Human body, health & diseases

Answer: (b) 1, 2 and 4 only

Pollution-derived magnetite nanoparticles form when iron-bearing material is burnt or heated by friction, so they come from vehicle engine exhaust, brake wear and combustion at power stations. A 2016 study found such particles in human brain tissue and linked them to oxidative damage of the kind seen in Alzheimer's disease. Microwave ovens and telephone lines are not among the sources it names.

• ✓ 1. Frictional heating of brake pads produces high-temperature magnetite nanoparticles at the roadside.
• ✓ 2. Magnetite nanoparticles have been captured from the exhaust plume of diesel engines; combustion is the main source.
• ✗ 3. The study names open fires and poorly sealed cooking or heating stoves as indoor sources of magnetite nanoparticles; microwave ovens are not among them.
• ✓ 4. The study shows spherical, fused magnetite particles collected at a power station, an example of industrial combustion.
• ✗ 5. Telephone lines are not among the sources the study names; they carry electrical signals, not iron-oxide particles from combustion or friction.

Remember · Airborne magnetite nanoparticles come from combustion and friction: vehicle exhaust, brake wear, power plants, open fires. They have been found in human brain tissue.

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (c) Both 1 and 2

Both statements are correct: a recombinant vector vaccine is built by genetic engineering, and the carrier (vector) that delivers the disease-causing agent's gene into our cells is a harmless virus or bacterium.

• ✓ 1. Recombinant DNA technology lets scientists make a pathogen's antigen in bacteria or yeast, as with the hepatitis B vaccine from yeast. Recombinant vector vaccines rest on the same gene-splicing methods.
• ✓ 2. NIAID, part of the US National Institutes of Health, describes recombinant vector vaccines as those that use a harmless virus or bacterium as a vector, or carrier, to introduce genetic material into cells. Covishield is a vectored vaccine that uses a virus as the carrier.

Remember · Recombinant vector vaccine = genetic engineering plus a harmless virus or bacterium as the carrier that delivers the pathogen's gene into our cells.

📘 Read it in NCERT: Class 12 Biology, Ch 7 (practise this chapter) · Class 12 Biology, Ch 9 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (c) Both 1 and 2

Both statements are correct: mitochondrial DNA comes only from the mother's egg, and mitochondrial replacement therapy swaps the faulty mitochondria either before fertilisation (spindle transfer) or after it (pronuclear transfer).

• ✓ 1. Two techniques are used: in maternal spindle transfer the mother's nuclear genetic material is moved into a donor egg before fertilisation, and in pronuclear transfer the fertilised embryo's nuclear material is moved into a donor embryo after fertilisation. Either way the child gets healthy donor mitochondria.
• ✓ 2. Only egg cells contribute mitochondria to the embryo, so only females pass on mitochondrial DNA variants; a father's sperm does not pass them on.

Remember · Mitochondrial DNA is inherited only from the mother. Mitochondrial replacement therapy: spindle transfer (before fertilisation) or pronuclear transfer (after fertilisation).

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) 1 and 2 only

Bacteria and fungi are living cells that can feed and multiply on a lab-made nutrient medium, so they can be cultured in it. A virus has no cell machinery of its own and multiplies only inside a living host cell, so it cannot grow in a cell-free artificial medium.

• ✓ 1. Bacteria grow as visible colonies on nutrient-rich gel or broth in a petri dish.
• ✓ 2. Fungi also grow as colonies in a petri dish on a suitable nutrient medium.
• ✗ 3. Viruses are acellular and multiply only after entering a living cell. To grow them, labs use living cells (cell culture, or fertilised eggs), not a synthetic medium.

Remember · Bacteria and fungi grow on artificial nutrient media; viruses need living host cells, so they cannot be cultured on a synthetic medium alone.

📘 Read it in NCERT: Class 12 Biology, Ch 8 (practise this chapter) · Class 8 Curiosity, Ch 2 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 2 only

Statement 2 is correct: adenoviruses can cause cold-like illness, and AIDS is caused by HIV, which is a retrovirus. Statement 1 is wrong on both counts, because adenoviruses have double-stranded DNA genomes, while retroviruses carry an RNA genome.

• ✗ 1. Adenoviruses are non-enveloped viruses with double-stranded DNA, not single-stranded DNA. Retroviruses, such as HIV, have an RNA genome (later copied into DNA inside the host cell), not a double-stranded DNA genome.
• ✓ 2. Adenoviruses cause respiratory infections, including mild cold-like illness. AIDS is caused by the Human Immunodeficiency Virus (HIV), a retrovirus.

Remember · Adenovirus: double-stranded DNA, respiratory infections. Retrovirus (HIV, cause of AIDS): RNA genome.

📘 Read it in NCERT: Class 12 Biology, Ch 7 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) spread of viral diseases

ACE2, short for angiotensin-converting enzyme 2, sits on the outer surface of human cells, and the spike of SARS-CoV-2 (the virus behind COVID-19) latches onto it to get inside. So it was discussed in the context of how a viral disease spreads.

• ✓ (d) The spike protein of SARS-CoV-2 binds to ACE2 on host cells, which lets the virus enter them. The earlier SARS coronavirus used the same receptor.
• ✗ (a) ACE2 is a human protein, not a gene introduced into genetically modified plants.
• ✗ (b) India's own satellite navigation system is NavIC; ACE2 has nothing to do with navigation or radio collars.

Remember · ACE2 is the human cell-surface receptor that SARS-CoV-2 (and SARS-CoV) binds to for entry into cells.

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Toiletries

Triclosan is an antibacterial chemical added to personal-care products such as some soaps, skin cleansers, deodorants and toothpastes, which are toiletries. It is a suspected endocrine (hormone-system) disruptor, so long exposure to high levels is a worry.

• ✓ (d) The US FDA says triclosan is added to some antibacterial soaps and body washes, toothpastes and cosmetics, all toiletries. Some short-term animal studies link high doses to lower levels of some thyroid hormones, which is why long exposure is a concern.
• ✗ (a) Food preservatives keep food from spoiling; triclosan is not a permitted food preservative. It is an antibacterial for personal-care products.
• ✗ (b) Fruit-ripening substances are chemicals that release ethylene, the ripening hormone of plants. Triclosan is not a ripening agent.
• ✗ (c) Triclosan is mainly an antibacterial added to personal-care products. The usual worry about reused plastic containers is a different one: chemicals such as BPA leaching out of the plastic.

Remember · Triclosan is an antibacterial agent in toiletries (soaps, toothpaste, deodorants) and a suspected endocrine disruptor.

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error