Human body, health & diseases

Answer: (d) prevention of mitochondrial diseases in offspring

Pronuclear transfer is a form of mitochondrial donation, used to stop a mother from passing a serious mitochondrial disease to her child. The nuclear DNA of her fertilised egg is moved into a donor egg that has healthy mitochondria, so the baby gets the parents' genes but the donor's healthy mitochondria.

• ✗ (a) Fertilising an egg in the lab with donor sperm is ordinary IVF. Pronuclear transfer is an extra step done on embryos, not a way of fertilising an egg.
• ✗ (b) The technique does not modify sperm-producing cells or edit genes; it swaps whole nuclear material between embryos.
• ✗ (c) It does not turn stem cells into embryos. It moves the nuclear genetic material of one embryo into another embryo whose own nucleus has been removed.
• ✓ (d) Mitochondrial donation treatment lets people with severe mitochondrial disease avoid passing it to their children. Pronuclear transfer is one of the two approved techniques, the other being maternal spindle transfer.

Remember · Pronuclear transfer = swap the nuclear DNA of an embryo into a donor embryo with healthy mitochondria, to prevent mitochondrial disease.

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 1 and 2 only

Pneumococcal conjugate vaccines (PCVs) protect against the diseases caused by the pneumococcus bacterium, chiefly pneumonia, meningitis and blood infection (sepsis), and fewer infections mean less reliance on antibiotics against resistant strains. No vaccine is free of side effects, so the claim in statement 3 is too absolute.

• ✓ 1. The Health Ministry says PCV protects children against severe pneumococcal disease such as pneumonia and meningitis. Pneumococcus (Streptococcus pneumoniae) also causes blood infection (sepsis), and the vaccine greatly reduced this burden where it was introduced.
• ✓ 2. After PCVs were introduced across the world, the share of pneumococci resistant to first-line antibiotics for pneumonia fell. Fewer infections and less resistance mean less dependence on failing antibiotics.
• ✗ 3. WHO's vaccine safety notes list mild reactions, such as swelling, redness, tenderness and fever, and say severe allergic reactions are very rare, not absent.

Remember · PCV prevents pneumonia, meningitis and sepsis and helps check antibiotic resistance, but every vaccine can have mild side effects and, rarely, allergy.

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) 1 and 3 only

A plant cell has a cellulose cell wall and, when mature, usually one large central vacuole, while an animal cell has no cell wall and only small vacuoles, if any. Statement 2 is wrong because every cell, plant or animal, is enclosed by a plasma membrane.

• ✓ 1. The plant cell wall is made mainly of cellulose. Animal cells lack a rigid cell wall, which lets them change shape easily.
• ✗ 2. The plasma membrane (cell membrane) is the universal boundary of a cell. Plant cells have it too, just inside the cell wall.
• ✓ 3. A mature plant cell usually has one large central vacuole filled with cell sap. Animal cells may have vacuoles, but they are not as large.

Remember · Cell wall (cellulose) and one big central vacuole belong to plant cells. The plasma membrane is present in all cells.

📘 Read it in NCERT: Class 9 Exploration, Ch 2 (practise this chapter) · Class 9 Exploration, Ch 2 (practise this chapter) · Class 9 Exploration, Ch 2 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) 1, 2 and 3 only

Benzene is a volatile chemical released when fuels and other organic material burn, so vehicle exhaust, tobacco smoke and wood burning are all recognised sources of exposure. Varnished wooden furniture and polyurethane products are not named in the official lists of benzene sources.

• ✓ 1. Benzene is present in motor vehicle exhaust and in petrol (gasoline) vapour.
• ✓ 2. Tobacco smoke contains benzene, and WHO calls active and passive smoke exposure a significant source of exposure.
• ✓ 3. Wood-burning fires are named among the common sources of benzene in air.
• ✗ 4. UPSC's key does not count this as a benzene source. EPA's summary names glues, paints and furniture wax among household sources, but not varnished wooden furniture itself.
• ✗ 5. Polyurethane products are not named among the recognised benzene sources in the EPA and WHO summaries, and UPSC's key does not count them.

Remember · Benzene comes from burning and fuels: vehicle exhaust, tobacco smoke, wood-burning fires, petrol vapour, and some glues and paints.

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error