UPSC Geoscientist

31. Ozone layer depletion is concentrated in:

Ozone layer depletion is concentrated in:

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mid-latitude regions.
high latitude regions.
equatorial regions.
tropical regions.
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Ozone layer depletion is most significantly observed in the high latitude regions, particularly over the Antarctic (forming the ‘ozone hole’) and to a lesser extent over the Arctic.
– Ozone depletion is concentrated at the poles.
– This phenomenon is driven by chemical reactions involving ozone-depleting substances (like CFCs) which are catalyzed on the surface of polar stratospheric clouds (PSCs) that form at very low temperatures in the polar stratosphere during winter.
– The depletion becomes pronounced in spring when sunlight returns, initiating the catalytic cycles.
– While ozone depletion occurs globally to some extent, the most severe and rapid depletion occurs in the high latitudes.
– Mid-latitude depletion is less severe than polar depletion.
– Equatorial and tropical regions experience relatively less ozone depletion due to different stratospheric temperature and circulation patterns.

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32. Which one of the following is the main natural source of Methane?

Which one of the following is the main natural source of Methane?

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Wetlands
Belching by cattle
Leakage from pipelines
Burning of wood
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Natural wetlands are the largest natural source of methane emissions globally. Methane is produced by anaerobic bacteria in waterlogged soils and sediments where organic matter decomposes in the absence of oxygen.
Anaerobic decomposition of organic matter in waterlogged environments like swamps, marshes, and bogs is the primary natural process generating methane.
Other significant natural sources include termites, oceans, geological seeps, and wildfires. Anthropogenic sources like livestock (belching), rice cultivation, landfills, and fossil fuel production (leakage from pipelines is an example) are also major contributors to the total atmospheric methane concentration, often exceeding natural sources in terms of total emissions. However, the question asks for the *main natural* source.

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33. Which one of the following greenhouse gases is the largest single cont

Which one of the following greenhouse gases is the largest single contributor to anthropogenic radiative forcing?

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Methane
Ozone
Nitrous oxide
Carbon dioxide
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Among the listed greenhouse gases, Carbon dioxide (CO2) is the largest single contributor to anthropogenic radiative forcing since the pre-industrial era. Its high concentration, long atmospheric lifetime, and significant increase due to the burning of fossil fuels and deforestation make it the primary driver of climate change.
Carbon dioxide is the most significant anthropogenic greenhouse gas contributing to the enhanced greenhouse effect and radiative forcing.
Radiative forcing is the change in the balance between incoming solar radiation and outgoing infrared radiation in the atmosphere. While methane (CH4) and nitrous oxide (N2O) have higher global warming potentials per molecule than CO2, the much larger increase in CO2 concentration in the atmosphere results in its dominant contribution to the overall anthropogenic radiative forcing. Ozone (O3) also contributes, but its distribution and lifetime are more variable.

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34. Biodiversity in terms of species richness is maximum in:

Biodiversity in terms of species richness is maximum in:

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natural grasslands.
semi-natural grasslands.
artificial grasslands.
well maintained and watered grasslands.
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Natural grasslands, untouched by intensive human management like heavy fertilization, frequent mowing, or planting of monocultures, typically exhibit the highest species richness compared to semi-natural or artificial (cultivated) grasslands. This is due to complex ecological interactions, varied microhabitats, and a lack of selective pressures from intensive management favoring only a few species.
Undisturbed or minimally managed natural ecosystems generally support greater biodiversity than managed or artificial ones.
Semi-natural grasslands, like traditionally managed meadows, can still have high biodiversity but might be slightly less diverse than pristine natural ones depending on the intensity and type of management. Artificial grasslands, such as pastures sown with only a few grass species for livestock or manicured lawns, have significantly lower species richness. Well-maintained and watered grasslands, if referring to artificial ones, would not be the most diverse.

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35. The salt in sea water comes from:

The salt in sea water comes from:

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rain.
chemical exchange between sea water and its substratum as well as hydrothermal emissions.
evaporation of water and concentration of dissolved salts.
mixing of different density waters during natural warm and cold current movements.
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The salt in sea water primarily originates from the weathering and erosion of rocks on land, with rivers carrying dissolved minerals and salts to the ocean. Additionally, significant contributions come from chemical reactions between seawater and the ocean floor (rock-water interactions) and from hydrothermal emissions at mid-ocean ridges and other volcanic activity, which release dissolved minerals into the water.
The salinity of the ocean is a result of geological processes involving the dissolution of minerals from rocks on land and the seabed, transported by rivers and released through volcanic and hydrothermal activity.
While evaporation concentrates the existing salts, it is not the *source* of the salts themselves. Rain contains very little dissolved salt. Mixing of water masses influences temperature and currents but doesn’t create the salts. Therefore, chemical exchange with the substratum and hydrothermal vents are key processes, alongside riverine input, that contribute to the ocean’s salt content.

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36. Which one of the following about anemophilous plants is correct?

Which one of the following about anemophilous plants is correct?

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Bright coloured flowers
Sweet smelling flowers
No nectar
Dwarf stigmata
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Anemophilous plants are pollinated by wind. Since they do not rely on attracting animal pollinators, their flowers typically lack features like bright colours, sweet scents, and nectar, which are adaptations for attracting insects or birds.
The absence of nectar, bright petals, and strong scents is a characteristic adaptation of wind-pollinated (anemophilous) flowers because they do not need to bribe or lure pollinators.
Other characteristics of anemophilous flowers include small, inconspicuous flowers, large production of light, smooth pollen grains that are easily carried by wind, and often exposed stamens and large, feathery or branched stigmas to efficiently capture airborne pollen. Examples include grasses, oaks, ragweed, and pine trees.

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37. Heliophile plants require mean maximum illumination of:

Heliophile plants require mean maximum illumination of:

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30,000 lux.
20,000 lux.
10,000 lux.
40,000 lux.
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Heliophile plants, also known as sun-loving plants, require high light intensity for optimal growth. While the exact threshold varies depending on the source and context, values around 30,000 lux or higher are typically associated with conditions suitable for heliophytes.
Heliophile plants are adapted to thrive in direct sunlight and require high illumination levels for maximum photosynthetic activity.
In contrast, sciophyte plants (shade-tolerant plants) require much lower light intensities, often below 5,000 lux. The mean maximum illumination experienced by plants varies significantly depending on latitude, time of day, season, and environmental factors like cloud cover and canopy shading. Full sunlight can exceed 100,000 lux.

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38. The edge effect at the contact of continental fresh water and sea wate

The edge effect at the contact of continental fresh water and sea water results in:

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non-deposition of sediments due to turbulence.
deposition of sand due to fall in system energy.
deposition of organic matter due to density difference.
flocculation of clays resulting in formation of mud deposits.
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When freshwater mixes with saltwater, especially in estuaries, the dissolved salts (ions) in the saltwater neutralize the negative charges on clay particles carried by the freshwater. This neutralization reduces the electrostatic repulsion between clay particles, causing them to clump together (flocculate) and settle out of suspension, forming mud deposits.
Flocculation of clay particles is a key process occurring at the salt-freshwater interface in estuaries, driven by changes in salinity.
This flocculation and subsequent deposition of fine sediments are major factors contributing to the formation of muddy bottoms, tidal flats, and salt marshes characteristic of estuarine environments. The mixing zone, where this occurs, is often referred to as the “turbidity maximum.”

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39. The term wetland implies:

The term wetland implies:

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land covered by rain water only.
slow moving water covered wet ground.
water logged wet ground.
fast moving water covered wet ground.
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A wetland is an area of land where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. This results in waterlogged, wet ground.
The defining characteristic of a wetland is the presence of water, which leads to saturated or waterlogged soil conditions that influence the types of plants and animals that can live there.
Wetlands can be static or flowing, shallow or deep, and can include marshes, swamps, bogs, fens, estuaries, and other similar environments. The presence of water affects the soil chemistry (often anaerobic conditions) and supports characteristic wetland vegetation (hydrophytes).

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40. The amount of sun energy trapped by plants is:

The amount of sun energy trapped by plants is:

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1 % - 3 %
12 % - 15 %
17 % - 20 %
23 % - 26 %
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The efficiency of plants in converting solar energy into chemical energy through photosynthesis is relatively low, typically ranging from 1% to 3% of the incident solar radiation that reaches the plant’s surface over a growing season.
Most of the solar energy incident on a plant is not used for photosynthesis; it is reflected, transmitted, or dissipated as heat. Only a small fraction is converted into biomass.
While theoretical maximum efficiencies can be higher under ideal conditions, actual net photosynthetic efficiency in ecosystems is limited by factors like light intensity, CO2 concentration, temperature, water availability, nutrient status, and respiration losses. Agricultural crops might achieve slightly higher efficiencies under optimized conditions, but 1-3% is a commonly cited range for overall ecosystem efficiency.

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