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.

Urban heat islands occur when built-up surfaces absorb and re-radiate more heat than vegetated rural landscapes. Concrete, asphalt and buildings store heat, while reduced vegetation lowers cooling from evapotranspiration. Waste heat from vehicles, air-conditioners and industry further raises temperatures. As a result, cities are often several degrees warmer than nearby rural areas, especially at night, which matches the description in option B.

Option A:
Option A is incorrect since it reverses the observed pattern; rural areas are generally cooler, not warmer, at night. Their vegetation and open spaces allow more rapid cooling.

Option B:
Option B is correct because it identifies both the temperature difference and the main causes. It links warmer cities to material properties and anthropogenic heat, which is how climatologists define urban heat islands.

Option C:
Option C is incorrect because tall buildings can also trap heat and reduce wind flow. Shade helps in the daytime, but overall urban form still tends to raise average temperatures.

Option D:
Option D is incorrect as rainfall patterns are influenced by many factors. Population density alone does not explain the heat island effect, which is specifically about temperature.

Afforestation involves establishing forests on lands that have not been forested for a long time or ever in recent history. It is used to increase forest area,store carbon and restore ecological functions on degraded lands. The stem clearly mentions planting trees on land not previously forested,which is the defining feature of afforestation. Therefore afforestation is the correct option.

Option A:
Deforestation is the removal of forest cover,usually for agriculture,settlement or logging. It leads to loss of biodiversity and carbon storage. Since the question describes planting trees rather than cutting them,deforestation is the opposite of what is intended.

Option B:
Reforestation refers to re planting trees on lands that were recently forested but have been cleared or degraded. It restores former forest areas but does not necessarily involve new forest establishment on non forest land. Hence it does not precisely match the stem.

Option C:
Afforestation contributes to increasing overall forest area beyond current levels and can help combat desertification and climate change. Because the stem emphasises new forest creation on non forest land,this option captures the concept accurately.

Option D:
Clear felling is a logging method in which most or all trees in an area are cut at once. It is a harvesting technique and not a planting or restoration activity,so it does not fit the description.

Urban sprawl refers to dispersed, low density development on the outskirts of cities,often lacking adequate public transport and services. It consumes large areas of land and contributes to habitat loss and pollution. The stem explicitly mentions unplanned horizontal expansion into rural areas with low density development, which is the hallmark of urban sprawl. Therefore urban sprawl is the correct term.

Option A:
Urban renewal involves redeveloping older urban areas to improve housing, infrastructure and services. It usually focuses on existing built up zones rather than outward expansion into rural land,so it does not fit the description in the question.

Option B:
Urban sprawl is typically associated with car dependence and fragmented land use patterns. This pattern increases energy use and greenhouse gas emissions. These negative outcomes align with the unplanned,spread out growth referred to in the stem.

Option C:
Smart growth is an alternative planning approach that promotes compact, mixed use and transit oriented development. It is designed to counteract sprawl,not to describe it,so it is not the right answer.

Option D:
Rural reconstruction focuses on improving social and economic conditions in rural areas through infrastructure,education and agriculture. It does not describe the outward expansion of cities,so it cannot fill the blank correctly.

Ecological succession describes the gradual change in species composition and community structure over time after disturbances. Human actions such as clearing forests, burning grasslands or building infrastructure can interrupt or restart this process by removing existing vegetation and altering soil conditions. Frequent or intense disturbances may prevent ecosystems from reaching later successional stages, or they may send succession along a different trajectory altogether.

Option A:
Option A is incorrect because it suggests humans alter succession by never disturbing ecosystems, which is unrealistic and does not describe the main way people influence successional dynamics.

Option B:
Option B is incorrect because humans cannot and do not completely stop all natural disturbances such as fires, storms and grazing everywhere.

Option C:
Option C is correct because repeated disturbances like deforestation, overgrazing and construction repeatedly push ecosystems back to earlier successional stages or redirect them into novel states.

Option D:
Option D is incorrect because ecological theory recognises multiple potential stable states and ongoing dynamics; it is unrealistic to expect all ecosystems to quickly reach and remain in a single climax state, especially under strong human influence.

The urban heat island effect describes the tendency of cities to be warmer than neighbouring rural regions, especially at night. Built surfaces such as concrete and asphalt absorb and store more solar energy than natural vegetated surfaces. Reduced vegetation also means less cooling through evapotranspiration, while waste heat from vehicles and buildings adds to warming. As a result, the explanation focusing on dense built-up surfaces and loss of vegetation correctly captures the causes of the heat island effect.

Option A:
Option A is incorrect because rural areas are generally cooler than urban areas when other factors are similar. Agricultural land and open fields often allow more cooling, not persistent warming, compared to dense city cores. So this statement reverses the typical temperature pattern.

Option B:
Option B is incorrect since tall buildings can create street canyons that trap heat and restrict air circulation. They do not simply block all solar radiation; in fact, many surfaces receive and store heat, which contributes to city warming.

Option C:
Option C is incorrect because waste heat from industrial chimneys is only one source of urban heating. Land cover changes, traffic, air-conditioning exhaust and reduced vegetation together create the cumulative warming pattern characteristic of urban heat islands.

Option D:
Option D is correct as it summarises the main physical reasons behind higher city temperatures. Impermeable, dark surfaces store heat, and the lack of trees and green spaces reduces natural shading and cooling, creating a persistent temperature difference between urban and rural environments.

The term urban heat island describes the pattern where city centres are warmer than nearby rural zones because of heat absorbing materials,anthropogenic heat release and lack of vegetation. The stem refers to this temperature difference between urban and rural environments. Therefore island is the correct word to complete the phrase.

Option A:
A heat wave is a prolonged period of excessively hot weather affecting large regions,not just urban areas. While heat waves can exacerbate urban heat islands,they are a different meteorological phenomenon.

Option B:
The urban heat island effect can increase energy demand, worsen air pollution and raise health risks. Its name emphasises that cities behave like “islands” of warmth within a cooler rural “sea”. This imagery matches the description in the question.

Option C:
Gradient would simply refer to a difference or slope in temperature but does not capture the widely used scientific and planning term. Hence it is not the best completion for the phrase.

Option D:
Storm is associated with turbulent weather systems and precipitation, which are unrelated to the steady temperature differences described here. Therefore it is not an appropriate option.