22 free Environment MCQs written in the UPSC Prelims exam pattern, each with a step-by-step solution. Tap an option for instant feedback — no sign-up, no ads.
Revise with smart repetition →✍️ These are original practice questions written in the UPSC Prelims pattern for the UPSC Civil Services Preliminary exam — not questions from any official past paper.
Q1. Which rainforest is often called the 'lungs of the Earth'?
B. The Amazon rainforest — The Amazon rainforest is called the 'lungs of the Earth' because it produces a large share of the world's oxygen and absorbs vast amounts of carbon dioxide.
Q2. 'Project Tiger', India's tiger-conservation programme, was launched in the year:
A. 1973 — Project Tiger was launched in 1973 to protect the Bengal tiger and its habitat through a network of tiger reserves.
Q3. The main greenhouse gas responsible for global warming, released by burning fossil fuels, is:
C. Carbon dioxide — Carbon dioxide (CO₂) is the principal greenhouse gas from fossil-fuel combustion. Oxygen, nitrogen and argon are not significant greenhouse gases.
Q4. Depletion of the ozone layer in the stratosphere is caused mainly by:
B. Chlorofluorocarbons (CFCs) — Chlorofluorocarbons (CFCs) release chlorine atoms that destroy ozone molecules, thinning the protective ozone layer. Their use is phased out under the Montreal Protocol.
Q5. The national park in Assam famous for protecting the one-horned rhinoceros is:
C. Kaziranga National Park — Kaziranga National Park in Assam is a UNESCO World Heritage Site home to about two-thirds of the world's one-horned rhinoceroses. Gir is known for the Asiatic lion; Corbett and Ranthambore for tigers.
Q6. A community of living organisms together with their physical environment, interacting as a system, is called a(n):
B. Ecosystem — An ecosystem is a community of interacting organisms (biotic) together with their non-living surroundings (abiotic), through which energy flows and nutrients cycle.
Q7. In an ecological pyramid, the amount of energy transferred from one trophic level to the next is approximately what fraction of the energy available at the lower level?
B. About 10% — By the ten percent law of Lindeman, only about 10% of the energy at one trophic level is passed on to the next; the rest is lost mainly as metabolic heat.
Q8. Which of the following best describes a 'keystone species'?
B. A species whose impact on its community is disproportionately large relative to its abundance — A keystone species exerts an effect on ecosystem structure far greater than its numbers would suggest; its removal can cause major changes or collapse of the community.
Q9. Eutrophication of a water body is most directly caused by the excessive enrichment of which nutrients?
A. Nitrogen and phosphorus — Nutrient enrichment, chiefly by nitrogen and phosphorus from fertilizers and sewage, triggers algal blooms whose decomposition depletes dissolved oxygen, defining eutrophication.
Q10. Under the IUCN Red List, which category indicates the highest risk for a species that still survives in the wild?
C. Critically Endangered — Among species still found in the wild, 'Critically Endangered' denotes the highest extinction risk, ranking above Endangered and Vulnerable in the IUCN threat categories.
Q11. The Ramsar Convention is an international treaty concerned primarily with the conservation of which type of ecosystem?
C. Wetlands — The Ramsar Convention (1971) provides for the conservation and wise use of wetlands and designates Wetlands of International Importance, known as Ramsar sites.
Q12. A biodiversity 'hotspot' is defined by two criteria: it must contain a high number of endemic plant species and it must have
A. Lost at least 70% of its original habitat — A hotspot must have at least 1,500 endemic vascular plant species and have lost 70% or more of its original primary vegetation, marking it as both rich and threatened.
Q13. Which pair of gases from the following contributes most to the greenhouse effect by trapping outgoing longwave (infrared) radiation?
B. Carbon dioxide and methane — Carbon dioxide and methane absorb and re-emit infrared radiation, warming the atmosphere. Nitrogen, oxygen and the noble gases are not effective greenhouse gases.
Q14. The process by which certain persistent toxic substances increase in concentration at successively higher trophic levels of a food chain is called
B. Biomagnification — Biomagnification is the increasing concentration of a persistent pollutant, such as DDT or mercury, at each higher trophic level. Bioaccumulation refers to build-up within one organism over time.
Q15. In situ conservation of biodiversity refers to protecting species
B. In their natural habitats — In situ conservation protects species within their natural habitats, as in national parks and biosphere reserves. Zoos, gene banks and seed vaults are examples of ex situ conservation.
Q16. The 'edge effect' in ecology refers to the distinctive conditions and species diversity found
A. At the boundary between two different ecosystems — The transition zone between two ecosystems is an ecotone, and the tendency for greater species richness and density there is termed the edge effect.
Q17. Which one of the following is a naturally occurring greenhouse gas that also protects life by absorbing harmful ultraviolet radiation in the stratosphere?
B. Ozone — Ozone is a greenhouse gas in the troposphere but in the stratosphere it forms a layer that absorbs most of the Sun's harmful ultraviolet radiation, shielding life on Earth.
Q18. Organisms that can tolerate a wide range of an environmental factor such as temperature are described as
B. Eurythermal — The prefix 'eury' means wide and 'thermal' refers to temperature, so eurythermal organisms tolerate a broad temperature range. 'Steno' denotes a narrow range; 'haline' refers to salinity.
Q19. A food web is more stable than a simple food chain primarily because
C. It offers alternative feeding pathways when one species declines — In a food web, consumers can shift to alternative prey if one food source falls, so the network of interconnected chains gives the ecosystem greater resilience than a single linear chain.
Q20. Which of the following soil conservation practices involves planting crops along the natural contour lines of a slope to reduce runoff and erosion?
B. Contour ploughing — Contour ploughing follows the contour lines of a slope so that the ridges slow water flow, reducing surface runoff and soil erosion. The other options tend to increase soil loss.
Q21. The primary ecological role of decomposers such as bacteria and fungi in an ecosystem is to
C. Break down dead organic matter and recycle nutrients — Decomposers break down dead plants and animals, releasing nutrients back into the soil and atmosphere so producers can reuse them, thus closing nutrient cycles.
Q22. Wetlands are often called the 'kidneys' of a landscape mainly because they
B. Filter pollutants and purify water passing through them — Wetlands trap sediments and absorb or break down nutrients and pollutants as water flows through them, filtering and purifying it much as kidneys filter blood, hence the nickname.
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