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

Detailed Explanation:

Answer: Option 2 — Rice

Rice cultivation is the most important anthropogenic source of both methane (CH₄) and nitrous oxide (N₂O) among the given crops. Flooded rice paddies create anaerobic conditions that promote methane production by methanogenic bacteria, which is then released through the rice plants. Additionally, the heavy use of nitrogen-based fertilizers in rice cultivation leads to nitrous oxide emissions when soil microbes convert excess nitrogen that is poorly absorbed by the rice plants.

📝 Short Notes: Greenhouse Gas Emissions from Agriculture

• Methane from Rice: Waterlogged paddy fields create oxygen-depleted (anaerobic) conditions ideal for methanogenic archaea, producing CH₄ that escapes through rice plant stems and soil.
• Nitrous Oxide from Fertilizers: Nitrogen fertilizers undergo microbial processes (nitrification and denitrification) in soil, releasing N₂O, especially when applied in excess.
• Global Warming Potential: CH₄ is 28-34 times more potent than CO₂ over 100 years; N₂O is approximately 265-298 times more potent than CO₂.
• Rice vs Other Crops: Cotton, wheat, and sugarcane are primarily upland crops without prolonged flooding, producing minimal methane. Rice paddies account for ~10-12% of global methane emissions.
• Mitigation Strategies: Alternate wetting and drying (AWD), improved fertilizer management, use of slow-release fertilizers, and development of low-emission rice varieties.

Detailed Explanation:

Answer: Option 3 — Creation of mini forests in urban areas

The Miyawaki method is a unique afforestation technique developed by Japanese botanist Dr. Akira Miyawaki that creates dense, multi-layered native forests in small urban spaces. This method enables the growth of forests 10 times faster, 30 times denser, and with 100 times more biodiversity compared to conventional plantation methods, making it ideal for creating mini forests in urban areas.

📝 Short Notes: Miyawaki Method of Urban Afforestation

• Developer: Dr. Akira Miyawaki, Japanese botanist and professor (since 1980); awarded the Blue Planet Prize in 2006
• Principle: Uses native species of plants in multi-layered plantation to replicate natural forest ecosystems
• Key Features: Grows 10x faster, 30x denser, with 100x more biodiversity than conventional methods
• Area Requirement: Can be implemented in areas as small as 20 square meters
• Success Rate: Over 2,000 forests successfully created worldwide using this method
• Advantages: Works irrespective of soil and climatic conditions; requires minimal maintenance after 2-3 years; improves air quality and urban biodiversity
• Indian Context: Adopted in several Indian cities including Bangalore, Mumbai, Delhi, and Chandigarh for urban greening initiatives

Detailed Explanation:

Answer: Option 2 — 2 and 4 only

Acid rain is caused by the presence of nitrogen oxides (NOₘ) and sulphur dioxide (SO₂) in the atmosphere, which react with water vapor to form nitric acid and sulphuric acid respectively. Carbon monoxide and ozone are pollutants but do not directly contribute to acid rain formation.

✅ Statement 2 – Correct: Nitrogen oxides (NOₓ) react with water and oxygen in the atmosphere to form nitric acid (HNO₃), a primary component of acid rain.
❌ Statement 1 – Incorrect: Carbon monoxide (CO) is a pollutant that contributes to ground-level ozone formation but does not cause acid rain.
❌ Statement 3 – Incorrect: Ozone (O₃) is a secondary pollutant and does not act as a precursor for acid rain formation.
✅ Statement 4 – Correct: Sulphur dioxide (SO₂) reacts with atmospheric moisture to form sulphuric acid (H₂SO₄), the other major component of acid rain.

📝 Short Notes: Acid Rain

• Definition: Acid rain refers to precipitation (rain, snow, fog) with a pH below 5.6, caused by atmospheric pollution.
• Primary Causes: Emissions of sulphur dioxide (SO₂) from coal combustion and nitrogen oxides (NOₓ) from vehicle exhausts and industrial processes.
• Chemical Reactions: SO₂ + H₂O → H₂SO₃ (sulphurous acid) → H₂SO₄ (sulphuric acid); NOₓ + H₂O → HNO₃ (nitric acid).
• Environmental Effects: Acidification of lakes and streams, damage to forests, corrosion of buildings and monuments (especially marble and limestone), soil degradation.
• Human Health Impact: Respiratory problems due to fine particulate matter formed from SO₂ and NOₓ.
• Control Measures: Use of low-sulphur fuels, installation of scrubbers in industries, catalytic converters in vehicles, and promotion of renewable energy sources.

Detailed Explanation:

Answer: Option 2 — 1, 3 and 4 only

This question tests knowledge about global climate initiatives and organizations. Statements 1, 3, and 4 are correct as they accurately describe The Climate Group's nature, EP100's objectives, and Indian corporate participation. Statements 2 and 5 are incorrect regarding the partnerships and secretariat roles.

✅ Statement 1 – Correct: The Climate Group is indeed an international non-profit organization founded in 2004 that drives climate action by building large networks of businesses, governments, and regional authorities across multiple offices globally.

❌ Statement 2 – Incorrect: EP100 is a global initiative led by The Climate Group in partnership with the Alliance to Save Energy, not the International Energy Agency (IEA).

✅ Statement 3 – Correct: EP100 brings together leading companies committed to improving energy productivity, driving innovation in energy efficiency, and increasing competitiveness while delivering on emission reduction goals.

✅ Statement 4 – Correct: Several Indian companies including Mahindra & Mahindra (first Indian member), Dalmia Cement, and UltraTech Cement are members of EP100.

❌ Statement 5 – Incorrect: The Climate Group, not the International Energy Agency, serves as the Secretariat to the Under2 Coalition—a global community of state and regional governments committed to limiting global temperature rise below 2°C.

📝 Short Notes: Global Climate Initiatives & Organizations

Detailed Explanation:

Answer: Option 4 — Aquatic plants absorb heavy metals and excess nutrients.

The analogy of wetlands as "kidneys of the Earth" is best reflected by their filtration function. Just as kidneys filter waste products and toxins from blood, wetlands act as natural filters by absorbing pollutants, heavy metals, and excess nutrients from water through aquatic plants and microbes. This phytoremediation and nutrient regulation process purifies water and prevents harmful substances from contaminating downstream ecosystems, paralleling the kidney's role in maintaining bodily health.

Why other options are less appropriate:
Option 1 describes the water cycle, which relates more to circulation than filtration. Option 2 explains the food web, not the purification function. Option 3 addresses sediment control, which is important but doesn't capture the filtering/cleansing aspect central to the kidney analogy.

📝 Short Notes: Wetland Functions

• Filtration & Purification: Wetlands remove pollutants, heavy metals, sediments, and excess nutrients through plant uptake and microbial action (phytoremediation and bioremediation).
• Nutrient Regulation: Absorb excess nitrogen and phosphorus, preventing eutrophication in water bodies downstream.
• Flood Control: Act as natural sponges, absorbing excess rainfall and reducing flood peaks.
• Groundwater Recharge: Facilitate percolation of water into aquifers, maintaining groundwater levels.
• Biodiversity Hotspots: Support diverse flora and fauna, including migratory birds, fish, and amphibians.
• Carbon Sequestration: Wetland vegetation and soils store significant amounts of carbon, helping mitigate climate change.
• Coastal Protection: Mangroves and coastal wetlands buffer against storms, tsunamis, and erosion.

Detailed Explanation:

Answer: Option 1 — Golden Mahseer

The Golden Mahseer (Tor putitora) is a species of large freshwater fish, not a bird. Often referred to as the 'Tiger of the Water', it is native to the Himalayan region and inhabits the rapid streams and rivers of the Indus, Ganga, and Brahmaputra basins. It is recognized by its large golden scales and is currently listed as Endangered on the IUCN Red List.

✅ Option 2 – Indian Nightjar: A nocturnal bird species found across the Indian subcontinent, belonging to the Caprimulgidae family.
✅ Option 3 – Spoonbill: A wading bird characterized by its distinctive spoon-shaped bill, found in wetlands and marshes.
✅ Option 4 – White Ibis: A wading bird with white plumage, commonly found in wetlands and coastal regions.

📝 Short Notes: Indian Wildlife Species

• Golden Mahseer (Tor putitora): Large freshwater fish found in Himalayan rivers; known as 'Tiger of the Water'; IUCN status: Endangered; threatened by overfishing, habitat degradation, and dam construction.
• Indian Nightjar: Nocturnal insectivorous bird; cryptic plumage provides excellent camouflage; found in dry scrublands and open forests.
• Spoonbill: Includes species like Eurasian Spoonbill; feeds by sweeping its spatulate bill through water; inhabits wetlands and shallow water bodies.
• White Ibis: Includes Black-headed Ibis (Threskiornis melanocephalus); wading bird found in wetlands; feeds on aquatic invertebrates and small fish.
• Conservation Significance: All these species are indicators of ecosystem health; wetland birds indicate water quality while mahseer indicates river health.

Detailed Explanation:

Answer: Option 1 — 1, 3 and 4 only

Nitrogen-fixing plants have a symbiotic relationship with rhizobia bacteria in their root nodules, which convert atmospheric nitrogen into forms usable by the plant. Among the listed options, only Alfalfa (1), Chickpea (3), and Clover (4) are leguminous nitrogen-fixing plants. Amaranth, Purslane (Kulfa), and Spinach are non-leguminous plants that depend on soil nitrogen and cannot fix atmospheric nitrogen.

✅ Statement 1 (Alfalfa) – Correct: Alfalfa is a legume with nitrogen-fixing capability through symbiotic rhizobia bacteria.
❌ Statement 2 (Amaranth) – Incorrect: Amaranth is a leafy vegetable that requires soil nitrogen and lacks nitrogen-fixing ability.
✅ Statement 3 (Chickpea) – Correct: Chickpea (a legume) has root nodules with nitrogen-fixing bacteria.
✅ Statement 4 (Clover) – Correct: Clover is a well-known leguminous nitrogen-fixer used in crop rotation and soil improvement.
❌ Statement 5 (Purslane/Kulfa) – Incorrect: Purslane is a succulent weed that does not fix nitrogen.
❌ Statement 6 (Spinach) – Incorrect: Spinach is a leafy vegetable requiring nitrogen from soil or fertilizers.

📝 Short Notes: Nitrogen-Fixing Plants

• Nitrogen Fixation: The process of converting atmospheric nitrogen (N₂) into ammonia or nitrates usable by plants, primarily performed by nitrogen-fixing bacteria.
• Symbiotic Nitrogen Fixation: Leguminous plants (family Fabaceae/Leguminosae) form symbiotic relationships with rhizobia bacteria in root nodules to fix nitrogen.
• Common Nitrogen-Fixing Plants: Include legumes like alfalfa, chickpea, clover, peas, beans, lentils, soybeans, and peanuts.
• Agricultural Importance: Nitrogen-fixing crops reduce the need for synthetic nitrogen fertilizers, improve soil fertility, and are commonly used in crop rotation systems.
• Non-Nitrogen-Fixing Plants: Most cereals, vegetables, and non-leguminous plants (like amaranth, spinach, purslane) cannot fix nitrogen and depend on soil nitrogen content.
• Elimination Strategy: Knowing that purslane is a common weed helps eliminate options containing it, as weeds typically do not have specialized nitrogen-fixing mechanisms.

Detailed Explanation:

Answer: Option 3 — Central Ground Water Authority

The Central Ground Water Authority (CGWA) was constituted under Section 3(3) of the Environment (Protection) Act, 1986, to regulate and control the development and management of groundwater resources in the country. It is the only body among the given options that derives its statutory authority directly from the EPA, 1986.

❌ Option 1 – Central Water Commission (Incorrect): Established in 1945 under the Ministry of Jal Shakti for water resource planning and development, but not constituted under EPA, 1986.

❌ Option 2 – Central Ground Water Board (Incorrect): A subordinate organization established in 1970 under the Ministry of Jal Shakti, functioning as the technical arm of CGWA, but not constituted under EPA, 1986.

❌ Option 4 – National Water Development Agency (Incorrect): An autonomous agency established in 1982 under the Societies Registration Act, 1860, focusing on interstate water disputes and interlinking of rivers, but not constituted under EPA, 1986.

📝 Short Notes: Water Resource Management Bodies in India

Detailed Explanation:

Answer: Option 1 — 1 and 3

Polyethylene terephthalate (PET) is a versatile polymer widely used in textiles and packaging. Statements 1 and 3 are correct as PET fibres can be blended with natural fibres to enhance properties, and PET bottles are highly recyclable. Statements 2 and 4 are incorrect because not all PET containers are suitable for storing all types of alcoholic beverages (especially high-proof spirits or at elevated temperatures due to potential chemical leaching), and incineration of PET inevitably produces greenhouse gas emissions, primarily CO₂.

✅ Statement 1 – Correct: PET fibres (polyester) are commonly blended with wool and cotton to improve wrinkle resistance, strength, and durability in textile applications.

❌ Statement 2 – Incorrect: While PET containers can store some alcoholic beverages, they are not suitable for all types, particularly high-alcohol content spirits or beverages stored at high temperatures, as chemicals may leach from the plastic.

✅ Statement 3 – Correct: PET bottles are among the most recycled plastics globally and can be reprocessed into new bottles, polyester clothing, carpets, automotive parts, and construction materials.

❌ Statement 4 – Incorrect: Incineration of PET releases greenhouse gases including carbon dioxide and potentially toxic compounds; it is not an environmentally friendly disposal method without causing emissions.

📝 Short Notes: Polyethylene Terephthalate (PET)

• Chemical Formula: (C₁₀H₈O₄)ₙ – a thermoplastic polymer resin of the polyester family
• Common Uses: Beverage bottles, food containers, synthetic fibres (polyester), packaging films, and engineering resins
• Recycling Code: #1 (PETE or PET) – one of the most widely recycled plastics worldwide
• Textile Applications: PET fibres (polyester) are blended with natural fibres like cotton and wool to enhance durability, wrinkle resistance, and moisture-wicking properties
• Recyclability: Can be mechanically or chemically recycled into rPET (recycled PET) for new bottles, clothing, carpets, and industrial materials
• Environmental Concerns: Non-biodegradable; incineration releases CO₂ and other pollutants; microplastic generation; requires proper waste management
• Storage Limitations: Not suitable for high-temperature storage or high-proof alcoholic beverages due to potential chemical leaching (acetaldehyde, antimony)
• Advantages: Lightweight, shatter-resistant, excellent barrier properties for gases and moisture, cost-effective, and energy-efficient to produce

Detailed Explanation:

Answer: Option 1 — Ant

Certain ant species, particularly leaf-cutter ants and others in the tribe Attini, are well-known for cultivating fungi. These ants practice sophisticated agriculture by cutting plant material, using it as substrate to grow specific fungus species in underground gardens, which then serve as their primary food source. This remarkable mutualistic relationship represents one of the most advanced examples of non-human agriculture in nature.

Why other options are incorrect:
• Cockroaches are omnivorous scavengers that do not cultivate fungi
• Crabs are aquatic scavengers or predators without fungal cultivation behavior
• Spiders are predators that capture prey and do not engage in fungal farming

📝 Short Notes: Fungus-Growing Ants

• Primary Species: Leaf-cutter ants (Atta and Acromyrmex genera) and fungus-growing ants (Tribe Attini) cultivate fungi as their primary food source
• Agricultural Process: Worker ants cut fresh plant material, chew it into a pulp, and use it as substrate for fungal cultivation in specialized underground chambers
• Fungal Species: They cultivate specific fungi from the family Lepiotaceae, which cannot survive outside the ant colonies
• Mutualistic Symbiosis: The ants provide the fungus with nutrients and protection, while the fungus provides specialized structures (gongylidia) as food for the ants
• Antibiotic Production: Some fungus-growing ants harbor bacteria (Actinomycetes) on their bodies that produce antibiotics to protect their fungal gardens from parasitic fungi
• Evolutionary Significance: This ant-fungus mutualism evolved approximately 50-60 million years ago and represents convergent evolution with human agriculture

Detailed Explanation:

Answer: Option 2 — 2 and 3

Primary producers in ocean food chains are organisms that produce organic compounds from inorganic substances through photosynthesis or chemosynthesis. Among the given organisms, cyanobacteria and diatoms are photosynthetic organisms that convert sunlight into chemical energy, forming the base of marine food webs. Copepods and foraminifera are consumers (zooplankton) that feed on primary producers.

❌ Statement 1 – Incorrect: Copepods are small crustacean zooplankton that function as primary consumers, feeding on phytoplankton and organic matter.
✅ Statement 2 – Correct: Cyanobacteria are photosynthetic bacteria capable of performing photosynthesis and are important primary producers in marine ecosystems.
✅ Statement 3 – Correct: Diatoms are unicellular algae (phytoplankton) that are among the most significant primary producers in oceans, contributing up to 40% of marine primary productivity.
❌ Statement 4 – Incorrect: Foraminifera are single-celled protists that are primarily consumers, feeding on organic particles and smaller organisms using pseudopodia.

📝 Short Notes: Marine Primary Producers and Plankton

• Primary Producers: Organisms that synthesize organic compounds from carbon dioxide through photosynthesis (using sunlight) or chemosynthesis, forming the base of food chains.
• Phytoplankton: Microscopic photosynthetic organisms drifting in water bodies; includes diatoms, dinoflagellates, cyanobacteria, and green algae.
• Diatoms: Most abundant phytoplankton with silica cell walls (frustules); responsible for 20-40% of Earth's oxygen production and major primary producers in oceans.
• Cyanobacteria: Photosynthetic bacteria (blue-green algae); can fix atmospheric nitrogen; some species form harmful algal blooms.
• Zooplankton: Heterotrophic organisms that feed on phytoplankton and organic matter; includes copepods, foraminifera, krill, and jellyfish larvae.
• Copepods: Small crustaceans that are the most abundant zooplankton; primary consumers linking phytoplankton to higher trophic levels.
• Foraminifera: Amoeboid protists with shells (tests); mostly marine; some are benthic while others are planktonic; feed on bacteria, algae, and detritus.

Detailed Explanation:

Answer: Option 2 — 2 and 3 Only

Copper smelting plants are a major environmental concern due to their emission of sulfur dioxide and the potential for heavy metal leaching from copper slag. The primary gaseous pollutant is SO₂, not carbon monoxide.

❌ Statement 1 – Incorrect: Copper smelting plants do not typically release lethal quantities of carbon monoxide; the primary gaseous pollutant of concern is sulfur dioxide (SO₂).

✅ Statement 2 – Correct: Copper slag, a byproduct of smelting, contains heavy metals like arsenic, lead, and cadmium, which can leach into soil and groundwater, causing environmental contamination.

✅ Statement 3 – Correct: Copper smelting releases large amounts of sulfur dioxide because most copper ores are sulfide minerals (like chalcopyrite), and sulfur is oxidized to SO₂ during roasting and smelting processes.

📝 Short Notes: Environmental Concerns of Copper Smelting

• Primary Pollutant: Sulfur dioxide (SO₂) is the main gaseous emission from copper smelting, as copper ores are predominantly sulfide minerals.
• Copper Slag: Contains heavy metals (arsenic, lead, cadmium, mercury) that can leach into environment, contaminating soil and water resources.
• Acid Rain: SO₂ emissions contribute to acid rain formation, damaging ecosystems, crops, and infrastructure.
• Health Impacts: SO₂ causes respiratory problems; heavy metals from slag can bioaccumulate and cause neurological and developmental issues.
• Mitigation Measures: Use of scrubbers to capture SO₂, proper slag management, adoption of cleaner smelting technologies, and recovery of sulfur for sulfuric acid production.

Detailed Explanation:

Answer: Option 1 — environmentally responsible practices in electronics recycling industry.

The R2 (Responsible Recycling) Code of Practices is a comprehensive set of standards specifically designed for the electronics recycling industry to ensure environmentally sound and socially responsible handling of electronic waste. It provides guidelines for data security, material handling, downstream vendor management, and worker health and safety in e-waste recycling operations.

📝 Short Notes: R2 Code of Practices

• Full Form: R2 stands for Responsible Recycling, developed for electronics recycling industry.
• Purpose: Establishes standards for safe, ethical, and environmentally responsible recycling of electronic equipment and e-waste.
• Key Areas Covered: Data security and destruction, material handling, downstream vendor accountability, environmental health and safety, worker protection.
• Certification: R2 certification is recognized globally as a mark of responsible e-waste recycling practices.
• Focus on E-Waste: Addresses growing concerns about toxic materials in electronics (lead, mercury, cadmium) and promotes proper disposal and recycling methods.

Detailed Explanation:

Answer: Option 4 — Toiletries

Triclosan (TCS) is an antibacterial and antifungal agent commonly found in various personal care and consumer products. It is most prevalently present in toiletries such as toothpaste, soaps, hand sanitizers, body washes, and deodorants. Long-term exposure to high levels of triclosan has raised health and environmental concerns, leading to restrictions and bans in several countries.

📝 Short Notes: Triclosan

• Chemical Nature: Triclosan is a synthetic antimicrobial compound used to reduce or prevent bacterial contamination.
• Common Products: Found in antibacterial soaps, toothpaste, hand sanitizers, body washes, detergents, cosmetics, and some medical equipment.
• Health Concerns: Prolonged exposure may disrupt hormone regulation (endocrine disruption), contribute to antibiotic resistance, and cause skin irritation.
• Environmental Impact: Triclosan can persist in the environment, contaminate water bodies, and harm aquatic ecosystems.
• Regulatory Actions: The US FDA banned triclosan from over-the-counter antiseptic wash products in 2016; the EU restricted its use in cosmetics in 2014.
• Alternatives: Manufacturers are increasingly using safer alternatives like alcohol-based sanitizers and natural antimicrobial agents.

Detailed Explanation:

Answer: Option 2 — Polycarbonate

Bisphenol A (BPA) is a key structural component in the manufacture of polycarbonate plastics. Polycarbonates are widely used in consumer products such as water bottles, food storage containers, eyeglass lenses, and CDs/DVDs. BPA has raised significant health concerns as it can act as an endocrine disruptor, interfering with the body's hormonal system.

📝 Short Notes: Types of Plastics and BPA

• BPA Health Concerns: Acts as endocrine disruptor, mimics estrogen, linked to reproductive issues, developmental problems, and metabolic disorders
• BPA-Free Alternatives: Many manufacturers now produce BPA-free polycarbonates or use alternative plastics
• Regulation: Several countries have banned BPA in baby bottles and food contact materials