After analysing the Question Paper it can be concluded that the examiner has focused on the understanding of the basics and the current issues based on Science.

There were 12 Questions from Science & Technology in 2021, of which

• 3 Questions from Bio-Technology (Vaccines, Bollgard, ACE2)
• 1 Questions from Genetics (Mitochondrial Diseases)
• 3 Questions from Physics (Pressure Cooker, LED, Light year)
• 3 Questions from Chemistry (Water, BPA, Triclosan)
• 2 Questions from Biology (Viruses, Microbial Culture)

The level of the questions was moderate to tough.

Most of the questions were aimed to test knowledge of the basics and analytical abilities.

Solved PYQs Science & Technology With Explanation 2021 UPSC Prelims (Previous Year Questions) 

1. With reference to recent developments regarding ‘Recombinant Vector Vaccines’, consider the following statements: 

1. Genetic engineering is applied in the development of these vaccines. 

2. Bacteria and viruses are used as vectors. 

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 

1. Ans: c

Explanation: 

A recombinant vaccine is a vaccine produced through recombinant DNA technology. This involves inserting the DNA encoding an antigen (such as a bacterial surface protein) that stimulates an immune response into bacterial or mammalian cells, expressing the antigen in these cells and then purifying it from them.

Hence, statement 1 is correct.

Recombinant vaccines are usually produced by benefiting from bacteria, yeast, mammalian, and insect cells. This type of vaccine requires the insertion and transference of the DNA section responsible for encoding the antigen. 

Most of the recombinant vaccines developed in the recent decays are classified as recombinant protein vaccines

In some live recombinant vaccines, an attenuated virus or bacterium is used as the carrier vector. These carriers make the immune system’s response very similar to that of natural infectious microorganisms. The microorganism’s DNA attaches to the vector and stimulates the human immune system.  

Hence, statement 2 is correct.

2. In the context of hereditary diseases, consider the following statements: 

1. Passing on mitochondrial diseases from parent to child can be prevented by mitochondrial replacement therapy either before or after in vitro fertilization of 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 

2. Ans: c

Explanation: 

Children inherit mitochondrial DNA (mDNA) exclusively from their mothers. If a mother has a mDNA mutation, there is a possibility that she may pass this mutation on to her offspring. Mitochondrial replacement therapy (MRT) is an advanced technique used in in vitro fertilisation (IVF), which involves fertilising an egg with sperm in a controlled laboratory environment. This therapy enables women with mDNA mutations to conceive and give birth to children while reducing the risk of transmitting the mutation to their descendants.   

MRT is performed using one of two methods: maternal spindle transfer or pronuclear transfer. 

Maternal Spindle Transfer (MST) 

Maternal Spindle Transfer (MST) is an innovative reproductive technique designed to prevent the transmission of mitochondrial DNA (mDNA) mutations from a mother to her child. The process begins with a careful selection of donor eggs. Each donor egg undergoes thorough screening to ensure that it is completely free from any mDNA mutations, guaranteeing a healthy source of mitochondria.

Once a suitable donor egg is identified, the next step involves the removal of the egg’s nuclear DNA (nDNA), effectively vacating the donor egg of its genetic material while preserving its healthy mitochondria. This crucial step leaves the donor egg with robust mDNA, which is essential for cellular energy production.

Following this, the mother’s nDNA, which carries her genetic traits, is precisely transplanted into the now-empty donor egg. This combination creates an egg that contains the biological mother’s nDNA and the donor’s healthy mDNA. 

The final phase of MST involves fertilizing the transformed donor egg using in vitro fertilization (IVF) techniques. Once fertilization occurs, the resulting embryo is carefully implanted into the mother’s uterus, allowing for the possibility of a healthy pregnancy while minimizing the risk of passing on mitochondrial diseases.

Pronuclear Transfer (PNT)

Pronuclear Transfer (PNT) is a sophisticated reproductive technique that is akin to Maternal Spindle Transfer (MST), but it utilises an egg fertilised in a laboratory setting by the mother and father’s genetic material. The process unfolds in several detailed steps:

Creation of the Lab-Fertilized Egg: Initially, a lab-fertilized egg is formed by combining the biological mother’s egg with sperm from the biological father. This step ensures that the resulting zygote contains the intended nuclear DNA (nDNA) from both parents.

Selection of a Donor Egg: Next, a suitable donor egg is meticulously selected. This egg must be screened thoroughly to guarantee it is devoid of any mitochondrial DNA (mDNA) mutations, ensuring the highest chances of a healthy pregnancy.

Removal of Donor nDNA: The selected donor egg, which possesses healthy mDNA, undergoes a process where its nDNA is carefully extracted. This step is crucial, as it prepares the donor egg to receive the genetic material from the lab-fertilized egg without introducing any foreign nuclear DNA.

Transplantation of nDNA: Following the extraction, the nDNA from the lab-fertilized egg is transplanted into the donor egg. This action effectively reconstitutes the egg with the biological parents’ genetic information while retaining the donor’s healthy mDNA.

Implantation into the Mother’s Uterus: Finally, the reconstructed egg is implanted into the biological mother’s uterus through in vitro fertilisation (IVF). This step marks the culmination of the PNT process, with the hope of achieving a successful pregnancy.

Through these carefully orchestrated steps, Pronuclear Transfer aims to provide couples with the opportunity to conceive healthy children while minimising the risk of inherited mitochondrial diseases.

Mitochondrial Inheritance

Mitochondria are organelle present in the cytoplasm of the cells which are primarily responsible for energy production for all cellular activities. 

Mitochondria contain their own distinct DNA, called mitochondrial DNA (mtDNA), which directs mitochondrial activities. Mitochondrial DNA has the same molecular structure and function as the DNA found in the nucleus, but it’s organized somewhat differently

All cells contain several hundred of these oval-shaped structures that convert energy (derived from the breakdown of nutrients) to a form that can be used by cells.

Each mitochondrion contains several copies of a ring-shaped DNA molecule, or chromosome. While mitochondrial DNA (mtDNA) is distinct from chromosomal DNA, its molecular structure and functions are the same. The entire molecule has been sequenced and is known to contain around 40 genes that direct the conversion of energy within cells.

Like the DNA in a cell’s nucleus, mtDNA is subject to mutations, and some of these mutations cause certain genetic disorders that result from impaired energy conversion.

Importantly, animals of both sexes inherit all their mtDNA, and thus all mitochondrial traits, from their mothers. Because mtDNA is inherited from only one parent, meiosis and recombination don’t occur. 

Hence, option c is correct.

3. Bollgard I and Bollgard 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 

3. Ans: b  

Explanation:

Bollgard® cotton is the trademark given to a number of varieties of cotton bio-engineered to produce an insecticidal protein Cry1Ac  from Bacillus thuringiensis (Bt). When produced by the modified cotton plants, this protein controls certain lepidopterous cotton insect pests.  

This product has reduced cotton production costs and insecticide use by providing an effective alternative to chemical insecticides for the control of tobacco budworm, Heliothisvirescens; cotton bollworm, Helicoverpa zea; and pink bollworm, Pectinophora gossypiella 

Bollgard‚ cotton, bio-engineered to resist lepidopterous insect pests, has had a dramatic effect on cotton production. 

The product concept 

Bacillus thuringiensis (Bt), a microorganism found in soil,was known to produce a potent, specific and safe protein insecticide Cry1Ac ). This protein was well characterized, considered safe, and  specific to the lepidopterous class of insects. 

By introducing the genetic information encoding the insecticidal protein of Bt into plants, these plants would produce their own insecticide. This simple concept promised to reduce insecticide applications, improve insect control, and provide opportunities for aggressive integrated pest management systems while maintaining the inherent safety of this insecticidal protein.

Bollgard(®) cotton, expresses Cry1Ac insecticidal protein.

Bollgard® II cotton was developed by inserting the cry2Ab gene into DP50B Bollgard cotton containing the cry1Ac gene. 

Tobacco budworm, cotton bollworm and pink bollworm are more susceptible to the Cry1Ac protein than to Cry2Ab, whereas fall armyworm, beet armyworm, cabbage looper and soybean looper are more susceptible to Cry2Ab than to Cry1Ac.

Bollgard I and II are approved in India.

In India Bt cotton is the only genetically modified (GM) crop that was approved for commercial cultivation in 2002.

Hence, option b is correct.

4. 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 

4. Ans: c

Explanation:   

According to the principle of Gay-lussac’s Law, P1/T1=P2/T2 i.e pressure and temperature are directly related. As pressure increases in the cooker, temperature also will naturally increase.  

According to the Ideal Gas Law PV=nRT, as pressure increases, temperature must also increase to balance out the equation on both sides.  

The pressure cooker works on the principle of increasing the internal pressure. Locking lids and the valve system release and regulate pressure in a pressure cooker. 

As pressure increases inside the cooker, the high-pressure gas moves around the food and the food is cooked through convection.

Thus, the temperature at which the food is cooked depends mainly upon internal pressure which is regulated by the lid and valve but not the temperature of the flame. 

Hence, option c is correct.

5. Consider the following: 

1. Bacteria 

2. Fungi 

3. Virus 

Which of the above can be cultured in an artificial /synthetic medium?

(a) 1 and 2 Only 

(b) 2 and 3 Only 

(c) 1 and 3 Only 

(d) 1, 2 and 3 

5. Ans: a

Explanation:

Microbes are diverse–protozoa, bacteria, fungi and microscopic animal and plant viruses, viroids and also prions that are proteinacious infectious agents. 

Bacteria

Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. Bacteria occur almost everywhere. They also live in extreme habitats such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many of them live in or on other organisms as parasites. Bacterial culture was the first method developed to study the human microbiota, using an artificial medium that allows the growth and isolation of bacteria. The first to have cultured a bacterium in a reproducible way was Louis Pasteur in 1860. 

Viruses

Viruses are microscopic organisms that are dead outside a living cell. They reproduce only inside the cells of the host organism, which may be a bacterium, plant, or animal. Viruses cannot be cultured synthetically. 

Fungi

The fungi constitute a unique kingdom of heterotrophic organisms. They show a great diversity in morphology and habitat. Some unicellular fungi, e.g., yeast are used to make bread and beer. Other fungi cause diseases in plants and animals; some are the source of antibiotics. Fungi are cosmopolitan and occur in air, water, soil and on animals and plants. They prefer to grow in warm and humid places. With the exception of yeasts which are unicellular, fungi are filamentous.

There are two general types of fungal culture media: natural and synthetic. Fungi can also be cultured synthetically. Media containing high carbohydrate source, nitrogen source are required for the growth of fungi at pH range of 5 to 6, and a temperature range from 15 to 37˚.

Hence, option a is correct.

6. Consider the following statements: 

1. Adenoviruses have single-stranded DNA genomes whereas retroviruses have double stranded DNA genomes. 

2. Common cold is sometimes caused by an adenovirus whereas AIDS is caused by a retrovirus. 

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 

6. Ans: b 

Explanation:

Adenovirus

Adenoviruses are non-enveloped, double-stranded DNA viruses. People with weakened immune systems are at high risk for developing severe illness caused by adenovirus infection. 

Adenoviruses most commonly cause respiratory illness. The illnesses can range from the common cold to pneumonia, croup, and bronchitis. Depending on the type, adenoviruses can cause other illnesses such as gastroenteritis, conjunctivitis, cystitis, and, less commonly, neurological disease.

Retrovirus

Retroviruses are linear single stranded RNA viruses with a lipid containing glycoprotein viral envelope. After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV, the virus that causes AIDS, is a retrovirus.

Hence, statement 1 is incorrect & statement 2 is correct.

7. 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 hydrogen 

7. Ans: a

Explanation:

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 i.e. the dipolar nature of water molecules. This allows the water molecule to become attracted to many other different types of inorganic 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.

Unique features of Water:

1. It exists as a liquid over a wide range of temperature i.e from 0⁰ to 100⁰C.
2. It has the highest specific heat, due to which it warms up and cools down very slowly without causing shocks of temperature jerks to the aquatic life.
3. It has a high latent heat of vaporisation. Hence, it takes a huge amount of energy for getting vaporised. That’s why it produces a cooling effect as it evaporates.
4. It is an excellent solvent for several nutrients. Thus, it can serve as a very good carrier of nutrients, including oxygen, which are essential to life. But, it can also easily dissolve various pollutants and become a carrier of pathogenic microorganisms.
5. Due to high surface tension and cohesion it can easily rise through great heights through the trunk even in the tallest of the trees like Sequoia.
6. It has an anomalous expansion behaviour i.e as it freezes, it expands instead of contracting and thus becomes lighter. It is because of this property that even in the extreme cold, the lakes freeze only on the surface. Being lighter the ice keeps floating whereas the bottom waters remain at a higher temperature and therefore, can sustain aquatic organisms even in extreme cold.

Hence, option a is correct.

8. 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-lights, sodium lamps have longer life span than LED lamps. 

3. The spectrum 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 

(a) 3 only 

(b) 2 only 

(c) 1 and 3 

(d) 1, 2 and 3 

8. Ans: c 

Explanation:

LEDs emit light in a specific direction, reducing the need for reflectors and diffusers that can trap light. The light of sodium vapor lights is omnidirectional, 360 degrees of light are produced using omnidirectional lighting. LED lights produce 180 degrees of light. Since light is frequently needed over a target region, this is usually advantageous (rather than all 360 degrees around the bulb).

Hence, statement 1 is correct.

Compared to all other lighting technologies, LEDs have a very long lifespan. New LEDs have a lifespan of at least 100,000 to 150,000 hours. So the lifespan of LED street lights is also very long. Sodium lamps fall well short of LEDs in lifespan, its life span is 18000 hours. 

Hence, statement 2 is incorrect.

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce monochromatic light at a characteristic wavelength near 589 nm. Two varieties of such lamps exist: low-pressure and high-pressure. 

LEDs can emit light in a range of colours. A mix of red, green, and blue LEDs is sometimes used to make white light. 

Hence, statement 3 is correct.

9. The term ‘ACE2’ is talked about in the context of: 

(a) genes introduced in the genetically modified plants 

(b) development of India’s own satellite navigation system 

(c) radio collar for wildlife tracking 

(d) spread of viral diseases 

9. Ans: d

Explanation:

The angiotensin-converting enzyme 2 (ACE2) is a protein that has different roles such as catalytic, transporter of amino acids or viral receptor. It has an essential role in different systems, from cardiovascular regulation to viral infection. 

The ACE attaches to cell membranes and works as the host functional receptor for the virus SARS-CoV-2 which causes Coronavirus Disease 2019 (COVID-19).  

The SARS-CoV and the SARS-CoV-2 enter the human cell through the ACE2 receptor. 

These two viruses have a surface anchored Spike (S) glycoprotein with surfaces receptor binding domains (RBD).

These two structures are critical for the entrance of the virus into the human cell. When the genetic material of the virus enters the cell, the membrane of the virus fusions with the host membrane cells. 

SARS-CoV-2 has a significantly higher ACE2 binding affinity.

The 3-dimensional structure of the SARS-CoV-2 binding site has a more compact conformation, improved binding stability, and potentially enhances the ACE2 receptor binding affinity.

ACE2 expression

ACE2 is widely expressed in many different cells of the body. 

It was observed to be highly expressed in endocrine tissues, gastrointestinal tract (e.g. ileum, liver and gallbladder), cardiovascular tissues, kidney and urinary bladder, testes and muscle tissues. 

It was observed that central nervous system and lymphoid tissues express relatively low ACE2 levels. 

They found that that the receptor it is not expressed in red blood cells. 

In the lung, high mRNA ACE2 expression was detected in the parenchyma and in primary and tertiary bronchi. Relevant for the transmission and respiratory manifestations of SARS-CoV-2 

Hence, option d is correct.

10. 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 

10. Ans: b 

Explanation:

PC (polycarbonate) has good transparency and average thermal stability, It also belongs to engineering plastics, such as organic glass, such as polymethyl methacrylate, polycarbonate, etc.

PC is a widely used material, such as phone cases, laptops, etc. It is particularly used in the manufacturing of baby bottles, space cups, etc. In recent years, milk bottles have been controversial due to their presence of bisphenol A. The residual bisphenol A in PC releases more and faster at higher temperatures. Therefore, PC water bottles should not be used to hold hot water. 

Bisphenol A (BPA) is a banned in many countries in food contact materials, due to its potentially harmful health impact. The ban means that BPA will not be allowed in products that come into contact with food or drink, such as the coating on metal cans, reusable plastic drink bottles, water distribution coolers and other kitchenware. 

Bureau of Indian Standards (BIS) banned the use of chemical Bisphenol A (BPA) in the manufacture of infant feeding bottles. 

Hence, option b is correct.

11. 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 

11. Ans: d 

Explanation:

Triclosan is an antimicrobial active ingredient used in several consumer products to increase their shelf life by stopping the growth of unwanted micro-organisms (bacteria, fungi, protozoa, etc), which might degrade the product.

A wide range of consumer products contain triclosan. More than 80% of triclosan usage is in personal care products, cosmetics and household cleaning products. These products contain between 0.1% and 0.3% triclosan. These items include:

• Fluoride toothpaste.
• Mouthwashes.
• Facial cleansers.
• Aftershave.
• Deodorants and body sprays.
• Lotions and creams.
• Cosmetics.
• Detergents and dishwashing liquids.
• Triclosan is part of other materials, including pesticides and textiles. 
• Clothing, shoes, carpeting, furniture, toys and kitchenware all contain the ingredient. 

In 2016, the U.S. Food and Drug Administration (FDA) banned the sale of consumer antiseptic wash products (soaps and body washes) containing triclosan. 

However, India lacks any such regulation so far on the use of trichlosan used products. The US FDA had banned triclosan from consumer anti bacterial soaps and body washes.

What are the side effects of triclosan?

Triclosan is an endocrine-disrupting chemical. That means it can harm endocrine system, leading to issues with proper hormone function. Exposure to the ingredient is of particular concern to females. That’s because it can cross the placenta and enter breast milk.

When a product containing triclosan is used, the body can absorb small amounts of it and the skin or mouth can absorb the ingredient within one to four hours.

Hence, option d is correct.

12. 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. 

12. Ans: d 

Explanation:

Light-year is the distance that light travels in one year. Light travels through interstellar space at 300,000 kilometers per second and 9.46 trillion kilometers per year in vacuum. The basic postulate of the ‘theory of relativity’ is that the speed of light is same in all inertial frames. This can be broken down into two parts:

• The speed of light is independent of the motion of the observer.
• The speed of light does not vary with time or place.

The distances between the stellar bodies are very large. These  bodies too are moving apart continuosly as the Universe is expanding. Therefore these above stated properties of light are the reasons that light is used to measure such large interstellar distances in light years.

Hence, option d is correct.