UGC NET Questions (Paper – 1)

Afforestation establishes new forests that remove carbon dioxide from the atmosphere and store it in biomass and soils, thereby acting as a carbon sink and helping to offset emissions.

Option A:
Incorrect; forests do not simply reflect all solar radiation, and their climatic effects are more complex than uniform cooling by reflection.

Option B:
Correct; it explains how planting trees sequesters carbon and lowers net greenhouse gas concentrations.

Option C:
Incorrect; even large-scale tree planting cannot eliminate the need to reduce emissions from sectors like energy, transport and industry.

Option D:
Incorrect; trees also emit water vapour and other gases; saying they emit only oxygen oversimplifies plant physiology.

Statements A, B and D are correct and together explain the distinction between mitigation and adaptation. Mitigation is about reducing emissions, adaptation is about adjusting systems to cope with impacts and climate-resilient crops are a clear example of adaptation. Statement C is conceptually incorrect in this context because afforestation and tree planting as carbon sinks are typically classified as mitigation actions, although they may have some adaptive co-benefits. Hence, the combination that includes A, B and D only is the correct answer.

Option A:
Option A is incorrect because it includes A and B but omits D, which is also a correct example of adaptation. While A and B provide definitions, leaving out D means the option does not fully represent the set of correct statements requested. A complete answer must recognise a concrete adaptation example as well.

Option B:
Option B is incorrect because it groups B and D only, leaving out A. Although B and D are correct, A is also correct in defining mitigation, and the question asks for all correct statements. Excluding a valid definition of mitigation makes this combination incomplete.

Option C:
Option C is correct because it brings together the accurate definition of mitigation, the accurate definition of adaptation and a valid example of adaptation in the form of climate-resilient crops. It appropriately excludes C, which mislabels a typical mitigation measure as adaptation. By balancing conceptual clarity with relevant examples, this option best fits the question.

Option D:
Option D is incorrect because it treats all four statements A, B, C and D as correct. Since C misclassifies tree planting solely as adaptation, accepting it alongside the other statements blurs the important conceptual distinction between mitigation and adaptation. The presence of this incorrect statement invalidates the combination.

In the carbon cycle, photosynthesis is the key biological process that takes up carbon dioxide from the atmosphere. Green plants, algae and some bacteria use CO2 and water in the presence of sunlight to produce carbohydrates and release oxygen. The carbon is stored temporarily in plant biomass and, through food chains, in other organisms. Thus, photosynthesis acts as a major carbon sink, making Option C the correct answer.

Option A:
Option A is incorrect because combustion of fossil fuels adds carbon dioxide to the atmosphere. It is a carbon source, not a sink, and contributes to climate change.

Option B:
Option B is incorrect since deforestation removes trees that would otherwise absorb CO2. It reduces the capacity of terrestrial ecosystems to act as carbon sinks and often releases stored carbon when biomass is burned or decomposes.

Option C:
Option C is correct as it points to the primary natural mechanism for withdrawing CO2 from the atmosphere. Protecting and enhancing photosynthetic ecosystems is a key strategy for climate mitigation.

Option D:
Option D is incorrect because volcanic eruptions release gases, including CO2, to the atmosphere. They are natural sources of carbon, not processes that remove it.