also known as the northern and southern lights. Auroras are caused by charged particles from the solar storm interacting with the Earth’s magnetic field and atmosphere.

Forest fires could take place over much of the planet:

• Solar storms do not cause forest fires. Forest fires are typically caused by human activity or natural phenomena like lightning. Solar storms and forest fires are unrelated phenomena.

Orbits of the satellites could be disturbed:

• Solar storms can affect satellites, including their orbits. The charged particles from a solar storm can cause drag on satellites, which can affect their orbits.

Shortwave radio communication of the aircraft flying over polar regions could be interrupted:

• Solar storms can disrupt radio communications, including shortwave radio communication of aircraft flying over polar regions. This is because the charged particles from a solar storm can cause fluctuations in the Earth’s magnetic field, which can interfere with radio signals.

Source: https://www.thehindubusinessline.com/blexplainer/all-about-solar-storms-and-how-they-affects-us/article65245445.ece

https://www.indiatoday.in/science/story/solar-flare-geomagnetic-storm-sun-space-weather-nasa-1827104-2021-07-12

Polyethylene terephthalate (PET) fibres can be blended with wool and cotton fibres to reinforce their properties.

• This statement is correct. PET is a synthetic fibre that can be blended with natural fibres such as cotton and wool to enhance their properties. The blending of PET with natural fibres results in fabrics that are strong, flexible, and resistant to wrinkles, shrinking, and tears.

Containers made of PET can be used to store any alcoholic beverage.

• This statement is incorrect. While PET containers are popular due to their ease of handling, safety, light weight, and superior barrier properties, they are not suitable for storing all types of alcoholic beverages³. Particularly for highly concentrated spirits in small PET bottles and high storage temperatures, the water permeation is unfavorable. The leaching effects of plastic and plastic chemical substances (such as ethylene glycol) have the tendency to leach considerably into alcohol stored if the temperature goes up during storage.

Bottles made of PET can be recycled into other products.

• This statement is correct. PET bottles can be recycled into a variety of products. The recycling process involves sorting, cleaning, decontaminating, and transforming the PET so that it can be reused. Recycled PET (rPET) can be used to make new bottles as well as many other products like winter jackets, rugs, playground equipment, dog beds, and more.

Articles made of PET can be easily disposed of by incineration without causing greenhouse gas emissions.

• This statement is incorrect. While incineration is a method of disposing of waste, it is not environmentally friendly when it comes to PET. The burning of plastics, including PET, releases toxic gases like dioxins, furans, mercury, and polychlorinated biphenyls (better known as BCPs) into the atmosphere. These emissions pose a threat to vegetation, and human and animal health.

Source: https://dst.gov.in/dst-supports-technologies-plastic-recycling

https://pib.gov.in/PressReleasePage.aspx?PRID=1842622

https://pib.gov.in/PressReleaseIframePage.aspx?PRID=1745433

They enable the digital representation of physical assets. -

• This statement is correct. NFTs can represent digital versions of physical assets. This makes it possible to buy, sell, and trade these assets in the digital world. For example, an artist can create a digital representation of their artwork and sell it as an NFT. This allows the artist to monetize their work in the digital space.

They are unique cryptographic tokens that exist on a blockchain. -

• This statement is correct. Each NFT is unique and cannot be replicated, which is why they are called ‘non-fungible’. They exist on a blockchain, which verifies their authenticity and ownership. This uniqueness is ensured by using blockchain technology such as Ethereum and smart contracts such as Binance Smart Chain which create a unique digital signature, thereby making them highly secure.

They can be traded or exchanged at equivalency and therefore can be used as a medium of commercial transactions. -

• This statement is incorrect. The key characteristic of NFTs is that they are non-fungible, meaning they are not interchangeable on a like-for-like basis because each one is unique. This differentiates them from cryptocurrencies like Bitcoin or Ethereum, which are fungible and can be traded at equivalency. However, NFTs have opened up new possibilities for commercial transactions in the digital space by enabling the tokenization of unique assets that are otherwise difficult to sell or hold ownership of.

• B cells and T cells are part of the immune system that helps protect the body from harmful substances such as pathogens and toxins.
• However, they are not specifically designed to protect against environmental allergens.
• Instead, the immune system sometimes mistakenly identifies harmless substances like pollen or dust mites as threats, leading to an allergic reaction.
• While B cells and T cells play a role in the body’s inflammatory response, they do not directly alleviate pain or inflammation.
• In fact, certain types of T cells can contribute to inflammation, which is a normal part of the body’s response to injury or infection. They are not typically involved in pain management.
• B cells and T cells are not immunosuppressants.
• They are key components of the immune system that help protect the body against infections.
• However, some specific subtypes of T cells, known as regulatory T cells, can suppress the immune response to prevent it from attacking the body’s own cells, thereby playing a role in preventing autoimmune diseases.
• B cells and T cells are crucial components of the immune system.
• B cells produce antibodies that can recognize and neutralize foreign substances (antigens), such as bacteria and viruses.
• T cells can directly kill infected cells or help other immune cells perform their functions.
• Together, they play a vital role in protecting the body from diseases caused by pathogens.

Source: https://cdsco.gov.in/opencms/opencms/en/biologicals

https://www.pib.gov.in/PressReleasePage.aspx?PRID=1725254

https://www.indiascienceandtechnology.gov.in/covid-19-vaccine/vaccine-introduction

Other than those made by humans, nanoparticles do not exist in nature.

• This statement is incorrect. Nanoparticles do indeed exist in nature beyond human-made sources.
• Nature itself produces various nanomaterials, including inorganic ash, soot, sulfur, and mineral particles found in the air or wells.
• Additionally, bacteria and yeasts produce sulfur and selenium nanoparticles.
• These natural nanomaterials have diverse properties and applications in fields such as medicine, nutrition, cosmetics, and agriculture.

Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics.

• This statement is correct. Nanoparticles of some metallic oxides are indeed used in the manufacture of cosmetics.
• These nanoparticles alter properties such as color, transparency, solubility, and chemical reactivity in cosmetic products.
• However, it is unclear to what extent insoluble nanoparticles are commonly used in cosmetics.

Nanoparticles of some commercial products which enter the environment are unsafe for humans.

• This statement is also correct. Nanoparticles from commercial products that enter the environment can indeed pose risks to human health.
• Research continues to focus on safety and regulatory considerations related to nanoparticles in cosmetics.

Source: https://dst.gov.in/scientific-programmes/mission-nano-science-and-technology-nano-mission

http://www.cense.iisc.ac.in/news/nanotechnology-india-current-status-and-future-prospects

Assess the age of a plant or animal:

• DNA Barcoding is not used to assess the age of plants or animals. It is primarily focused on identifying species through genetic sequences. The technique does not provide information about the age of an organism​​.

Distinguish among species that look alike:

• DNA Barcoding is highly effective in distinguishing among species that look alike. It uses short sequences of DNA to identify species, even those that are morphologically similar, making it a powerful tool for taxonomy and biodiversity research​​.

Identify undesirable animal or plant materials in processed foods:

• DNA Barcoding can indeed identify undesirable animal or plant materials in processed foods. By analyzing the genetic material found in food products, DNA Barcoding can detect the presence of species that are not listed on the product label or are not supposed to be there, ensuring food safety and compliance with labeling regulations​​.

Source: https://www.rgcb.res.in/dna.php

https://www.ibol.org/phase1/india-announces-10m-barcoding-initiative/

Biofilms can form on medical implants within human tissues:

• This statement is correct. Biofilms are a complex group of microbial cells that can adhere to the exopolysaccharide matrices available on the surface of various medical devices, such as intravascular catheters, urinary catheters, dental implants, breast implants, and orthopedic implants. They are responsible for the failure of devices such as catheters and ventilator.

Biofilms can form on food and food processing surfaces:

• This statement is correct. Biofilms can form on food and food processing surfaces. They affect product quality and safety of food, and bacterial adhesion onto surfaces of processing equipment in contact with foods is indicated by the formation of biofilms.

Biofilms can exhibit antibiotic resistance:

• This statement is correct. Bacteria living in a biofilm can exhibit a 10 to 1,000-fold increase in antibiotic resistance compared to similar bacteria living in a planktonic state. Many times bacteria form biofilms to resist the action of antibiotics.

Source: https://vigyanprasar.gov.in/isw/seaweed-silver-combo-can-fight-drug-resistant-bacteria-biofilms.html

https://pharmaceuticals.gov.in/nipers

Fruits stored in a cold chamber last longer because the low temperature decreases their respiration rate. The key factors are:

• Respiration produces the energy fruits need to ripen and continue living. Slowing respiration slows down the ripening and aging process.
• Respiration requires enzymes to function, and enzyme activity decreases with temperature. At colder temperatures, the enzymes in fruits work more slowly, causing respiration to slow down.
• Microbes that spoil fruits grow more slowly in the cold. So decreased respiration and slower microbial growth both help preserve fruits in cold storage.

While options (a) and (d) (preventing sunlight exposure and increasing humidity) can help with fruit storage, they do not directly slow respiration like decreased temperature does.

And option (b) (increasing carbon dioxide) would not slow respiration and preserve fruits. Fruits do best in environments with adequate oxygen and moderate CO2, so increased CO2 would have a negative effect.

Therefore, option (c) (decreasing the rate of respiration) is the primary reason why cold temperature leads to longer fruit storage life.

Options a, b and d may be secondary contributors but do not have as direct an effect on slowing respiration as temperature.

Ball bearings are used for multiple reasons, but the key reason is that they reduce friction between moving parts like wheels and axles. They do this by reducing the effective contact area between the parts.

The key benefits of using ball bearings are:

• They have a small contact area, so there is less surface area for friction to act on. This reduces heat and energy waste.
• They roll smoothly, transforming sliding friction into rolling friction, which is less resistant. This makes motion more efficient.
• They minimize friction in all directions since they can roll omni-directionally. This gives free rotation.
• The small, round ball bearings can move around and adjust to different forces, distributing weight and reducing wear.

So in short, ball bearings make the interaction between wheel and axle more efficient by decreasing friction - and they do this primarily by reducing the effective contact area compared to a flat surface.

Option (d) is incorrect since there are clear reasons why ball bearings are useful.

Options (a) and (b) are false because they imply ball bearings increase contact area, when the opposite is true.

So the correct answer is option (c).

• Size of the sun at dusk - This is an optical illusion. The sun only appears larger at dusk because of how our eyes perceive objects near the horizon, not because of an actual change in size.
• Colour of the sun at dawn - The reddish hue of the sun at dawn and sunset is also an optical illusion caused by the scattering of light through the atmosphere at low sun angles. The sun does not actually change color.
• Moon being visible at dawn - Seeing the moon in the daytime sky during dawn and dusk is not an optical illusion. It is visible at these times because of its actual position in the sky during the day as the sun is rising/setting. While less common, it can happen and is not illusory.
• Twinkle of stars in the sky - The twinkling of stars is an optical illusion caused by atmospheric turbulence and refraction of starlight. The stars themselves do not actually twinkle or change brightness.
• Polestar being visible in the sky - The visibility of the Polestar (Polaris) in the night sky is not an illusion. It remains visible much of the night because it lies very close to the north celestial pole, so its pinpoint movement means it rarely sets or rises for most viewers.

So options (a), (b) and (d) are incorrect because they include non-illusions like the visibility of the moon and Polestar.

Only option (c) lists three phenomena that qualify as actual optical illusions.

A rainbow is produced due to the following physical phenomena:

• Dispersion: When white light from the sun enters a water droplet, the light is dispersed into the colors of the visible spectrum (red, orange, yellow, green, blue, indigo, violet) due to different wavelengths. This is known as dispersion.
• Refraction: As the light is dispersed, each color is refracted at a different angle. The amount of refraction depends on the wavelength of the light. Red light is refracted the least while violet light is refracted the most. This is known as refraction.
• Internal reflection: The refracted light inside the water droplet undergoes internal reflection once before emerging from the droplet. This is known as internal reflection.

Therefore, the correct option is (d): 1, 2 and 3. All three physical phenomena - dispersion, refraction and internal reflection are responsible for producing the rainbow.

The options (a) and (c) are incorrect because both dispersion and internal reflection, and refraction and internal reflection are needed to produce the rainbow, not just any two of the phenomena.

Option (b) is also incorrect because refraction and internal reflection alone cannot produce the rainbow without dispersion of white light.

Root hairs are delicate hair-like projections from the roots that help in absorbing water and minerals from the soil. During transplantation, most of these root hairs get damaged or broken off from the roots. Since the root hairs are critical for absorption of water and minerals, losing them leads to the seedling not being able to absorb enough nutrients to support growth.

The other options are incorrect:

• (a) The new soil lacking favorable minerals may be a issue for growth eventually, but the immediate effect of transplantation is the loss of root hairs. Mineral deficiency becomes a problem over longer periods of time.
• (b) The root hairs gripping the new soil too hard is not a real issue. The root hairs simply help in absorption, they do not grip the soil.
• (d) Leaf damage, while possible, will not directly impact the roots' ability to absorb water and minerals which is critical for growth. Leaf damage is a secondary effect.
• So the correct answer is option (c): most of the root hairs are lost during transplantation. This directly explains why new seedlings are unable to grow initially after being transplanted.

The incorrect statement among the given options is option (a): Gravity is the strongest of the four.

The four fundamental forces of nature and their strengths are:

• Strong nuclear force: It is the strongest of the four forces. It holds protons and neutrons together in the nucleus of an atom.
• Electromagnetism: It is stronger than gravity but weaker than the strong nuclear force. It acts between charged particles like electrons and protons. It causes electromagnetic radiation and holds atoms and molecules together.
• Weak nuclear force: It is weaker than electromagnetism but stronger than gravity. It is responsible for radioactive decay of subatomic particles like beta decay.
• Gravity: It is the weakest of the four forces. It acts between all masses in the universe. Despite being the weakest force, it has infinite range.

The other options are correct:

b) Electromagnetism acts only on particles with an electric charge. (True)

c) Weak nuclear force causes radioactivity. (True)

d) Strong nuclear force holds protons and neutrons inside the nucleus of an atom. (True)

So the correct answer is option (a): Gravity is the strongest of the four. This statement is incorrect as gravity is the weakest among the four forces of nature.

Aflatoxins are produced by certain species of Aspergillus molds, especially Aspergillus flavus and Aspergillus parasiticus. These molds can contaminate cereal grains and oilseeds when they are improperly stored in warm and humid conditions. Aflatoxins are toxic metabolites produced by these molds. They are not destroyed by normal cooking processes and pose health hazards.

So the answer is option c: moulds

• Acid rain is caused by air pollution that releases sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere.
• When these gases react with water molecules in the atmosphere, they produce acids like sulfuric acid and nitric acid.
• The sulfuric and nitric acids then fall to the ground in the form of rain, fog or snow.
• So the primary pollutants that cause acid rain are sulfur dioxide (SO2) and nitrogen oxides (NOx), especially nitrogen dioxide (NO2).

Options a and b are incorrect because carbon dioxide and carbon monoxide do not lead to acid rain.
Option c is incorrect because ozone is not a primary pollutant for acid rain.

Therefore, the answer is option d: nitrous oxide and sulphur dioxide.

Hepatitis B and HIV/AIDS:

• These viruses can definitely spread through used needles and infected blood during tattooing if proper sterilization is not done. This is well established. So these diseases can clearly spread through tattooing.

Chikungunya:

• Chikungunya itself is spread through mosquito bites, not through blood or needles.
• However, infected blood used in tattoo ink could theoretically spread Chikungunya if the infected blood contained the Chikungunya virus and proper sterilization was not done.
• There have been a few reported cases of Chikungunya linked to tattooing, but most major health organizations do not officially consider tattooing to be a common mode of transmission for Chikungunya.

Hepatitis B and HIV/AIDS can clearly spread through unsafe tattooing.
Chikungunya spread through tattooing, while theoretically possible, seems to be rare or unlikely according to most experts. Simply mosquito bites are the main mode of transmission.

So options (b) is incorrect. 

• Photochemical smog is produced through chemical reactions involving nitrogen oxides like NO2, volatile organic compounds like peroxyacetyl nitrate and sunlight.
• Ozone O3 is also formed in these reactions.
• The key requirements for photochemical smog formation are:
  • Presence of NOx (like NO2) and VOCs (like peroxyacetyl nitrate)
  • Sunlight - ultraviolet radiation
  • Stable atmospheric conditions like warm temperature and lack of wind
• Options (b) and (c) do not have all these components, so they are incorrect.
• Option d mentions high concentrations in the evening when sunlight is not present, so it is also incorrect.
• Option a has NO2, O3 and peroxyacetyl nitrate as pollutants and also correctly indicates the need for sunlight. Therefore, option (a) is the right choice.

Calcium:

• Calcium ions (Ca2+) are essential signaling molecules for muscle contractions.
• When a nerve stimulates a muscle cell, calcium channels open and allow Ca2+ to flow into the cell.
• The increased Ca2+ activates muscle contraction proteins (actin and myosin), causing the muscles to contract.
• Without calcium, our muscles would not be able to contract on command from our nerves.

Sodium:

• Important for maintaining electrolyte balance and muscle cell function. Muscle contractions require the proper functioning of muscle cells, so sodium is required.
• Na+ also helps generate the electric signals in muscle cells that come from our nerves. This electric activity then triggers the calcium release needed for contraction.
• If Na+ levels get too low, muscles become weak and unresponsive - indicating it is required for muscle contractions, though more indirectly than calcium.

Iron:

• Iron (Fe) is necessary for the production of hemoglobin, which carries oxygen in the blood.
• Oxygen is essential for the physiological process that generates energy in our muscle cells during contractions.
• Without adequate oxygen delivery to muscles via hemoglobin, muscle performance and contraction would suffer greatly due to lack of energy.
• So iron is required to ensure enough oxygen reaches our working muscles, even if it does not directly trigger contractions like calcium.

So the correct answer is option (d): 1, 2 and 3  - all the minerals listed are required for muscle contraction in some form.

Sea cow

• Sea cows, also known as manatees, are large marine mammals. They breathe air, give live birth, and nurse their young - all characteristics of mammals.

Sea horse

• Sea horses are fish, not mammals. They live their entire lives in water, breathe using gills, and lay eggs - characteristics of fish.

Sea lion

• Sea lions are pinnipeds, which are semi-aquatic marine mammals. Like sea cows, they breathe air, give live birth, and nurse their young.

So sea cows and sea lions share key characteristics of mammals like air breathing, live birth and nursing. Sea horses are fish, not mammals.

Therefore, the only options that include exclusively mammals are choice b: 1 and 3 only  - the sea cow and sea lion.

Choices a, c and d are incorrect because they include the sea horse, which is not a mammal.