Biodiversity, plants & animals

Answer: (c) 2 and 3

Lichens and mosses are pioneer organisms: they cling to bare rock, walls and bark and are among the first to colonise weathered rock before any soil exists. Ferns arrive only after some soil and humus has built up, and mushrooms need dead organic matter to feed on.

• ✗ 1. Ferns are vascular plants with roots; in soil formation they appear later, once humus has accumulated.
• ✓ 2. A lichen is a partnership of a fungus and an alga that grows directly on rocks and tree bark.
• ✓ 3. Mosses have root-like rhizoids rather than true roots and form green mats on damp rocks and old walls.
• ✗ 4. Mushrooms are fungi that cannot make food; they absorb nutrients from dead and decaying matter, so they grow on soil, litter or wood.

Remember · Pioneers on bare rock: lichens and mosses. They start soil formation; ferns, grasses and trees follow.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter) · Class 7 Curiosity, Ch 2 (practise this chapter) · Class 9 Exploration, Ch 12 (practise this chapter) · Class 9 Exploration, Ch 12 (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: (c) Lemongrass

Lemongrass (Cymbopogon species) yields an aromatic essential oil rich in citral, and this oil is used in insect-repellent preparations and has been shown to repel mosquitoes. Congress grass (Parthenium) is a weed, and elephant grass is a fodder grass.

• ✓ (c) Lemongrass oil, distilled from the leaves, has a strong lemon-like smell from its citral and goes into insect-repellent preparations (National Horticulture Board); laboratory studies show it repels mosquitoes.
• ✗ (a) Congress grass is Parthenium hysterophorus (carrot grass), an invasive weed that causes pollen allergy; it is not used to repel insects.
• ✗ (b) Elephant grass (Napier grass, Pennisetum purpureum) is a tall tropical grass that gives good fodder for grazing animals when young; it is not a repellent.

Remember · Lemongrass (Cymbopogon) oil, rich in citral, is a plant-based mosquito repellent. Congress grass (Parthenium) is an invasive weed; elephant (Napier) grass is fodder.

📘 Read it in NCERT: Class 12 Biology, Ch 1 (practise this chapter) · Class 12 Biology, Ch 13 (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: (d) 1 and 3

Both the hedgehog (covered in spines) and the pangolin (covered in hard scales) curl into a tight ball when threatened, so that only the armour faces the predator and the soft parts are hidden. The marmot, a burrowing rodent, instead whistles an alarm and runs into its burrow.

• ✓ 1. When frightened, a hedgehog rolls into a tight ball with its snout and limbs tucked under its body, which makes its spines erect and shields the soft parts.
• ✗ 2. Marmots are burrowing rodents; when danger is near, a sentinel marmot whistles sharply so that colony members can escape into the nearest burrow, rather than rolling up.
• ✓ 3. The Indian pangolin is armoured with overlapping horny scales and rolls into a ball when threatened.

Remember · Roll-up defence: hedgehog (spines) and pangolin (scales). Marmots whistle an alarm and flee to burrows.

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) Oyster

A filter feeder draws in water and strains out tiny food particles such as plankton and algae. The oyster, a bivalve mollusc fixed to one spot, feeds exactly this way, pumping water through its gills; the others actively hunt or scavenge.

• ✓ (c) Oysters feed by filtering algae out of the water; one oyster can filter up to about 50 gallons (roughly 190 litres) a day, which also cleans estuary water.
• ✗ (b) The octopus is an active predator that catches crabs, shellfish and fish with its arms.
• ✗ (d) Pelicans scoop up fish in their throat pouch and drain the water out; they are fish-eaters, not strainers of plankton.

Remember · Filter feeders strain food from water: oysters, mussels, clams, sponges, krill, baleen whales, whale sharks, flamingos. Oyster reefs clean estuary water.

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) 1, 2 and 3

All three groups contain species that live in close, often mutually beneficial, partnerships with other organisms. Reef-building corals (cnidarians) host photosynthetic zooxanthellae; fungi form lichens and mycorrhizae; and many protozoa live as symbionts, some carrying algae inside their own cells.

• ✓ 1. Corals, which are cnidarians, house zooxanthellae in their tissues; the algae supply sugars from photosynthesis and the coral gives them shelter and carbon dioxide.
• ✓ 2. Fungi team up with algae or cyanobacteria to form lichens, and with plant roots to form mycorrhizae that help plants absorb phosphorus.
• ✓ 3. Many protozoa live as symbionts; the ciliate Paramecium bursaria, for instance, carries symbiotic Chlorella algae in its cytoplasm. The two benefit each other: the ciliate gives the algae a protected habitat and the algae add to its nutrition through photosynthesis.

Remember · Mutualism examples: coral + zooxanthellae, fungus + alga (lichen), fungus + root (mycorrhiza), Paramecium bursaria + algae, legume + Rhizobium.

📘 Read it in NCERT: Class 9 Exploration, Ch 12 (practise this chapter) · Class 12 Biology, Ch 11 (practise this chapter) · Class 9 Exploration, Ch 12 (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: (b) 3, 4 and 5

UPSC's key marks statements 3, 4 and 5 correct, while 1 and 2 are wrong: moringa is a deciduous tree of its own family, not a legume, and tamarind is not endemic to South Asia, having originated in Madagascar (Spices Board).

• ✗ 1. Moringa (Moringa oleifera) is a small deciduous tree of the family Moringaceae, so it is neither a legume nor evergreen.
• ✗ 2. The Spices Board says tamarind originated in Madagascar and is now cultivated widely in India and other countries, so it is not endemic to South Asia.
• ✓ 3. Tamarind, with seeds and de-seeded, is on the Ministry of Tribal Affairs' list of minor forest produce with a minimum support price, the gathering of which is a livelihood for tribal collectors.
• ✓ 4. UPSC's official key treats this statement as correct; we could not confirm the detail from an official source, so we do not explain it here.
• ✓ 5. UPSC's official key treats this statement as correct; we could not confirm the detail from an official source, so we do not explain it here.

Remember · Moringa is a deciduous Moringaceae tree, not a legume; tamarind originated in Madagascar and is a listed minor forest produce with an MSP.

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