Q10. What chiefly prevents grasses from being fully replaced by trees in many grassland successions?
[UPSC CSE Prelims GS Paper I (2013)]
(A) Insects and fungi only
(B) Lack of all sunlight
(C) Water limitation and recurring fire
(D) Constant coastal flooding
Answer: (C) Water limitation and recurring fire
Explanation: Seasonal moisture deficits and periodic fires suppress establishment of young trees while favouring grasses, whose growth points often survive near the soil surface. Grazing and other local factors can also sustain grassland structure.
Q9. Which are major decomposers in food webs: viruses, fungi and bacteria?
[UPSC CSE Prelims GS Paper I (2013)]
(A) Viruses only
(B) Fungi and bacteria
(C) Viruses and bacteria
(D) All three
Answer: (B) Fungi and bacteria
Explanation: Fungi and many bacteria break down dead organic matter and release mineral nutrients back into ecosystems. Viruses reproduce through hosts and are not conventionally regarded as the primary decomposer organisms in such food chains.
Q8. Which ecological services can release nitrogen back into soils: urea excretion, coal burning and dead vegetation?
[UPSC CSE Prelims GS Paper I (2013)]
(A) Urea only
(B) Coal burning and plant decay
(C) Urea and plant decay
(D) All three
Answer: (C) Urea and plant decay
Explanation: Nitrogen-containing wastes and dead plant material are decomposed and mineralised by soil organisms, replenishing available nitrogen forms. Burning coal primarily emits pollutants to air and is not the direct soil-nutrient addition intended in this question.
2012
Q7. Which among bats, bees and birds can serve as flower pollinators?
[UPSC CSE Prelims GS Paper I (2012)]
(A) Bats and bees only
(B) Bees only
(C) Bats and birds only
(D) All three
Answer: (D) All three
Explanation: Many flowering plants are pollinated by insects, especially bees, but some rely on nectar-feeding birds or bats. Their flower shapes, colours and opening times often reflect adaptations to different animal pollinators.
Q6. Which is a supporting ecosystem service in the Millennium Ecosystem Assessment framework?
[UPSC CSE Prelims GS Paper I (2012)]
(A) Food and water provisioning
(B) Climate and disease regulation
(C) Nutrient cycling
(D) Supply of timber and fish
Answer: (C) Nutrient cycling
Explanation: Supporting services underpin the production of other ecosystem benefits. Nutrient cycling and soil formation maintain productivity and ecological processes. Food supply is provisioning, while climate and disease control are generally classified as regulating services.
2011
Q5. Why does deep-water upwelling increase marine productivity?
[UPSC CSE Prelims GS Paper I (2011)]
(A) It lifts decomposers exclusively
(B) It transports nutrients into sunlit surface water
(C) It directly carries seabed fish to the surface
(D) It creates freshwater in oceans
Answer: (B) It transports nutrients into sunlit surface water
Explanation: Upwelling moves nutrient-rich deep water into the sunlit upper ocean, where phytoplankton can use these nutrients for photosynthesis. This increases primary productivity and often supports exceptionally rich marine fisheries.
Q4. Why can a cleared tropical rainforest recover less rapidly than a tropical deciduous forest?
[UPSC CSE Prelims GS Paper I (2011)]
(A) Its soil often has low available nutrient reserves
(B) Rainforest seeds are always sterile
(C) Every rainforest tree grows slowly
(D) Only exotic invasion matters
Answer: (A) Its soil often has low available nutrient reserves
Explanation: Much rainforest nutrient capital is held in standing vegetation rather than fertile mineral soil. Heavy rainfall and rapid nutrient cycling can leave exposed soils vulnerable to leaching after clearing, constraining forest regrowth.
2003
Q3. Which pollutant is formed secondarily during photochemical smog development?
[UPSC CSE Prelims GS Paper I (2003)]
(A) Hydrocarbons
(B) Nitrogen oxides
(C) Ozone
(D) Methane
Answer: (C) Ozone
Explanation: Sunlight drives reactions between nitrogen oxides and volatile organic compounds, producing ground-level ozone and other oxidants. This is the hallmark of photochemical smog, whereas hydrocarbons and nitrogen oxides are major precursors.
2002
Q2. Which Indian coast is renowned for mass nesting of Olive Ridley sea turtles?
[UPSC CSE Prelims GS Paper I (2002)]
(A) Goa
(B) Gujarat
(C) Odisha (formerly Orissa)
(D) Tamil Nadu
Answer: (C) Odisha (formerly Orissa)
Explanation: Odisha’s Gahirmatha and nearby nesting beaches are internationally noted for large Olive Ridley arribadas. These mass nesting events demand protection from disturbance, coastal habitat damage and accidental capture in fishing gear.
Q1. Arrange these ecosystems by decreasing albedo:
1. Taiga
2. Tropical evergreen forest
3. Tropical deciduous forest
4. Tundra.
[UPSC CSE Prelims GS Paper I (2002)]
(A) 1, 4, 3, 2
(B) 4, 1, 2, 3
(C) 4, 1, 3, 2
(D) 1, 4, 2, 3
Answer: (C) 4, 1, 3, 2
Explanation: Snow-covered tundra reflects the largest share of sunlight; taiga can also be highly reflective seasonally. Tropical deciduous forest generally reflects more than dense evergreen rainforest. This gives the decreasing order tundra, taiga, deciduous, evergreen.
