Biodiversity, plants & animals

Answer: (d) 1, 2 and 3

All three are ways in which dry-area plants cut water loss through transpiration. A waxy coat seals the surface, small leaves expose less evaporating surface, and thorns or spines replace leaves almost entirely.

• ✓ 1. A thick, waxy cuticle on hard leaves slows the escape of water vapour; plants of very dry habitats often have such a coat.
• ✓ 2. Small leaves have less surface from which water can evaporate and heat up less in the sun.
• ✓ 3. In plants such as cacti the leaves are reduced to thorns or spines, so the plant loses very little water through leaves at all.

Remember · Desert (xerophytic) plants save water with waxy coats, small leaves, thorns/spines, deep roots and fleshy water-storing stems.

Question and answer: UPSC's official GS Paper I (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Mankind's over-exploitation/misuse of natural resources, fragmentation/loss of natural habitats, destruction of ecosystems, pollution and global climate change.

The "sixth extinction" is the loss of species happening now, at a pace far above the natural rate, and it is driven by human activity: habitat loss and fragmentation, over-exploitation, invasive species and the like. Option (d) names these human pressures. Earlier mass extinctions were natural events, and the current one is what makes this episode different.

• ✓ (d) Species are now disappearing an estimated 100 to 1,000 times faster than before humans, and human activities are responsible. Habitat loss and fragmentation, over-exploitation, alien species and co-extinctions are the main causes.
• ✗ (b) This describes a feared natural event, a meteorite impact. The sixth extinction is not a fear about the future but an ongoing loss caused by people.
• ✗ (a) Monoculture and chemical use damage ecosystems, but they are only some of the pressures. They do not define the term, which covers the whole human-driven loss of species.
• ✗ (c) Loss of native crop varieties is a narrower concern, agricultural biodiversity. The sixth extinction is about species loss across all ecosystems.

Remember · Five natural mass extinctions came before; the sixth is human-driven, at 100 to 1,000 times the pre-human rate. The four main causes are the 'Evil Quartet'.

📘 Read it in NCERT: Class 12 Biology, Ch 13 (practise this chapter) · Class 12 Biology, Ch 13 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) It tends to reduce the biodiversity in the area in which it grows.

Prosopis juliflora (vilayati babul or vilayati kikar) is an invasive alien tree from South America. It spreads fast and pushes out native plants and the animals that depend on them, so it is in the news for removal drives.

• ✓ (b) The Wildlife Institute of India calls it one of the worst invaders affecting ecosystems and local biodiversity in Tamil Nadu. NCERT explains that alien species that turn invasive cause decline or extinction of native species.
• ✗ (a) The plant is not in the news for any cosmetics extract; in India it was introduced for fuelwood and to green degraded land.
• ✗ (c) It is not in the news as a source of pesticide raw material; it is in the news for the harm it does as an invader.

Remember · Prosopis juliflora (vilayati babul) is an invasive alien tree that displaces native species and lowers biodiversity.

📘 Read it in NCERT: Class 11 Understanding Society, Ch 3 (practise this chapter) · Class 12 Biology, Ch 13 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) 1, 2 and 3

All three statements are taken as correct. NCERT places coral reefs in the tropical oceans; half of all reef area is in just five countries, and Australia, Indonesia and the Philippines alone hold about 42% of it; and reefs host 32 of the 34 recognised animal phyla (UN).

• ✓ 1. NCERT describes atolls as low islands of coral reefs found in the tropical oceans, so most reefs lie in tropical waters.
• ✓ 2. Half of the world's reef surface lies in only five countries: Australia, Indonesia, the Philippines, France and Papua New Guinea. The GCRMN ranking gives Australia 16.88%, Indonesia 15.26% and the Philippines 9.74% of reef surface, a cumulative 41.88% for the three, which is more than one-third.
• ✓ 3. The UN's World Ocean Assessment says reefs host 32 of the 34 recognised phyla, nearly all of them. UPSC's official key treats this statement as correct; we could not confirm the comparison with rainforests from an official source, so we do not explain it here.

Remember · Reefs: mostly tropical, concentrated in a few countries (Australia, Indonesia, Philippines hold about 42%), and home to 32 of 34 animal phyla.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 12 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error