Prelims Questions: Biosphere & Working of Ecosystem | Environment for UPSC CSE PDF Download

Q1: With reference to the planet Earth, consider the following statements:    (2025)
I. Rain forests produce more oxygen than that produced by oceans. 
II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world's oxygen. 
III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.
Which of the statements given above is/are correct?
(a) I and II
(b) II only
(c) I and III
(d) None of the above statements is correct

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Correct Answer: (b)
Oxygen on Earth primarily comes from photosynthesis, with marine phytoplankton playing a significant role. The statements provided are evaluated as follows:

• Statement I is false: Marine phytoplankton in oceans contribute more oxygen to the atmosphere than rainforests do.
• Statement II is true: Approximately half of the world's oxygen is produced by marine phytoplankton and photosynthetic bacteria.
• Statement III is false: Atmospheric air contains significantly more oxygen than surface water, not the other way around.

Thus, the correct answer is B.

Q2: Consider the following statements:    (2025)
Statement I: Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries.
Statement II: Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals.
Statement III: Activated carbon can be easily synthesized from environmental wastes with high carbon content.
Which one of the following is correct in respect of the above statements?
(a) Both Statement II and Statement III are correct and both of them explain Statement I
(b) Both Statement II and Statement III are correct but only one of them explains Statement I
(c) Only one of the Statements II and III is correct and that explains Statement I
(d) Neither Statement II nor Statement III is correct

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Correct Answer: (a)
Activated carbon is extensively utilized for pollutant removal due to its distinctive properties and environmentally friendly production methods.

• Statement I is true: Activated carbon efficiently removes pollutants from industrial effluents, leveraging its high adsorption capacity, making it a staple in water treatment and pollution control.
• Statement II is true: Its effectiveness stems from a vast surface area created by a porous structure, which enables it to capture heavy metals and other contaminants effectively.
• Statement III is true: Activated carbon can be sustainably and cost-effectively produced from carbon-rich agricultural wastes, such as coconut shells and rice husks, enhancing its eco-friendliness.

Therefore, Statements II and III are correct and collectively explain the validity of Statement I.

Q3: Consider the following statements:    (2025)
I. Carbon dioxide (CO₂) emissions in India are less than 0.5 t CO₂/capita. 
II. In terms of CO₂ emissions from fuel combustion, India ranks second in Asia-Pacific region. 
III. Electricity and heat producers are the largest sources of CO₂ emissions in India.
Which of the statements given above is/are correct?
(a) I and III only
(b) II only
(c) II and III only
(d) I, II and III

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​Correct Answer: (c)
​Statement I is incorrect: India's per capita CO₂ emissions are approximately 1.9–2.0 tonnes, which is significantly higher than the 0.5 tonnes per capita mentioned.
Statement II is correct: India is the second-largest emitter of CO₂ from fuel combustion in the Asia-Pacific region, following China.
Statement III is correct: The primary source of India’s CO₂ emissions is electricity and heat production, predominantly from coal-based power generation.
Thus, the correct answer is C.

Q4: The World Bank warned that India could become one of the first places where wet-bulb temperatures routinely exceed 35 °C. Which of the following statements best reflect(s) the implication of the above‐said report?
I. Peninsular India will most likely suffer from flooding, tropical cyclones and droughts. 
II. The survival of animals including humans will be affected as shedding of their body heat through perspiration becomes difficult.
Select the correct answer using the code given below.    (2025)
(a) I only
(b) II only
(c) Both I and II
(d) Neither I nor II

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​Correct Answer: (b)
​Statement I is incorrect: The World Bank's warning specifically addresses the dangers of wet-bulb temperatures, not flooding, cyclones, or droughts, which are separate climate-related threats.
Statement II is correct: A wet-bulb temperature above 35°C prevents the human body from cooling itself through sweating, as it cannot release heat, leading to potentially fatal conditions for humans and animals.
Thus, the correct answer highlights the critical impact of high wet-bulb temperatures on survival.

Q5: Consider the following statements:    (2025)
Statement I: Circular economy reduces the emissions of greenhouse gases.
Statement II: Circular economy reduces the use of raw materials as inputs.
Statement III: Circular economy reduces wastage in the production process.
Which one of the following is correct in respect of the above statements?
(a) Both Statement II and Statement III are correct and both of them explain Statement I
(b) Both Statement II and Statement III are correct but only one of them explains Statement I
(c) Only one of the Statements II and III is correct and that explains Statement I
(d) Neither Statement II nor Statement III is correct

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Correct Answer: (a)

• Statement I is correct: The circular economy reduces greenhouse gas emissions by minimizing waste and optimizing energy use.
• Statement II is correct: It conserves raw materials by promoting reuse, recycling, and extending product lifecycles.
• Statement III is correct: Sustainable design and efficient processes in the circular economy help reduce production waste.

Thus, all three statements are true, confirming that the circular economy effectively supports waste reduction, resource conservation, and emission cuts.

Q6: Which one of the following is the correct sequence of a food chain? (2014)
(a) Diatoms-Crustaceans-Herrings
(b) Crustaceans-Diatoms-Herrings
(c) Diatoms-Herrings-Crustaceans
(d) Crustaceans-Herrings-Diatoms

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Correct Answer: (a)

Q7: With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms? (2013)
1. Virus
2. Fungi
3. Bacteria

Select the correct answer using the codes given below:
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

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Correct Answer: (b)

 Q8: With reference to food chains in ecosystems, consider the following statements: (2013)
1. A food chains illustrates the order in which a chain of organisms feed upon each other.
2. Food chains are found within the populations of a species.
3. A food chain illustrates the numbers of each organism which are eaten by others.

Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 1, 2 and 3
(d) None

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Correct Answer: (a)

Q9: Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity? (2013)
(a) Oceans, lakes, grasslands, mangroves
(b) Mangroves, oceans, grasslands, lakes
(c) Mangroves, grasslands, lakes, oceans
(d) Oceans, mangroves, lakes, grasslands

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Correct Answer: (c)

Q10: In the grasslands, trees do not replace the grasses as a part of an ecological succession because of- (2013)
(a) insects and fungi
(b) limited sunlight and paucity of nutrients
(c) water limits and fire
(d) None of the above

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Correct Answer: (c)

 Q11: What would happen if the phytoplankton of an ocean is completely destroyed for some reason? (2012)
1. The ocean as a carbon sink would be adversely affected.
2. The food chains in the ocean would be adversely affected.
3. The density of ocean water would drastically decrease.

Select the correct answer using the codes given below:
(a) 1and 2 only
(b) 2 only
(c) 3only
(d) 1, 2 and 3

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Correct Answer: (a)

Q12: The Millennium Ecosystem Assessment describes: The following major categories of ecosystem services—provisioning, supporting, regulating, preserving and cultural. Which one of the following is a supporting service? (2012)
(a) Production of food and water
(b) Control of climate and disease
(c) Nutrient cycling and crop pollination
(d) Maintenance of diversity
In the context of ecosystem productivity, marine upwelling zones are important as they increase marine productivity by bringing the-(2011)
1. Decomposer microorganisms to the surface.
2. Nutrients to the surface.
3. Bottom-dwelling organisms to the surface.
Which of the statements given above is/are correct?
(a) 1 and 2
(b) 2 only
(c) 2 and 3
(d) 3 only

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Correct Answer: (c)

Q13: If a tropical rain forest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because: (2011)
(a) The soil of rain forest is deficient in nutrients
(b) Propagules of the trees in a rain forest have poor viability
(c) The rain forest species are slow growing
(d) Exotic species invade the fertile soil of rain forest

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Correct Answer: (a)

Q14: In the context of ecosystem productivity, marine upwelling zones are important as they increase marine productivity by bringing the-(2011)
1. Decomposer microorganisms to the surface.
2. Nutrients to the surface.
3. Bottom-dwelling organisms to the surface.

Which of the statements given above is/are correct?
(a) 1 and 2 
(b) 2 only
(c) 2 and 3 
(d) 3 only

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Correct Answer: (b)

 Q15: Consider the following organisms: (2013)
1. Agaricus
2. Nostoc
3. Spirogyra
Which of the above is/are used as biofertilizer/biofertilizers?
(a) 1 and 2
(b) 2 only
(c) 2 and 3
(d) 3 only

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Correct Answer: (b)

Q16: Which one of the following terms describes not only the physical space occupied by an organism but also its functional role in the community of organisms? (2013)
(a) Ecotone
(b) Ecological niche
(c) Habitat
(d) Home range Ecology

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Correct Answer: (b)

Q17: A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is: Food crop – Rat - Snake - Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following? (2010)
(a) Food crop
(b) Rat
(c) Snake
(d) Hawk

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Correct Answer: (d)