UPSC Prelims 2021 Environment questions: topic-wise weightage
UPSC Prelims 2021 asked 21 environment questions in GS Paper I, spread over 4 topics. See the environment weightage for 2021 below, then attempt each question with the official answer and an explanation.
Environment 2021: questions by topic
- Ecology and ecosystems9
- Biodiversity and species3
- Climate change and international conventions2
- Pollution, environmental laws and green technology7
Counted from the 21 questions on this page, tagged by topic in the Battle IAS PYQ bank.
Seeing 21 Environment questions spread over 4 topics can feel overwhelming. That's exactly why the Battle IAS PYQ Book maps every question topic by topic, so you know what to study first. Download free sample
Ecology and ecosystems 9
In the nature, which of the following is/are most likely to be found surviving on a surface without soil?
- 1. Fern
- 2. Lichen
- 3. Moss
- 4. Mushroom
Select the correct answer using the code given below.
Answer (c) & explanation
Lichens and mosses survive on surfaces without soil (c). Lichens, a partnership of a fungus and an alga or cyanobacterium, and mosses are the pioneer species on bare rock. They cling to the surface, release acids that slowly break it down, and trap dust and dead matter, which starts soil formation. This begins primary succession. Item 1 is wrong: ferns have roots that need some soil. Item 4 is wrong: mushrooms are fungi that need dead organic matter to feed on.
Notice that lichens are indicators of clean air: they disappear where sulphur dioxide pollution is high. The final stable community in succession is the climax community, such as a forest.
Answer as per the official UPSC answer key.
Consider the following kinds of organisms :
- 1. Copepods
- 2. Cyanobacteria
- 3. Diatoms
- 4. Foraminifera
Which of the above are primary producers in the food chains of oceans?
Answer (b) & explanation
Cyanobacteria and diatoms are primary producers (b). Primary producers make their own food by photosynthesis, forming the base of the food chain. Item 2 is right: cyanobacteria (blue-green algae) photosynthesise and also fix nitrogen. Item 3 is right: diatoms are phytoplankton with glass-like silica shells, and they produce much of the world's oxygen. Item 1 is wrong: copepods are tiny crustaceans that eat phytoplankton, so they are consumers. Item 4 is wrong: foraminifera are shelled protists that mostly feed on other organisms.
Notice that marine phytoplankton produce about half of Earth's oxygen. Foraminifera shells pile up on the ocean floor and help scientists study past climates.
Answer as per the official UPSC answer key.
Which one of the following is a filter feeder?
Answer (c) & explanation
The oyster is a filter feeder (c). An oyster pumps water through its gills and strains out plankton and fine organic particles, so it is a filter feeder. One adult oyster can filter many litres of water an hour, which also cleans the water and makes oyster reefs valuable to coastal ecosystems. Option (a) is wrong: a catfish is a bottom feeder and scavenger that eats insects, fish and debris. Option (b) is wrong: an octopus is a predator that catches crabs and fish. Option (d) is wrong: a pelican scoops up fish in its throat pouch; it drains the water but does not filter food.
Notice other filter feeders: clams, mussels, sponges, barnacles, flamingos, and the baleen whales and whale shark.
Answer as per the official UPSC answer key.
In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?
Answer (c) & explanation
The phosphorus cycle depends on rock weathering (c). The phosphorus cycle has no important gas phase. Phosphorus is locked in rocks as phosphate minerals and enters soil and water only as rocks weather. Plants take it up, animals eat the plants, and it returns to soil and the sea when they die, finally settling as sediment that becomes rock again. Option (a) is wrong: carbon cycles mainly through the air as CO₂. Option (b) is wrong: nitrogen enters mainly from the air through fixation. Option (d) is wrong: sulphur has both rock and gas sources, such as volcanoes and SO₂.
Notice that phosphorus is often the limiting nutrient in lakes, and excess phosphate from fertilisers and detergents causes eutrophication.
sulphur also comes from rocks, but it has a large gas phase (SO2, H2S). Phosphorus has none.
Answer as per the official UPSC answer key.
Which of the following are detritivores?
- 1. Earthworms
- 2. Jellyfish
- 3. Millipedes
- 4. Seahorses
- 5. Woodlice
Select the correct answer using the code given below.
Answer (c) & explanation
Earthworms, millipedes and woodlice are detritivores (c). Detritivores feed on detritus: dead plant and animal matter, such as fallen leaves and rotting wood. They break it into small pieces, which helps decomposers like bacteria and fungi finish the job and return nutrients to the soil. Item 1 is right: earthworms eat dead matter in soil. Item 3 is right: millipedes eat decaying leaves on the forest floor. Item 5 is right: woodlice are small crustaceans that eat rotting wood and leaves. Items 2 and 4 are wrong: jellyfish and seahorses are predators that catch small animals.
Notice the difference: detritivores eat detritus, while decomposers break it down chemically. Notice vermicomposting, which uses earthworms to make compost.
Answer as per the official UPSC answer key.
Which of the following have species that can establish symbiotic relationship with other organisms?
- 1. Cnidarians
- 2. Fungi
- 3. Protozoa
Select the correct answer using the code given below.
Answer (d) & explanation
All three groups have symbiotic species (d). Symbiosis is a close, long-term relationship between two different species. Item 1 is right: corals, which are cnidarians, host algae called zooxanthellae that give them food and colour; losing them causes coral bleaching. Item 2 is right: fungi form mycorrhizae with plant roots, helping them absorb water and phosphorus, and they team up with algae as lichens. Item 3 is right: protozoa in a termite's gut digest the cellulose in the wood it eats.
Notice the types of symbiosis: mutualism (both gain), commensalism (one gains, the other is unaffected) and parasitism (one gains at the other's cost). Rhizobium bacteria in legume roots are another mutualism.
Answer as per the official UPSC answer key.
“Leaf litter decomposes faster than in any other biome and as a result the soil surface is often almost bare. Apart from trees, the vegetation is largely composed of plant forms that reach up into the canopy vicariously, by climbing the trees or growing as epiphytes, rooted on the upper branches of trees.” This is the most likely description of
Answer (d) & explanation
This describes the tropical rain forest (d). Leaf litter decays fastest where heat and moisture are constant all year: the tropical rain forest. Microbes, fungi and insects break down fallen leaves within weeks, so the soil surface is often almost bare. Little light reaches the floor, so many plants climb (lianas) or grow on branches (epiphytes, such as orchids and ferns) to reach the canopy. Coniferous forests (a) are cold, so litter decays slowly. Dry deciduous forests (b) have a long dry season. Mangroves (c) are coastal and waterlogged.
Notice that rain forest soils are poor, because nutrients are quickly taken up by plants and washed out by rain. India's rain forests are in the Western Ghats, the North-East and the Andamans.
Answer as per the official UPSC answer key.
The vegetation of savannah consists of grassland with scattered small trees, but extensive areas have no trees. The forest development in such areas is generally kept in check by one or more or a combination of some conditions. Which of the following are such conditions?
- 1. Burrowing animals and termites
- 2. Fire
- 3. Grazing herbivores
- 4. Seasonal rainfall
- 5. Soil properties
Select the correct answer using the code given below.
Answer (c) & explanation
Fire, grazing and seasonal rainfall keep savannahs open (c). Savannahs are grasslands with scattered trees. Item 2 is right: frequent fires in the dry season kill young trees, while grasses regrow from their roots. Item 3 is right: grazing and browsing animals, such as zebras, antelopes and elephants, eat young trees and shrubs. Item 4 is right: seasonal rainfall, with a long dry season, limits tree growth. Items 1 and 5 can play a part locally, but they are not the standard explanation, and only option (c) groups the three main conditions.
Notice that the largest savannahs are in Africa, such as the Serengeti. In South America they are called llanos and campos. India's tropical grasslands include the Banni of Kachchh.
Answer as per the official UPSC answer key.
Consider the following statements :
- Statement 1 : The United Nations Capital Development Fund (UNCDF) and the Arbor Day Foundation have recently recognized Hyderabad as 2020 Tree City of the World.
- Statement 2 : Hyderabad was selected for the recognition for a year following its commitment to grow and maintain the urban forests.
Which one of the following is correct in respect of the above statements?
Answer (d) & explanation
Statement 1 is wrong, statement 2 is right (d). Statement 1 is wrong: Hyderabad was named a Tree City of the World for 2020, but the programme is run by the Food and Agriculture Organization (FAO) with the Arbor Day Foundation, not the UNCDF. Statement 2 is right: Hyderabad was recognised for its commitment to growing and maintaining urban trees and forests, helped by the Telangana government's Haritha Haram greening programme.
Notice the five standards for the title: assigning responsibility for trees, setting rules, keeping an inventory, allotting resources, and holding a celebration of trees. Mumbai later joined the list. Notice too the Nagar Van Yojana (2020), which aims to create urban forests in Indian cities.
the city and year are correct; only the UN body is swapped.
Answer as per the official UPSC answer key.
Biodiversity and species 3
Which one of the following is used in preparing a natural mosquito repellent?
Answer (c) & explanation
Lemongrass is used in natural mosquito repellent (c). Lemongrass oil contains citronella-like compounds such as citral, which keep mosquitoes away, and it is used in creams, sprays and candles. Option (a) is wrong: Congress grass (Parthenium) is a harmful, invasive weed that causes allergies and skin problems. Option (b) is wrong: elephant grass is a tall grass grown as fodder and habitat for animals like rhinos. Option (d) is wrong: nut grass is a common weed of farms.
Notice that India is a major producer of lemongrass oil, and the CSIR Aroma Mission promotes it, especially in dry and degraded lands. Other natural repellents include neem and citronella oil.
Answer as per the official UPSC answer key.
Consider the following animals :
- 1. Hedgehog
- 2. Marmot
- 3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
Answer (d) & explanation
The hedgehog and pangolin roll up (d). Item 1 is right: a hedgehog curls into a tight ball of spines when threatened, hiding its soft belly and face. Item 3 is right: a pangolin rolls into a ball of hard, overlapping scales made of keratin, which even lions find hard to break. Item 2 is wrong: a marmot is a large ground squirrel of mountains; it gives a loud whistle to warn others and runs into its burrow.
Notice that the pangolin is the world's most trafficked mammal, hunted for its scales and meat. India has the Indian pangolin and the Chinese pangolin, both in Schedule I. The Himalayan marmot lives in Ladakh and Sikkim.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Moringa (drumstick tree) is a leguminous evergreen tree.
- 2. Tamarind tree is endemic to South Asia.
- 3. In India, most of the tamarind is collected as minor forest produce.
- 4. India exports tamarind and seeds of moringa.
- 5. Seeds of moringa and tamarind can be used in the production of biofuels.
Which of the statements given above are correct?
Answer (b) & explanation
Statements 3, 4 and 5 are correct (b). Statement 1 is wrong: moringa (drumstick) belongs to its own family, Moringaceae, not the legumes, and it is deciduous, shedding its leaves in the dry season. Statement 2 is wrong: tamarind came from tropical Africa, so it is not endemic to South Asia. Statement 3 is right: most Indian tamarind is gathered from forests and village trees as minor forest produce. Statement 4 is right: India exports both tamarind and moringa seeds. Statement 5 is right: the seed oils of both can be used to make biofuel.
Notice that India is the world's largest producer of moringa. Tamarind is among the items under MSP for minor forest produce, run through TRIFED.
tamarind is so Indian in the kitchen that "endemic" feels right.
Answer as per the official UPSC answer key.
Climate change and international conventions 2
What is blue carbon?
Answer (a) & explanation
Blue carbon is carbon captured by oceans and coastal ecosystems (a). Blue carbon is the carbon stored by ocean and coastal ecosystems, mainly mangroves, salt marshes and seagrass meadows. Area for area, they lock away carbon much faster than land forests and keep it in their waterlogged soils for centuries. Option (b) describes green carbon, held in land forests and soils. Option (c) describes fossil carbon in petroleum and natural gas, sometimes called brown or black carbon. Option (d) describes carbon already in the atmosphere, mostly as CO₂.
Notice the MISHTI scheme (2023) for planting mangroves along India's coasts. Sundarbans is the world's largest mangrove forest. Losing these habitats releases their stored carbon.
Answer as per the official UPSC answer key.
With reference to the ‘New York Declaration on Forests’, which of the following statements are correct?
- 1. It was first endorsed at the United Nations Climate Summit in 2014.
- 2. It endorses a global timeline to end the loss of forests.
- 3. It is a legally binding international declaration.
- 4. It is endorsed by governments, big companies and indigenous communities.
- 5. India was one of the signatories at its inception.
Select the correct answer using the code given below.
Answer (a) & explanation
Statements 1, 2 and 4 are correct (a). Statement 1 is right: the New York Declaration on Forests came out of the UN Climate Summit in September 2014. Statement 2 is right: it set a global timeline to halve natural forest loss by 2020 and end it by 2030. Statement 4 is right: it was endorsed by governments, big companies, NGOs and indigenous groups. Statement 3 is wrong: it is a voluntary, non-binding declaration. Statement 5 is wrong: India did not sign it at its launch.
Notice the later Glasgow Leaders' Declaration on Forests (COP26, 2021), which again pledged to end deforestation by 2030; India did not sign that either. Bonn Challenge targets land restoration.
"declaration" plus "legally binding" is a contradiction you can spot.
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Answer as per the official UPSC answer key.
Pollution, environmental laws and green technology 7
‘R2 Code of Practices’ constitutes a tool available for promoting the adoption of
Answer (a) & explanation
R2 promotes responsible electronics recycling (a). R2, short for "Responsible Recycling", is a certification standard for firms that repair, refurbish and recycle electronics. It covers the safe handling of e-waste, data security when old devices are wiped, worker health and safety, and tracking of materials through the recycling chain. Option (b) is a trap: the "R" stands for recycling, not Ramsar. Option (c) is wrong: it does not deal with crops on degraded land. Option (d) is wrong: it is not an EIA tool.
Notice India's E-Waste (Management) Rules, 2022, based on Extended Producer Responsibility (EPR). India is among the world's top three e-waste producers, after China and the US.
Answer as per the official UPSC answer key.
Why is there a concern about copper smelting plants?
- 1. They may release lethal quantities of carbon monoxide into environment.
- 2. The copper slag can cause the leaching of some heavy metals into environment.
- 3. They may release sulphur dioxide as a pollutant.
Select the correct answer using the code given below.
Answer (b) & explanation
Slag leaching and sulphur dioxide are the concerns (b). Statement 2 is right: the leftover copper slag can leach heavy metals such as arsenic and lead into soil and water. Statement 3 is right: most copper ores are sulphides, so smelting gives off sulphur dioxide, which causes acid rain and breathing problems. Statement 1 is wrong: carbon monoxide is not a major pollutant from copper smelters; it comes mostly from incomplete burning in vehicles.
Notice the Sterlite copper plant at Thoothukudi, Tamil Nadu, which was closed in 2018 after protests in which 13 people were killed in police firing. The Supreme Court upheld the closure in 2024. Smelters often capture SO₂ to make sulphuric acid.
Answer as per the official UPSC answer key.
With reference to furnace oil, consider the following statements :
- 1. It is a product of oil refineries.
- 2. Some industries use it to generate power.
- 3. Its use causes sulphur emissions into environment.
Which of the statements given above are correct?
Answer (d) & explanation
All three statements are correct (d). Statement 1 is right: furnace oil is a heavy, dark fuel left after the lighter fractions, such as petrol and diesel, are taken out at an oil refinery. Statement 2 is right: factories burn it in boilers, furnaces and generators to make heat and power. Statement 3 is right: it is high in sulphur, so burning it releases sulphur dioxide.
Notice that the Supreme Court banned furnace oil and pet coke in Delhi-NCR in 2017 to fight air pollution. Ships face similar limits: the IMO 2020 rule cut sulphur in marine fuel to 0.5%. India moved to BS-VI fuel in 2020, with sulphur limited to 10 ppm.
Answer as per the official UPSC answer key.
Magnetite particles, suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following?
- 1. Brakes of motor vehicles
- 2. Engines of motor vehicles
- 3. Microwave stoves within homes
- 4. Power plants
- 5. Telephone lines
Select the correct answer using the code given below.
Answer (b) & explanation
Vehicle brakes, engines and power plants produce magnetite (b). Magnetite is a magnetic iron oxide. Its tiny nanoparticles come from combustion and friction. Item 1 is right: brake wear grinds off iron particles. Item 2 is right: vehicle engines release them in exhaust. Item 4 is right: burning coal and other fuels in power plants produces them. Items 3 and 5 are wrong: microwave ovens and telephone lines give off no such particles.
Notice the 2016 study (Maher and others) that found magnetite particles in human brain tissue and linked them to air pollution, raising concern about Alzheimer's disease. Such particles fall within PM2.5, which the National Clean Air Programme (2019) aims to reduce.
Answer as per the official UPSC answer key.
The ‘Common Carbon Metric’, supported by UNEP, has been developed for
Answer (a) & explanation
It assesses the carbon footprint of building operations (a). The Common Carbon Metric was developed by UNEP's Sustainable Buildings and Climate Initiative (UNEP-SBCI). It gives one standard way to measure the energy use and greenhouse gas emissions of buildings in operation, so that buildings anywhere in the world can be compared and reported on the same basis. Option (b) is wrong: it is not for farm carbon trading. Option (c) is wrong: national footprints are reported through UNFCCC inventories. Option (d) is wrong: it does not measure global fossil fuel use.
Notice that buildings account for nearly 40% of global energy-related emissions. India's tools include the Energy Conservation Building Code (ECBC) and the GRIHA green rating system.
Answer as per the official UPSC answer key.
Bisphenol A (BPA), a cause of concern, is a structural/key component in the manufacture of which of the following kinds of plastics?
Answer (b) & explanation
BPA is a key component of polycarbonate (b). Bisphenol A is the building block of hard, clear polycarbonate plastic, used in water bottles and food containers, and of epoxy resins that line food cans. It can leach into food and drinks, especially when heated, and acts like the hormone oestrogen, making it an endocrine disruptor. Low-density polyethylene (a) is used in bags. PET (c) is used in most soft-drink bottles. PVC (d) is used in pipes. None of them is built from BPA.
Notice that India, through the BIS, banned BPA in baby feeding bottles in 2015. Phthalates are another group of plastic chemicals that disrupt hormones.
Answer as per the official UPSC answer key.
‘Triclosan’, considered harmful when exposed to high levels for a long time, is most likely present in which of the following?
Answer (d) & explanation
Triclosan is most likely in toiletries (d). Triclosan is an antibacterial and antifungal agent added to soaps, toothpastes, deodorants, hand washes and some cosmetics. Long exposure at high levels is linked to hormone disruption, especially of thyroid hormones, and to germs becoming resistant to antibiotics. It also builds up in rivers and harms aquatic life. It is not used in food preservatives (a), fruit-ripening agents (b) such as calcium carbide or ethylene, or in reused plastic containers (c).
Notice that the US FDA banned triclosan in consumer antiseptic hand washes in 2016. Notice related concerns: antimicrobial resistance (AMR), which India tackles under its National Action Plan on AMR.
Answer as per the official UPSC answer key.
All years by topic
Every question from 2011 to 2026, grouped by syllabus topic, with year-wise trends.