UPSC Prelims 2024 Environment questions: topic-wise weightage

The Congo Basin has the world's largest tropical peatland (b). The Cuvette Centrale peatland in the Congo Basin, spread across the Republic of Congo and the DR Congo, was mapped only in 2017. It is the largest tropical peatland known, storing about 29 billion tonnes of carbon, roughly three years of the world's fossil-fuel emissions. Peat is waterlogged, half-rotted plant matter; if drained or burnt, it releases that carbon. The Amazon (a) has peatlands too, but smaller. The Kikori (c) in Papua New Guinea and the Rio de la Plata (d) are not the largest.

Notice the threats: plans for oil drilling and farming. Indonesia's peat fires of 2015, from forest clearing for palm oil, showed how fast peat can release carbon.

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The fig has a unique relationship with its fig wasp (a). Each fig species is pollinated by its own tiny fig wasp. The female wasp enters the closed fig, called a syconium, through a small opening, pollinates the flowers inside, and lays her eggs there. Her young grow inside the fig, and the new females fly off carrying pollen to another fig. Neither partner can complete its life cycle without the other. This one-to-one mutualism is a classic example of coevolution. Mahua (b), sandalwood (c) and silk cotton (d) are pollinated by many animals, such as bats, birds and insects.

Notice why figs matter: they fruit all year and feed many animals, so they are called keystone species in tropical forests. India's banyan and peepal are figs.

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Parasitoids are found in three of the five (b). A parasitoid lives in or on a host as a larva, feeds on it and finally kills it, unlike a true parasite, which usually keeps its host alive. Most parasitoids are wasps (item 5) and flies (item 3), such as tachinid flies. A few carabid (ground) beetles (item 1) have parasitoid larvae. Item 2 is wrong: centipedes are predators. Item 4 is wrong: termites feed on dead wood and plant matter.

Notice their use in farming: parasitoid wasps such as Trichogramma are released to control crop pests like the sugarcane borer and cotton bollworm. This biological control cuts the need for chemical pesticides and is part of integrated pest management.

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All three belong to the pea family (c). The pea family, Fabaceae or the legumes, bears seeds in pods and has root nodules, where Rhizobium bacteria fix nitrogen from the air. Groundnut (item 1) is a legume, though it ripens its pods underground. Horse-gram (item 2) is a hardy pulse grown in dry areas of the south. Soybean (item 3) is a legume, even though, like groundnut, it is used mainly as an oilseed in India. So options (a), (b) and (d) are wrong.

Notice why legumes matter: they enrich the soil with nitrogen, so farmers rotate or intercrop them with cereals. India is the world's largest producer and consumer of pulses. 2016 was the UN's International Year of Pulses.

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UPSC dropped this question, so no answer was counted. The facts are still worth knowing. Statement II is wrong: the Indian flying fox is a large fruit bat; it eats fruit and nectar, not blood. It helps pollinate flowers and spread seeds. Statement I was the problem: the bat was listed as vermin in Schedule V of the 1972 Act, but the 2022 amendment removed the vermin schedule altogether, cutting the schedules to four. That change made Statement I unclear, and the question was dropped.

Notice that only three bat species in the world feed on blood, the vampire bats of Latin America. Fruit bats came into the news during Nipah virus outbreaks in Kerala, since they carry the virus naturally.

UPSC dropped this question from evaluation; there is no official answer.

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All three are insects (c). Cicadas are known for their loud summer calls, made by males to attract mates; some species spend 13 or 17 years underground as young. Froghoppers, or spittlebugs, are known for the frothy "cuckoo spit" their young make on plants to hide in, and the adults are among the best jumpers in the animal world. Pond skaters, or water striders, walk on water using surface tension and water-repelling hairs on their legs. None of them is a bird (a), fish (b) or reptile (d).

Notice the shared trait: all three are true bugs (Hemiptera), with mouthparts made for sucking plant sap or prey fluids. Like all insects, they have six legs and three body parts.

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None of the pairs is correctly matched (d). UPSC shuffled the pairs. Pair 1 is wrong: the indri, the largest living lemur, is found only in Madagascar, not Brazil. Pair 2 is wrong: elk are large deer of the northern forests of North America and Eurasia, not tropical Indonesia. Pair 3 is wrong: the bonobo, a great ape close to the chimpanzee, lives only in the DR Congo, south of the Congo river, not Madagascar.

Notice the theme of endemism: species found in only one place. Madagascar split from Africa and India long ago, so about 90% of its wildlife, including all lemurs, is found nowhere else. Indonesia's famous endemics are the Komodo dragon and the orangutan.

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Statements 1 and 2 are correct (a). Statement 1 is right: lions have no fixed breeding season; they can mate at any time of the year, and lionesses in a pride often give birth around the same time. Statement 2 is right: cheetahs cannot roar, unlike lions, tigers, leopards and jaguars; they purr, chirp and hiss, because their voice box is built differently. Statement 3 is wrong: male leopards do mark their territory, by spraying urine, scraping trees and leaving scat, just as lions do.

Notice India's link: Project Cheetah brought African cheetahs to Kuno National Park, Madhya Pradesh, in 2022, the first intercontinental move of a large wild carnivore. The Asiatic lion survives only in Gir, Gujarat.

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All three have poisonous species (c). Item 1 is right: monarch butterflies store toxins from the milkweed plants they eat as caterpillars, so birds that eat them get sick; their bright colours warn predators. Item 2 is right: pufferfish carry tetrodotoxin, a deadly nerve poison; in Japan, only licensed chefs may prepare it as fugu. Item 3 is right: the bright poison dart frogs of South America are among the most toxic animals on Earth; tribes used their poison on darts.

Notice the term aposematism: bright warning colours that advertise poison. Some harmless species copy them, called Batesian mimicry. Note the difference: poisonous animals harm you when eaten or touched, while venomous animals, such as snakes, inject toxin.

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Only one of them is native to India (a). Item 3 is right: red sanders (Pterocarpus santalinus) is native to India, found only in the southern Eastern Ghats of Andhra Pradesh, especially the Seshachalam hills. It is Endangered because of heavy smuggling for its deep red wood, prized in China and Japan. Item 1 is wrong: cashew came from Brazil. Item 2 is wrong: papaya came from Central America. Both were brought to India by the Portuguese in the 16th century.

Notice other crops the Portuguese brought: chilli, potato, tomato, tobacco, pineapple and groundnut, all from the Americas. Today India is a top producer of cashew and the largest producer of papaya. Red sanders is also listed in CITES Appendix II.

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100 Million Farmers is a platform for net-zero, nature-positive food systems (a). 100 Million Farmers is a World Economic Forum platform. It aims to move food and water systems towards net-zero emissions and nature-positive farming, while making farmers more resilient and better paid, by bringing companies, governments and farmer groups together. Option (b) describes an organic livestock network, not this. Option (c) describes a blockchain fertiliser trading platform. Option (d) describes support for Farmer Producer Organisations and market access. It is about climate-friendly farming, not trading or marketing.

Notice India's matching efforts: natural farming missions, the PM-PRANAM scheme to cut chemical fertiliser use, and the National Mission on Natural Farming (2024). Farming produces about a fifth of global greenhouse gases.

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Fossil-fuel power plants are the largest source of sulphur dioxide (d). Sulphur dioxide (SO₂) comes mainly from burning sulphur-rich coal and oil. The US EPA names power plants and other industrial facilities that burn fossil fuels as the largest source. Option (a) is wrong: locomotives add only a small share. Option (b) is wrong: ships burning heavy fuel oil add some, but less. Option (c) is wrong: metal smelting from ores is a smaller source.

Notice the effects: SO₂ causes acid rain and breathing problems, and forms fine sulphate particles. India told coal plants to fit flue-gas desulphurisation (FGD) units, but deadlines have been pushed back many times, and in 2025 most plants were exempted. India is a top SO₂ emitter.

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All three statements are correct (d). PFAS, or per- and polyfluoroalkyl substances, are used in non-stick pans, stain- and water-proof fabrics, firefighting foams and grease-proof food wrappers. Statement 1 is right: they now turn up in drinking water, food and food packaging almost everywhere. Statement 2 is right: their carbon-fluorine bond is one of the strongest in chemistry, so they hardly break down: hence the name "forever chemicals". Statement 3 is right: they build up in the bodies of animals and people over time, called bioaccumulation.

Notice the health risks: links to some cancers, thyroid problems and weakened immunity. The USA set its first legal limits for PFAS in drinking water in 2024, and the Stockholm Convention has listed several PFAS for elimination.

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Both statements are correct and II explains I (a). Statement I is right: discarded chewing gum is a major source of litter and pollution: spat-out gum sticks to streets and pavements for years, and is costly to clean. Statement II is right and explains it: most modern gum bases are synthetic polymers such as polyvinyl acetate and polyisobutylene, which are plastics, in place of the old natural chicle from the sapodilla tree. These do not break down, so gum stays in the environment.

Notice that Singapore has banned the sale of most chewing gum since 1992. Gum also adds to microplastics, and studies have found that chewing it can release microplastic particles into saliva. Some makers are going back to natural, biodegradable gum bases.

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Only statement 2 is correct (a). Statement 1 is wrong: the World Toilet Organization is a non-profit founded in Singapore in 2001 by Jack Sim, not a UN agency. Statement 2 is right: it started the World Toilet Summit, the World Toilet College and World Toilet Day on 19 November, which the UN adopted as an official day in 2013. Statement 3 is wrong: it campaigns, trains and raises awareness; it is not a funding body that gives grants to countries.

Notice India's Swachh Bharat Mission (2014), which built over 10 crore toilets and declared rural India open defecation free in 2019. Its second phase, ODF Plus, focuses on waste management. SDG 6 aims at sanitation for all by 2030.

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The exhaust emission is water vapour (d). A fuel cell combines hydrogen with oxygen from the air to make electricity, which runs the vehicle's motor. The only by-product is water, which leaves the exhaust as vapour. There is no carbon dioxide or smoke. Option (a) is wrong: hydrogen peroxide is not produced. Option (b) is wrong: hydronium ions exist only in water solutions, not as an exhaust. Option (c) is wrong: oxygen is used up, not released.

Notice India's trials: hydrogen fuel cell buses run in Leh and Delhi, and Toyota's Mirai car was tested here. The catch is cost: making green hydrogen and building filling stations is expensive. Indian Railways is also testing a hydrogen train on the Jind–Sonipat route.

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Membrane bioreactors are a wastewater treatment technology (d). A membrane bioreactor treats sewage in two steps in one unit. First, microbes break down the dirt and organic matter, as in normal treatment. Then a fine membrane filters out solids, bacteria and even some viruses. The clean water can be reused for gardens, industry or toilet flushing. It is compact, so it is popular where land is short, such as cities and apartment blocks. Options (a), (b) and (c), about IVF, nanomedicine and vaccines, do not fit.

Notice India's need: cities treat only part of their sewage, and the Namami Gange and AMRUT schemes fund new plants. Reusing treated water is key in water-stressed cities like Chennai and Bengaluru.

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All four can be used to make Sustainable Aviation Fuel (c). Sustainable Aviation Fuel (SAF) is jet fuel made from non-fossil carbon, so it can cut lifecycle emissions by up to 80%. Item 2 is right: corn grain gives ethanol, which can be turned into jet fuel by the alcohol-to-jet route. Items 1, 3 and 4 are right: crop residues, sewage sludge and wood mill waste can all be converted, through processes like gasification and pyrolysis. Used cooking oil is another common feedstock.

Notice India's targets: 1% SAF blending in international flights by 2027 and 2% by 2028. India's first SAF-blended commercial flight flew in 2023. The Global Biofuels Alliance, launched at the G-20 in New Delhi, supports such fuels.

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