UPSC CSE Prelims
Environment & Ecology Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 3 — Insects

All three organisms—Cicada, Froghopper, and Pond Skater—are classified as insects belonging to different families within the class Insecta. Cicadas are known for their loud mating calls, froghoppers (spittlebugs) are famous for the foam they produce as nymphs, and pond skaters use surface tension to walk on water.

📝 Short Notes: Classification of Common Insects

• Cicada: Order Hemiptera; known for their distinctive loud buzzing sounds produced by males during mating season; have a long lifecycle with some species emerging every 13-17 years.
• Froghopper (Spittlebug): Order Hemiptera; small jumping insects; nymphs produce foam (cuckoo spit) on plants for protection; adults are powerful jumpers.
• Pond Skater (Water Strider): Order Hemiptera, family Gerridae; use surface tension and hydrophobic legs to walk on water; predators of small aquatic organisms.
• Common Feature: All three belong to Order Hemiptera (true bugs), characterized by piercing-sucking mouthparts and incomplete metamorphosis.
• Ecological Role: These insects play important roles as herbivores, predators, and prey in their respective ecosystems.

Detailed Explanation:

Answer: Option 1 — Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

Chewing gums are a significant source of environmental pollution, and Statement-II directly explains why this is the case.

✅ Statement-I – Correct: Many chewing gums found in the market are considered a source of environmental pollution due to their non-biodegradable nature and improper disposal, leading to persistent litter in public spaces.

✅ Statement-II – Correct: Many chewing gums contain plastic polymers (such as polyisobutylene, polyvinyl acetate, or polyethylene) as their gum base, which makes them non-biodegradable and environmentally persistent.

Explanation: Statement-II explains Statement-I because the presence of plastic-based gum base is the primary reason why chewing gums become environmental pollutants. These synthetic polymers do not decompose naturally and remain in the environment for years, creating cleanup challenges and contributing to plastic pollution.

📝 Short Notes: Chewing Gum and Environmental Pollution

• Gum Base Composition: Modern chewing gums typically use synthetic polymers (plastics) like polyisobutylene and polyvinyl acetate instead of natural chicle latex.
• Non-Biodegradable Nature: These plastic-based gum bases can take years to decades to break down in the environment, persisting as microplastic pollution.
• Urban Pollution: Discarded chewing gum is one of the most common forms of street litter, requiring expensive removal processes (often using chemical solvents or freezing techniques).
• Environmental Impact: Improperly disposed gum contributes to plastic pollution, can harm wildlife if ingested, and creates unsightly stains on pavements and public infrastructure.
• Biodegradable Alternatives: Some companies are now developing plant-based, biodegradable gum alternatives to address environmental concerns.

Detailed Explanation:

Answer: Option 4 — Power plants using fossil fuels

Power plants burning fossil fuels, particularly coal, are the largest source of sulfur dioxide (SO₂) emissions globally according to the EPA. Coal contains high levels of sulfur, and when combusted for electricity generation, it releases substantial amounts of SO₂ into the atmosphere. While ships using bunker fuel, metal extraction processes, and locomotives also contribute to SO₂ emissions, their combined contribution is significantly lower than emissions from fossil fuel-based power generation.

📝 Short Notes: Sulfur Dioxide (SO₂) Emissions

• Primary Source: Coal-fired power plants are responsible for approximately 65-70% of global SO₂ emissions, as coal contains 0.5-3% sulfur by weight.
• Ships: Maritime vessels using heavy bunker fuel (high sulfur content) are the second major source, especially in coastal and port areas; regulations like MARPOL Annex VI now limit sulfur content in marine fuels.
• Metal Smelting: Extraction of metals like copper, zinc, and lead from sulfide ores releases SO₂ during roasting and smelting processes, contributing 5-10% of total emissions.
• Locomotives: Diesel-powered trains contribute minimally to SO₂ emissions due to lower sulfur content in diesel fuel and relatively smaller fuel consumption compared to power plants.
• Environmental Impact: SO₂ causes acid rain, respiratory problems, and contributes to particulate matter (PM2.5) formation; it also damages vegetation and corrodes buildings.
• Control Measures: Flue gas desulfurization (FGD/scrubbers), switching to low-sulfur fuels, and renewable energy transition are key mitigation strategies.

Detailed Explanation:

Answer: Option 4 — None

None of the given country-animal pairs are correctly matched. Each animal mentioned is native to a completely different geographical region than the country paired with it.

❌ Pair 1 – Incorrect: Indri is a lemur species endemic only to Madagascar, not Brazil.
❌ Pair 2 – Incorrect: Elk (Cervus canadensis) are found in North America and parts of Asia, not in Indonesia.
❌ Pair 3 – Incorrect: Bonobo (Pan paniscus) is a great ape found exclusively in the Democratic Republic of Congo, not Madagascar.

📝 Short Notes: Endemic Species and Their Natural Habitats

• Endemic species: Species found exclusively in one geographic location and nowhere else naturally in the world
• Madagascar biodiversity: Island isolation for ~88 million years has led to extraordinary endemic biodiversity, especially lemurs, chameleons, and unique flora
• Conservation importance: Understanding natural habitats is crucial for wildlife conservation and preventing extinction of endemic species

Detailed Explanation:

Answer: Option 1 — Only one

Among the three trees mentioned, only Red Sanders is native to India, specifically endemic to the Eastern Ghats of Andhra Pradesh. Both Cashew and Papaya are exotic species that were introduced to India from the Americas by European traders during the colonial period.

✅ Red Sanders – Native to India: Endemic to the Eastern Ghats, particularly Andhra Pradesh, known for its valuable reddish wood.
❌ Cashew – Not native: Originally from Brazil, introduced to India by Portuguese traders in the 16th century.
❌ Papaya – Not native: Originated in southern Mexico and Central America, brought to India during colonial times.

📝 Short Notes: Native vs. Exotic Trees of India

• Red Sanders (Pterocarpus santalinus): Endemic to India, found exclusively in the Eastern Ghats of Andhra Pradesh and parts of Karnataka. It is listed in CITES Appendix II due to illegal logging and trade. The tree produces valuable red heartwood used in furniture, musical instruments, and traditional medicine.
• Cashew (Anacardium occidentale): Native to Brazil, introduced to Goa by Portuguese colonizers in the 16th century. India is now the world's largest producer and exporter of cashew nuts, with major cultivation in Kerala, Karnataka, Goa, and Maharashtra.
• Papaya (Carica papaya): Originated in tropical Americas (southern Mexico and Central America). Brought to India by Portuguese and Spanish traders. India is now one of the largest producers of papaya globally, cultivated throughout tropical and subtropical regions.
• Other Native Indian Trees: Neem (Azadirachta indica), Banyan (Ficus benghalensis), Peepal (Ficus religiosa), Sal (Shorea robusta), Teak (Tectona grandis), and Sandalwood (Santalum album).
• Other Exotic Trees in India: Eucalyptus (Australia), Pine (temperate regions), Rubber (Brazil), Coffee (Ethiopia), and Tea (China).
• Conservation Concern: Red Sanders is classified as 'Endangered' on the IUCN Red List due to overexploitation for its valuable timber, leading to strict protection measures and anti-smuggling operations.

Detailed Explanation:

Correct Answer: ✅ Option 1

The 100 Million Farmers (100MF) initiative is a global platform launched by the World Economic Forum to accelerate the transition towards net-zero, nature-positive, and resilient food and water systems. It aims to support farmers in adopting sustainable agricultural practices while improving livelihoods and climate resilience.

✅ Statement I is Correct: The initiative focuses on creating net-zero (carbon), nature-positive, and water-resilient agricultural systems.

✅ Statement II is Correct: It aims to enhance farmer resilience, improve productivity, and promote regenerative agriculture practices.

❌ Option B is Incorrect: This describes organizations promoting organic animal husbandry, not the 100 Million Farmers initiative.

❌ Option C is Incorrect: This refers to a blockchain-based fertilizer trading platform, unrelated to 100 Million Farmers.

❌ Option D is Incorrect: While FPOs improve market access, the primary goal of 100 Million Farmers is sustainable agricultural transformation, not merely forming producer organizations.

Short Notes: 100 Million Farmers Initiative

• Launched by the World Economic Forum (WEF).

• Target: Support 100 million farmers by 2030.

• Promotes regenerative and climate-smart agriculture.

• Focuses on net-zero, nature-positive food systems.

• Enhances soil health, biodiversity, and water efficiency.

• Seeks to improve farmer incomes and resilience.

• Encourages public-private partnerships in agriculture.

• Contributes to global climate and sustainability goals.

Detailed Explanation:

Correct Answer: ✅ Option 1 (Statement 2 only)

The World Toilet Organization (WTO) is an international non-profit organization dedicated to improving sanitation and ending the global sanitation crisis through advocacy, awareness, and capacity building.

❌ Statement 1 is Incorrect: The World Toilet Organization is not a United Nations agency. It is an independent international non-profit organization founded in 2001 in Singapore.

✅ Statement 2 is Correct: The organization launched initiatives such as World Toilet Summit, World Toilet College, and played a key role in promoting World Toilet Day to raise awareness about sanitation issues worldwide.

❌ Statement 3 is Incorrect: Its primary role is advocacy, education, networking, and capacity building, not providing grants to countries. Funding sanitation projects is mainly undertaken by governments, development banks, and international agencies.

Short Notes: World Toilet Organization (WTO)

• Established in 2001 in Singapore.

• It is an international non-profit organization, not a UN agency.

• Works to improve global sanitation and hygiene.

• Organizes the World Toilet Summit to discuss sanitation challenges.

• Founded the World Toilet College for sanitation training and capacity building.

• Instrumental in advocating for World Toilet Day (19 November).

• Focuses on awareness, advocacy, partnerships, and knowledge sharing.

• Supports the achievement of SDG 6 (Clean Water and Sanitation).

Detailed Explanation:

Answer: Option 3 — Only three

Hydrofluorocarbons (HFCs) are synthetic compounds primarily used as replacements for ozone-depleting substances. Among the given applications, HFCs are used in aerosols (as propellants), foam agents (for blowing plastic foams), and fire retardants (as clean fire suppressants), but NOT in lubricants.

✅ Aerosols – Correct: HFCs serve as non-flammable propellants in aerosol products like hairsprays, deodorants, and cleaning sprays.
✅ Foam agents – Correct: HFCs are widely used as foam-blowing agents in manufacturing polyurethane and polystyrene foams for thermal insulation.
✅ Fire retardants – Correct: HFCs (such as HFC-227ea) are used as "clean agents" in fire suppression systems, replacing ozone-depleting Halons.
❌ Lubricants – Incorrect: Lubricants are formulated from mineral oils, synthetic hydrocarbons (polyalphaolefins), or esters, not HFCs.

📝 Short Notes: Hydrofluorocarbons (HFCs)

• Nature: Synthetic organic compounds containing hydrogen, fluorine, and carbon atoms; do not contain chlorine.
• Ozone Impact: HFCs do not deplete the ozone layer (unlike CFCs and HCFCs) as they lack chlorine and bromine.
• Climate Impact: Potent greenhouse gases with high Global Warming Potential (GWP), ranging from hundreds to thousands of times that of CO₂.
• Common Uses: Refrigeration and air conditioning, aerosol propellants, foam-blowing agents, fire suppression systems, and solvent applications.
• Regulatory Framework: Controlled under the Kigali Amendment (2016) to the Montreal Protocol, which mandates phased reduction of HFC production and consumption.
• India's Commitment: India ratified the Kigali Amendment in 2021, committing to reduce HFC use by 85% by 2047.
• Alternatives: Natural refrigerants (ammonia, CO₂, hydrocarbons), HFOs (hydrofluoroolefins) with lower GWP.

Detailed Explanation:

Answer: Option 2 — Only two

The question tests knowledge about the behavioral ecology of Indian squirrels. Out of the three statements, two are correct (statements 2 and 3), while statement 1 is incorrect as Indian squirrels are primarily arboreal and build tree nests rather than ground burrows.

❌ Statement 1 – Incorrect: Indian squirrels like the Indian Palm Squirrel (Funambulus) and Malabar Giant Squirrel (Ratufa indica) are arboreal species that build nests (dreys) in tree branches, hollows, or crevices using twigs and leaves, not ground burrows.

✅ Statement 2 – Correct: Indian squirrels exhibit scatter hoarding behavior, burying nuts and seeds in shallow ground locations for later retrieval, which also aids in seed dispersal and forest regeneration.

✅ Statement 3 – Correct: Squirrels are opportunistic omnivores; while their primary diet includes seeds, nuts, fruits, and fungi, they also consume insects, caterpillars, bird eggs, and occasionally small vertebrates.

📝 Short Notes: Indian Squirrels - Ecology & Behavior

• Common Species: Indian Palm Squirrel (Funambulus palmarum), Three-striped Palm Squirrel (F. tristis), Malabar Giant Squirrel (Ratufa indica), and Indian Giant Squirrel (Ratufa macroura)
• Habitat: Predominantly arboreal (tree-dwelling); found in forests, urban parks, gardens, and agricultural landscapes
• Nesting: Build dreys (leaf and twig nests) in tree branches or use tree hollows; do not make ground burrows unlike ground squirrels found in other regions
• Food Storage: Practice scatter hoarding - bury food items in multiple scattered locations rather than one central cache; excellent spatial memory for retrieval
• Diet: Omnivorous - primarily herbivorous (nuts, seeds, fruits, flowers, bark) but also consume insects, bird eggs, and occasionally small animals
• Ecological Role: Important seed dispersers for many tree species; forgotten caches germinate into new plants, aiding forest regeneration
• Conservation Status: Most species are Least Concern, but habitat specialists like the Malabar Giant Squirrel face threats from habitat fragmentation

Detailed Explanation:

Answer: Option 1 — Only one

Among the three fauna listed, only the Malabar Civet is a nocturnal animal, being primarily active during the night. The Lion-tailed Macaque is a diurnal species, active during the day, while the Sambar Deer is crepuscular, most active during dawn and dusk rather than after sunset.

Analysis of Each Species:
🦁 Lion-tailed Macaque: Diurnal primate found in Western Ghats, active during daylight hours.
🐆 Malabar Civet: Nocturnal carnivore endemic to Western Ghats, most active after sunset. ✅
🦌 Sambar Deer: Crepuscular herbivore, most active at dawn and dusk, not strictly nocturnal.

📝 Short Notes: Activity Patterns in Animals

Detailed Explanation:

Answer: Option 2 — Orangutan

Orangutans are highly intelligent great apes known for their remarkable tool-use capabilities. They have been extensively observed using sticks to scrape and extract insects from holes in trees and logs, probe for honey, and even fashion leaves into gloves or napkins. This behavior demonstrates their advanced cognitive abilities and problem-solving skills, making them one of the most tool-proficient non-human primates.

📝 Short Notes: Tool Use in Animals

• Orangutans: Use sticks to extract insects, honey, and seeds; use leaves as umbrellas, gloves, and napkins; found in Borneo and Sumatra.
• Chimpanzees: Use sticks to fish for termites, stones to crack nuts, and leaves as sponges for drinking water.
• Crows: Craft hooked tools from twigs to extract insects; demonstrate advanced problem-solving abilities.
• Sea Otters: Use rocks as anvils to crack open shellfish while floating on their backs.
• Elephants: Use branches to swat flies, scratch themselves, and modify sticks to reach food.
• Dolphins: Use marine sponges to protect their rostrums while foraging on the seabed.

Detailed Explanation:

Answer: Option 3 — All three

Green hydrogen, produced through electrolysis of water using renewable electricity, is expected to play a significant role in decarbonizing all three heavy industries mentioned. It offers a clean alternative to fossil fuels in energy-intensive industrial processes, thereby reducing carbon emissions substantially.

1. Fertilizer plants: Green hydrogen can replace natural gas in ammonia synthesis, which is the primary feedstock for fertilizer production. This eliminates the carbon-intensive steam methane reforming process currently used.

2. Oil refineries: Refineries use hydrogen for hydrocracking and desulfurization processes. Green hydrogen can replace the hydrogen currently produced from fossil fuels, reducing the refinery's carbon footprint.

3. Steel plants: Green hydrogen can replace coal and coke in the direct reduction of iron ore (DRI process), eliminating one of the largest sources of industrial CO₂ emissions. Several pilot projects globally are already testing hydrogen-based steelmaking.

📝 Short Notes: Green Hydrogen and Industrial Decarbonization

• Green Hydrogen: Hydrogen produced via electrolysis of water using electricity from renewable sources (solar, wind, hydro). It is carbon-free if the electricity is 100% renewable.
• Fertilizer Industry: Uses hydrogen to produce ammonia (NH₃) via the Haber-Bosch process. Currently, ~1-2% of global energy and CO₂ emissions come from ammonia production using fossil fuel-derived hydrogen.
• Oil Refining: Refineries consume significant hydrogen for upgrading heavy crude, hydrocracking, and removing sulfur. Green hydrogen can directly substitute fossil-fuel-derived hydrogen.
• Steel Industry: Traditional blast furnace method uses coke (from coal) as a reducing agent. Green hydrogen-based Direct Reduced Iron (DRI) technology can replace this, producing water instead of CO₂.
• National Green Hydrogen Mission (India): Launched in 2023 with ₹19,744 crore outlay to make India a global hub for green hydrogen production and export by 2030.
• Challenges: High production cost, infrastructure development, storage and transportation issues, and scaling up electrolyzer manufacturing capacity.

Detailed Explanation:

Answer: Option 2 — Only two

This question tests understanding of biofilter functions in Recirculating Aquaculture Systems (RAS). Out of three statements, two are correct regarding waste treatment and ammonia conversion, while the statement about phosphorus is incorrect.

✅ Statement 1 – Correct: Biofilters provide waste treatment by removing uneaten fish feed and organic matter, as beneficial bacteria on biofilter media break down these wastes.

✅ Statement 2 – Correct: Biofilters convert toxic ammonia from fish waste to less harmful nitrate through the nitrification process performed by beneficial bacteria (ammonia → nitrite → nitrate).

❌ Statement 3 – Incorrect: Biofilters do not increase phosphorus levels in water; their primary role is waste removal and ammonia conversion, while phosphorus management is handled through feed formulation and water quality control.

📝 Short Notes: Recirculating Aquaculture System (RAS) and Biofilters

• RAS Definition: A technology for farming fish in tanks where water is filtered and recirculated, minimizing water usage and waste discharge.
• Biofilter Function: Core component of RAS that hosts beneficial bacteria for biological filtration and waste treatment.
• Nitrification Process: Two-step bacterial process where Nitrosomonas bacteria convert ammonia (NH₃) to nitrite (NO₂⁻), then Nitrobacter bacteria convert nitrite to nitrate (NO₃⁻).
• Waste Removal: Biofilters remove solid wastes including uneaten feed, fish feces, and other organic matter through bacterial decomposition.
• Phosphorus Management: Controlled through fish feed formulation, mechanical filtration, and water exchange, not through biofilters.
• Benefits of RAS: Water conservation, reduced environmental impact, disease control, and intensive fish production in limited space.

Detailed Explanation:

Answer: Option 3 — Statement-I is correct but Statement-II is incorrect

This question tests knowledge about the biogeographical distribution of marsupials and their ecological adaptations. Statement I correctly identifies that marsupials are not naturally found in India, while Statement II incorrectly restricts their habitat requirements.

✅ Statement I – Correct: Marsupials are indeed not naturally found in India. They are primarily native to Australia (kangaroos, koalas, wombats), the Americas (opossums), and Papua New Guinea. India falls outside the natural distribution range of marsupials.

❌ Statement II – Incorrect: This statement is factually wrong on multiple counts. Marsupials do not require montane grasslands exclusively and can thrive in diverse habitats including forests, deserts, savannas, wetlands, and even urban areas. They also coexist with various predators in their natural habitats (e.g., dingoes in Australia). The claim that they can thrive "only" in montane grasslands with no predators is completely false.

📝 Short Notes: Marsupials - Distribution and Ecology

• Definition: Marsupials are mammals characterized by giving birth to relatively undeveloped young that continue development in a pouch (marsupium).
• Primary Distribution: Australia (~70% of all marsupial species), Americas (opossums), Papua New Guinea, and nearby islands.
• Habitat Diversity: Marsupials occupy varied habitats - rainforests (tree kangaroos), deserts (bilbies), grasslands (kangaroos), forests (koalas), and wetlands (water opossums).
• Examples: Kangaroos, wallabies, koalas, wombats, Tasmanian devils, possums, and opossums.
• Evolutionary Significance: Marsupials represent an ancient mammalian lineage that thrived in Gondwanaland before continental drift isolated populations.
• Indian Context: No native marsupials exist in India due to biogeographical separation and different evolutionary pathways in the Indian subcontinent.

Detailed Explanation:

Answer: Option 1 — The International Union for Conservation of Nature

The Invasive Species Specialist Group (ISSG) is a global network of scientific and policy experts on invasive species, organized under the auspices of the Species Survival Commission (SSC) of the International Union for Conservation of Nature (IUCN). The ISSG develops and maintains the Global Invasive Species Database, which is a comprehensive resource on alien and invasive species that threaten biodiversity and ecosystems worldwide.

📝 Short Notes: IUCN and Its Specialist Groups

• IUCN (International Union for Conservation of Nature): Founded in 1948, it is the world's oldest and largest global environmental organization, working on biodiversity conservation and sustainable use of natural resources.
• Species Survival Commission (SSC): The largest of IUCN's six commissions, comprising over 10,000 experts organized into ~160 Specialist Groups focused on various species and conservation issues.
• Invasive Species Specialist Group (ISSG): Established in 1994, it aims to reduce threats to natural ecosystems and native species by increasing awareness of invasive alien species and providing tools for prevention and management.
• Global Invasive Species Database: Maintained by ISSG, it contains information on over 1,000 invasive species, including their ecology, distribution, impacts, and management strategies.
• IUCN Red List: Another major IUCN initiative that assesses the conservation status of species globally, widely recognized as the most comprehensive inventory of biological diversity.