UPSC 2021 Prelims [SCIENCE AND TECHNOLOGY Answer Key with Explanation]

Question Bank 5 Pages

Union Public Service Commission (Prelims)

Miscellaneous

Contributed by

Devendra Chaudhary

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UPSC 2021 Prelims
SCIENCE AND TECHNOLOGY Answer Key with Explanation

1. In the context of hereditary diseases, consider the following statements:
1. Passing on mitochondrial diseases from parents to child can be prevented by
mitochondrial replacement therapy either before or after in vitro fertilization of the egg.
2. A child inherits mitochondrial diseases entirely from mother and not from father.
Which of the statements given above is/ are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: D
Explanation
● Both the statements are incorrect. MRT can be done only before the egg is fertilised
through in-vitro method..
https://www.winfertility.com/blog/mitochondrial-replacement-therapy-explained/
● Comes from both parents
https://www.pbs.org/wgbh/nova/article/dads-mitochondrial-dna/

2. Bollgard I and II technologies are mentioned in the context of
(a) clonal propagation of crop plants
(b) Developing genetically modified crop plants
(c) Production of plant growth substances
(d) Production of biofertilizers
Answer B
Explanation
● Bollgard® Bt cotton (single-gene technology) is India’s first biotech crop technology
approved for commercialization in India in 2002, followed by Bollgard® II – double-gene
technology in mid-2006, by the Genetic Engineering Approval Committee (GEAC), the
Indian regulatory body for biotech crops.
https://www.cropscience.bayer.in/en/Products-H/Brands/Seeds-and-Traits/Traits-
Bollgard.aspx
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3. In a pressure cooker the temperature at which the food is cooked depends
mainly upon which of the following?
1. Area of the hole in the lid
2. Temperature of the flame
3. Weight of the lid
Select the correct answer using the code given below
(a) 1 and 2 only
(b) 2 and 3 only
(c ) 1 and 3 only
(d) 1,2 and 3
Answer: D
Explanation

4. Consider the following:
1. Bacteria
2. Fungi
3. Virus
Which of the above can be cultured in artificial / synthetic medium?
(a) 1 and 2 only
(b) 2 and 3 only
(c ) 1 and 3 only
(d) 1, 2 and 3
Answer: A
Explanation
● Viruses are infectious agents with both living and nonliving characteristics.
● Living characteristics of viruses include the ability to reproduce – but only in living host
cells – and the ability to mutate.
● Nonliving characteristics include the fact that they are not cells, have no cytoplasm or
cellular organelles, and carry out no metabolism on their own and therefore must
replicate using the host cell's metabolic machinery.
● Viruses can infect animals, plants, and even other microorganisms.
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● Since viruses lack metabolic machinery of their own and are totally dependent on their
host cell for replication, they cannot be grown in synthetic culture media.
https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Kaiser)
/Unit_4%3A_Eukaryotic_Microorganisms_and_Viruses/10%3A_Viruses/10.01%3A_Gen
eral_Characteristics_of_Viruses

5. Water can dissolve more substances than any other liquid because.
(a) it is dipolar in nature
(b) it is a good conductor of heat
(c ) it has high value of specific heat
(d) it is an oxide of hudrogen
Answer: A
Explanation
● Water is called the "universal solvent" because it is capable of dissolving more substances
than any other liquid.
● It is water's chemical composition and physical attributes that make it such an excellent
solvent. Water molecules have a polar arrangement of oxygen and hydrogen atoms—
one side (hydrogen) has a positive electrical charge and the other side (oxygen) had a
negative charge. This allows the water molecule to become attracted to many other
different types of molecules.
● Water can become so heavily attracted to a different compound, like salt (NaCl), that it
can disrupt the attractive forces that hold the sodium and chloride in the salt compound
together and, thus, dissolve it.
https://www.usgs.gov/special-topic/water-science-school/science/water-qa-why-
water-universal-solvent?qt-science_center_objects=0#qt-science_center_objects

6. With reference to street lighting, how do sodium lamps differ from LED lamps?
1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
2. As street – light, sodium lamps have a longer lifespan than LED lamps.
3. The spectrum of visible light from sodium of visible light from sodium lamps is almost
monochromatic while LED lamps offer significant colour advantages in street- lighting .
Select the Correct answer using the code given below.
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(a) 3 only
(b) 2 only
(c ) 1 and 3 only
(d) 1,2 and 3
Answer: C
Explanation
Sodium lamps
LED lamps
Lifespan: High Pressure Sodium lights
tend to have a lifespan averaging 24,000
hours.
Lifespan: Range of 25,000 to 200,000
hours.
Efficacy: High efficacy that is easily
comparable to LED lights.
Efficacy: The most efficiency lights on the
market with high efficacy averaging about
50
Bulb Angle: 360-degree bulb angle
Bulb Angle: 180-degree bulb angle to
preserve light efficiency and allow for
target lighting over areas.
The spectrum of visible light from sodium of
visible light from sodium lamps is almost
monochromatic .
LED lamps offer significant colour advantages
in street- lighting .

7. Bisphenol A (BPA), a cause of concern, is a structural /key component in the
manufacture of which of the following kinds of plastics?
(a) Low- density polyethylene
(b) Polycarbonate
(c ) Polyethylene terephthalate
(d) Polyvinyl chloride
Answer: B
Explanation
● Bisphenol A (BPA) is a chemical produced in large quantities for use primarily in the
production of polycarbonate plastics and epoxy resins.
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https://www.niehs.nih.gov/health/topics/agents/sya-bpa/index.cfm

8. “Triclosan’, considered harmful when exposed to high levels for a long time, is
most likely present in which of the following?
(a) Food preservatives
(b) Fruit – ripening substances
(c) Reused plastic containers
(d) Toiletries
Answer: D
Explanation
● Triclosan is an ingredient added to many consumer products intended to reduce or
prevent bacterial contamination. It is added to some antibacterial soaps and body
washes, toothpastes, and some cosmetics—products regulated by the U.S. Food and Drug
Administration.
https://www.fda.gov/consumers/consumer-updates/5-things-know-about-triclosan

9. Which one of the following is a reason why astronomical distances are measured
in light-years?
(a) Distances among stellar bodies do not change.
(b) Gravity of stellar bodies does not change.
(c) Light always travels in a straight line.
(d) Speed of light is always the same.
Answer: D
Explanation
● A light-year is the distance a beam of light travels in a single Earth year, or 6 trillion miles
(9.7 trillion kilometers). It is used to measure astronomical distance because the speed of
light is constant throughout the universe and is known to high precision.

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