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

Detailed Explanation:

Correct Answer: ✅ Option 3

At COP28, India did not sign the Declaration on Climate and Health. India's concern was not about the objective of climate-resilient healthcare, but about the practical implications of rapid decarbonization in a developing country where ensuring reliable and accessible healthcare remains a priority.

✅ Statement I is Correct: India refrained from signing the COP28 Declaration on Climate and Health.

❌ Statement II is Incorrect: The declaration is voluntary and non-binding. Signing it does not create a legal obligation to decarbonize the health sector.

✅ Statement III is Correct: India expressed concerns that aggressive decarbonization requirements could affect the resilience, accessibility, and reliability of healthcare services, especially in resource-constrained settings.

✅ Statement III explains Statement I: Concerns regarding healthcare resilience and developmental priorities contributed to India's decision not to sign the declaration.

❌ Statement II does not explain Statement I: Since the declaration is not legally binding, this statement is factually incorrect.

Short Notes: COP28 Declaration on Climate and Health

• The declaration was launched at COP28 (Dubai, 2023).

• It highlights the link between climate change and public health.

• The declaration is voluntary and non-binding.

• It encourages countries to build climate-resilient and sustainable health systems.

• More than 120 countries supported the declaration.

• India did not sign due to concerns over healthcare accessibility and developmental priorities.

• Climate change increases risks from heatwaves, diseases, floods, and extreme weather events.

Detailed Explanation:

Correct Answer: ✅ Option 1

Article 6 of the Paris Agreement provides a framework for international cooperation in achieving climate goals. It covers both market-based approaches (carbon markets) and non-market approaches, making it one of the most discussed and important provisions of the Paris Agreement.

✅ Statement I is Correct: Article 6 is frequently discussed because it establishes mechanisms through which countries can cooperate to achieve their climate commitments.

✅ Statement II is Correct: Article 6 lays down the framework for international carbon markets, including the transfer and trading of carbon credits.

✅ Statement III is Correct: Article 6 also promotes non-market approaches such as technology transfer, capacity building, policy coordination, and sustainable development cooperation.

✅ Statement II explains Statement I: Carbon markets are a major reason why Article 6 receives significant global attention.

✅ Statement III explains Statement I: Non-market cooperation mechanisms are also central to climate negotiations and sustainable development discussions.

Short Notes: Article 6 of the Paris Agreement

• Article 6 focuses on international cooperation to achieve climate targets.

• It allows countries to trade carbon credits through market mechanisms.

• Article 6.2 deals with bilateral and multilateral carbon trading.

• Article 6.4 establishes a UN-supervised global carbon market mechanism.

• Article 6.8 promotes non-market approaches for climate action.

• It aims to reduce the cost of achieving Nationally Determined Contributions (NDCs).

• Proper implementation helps prevent double counting of emission reductions.

Detailed Explanation:

Correct Answer: ✅ Option 2

The cement industry is a major contributor to global carbon emissions, accounting for roughly 5–8% of global CO₂ emissions. While both limestone and clay are essential raw materials in cement production, the primary source of CO₂ emissions is the calcination of limestone during clinker manufacturing.

✅ Statement I is Correct: Cement manufacturing contributes more than 5% of global CO₂ emissions, mainly due to clinker production and energy consumption.

✅ Statement II is Correct: Silica-bearing clay is mixed with limestone to provide silica, alumina, and iron oxides required for cement production.

✅ Statement III is Correct: During clinker production, limestone (CaCO₃) is heated and converted into lime (CaO), releasing large amounts of CO₂.

❌ Statement II does not explain Statement I: Mixing clay with limestone is a raw-material requirement and is not the direct cause of significant carbon emissions.

✅ Statement III explains Statement I: The conversion of limestone into lime (calcination) releases CO₂ and is the principal reason for high emissions from the cement industry.

Short Notes: Cement Industry and Carbon Emissions

• The cement industry contributes about 5–8% of global CO₂ emissions.

• The main raw materials are limestone and clay.

• Clinker is the intermediate product used to manufacture cement.

• Calcination reaction: CaCO₃ → CaO + CO₂.

• Around 60% of cement emissions come from the calcination process.

• The remaining emissions mainly come from fuel combustion in kilns.

• Low-carbon cement and carbon capture technologies are being developed to reduce emissions.

Detailed Explanation:

Correct Answer: ✅ Option 3 (All the three)

Many common items contain plastic materials, even when they do not appear to be made of plastic. Cigarette filters, modern eyeglass lenses, and car tyres all contain synthetic polymer-based materials that qualify as plastics or plastic-derived products.

✅ I. Cigarette Butts – Correct: Cigarette filters are primarily made of cellulose acetate, a synthetic plastic polymer.

✅ II. Eyeglass Lenses – Correct: Most modern eyeglass lenses are made from plastics such as polycarbonate or CR-39 resin, rather than glass.

✅ III. Car Tyres – Correct: Tyres contain synthetic rubber and other polymer-based materials derived from petrochemicals, which are forms of plastic.

Short Notes: Plastics in Everyday Life

• Cellulose acetate used in cigarette filters is a type of plastic.

• Most modern eyeglass lenses are made from polycarbonate due to its light weight and impact resistance.

• Car tyres contain both natural rubber and synthetic polymers.

• Synthetic rubber is produced from petroleum-based chemicals.

• Plastic waste can persist in the environment for hundreds of years.

• Cigarette butts are among the most common forms of plastic litter worldwide.

• Microplastics can be generated from the wear and tear of vehicle tyres.

Detailed Explanation:

Correct Answer: ✅ Option 1 — The Asian Development Bank (ADB)

The Asian Development Bank launched the Nature Solutions Finance Hub for Asia and the Pacific to mobilize investments for nature-based solutions (NbS). The initiative aims to address climate change, biodiversity loss, and ecosystem degradation by supporting projects that use natural systems for environmental resilience.

✅ Option 1 is Correct: ADB launched the Nature Solutions Finance Hub for Asia and the Pacific.

❌ Option 2 is Incorrect: The Asian Infrastructure Investment Bank did not launch this initiative.

❌ Option 3 is Incorrect: The New Development Bank is not associated with this hub.

❌ Option 4 is Incorrect: The International Bank for Reconstruction and Development did not launch the Nature Solutions Finance Hub.

Short Notes: Nature-Based Solutions (NbS)

• Nature-based Solutions use natural ecosystems to address environmental challenges.

• Examples include mangrove restoration, afforestation, wetland conservation, and watershed management.

• NbS help in climate mitigation, climate adaptation, and biodiversity conservation.

• The ADB Nature Solutions Finance Hub focuses on Asia-Pacific countries.

• It aims to mobilize public and private finance for environmental projects.

• Healthy ecosystems provide services such as carbon sequestration, flood control, and water purification.

• NbS are increasingly recognized as cost-effective climate solutions.

Detailed Explanation:

Correct Answer: ✅ Option 1

Activated carbon is one of the most widely used adsorbents in water and wastewater treatment. Its effectiveness comes from its highly porous structure and enormous surface area, while its low-cost production from carbon-rich wastes makes it an attractive and sustainable pollution-control material.

✅ Statement I is Correct: Activated carbon is extensively used to remove pollutants from industrial effluents and contaminated water through adsorption.

✅ Statement II is Correct: Activated carbon has a very large surface area and strong adsorption capacity, enabling it to capture heavy metals and other pollutants efficiently.

✅ Statement III is Correct: Activated carbon can be produced from agricultural and environmental wastes such as coconut shells, rice husks, sawdust, and other carbon-rich materials.

✅ Statement II explains Statement I: Its large surface area and adsorption capacity make it effective in pollutant removal.

✅ Statement III explains Statement I: Easy and low-cost production from waste materials makes it an attractive and sustainable remediation tool.

Short Notes: Activated Carbon

• Activated carbon is a highly porous carbon material used as an adsorbent.

• It has a surface area that can exceed 1,000 m²/g.

• Used in water purification, air filtration, and wastewater treatment.

• Effective in removing heavy metals, dyes, pesticides, and organic pollutants.

• Common raw materials include coconut shells, wood, coal, and agricultural residues.

• Works mainly through the process of adsorption, not absorption.

• It is widely used in environmental remediation and pollution control.

Detailed Explanation:

Answer: Option 4 — Wastewater treatment technologies

Membrane Bioreactors (MBRs) are advanced wastewater treatment systems that combine conventional biological treatment processes with membrane filtration (microfiltration or ultrafiltration). They are highly efficient in removing contaminants, producing high-quality effluent, and require less space compared to traditional treatment methods. MBRs are widely used in municipal and industrial wastewater treatment applications due to their superior performance in removing suspended solids, pathogens, and organic pollutants.

📝 Short Notes: Membrane Bioreactors (MBRs)

• Technology: Combines biological degradation with membrane filtration in a single unit
• Membrane Types: Uses microfiltration (MF) or ultrafiltration (UF) membranes with pore sizes of 0.1-0.4 microns
• Advantages: High effluent quality, smaller footprint, complete retention of biomass, and better pathogen removal
• Applications: Municipal wastewater treatment, industrial effluent treatment, water reuse and recycling
• Limitations: Higher capital and operational costs, membrane fouling issues, energy-intensive operation
• Environmental Significance: Enables water reuse, reduces pollution load, and supports circular economy in water management

Detailed Explanation:

Answer: Option 1 — 1 and 2 only

This question tests knowledge about the behavioral characteristics of big cats, particularly lions, cheetahs, and leopards. Understanding territorial marking, breeding patterns, and vocal capabilities of these species is important for wildlife ecology.

✅ Statement 1 – Correct: Lions do not have a strictly defined breeding season and can breed throughout the year, though some seasonal peaks may occur depending on environmental conditions like prey availability and rainfall.

✅ Statement 2 – Correct: Cheetahs lack the specialized larynx structure (hyoid bone apparatus) that allows other big cats to roar; instead, they produce chirps, purrs, and high-pitched calls similar to birds.

❌ Statement 3 – Incorrect: Male leopards, like male lions, actively use scent marking (urine spraying, scraping, and fecal deposits) to proclaim and defend their territories; this statement incorrectly suggests leopards do not engage in territorial scent marking.

📝 Short Notes: Big Cats - Behavioral Characteristics

• Roaring mechanism: Lions, tigers, leopards, and jaguars belong to genus Panthera with a flexible hyoid bone that enables roaring.
• Cheetah distinction: Belongs to genus Acinonyx; has a fixed hyoid bone, preventing roaring but allowing continuous purring.
• Territorial behavior: All big cats use scent marking (urine, feces, gland secretions) and visual cues (scratch marks) to establish territories.
• Breeding patterns: Most big cats can breed year-round, but environmental factors (prey density, climate) influence peak breeding times.

Detailed Explanation:

Answer: Option 2 — Only three

Parasitoid species are organisms that live on or in a host organism, eventually killing it. Among the listed organisms, parasitoid species are found in Carabid beetles (some species are parasitoids of other insects), Flies (Tachinid flies and other Diptera families include numerous parasitoids), and Wasps (Hymenoptera has extensive parasitoid families). Centipedes are predators that directly hunt and kill prey, while termites are herbivorous social insects feeding on plant matter, neither being parasitoids.

📝 Short Notes: Parasitoids

• Definition: Parasitoids are organisms that spend a significant portion of their life attached to or within a single host organism, which they ultimately kill. They differ from true parasites (which usually don't kill the host) and predators (which kill multiple prey).
• Carabid Beetles: While most are predatory, some species (particularly in genera like Brachinus and Lebia) exhibit parasitoid behavior, especially targeting pupae of other insects.
• Flies (Diptera): Tachinidae family is the largest group of parasitoid flies, with over 10,000 species. Other families like Bombyliidae and Sarcophagidae also include parasitoid species.
• Wasps (Hymenoptera): The most diverse parasitoid group, including families like Ichneumonidae, Braconidae, Chalcidoidea, and many others. They parasitize various life stages of insects and other arthropods.
• Centipedes: Chilopoda are venomous predators that actively hunt arthropods and small invertebrates; they do not exhibit parasitoid behavior.
• Termites: Isoptera are eusocial insects primarily feeding on cellulose from wood and plant material; they are decomposers, not parasitoids.

Detailed Explanation:

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

This question tests knowledge about the Indian Flying Fox and the Wild Life (Protection) Act, 1972. While the current model answer states both statements are incorrect, the correct answer as per the original marking was Option 3, indicating Statement-I was considered correct at the time of the exam.

✅ Statement-I – Correct (as per original context): Historically, the Indian Flying Fox was placed under Schedule V (vermin category) in the Wild Life (Protection) Act, 1972, before the 2022 amendments abolished this schedule.

❌ Statement-II – Incorrect: The Indian Flying Fox (Pteropus medius) is a large frugivorous bat that feeds on fruits, nectar, and flowers, not on blood. Blood-feeding behavior is characteristic of vampire bats found in Latin America, not fruit bats.

📝 Short Notes: Indian Flying Fox and Wildlife Protection

Detailed Explanation:

Answer: Option 3 — 1, 2, 3 and 4

All four materials listed can serve as feedstock for producing Sustainable Aviation Fuel (SAF). Agricultural residues and wood mill waste are lignocellulosic biomass sources that can be converted through thermochemical or biochemical processes. Corn grain provides fermentable sugars for ethanol production, which can be upgraded to SAF. Wastewater treatment sludge, rich in organic matter, can undergo anaerobic digestion to produce biogas, subsequently convertible to SAF.

✅ Statement 1 – Correct: Agricultural residues (crop stalks, husks, leaves) are viable lignocellulosic biomass sources for SAF production through various conversion pathways.
✅ Statement 2 – Correct: Corn grain contains fermentable sugars that can be converted to ethanol and further processed into SAF via alcohol-to-jet fuel pathways.
✅ Statement 3 – Correct: Wastewater treatment sludge is rich in organic matter and can be converted to biogas through anaerobic digestion, which can then be upgraded to SAF.
✅ Statement 4 – Correct: Wood mill waste (sawdust, wood chips, bark) is a lignocellulosic material convertible to SAF through gasification, pyrolysis, or other thermochemical processes.

📝 Short Notes: Sustainable Aviation Fuel (SAF)

• Definition: SAF is a drop-in replacement for conventional jet fuel, produced from sustainable feedstocks, reducing lifecycle carbon emissions by up to 80%.
• Feedstock Categories: Includes agricultural residues, forestry waste, municipal solid waste, industrial waste, algae, and dedicated energy crops.
• Production Pathways: Major technologies include Fischer-Tropsch synthesis, Hydroprocessed Esters and Fatty Acids (HEFA), Alcohol-to-Jet (ATJ), and gasification.
• Certification: SAF must meet ASTM D7566 standards and can be blended with conventional jet fuel up to 50% (some pathways allow 100%).
• Global Initiatives: ICAO's CORSIA scheme, EU's ReFuelEU Aviation, and US SAF Grand Challenge aim to scale SAF production and adoption.
• Indian Context: India is exploring SAF production from agricultural waste, used cooking oil, and other biomass sources to decarbonize aviation sector.

Detailed Explanation:

Answer: Option 3 — All three

All three groups mentioned in the question—butterflies, fish, and frogs—have poisonous species among them. Butterflies like the Monarch sequester toxins from their larval diet of milkweed, making them poisonous to predators. Many fish species such as pufferfish, lionfish, and stonefish possess deadly venom or toxins. Poison dart frogs are classic examples of amphibians that secrete potent toxins through their skin as a defense mechanism.

📝 Short Notes: Poisonous Species in Different Animal Groups

• Poisonous Butterflies: Monarch butterflies accumulate cardiac glycosides from milkweed plants during their caterpillar stage, making them toxic to birds and other predators. Other examples include the Pipevine Swallowtail.
• Poisonous Fish: Pufferfish contain tetrodotoxin, a neurotoxin deadly to humans. Lionfish and stonefish have venomous spines. Stingrays possess venomous barbs on their tails.
• Poisonous Frogs: Poison dart frogs (family Dendrobatidae) of Central and South America secrete alkaloid toxins through their skin. The Golden Poison Frog is one of the most toxic vertebrates on Earth.
• Mechanism of Toxicity: Some species produce toxins endogenously (within their bodies), while others sequester them from their diet (like Monarch butterflies and poison dart frogs).
• Purpose of Poison: These toxins serve primarily as defense mechanisms against predators, advertised through warning coloration (aposematism) in many cases.

Detailed Explanation:

Answer: Option 1 — Fig

Fig trees share a unique obligate mutualistic relationship with fig wasps, which are the only insects capable of pollinating fig flowers. The fig wasp enters the enclosed syconium (fig fruit structure) through a tiny opening called the ostiole to lay eggs, simultaneously pollinating the internal flowers. This highly specialized relationship is a classic example of coevolution, where both species have evolved together over millions of years, making them entirely dependent on each other for survival and reproduction.

Why other options are incorrect:
❌ Option 2 – Mahua: Mahua (Madhuca indica) is pollinated by various insects including bees, moths, and even bats, not a single specialized pollinator.
❌ Option 3 – Sandalwood: Sandalwood is primarily pollinated by bees and flies; it is a hemiparasitic plant that relies on host trees for nutrients but has no unique insect pollinator.
❌ Option 4 – Silk Cotton: Silk cotton trees are pollinated by bats and birds, not by a specialized insect species.

📝 Short Notes: Fig-Wasp Mutualism

• Obligate Mutualism: Both fig and fig wasp are entirely dependent on each other—figs cannot reproduce without fig wasps, and fig wasps cannot reproduce without figs.
• Syconium Structure: The fig is not a true fruit but a syconium—a hollow, fleshy structure with flowers enclosed inside.
• Pollination Process: Female fig wasps enter through the ostiole (small opening), lay eggs inside ovaries, and pollinate flowers in the process. Male wasps are wingless and mate inside the fig.
• Coevolution: This relationship has evolved over approximately 80 million years, with over 750 species of figs, each typically having its own specialized wasp species.
• Ecological Importance: Figs are keystone species in tropical ecosystems, providing food for numerous animals during lean periods when other fruits are scarce.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements about PFAS (perfluoroalkyl and polyfluoroalkyl substances) are correct. These synthetic chemicals, often called 'forever chemicals', are widely used in consumer products and are characterized by their environmental persistence and bioaccumulation potential.

✅ Statement 1 – Correct: PFAS are widely detected in drinking water, food items, and food packaging materials due to their extensive use in consumer products and their ability to leach into the environment.
✅ Statement 2 – Correct: PFAS are called 'forever chemicals' because the strong carbon-fluorine bond makes them extremely resistant to environmental degradation processes.
✅ Statement 3 – Correct: Due to their persistence, PFAS accumulate in the tissues of animals and humans over time, leading to bioaccumulation and potential health risks.

📝 Short Notes: PFAS (Forever Chemicals)

• Full Form: Perfluoroalkyl and Polyfluoroalkyl Substances
• Nickname: 'Forever Chemicals' due to their extremely persistent nature
• Chemical Structure: Contain strong carbon-fluorine bonds that resist breakdown
• Common Uses: Non-stick cookware, water-repellent fabrics, firefighting foams, food packaging, cosmetics
• Environmental Persistence: Do not degrade naturally; accumulate in soil, water, and air
• Health Concerns: Bioaccumulation leads to potential cancer risk, liver damage, immune system effects, and developmental issues
• Global Concern: Found in blood samples of humans and wildlife worldwide; subject to increasing regulatory scrutiny

Detailed Explanation:

Answer: Option 2 — Congo Basin

The Congo Basin contains the world's largest tropical peatland complex, known as the Cuvette Centrale, which spans approximately 145,000 square kilometres across the Republic of Congo and the Democratic Republic of Congo. This peatland stores about 30 billion tonnes of carbon—equivalent to roughly three years of global fossil fuel emissions—making its preservation critical for climate stability. The destruction of this peatland through drainage or land-use changes would release massive amounts of carbon dioxide, significantly accelerating global climate change.

📝 Short Notes: Major Tropical Peatlands

• Peatlands are wetland ecosystems where waterlogged conditions prevent organic matter from fully decomposing, leading to carbon accumulation over thousands of years
• Tropical peatlands store carbon both in vegetation and in deep peat soils (can be several meters deep)
• Drainage and conversion of peatlands for agriculture releases stored carbon as CO₂ and N₂O
• Protection of peatlands is crucial for climate change mitigation strategies