CUET UG 2025 Environmental Science Previous Year Solved Paper

wer: 3. (World Biocapacity / World Ecological Footprint) × 365
Earth Overshoot Day is the calendar date when humanity’s resource use
(ecological footprint) exceeds what Earth can regenerate (biocapacity) in that
year. Hence, the day number =

wer: 3. 22 April, 1970
The first Earth Day was organized in the United States by Senator Gaylord
Nelson and celebrated on 22 April 1970, marking the start of the modern
environmental movement.

wer: 3. Deep Ecology
Deep ecology advocates the intrinsic value of all living beings, preservation of
wild species, reducing human population impact, and simple living to maintain
ecological balance.

wer: 4. Ernst Haeckel
Ernst Haeckel coined the term “Oecologie/Oekologie” (ecology) in 1866 to
describe the study of organisms’ relationships with their environment.

wer: 3. Alpha diversity

Alpha diversity means within-habitat (local) species diversity—the variety and
relative abundance of species at a single site/community. Beta = between
habitats; Gamma = regional; Genetic = within species.

wer: 3. (A)-(I), (B)-(II), (C)-(IV), (D)-(III)
Matching:
• (A) Wildlife (Protection) Act → 1972
• (B) Indian Forest Act → 1927
• (C) Madras Wild Elephant Preservation Act → 1873
• (D) Cruelty Against Animals (Prevention of Cruelty to Animals) Act
→ 1960

wer: 3. T. R. Malthus
Thomas Robert Malthus proposed that population increases geometrically
(exponentially) while food supply grows only arithmetically (linearly), leading
to potential checks like famine and disease.

wer: 2. Pioneer
The first species to colonize a bare, previously uninhabited area are
called pioneer species; they initiate succession and modify conditions for later
communities.

wer: 4. (A)-(II), (B)-(I), (C)-(III), (D)-(IV)
• Deserts → Capparis (II)
• Grasslands → Cymbopogon (I)
• Ponds & Lakes → Hydrilla (III)

• Moist deciduous forests → Tectona (teak) (IV)

wer: 3. Fragmentation
In detritus food chain, earthworms (detritivores) mechanically break litter into
smaller pieces—this is called fragmentation. (Leaching = soluble removal;
Humification = formation of humus; Catabolism = enzymatic breakdown by
microbes.)

wer: 2. (D), (B), (A), (C), (E)
Lithosere sequence: Crustose lichens → Foliose lichens → Moss →
Herbs/Grasses → Shrubs (→ Trees). Hence D → B → A → C → E.

Solution could not be extracted cleanly from the source PDF for this question.

wer: A–III, B–I, C–II, D–IV
• Dudhwa lies in the Terai of Uttar Pradesh near Nepal.
• Kanha is a major tiger reserve in Madhya Pradesh (home of the hard-
ground barasingha).
• Bandipur is in the Nilgiri biosphere, Karnataka.
• Kaziranga sits on the Brahmaputra floodplains of Assam (one-horned
rhino).

wer: 1.

None of the four printed options exactly match K−NK
This appears to
be a misprint—the correct form has (K − N) in the numerator and K in the
denominator.

wer: 4. Unidirectional
Energy enters as sunlight → producers → consumers → decomposers, and
much is lost as heat at each step. Unlike nutrients, energy is not recycled back
to the sun—so the flow is one-way only.

wer: 1. Ash from a volcanic eruption
Why: It’s emitted directly into the air (primary pollutant).
Tropospheric ozone and PAN are secondary (formed by reactions in air).
Stratospheric ozone isn’t a pollutant—it protects from UV.

wer: 2. Nitrogen and Phosphorus
Why: Excess nitrates (N) and phosphates (P) from fertilizers wash into
lakes/rivers, causing algal blooms → oxygen depletion → fish kills.
Quick tip: Eutrophication = N + P (think “N-P = No Peace for lakes”).

wer: 3. K₂Cr₂O₇ + H₂SO₄
Standard COD uses acidic potassium dichromate (in sulfuric acid) as the
oxidant (often with Ag₂SO₄ catalyst, HgSO₄ to complex chlorides). Nitric or
hydrochloric acid aren’t used with dichromate for COD.

wer: 4. Loamy soils

Loam is a balanced mix of sand, silt, and clay—so it holds water and nutrients
well without getting waterlogged, and still has good aeration and structure.
Ideal for roots and most crops.

wer: 2. NO₂ and SO₂
These gases oxidize in the atmosphere to HNO₃ and H₂SO₄, the main acids in
acid rain. (O₃ isn’t an acid precursor; CO₂ is weakly acidic but not the cause of
acid rain; NH₃ tends to neutralize acids.)

wer: 3. Bronchitis
Why:
• Cholera, Giardiasis, Dracontiasis are all water-borne (spread via
contaminated water).
• Bronchitis is a respiratory condition
(viral/bacterial/irritants), not transmitted through water.

wer: 3. High Volume Sampler
Baghouse filters, cyclone separators, and electrostatic
precipitators remove particulates from emissions (control devices). A High
Volume Sampler is for monitoring/sampling ambient particulates, not for
controlling pollution.

wer: 4. (A)–(III), (B)–(IV), (C)–(I), (D)–(II)
• Azonal soils → lack well-developed horizons (III)
• Regoliths → loose, weathered rock material (IV)
• Ped → natural aggregate/clod of soil particles (I)
• Edaphons → soil-dwelling organisms (II)

wer: 4. (E), (B), (D), (A), (C)
Reason: Typical atmospheric concentrations →
Neon ~0.0018% < CO₂ ~0.04% < Argon ~0.93% < Oxygen ~21% < Nitrogen
~78%.
So increasing order: Neon (E) < CO₂ (B) < Argon (D) < Oxygen (A) < Nitrogen
(C).

wer: 1. (A)–(III), (B)–(I), (C)–(II), (D)–(IV)
• Carbon → 55–60%
• Oxygen → 35–40%
• Hydrogen → ~5%
• Nitrogen → 15% (as per the given options; standard texts often note ~3–
6%).

wer: Pyrolysis
Pyrolysis is a process in which organic or waste materials are heated at high
temperatures (about 300°C–700°C) in the complete absence of oxygen. This
causes the material to decompose chemically into three products — char
(solid), bio-oil (liquid), and gases (like CO and H₂). Because no oxygen is
present, the material doesn’t burn completely; it breaks down instead.
In contrast, incineration burns waste in the presence of oxygen, gasification
uses a limited supply of oxygen, and composting is a biological decomposition
process that also needs oxygen.

wer: (2) Oxidation of CO and reduction of Nox

Catalytic converters are emission-control devices used in vehicles to reduce
harmful gases released from exhaust. They contain catalysts like platinum (Pt),
palladium (Pd) and rhodium (Rh) coated on a ceramic honeycomb structure.
Inside the converter, two main chemical processes occur simultaneously:
• Oxidation reactions:
o Carbon monoxide (CO) and unburnt hydrocarbons (HC) are
oxidized (react with oxygen) to form carbon dioxide (CO₂) and
water (H₂O).

Reduction reactions:
• Nitrogen oxides (NOx) are reduced (oxygen removed) to form harmless
nitrogen gas (N₂).

Hence, catalytic converters oxidize CO and reduce NOx, making exhaust gases
less polluting.

wer: (4). (B) and (D) only
Bihar has a well-known traditional water management method called the
Ahar–Pyne system. It is one of the oldest and most effective indigenous
systems of irrigation in eastern India.
• Ahar:
Ahar is a catchment basin or small reservoir built in low-lying fields to
collect and store rainwater and runoff from nearby rivers or canals.

• Pyne:
Pyne is a channel or artificial canal dug to divert water from rivers or
streams into the Ahar fields.
The stored water is later used for irrigation during dry periods.
This Ahar–Pyne system ensures sustainable irrigation and groundwater
recharge in regions where rainfall is uneven.

wer: (2). (A), (B) and (C) only
Gandhian philosophy focuses on upliftment of the poorest (Antyodaya),
welfare of all (Sarvodaya), and village self-rule (Panchayati Raj) for true
national development.
Reverse migration is not a direct Gandhian concept.

wer: (4). Phosphorus cycle
The phosphorus cycle is a sedimentary biogeochemical cycle because
phosphorus moves through rocks, soil, water, and organisms, but not through
the atmosphere. Its main reservoir is the Earth’s crust (rocks and sediments).
In contrast, carbon, oxygen, and nitrogen cycles are gaseous cycles since these
elements have a major reservoir in the atmosphere.

wer: (3). (A), (B), (C) and (D)
The DEWAT system is a low-cost, decentralized wastewater treatment system
suitable for rural and peri-urban areas. Its features include:
• Low primary investment (A)
• Easy operation and maintenance (B)
• Baffled filter reactor (BFR) filled with stones for filtration (C)
• Sedimentation chambers at the start to settle sludge (D)

All four statements correctly describe DEWAT.

wer: (2) Potential resources
Potential resources are those found in nature but not yet utilized because of
lack of technology, knowledge, or means to extract or use them.
• Reserve resources → part of actual resources that can be used with
current technology.
• Stock resources → resources that exist but cannot be used with current
technology; similar concept, but in geography, potential resources is the
standard term.
• Actual resources → currently being used.

wer: (3). Norman E. Borlaug
Norman E. Borlaug, an American agronomist, is called the Father of the Green
Revolution for developing high-yielding wheat varieties and modern
agricultural techniques that dramatically increased food production in the
1960s. He was awarded the Nobel Peace Prize in 1970 for his contribution to
world food security.
• M. S. Swaminathan → Pioneer of Green Revolution in India, but not the
global “father.”
• Norman Fukuoka → Known for natural farming.

wer: (4). Cuba
Organoponics is a method of urban organic agriculture, mainly using raised
beds, organic compost, and minimal mechanization. It was first developed in
Cuba in the 1970s as a response to food shortages after the collapse of the
Soviet Union, promoting local, sustainable, and labor-intensive farming in
cities.

• India, Sri Lanka, and China use organic farming, but Organoponics as a
structured urban system originated in Cuba.

wer: (3). Positive consumption externalities
When products like smartphones are used in a networked system, the benefit
of one user increases the benefit for others (e.g., more people using a
messaging app or social network makes it more valuable for everyone).
• This is a positive effect arising from consumption, not production.
• Positive production externalities → benefit others when producing (like
a beekeeper helping nearby crops).
• Negative externalities → impose costs on others (pollution, noise, etc.).

wer: (4). (A), (C), (B), (D)
The Global Warming Potential (GWP) of greenhouse gases indicates their
contribution to warming:
• CH₄ (Methane): Moderate warming potential
• CFCs: High GWP (much higher than CO₂ per unit, but lower in overall
contribution due to smaller atmospheric concentration)
• N₂O (Nitrous oxide): Higher GWP than CH₄ and CO₂
• CO₂ (Carbon dioxide): Although its GWP per molecule is lower, its
abundance makes it the largest contributor to global warming overall
So, in terms of overall contribution to global warming, the ascending order is:
CH₄ < CFCs < N₂O < CO₂

wer: (3). (B), (A), (E), (D), (C)
The frequency of electromagnetic waves increases as the wavelength
decreases. Typical order from low frequency to high frequency is:

• Radio waves → lowest frequency
• Microwaves → higher than radio waves
• Infrared (IR) radiation → higher than microwaves
• Ultraviolet (UV) rays → higher than IR
• Gamma rays → highest frequency
So, the ascending order of frequency is:
Radio-wave (B) < Microwave (A) < Infrared (E) < UV (D) < Gamma rays (C)

wer: (3). (A) and (B) only
Push factors are conditions that force people to leave rural areas and move to
cities, such as:
• Floods → damage homes and crops (A)
• Political instability → insecurity or conflict (B)
Pull factors, on the other hand, attract people to urban areas:
• Better job opportunities (C)
• High agricultural yields (D) → indicate prosperity, so they retain people
rather than push them out
Hence, the correct push factors are flood and political instability.

wer: (4). Provisioning ecosystem services
Provisioning ecosystem services are the products directly obtained from
ecosystems, such as:
• Food (crops, fish, fruits)
• Raw materials (wood, fibers)
• Genetic resources (for medicine and crop improvement)

Other ecosystem services:
• Regulating → control climate, disease, water purification
• Supporting → nutrient cycling, soil formation
• Cultural → recreational, spiritual benefits

wer: (2) Montreal Protocol
The Montreal Protocol (1987) is an international treaty designed to phase out
the production and consumption of ozone-depleting substances (ODS) such as
CFCs, halons, and other chemicals that harm the ozone layer.
Other treaties:
• Kyoto Protocol → deals with greenhouse gas emissions and climate
change
• Paris Agreement → global climate change mitigation and adaptation
• Geneva Protocol → bans use of chemical and biological weapons

wer: (3). Conflicts in foreign policies of trading countries
International trade is based on comparative advantage, complementarity, and
mutual benefits, supported by production specialization and good transport.
Conflicts in foreign policies hinder trade, so they are not a foundation.

wer: (1). In agriculturally important countries, agricultural products are
expected to be exchanged for manufactured goods.
Countries specialize based on resources and economic development.
Agricultural nations export food and import manufactured goods. Options 2, 3,
and 4 are incorrect because industrialized nations export machinery and
manufactured goods, and economic development does affect trade patterns.

wer: (3). Export of Banana from the tropical regions
Climatic conditions determine the type of agricultural products. Bananas grow
in tropical climates, so export of bananas is directly influenced by climate.
Other options are based on craftsmanship or industry, not climate.

wer: (3). World Trade Organization
The World Trade Organization (WTO) replaced the General Agreement on
Tariffs and Trade (GATT) in 1995 to regulate international trade and tariffs.

wer: (3). Barter System
In primitive societies, goods were exchanged directly without money. This is
called the barter system. Other options are unrelated.

wer: (2). Reclamation of degraded lands
Reclaiming degraded lands improves productivity, so it is not a cause of low
productivity. Other factors like lack of credit, uncertain monsoons, and small
landholdings limit agricultural efficiency.

wer: (3). Use of chemical fertilizers and pesticides
While chemical fertilizers and pesticides increased yields, their excessive use
harmed soil fertility, so it is not considered an advantage. Other points (HYV
seeds, credit schemes, irrigation) were actual advantages.

wer: (4). Reliance on modern farming tools and techniques
Subsistence farming is traditional and low-tech, relying on natural resources. It
does not use modern tools or techniques.

wer: (4) Decreasing cropping intensity
Increasing cropping intensity improves productivity, not decreasing it. Other
measures like land reforms, dryland farming, and scientific practices help
productivity.

wer: (3). Rajasthan
The initial Green Revolution mainly benefited Punjab, Haryana, western Uttar
Pradesh (wheat) and deltaic regions of east coast (rice). Rajasthan was not a
direct beneficiary in the early stages.