UPSC Geoscientist Archives

41. Which one of the following groups contributes the maximum number of sp

Which one of the following groups contributes the maximum number of species to the biosphere?

Reptiles

Mammals

Insects

Birds

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Insects constitute the largest group of animals on Earth, both in terms of the number of species and the number of individuals. Their diversity far surpasses that of reptiles, mammals, or birds.

– Insects belong to the class Insecta, which is the most speciose class within the phylum Arthropoda.
– Estimates for the number of insect species vary widely, but most sources agree that there are millions of species, significantly more than all other animal groups combined.

Other highly diverse groups include fungi, bacteria, and certain plant groups, but among the animal groups listed in the options, insects are overwhelmingly the most numerous in terms of species count in the biosphere.

42. When two species can very well ignore each other totally, each remaini

When two species can very well ignore each other totally, each remaining perfectly neutral and causing no advantage or inconvenience to its neighbour, the relationship is termed as

commensalism

amensalism

symbiosis

mutualism

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The description “When two species can very well ignore each other totally, each remaining perfectly neutral and causing no advantage or inconvenience to its neighbour” precisely defines the ecological relationship known as **Neutralism (0/0)**. However, Neutralism is not provided as an option. Among the given choices, Symbiosis is a broad term referring to a close and long-term interaction between two different biological organisms. While modern ecological definitions of symbiosis typically include interactions that have a defined effect on at least one partner (mutualism +/+, commensalism +/0, parasitism +/-), the word ‘symbiosis’ literally means “living together”. In a very broad, potentially outdated or simplified interpretation, it could be argued that species co-existing neutrally are still “living together”. Given that none of the specific interaction types (commensalism, amensalism, mutualism) fit the description of neutrality, and Symbiosis is the only option that refers to species sharing space, it is the most likely intended answer, despite the ecological inaccuracy of classifying neutralism as a type of symbiosis in modern terminology.

– The described relationship (0/0 effect) is called Neutralism.
– Neutralism is not listed as an option.
– Commensalism (+/0), Amensalism (0/-), and Mutualism (+/+) describe specific interactive effects, none of which are neutral for both parties.
– Symbiosis refers to a close and long-term relationship of “living together”.

Ecological interactions are typically classified based on the effect on each species: Positive (+), Negative (-), or Neutral (0). Neutralism (0/0) is the state where two species have no detectable effect on each other. While technically distinct from symbiotic interactions (which imply a close relationship with effect), Symbiosis is sometimes used in a very general sense to mean cohabitation. If this question is based on such a general interpretation, Symbiosis would be the intended answer despite the lack of fit with the specific description of neutrality.

43. Azotobacter and Clostridium convert

Azotobacter and Clostridium convert

gaseous molecular nitrogen into ammonia

ammonia present in soil to gaseous nitrogen

humus present in soil to mineralized constituents

normal healthy soil to toxic soil

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Azotobacter and Clostridium are genera of free-living bacteria known for their ability to fix atmospheric nitrogen. Nitrogen fixation is the process by which gaseous molecular nitrogen (N₂, which is abundant in the atmosphere but unusable by most organisms) is converted into ammonia (NH₃), which can then be incorporated into organic molecules usable by plants and other organisms. Azotobacter is aerobic, while Clostridium is anaerobic.

– Azotobacter and Clostridium are free-living nitrogen-fixing bacteria.
– Nitrogen fixation is the conversion of N₂ gas into ammonia (NH₃).
– This process is essential for making nitrogen available in ecosystems.
– Ammonia can be further converted into other nitrogen compounds like nitrates by other bacteria (nitrification).

Nitrogen fixation is a crucial part of the nitrogen cycle. Besides free-living bacteria like Azotobacter and Clostridium, symbiotic bacteria (like Rhizobium in legume root nodules) are also major nitrogen fixers. Denitrification, the conversion of nitrates back to N₂, is carried out by a different group of bacteria.

44. The term ‘lotic facies’ is used to denote water of

The term ‘lotic facies’ is used to denote water of

rivers and streams

sag ponds

ponds

deep ocean floor

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In ecology, the term ‘lotic’ refers to freshwater ecosystems characterized by flowing water, such as rivers and streams. The ‘lotic facies’ describes the biological community and environmental conditions found in such flowing water habitats.

– Lotic environments are characterized by flowing water.
– Examples include rivers, streams, and creeks.
– Lentic environments are characterized by standing water (e.g., ponds, lakes, swamps).
– ‘Facies’ in ecology often refers to a specific type of habitat or community within a larger environment.

Organisms inhabiting lotic environments exhibit adaptations to cope with water currents, such as streamlined bodies, holdfasts, or living under rocks. The environmental conditions (e.g., oxygen levels, temperature, substrate type) in lotic systems are significantly influenced by water flow.

45. Eagle fern, horsetail, chrysanthemum grow well in

Eagle fern, horsetail, chrysanthemum grow well in

acidic soil

extremely alkaline soil

neutral soil

highly alkaline soil

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Eagle fern (Pteridium aquilinum) is widely recognized as an indicator plant for acidic soils. It thrives in low-pH conditions where many other plants struggle. Horsetail (Equisetum species) can tolerate various soil conditions but is often found in damp, acidic, or nutrient-poor soils. While Chrysanthemums prefer slightly acidic to neutral soil, Eagle fern is a particularly strong indicator of acidity among the listed plants. Therefore, acidic soil is the most likely common condition where these plants grow well.

– Soil pH is a crucial factor affecting plant growth and distribution.
– Some plants are indicators of specific soil pH ranges.
– Eagle fern is strongly associated with acidic soils.
– Horsetail and Chrysanthemum also have preferences or tolerances that can include acidic conditions.

Soil acidity (low pH) can affect nutrient availability and the presence of toxic substances (like aluminum). Plants adapted to acidic soils have mechanisms to cope with these conditions. Extremely alkaline soils (high pH) present different challenges, such as nutrient deficiencies (e.g., iron, zinc) and are favoured by different plant species (calcicoles).

46. Soils which reflect the composition of underlying rocks are always

Soils which reflect the composition of underlying rocks are always

young

highly evolved

mature

moderately old

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Soils develop over time through processes like weathering, decomposition, and horizon formation (pedogenesis). Young or immature soils have undergone limited pedogenic development. As a result, their properties, including mineral composition, strongly reflect the composition of the underlying parent material (bedrock or unconsolidated deposits). Highly evolved or mature soils have distinct horizons and properties that may differ significantly from the parent material due to long-term processes.

– Soil formation (pedogenesis) is a gradual process.
– Young soils are characterized by limited horizon development.
– The characteristics of young soils are strongly influenced by the parent material.
– Mature soils have well-developed horizons and properties modified by time, climate, organisms, and topography.

The degree to which a soil’s composition reflects its parent material is often used as an indicator of soil age and development stage. In highly weathered (evolved/mature) soils, many original minerals from the parent rock may have been altered or leached away, leaving behind more resistant materials or newly formed secondary minerals.

47. Which one of the following results due to the ‘edge effect’ between co

Which one of the following results due to the ‘edge effect’ between cold and warm ocean waters?

Development of dense phyto- planktons rich in diatoms

Decrease in fish population in the area

Decrease in mussel population in the area

Decrease in primary productivity of the area

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The boundary between cold and warm ocean waters (an ‘edge effect’) often results in turbulent mixing or upwelling. This process brings nutrient-rich water from deeper layers to the surface. The increased availability of nutrients in the sunlit surface zone stimulates high primary productivity, leading to dense blooms of phytoplankton, especially diatoms, which are a major component of marine phytoplankton and thrive in nutrient-rich conditions.

– ‘Edge effect’ between distinct water masses (like cold and warm currents) causes mixing and/or upwelling.
– Upwelling brings nutrients from the deep ocean to the surface.
– Increased surface nutrients fuel phytoplankton growth (primary productivity).
– Diatoms are common and abundant phytoplankton in nutrient-rich waters.

Areas of oceanographic fronts and upwellings, like the edge of the Gulf Stream, are often highly productive ecosystems, forming the base of rich food webs that support large fish populations, marine mammals, and seabirds. This explains why many major fisheries are located in areas of upwelling.

48. A juvenile ecosystem is characterized by energy usage which is primari

A juvenile ecosystem is characterized by energy usage which is primarily directed towards

multiplication and growth of organisms

maintenance of biocenose

conservation of biocenose

reduced growth of plants

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A juvenile or early successional ecosystem is characterized by high energy input directed primarily towards the accumulation of biomass, meaning rapid growth and reproduction (multiplication) of organisms, particularly primary producers. Energy efficiency in terms of complex food webs and nutrient cycling is lower compared to mature ecosystems.

– Juvenile ecosystems (early successional stages) focus on production and growth.
– Energy is channeled into accumulating biomass and increasing population size.
– Net primary productivity is often high, but respiration (maintenance cost) is relatively low per unit biomass compared to mature systems.
– Mature ecosystems focus more on maintenance, diversity, and efficient nutrient cycling.

Ecological succession describes the process of change in the species structure of an ecological community over time. Early stages are pioneer stages (juvenile ecosystems), while later stages are climax communities (mature ecosystems). Energy flow patterns change significantly during succession.

49. Earthworm is a well-known example of

Earthworm is a well-known example of

saprophage

coprophage

necrophage

geophage

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Earthworms are well-known examples of geophages. Geophagy is the practice of eating earth or soil. Earthworms consume large quantities of soil as they burrow, digesting the organic matter and associated microorganisms within the soil matrix.

– Geophage: An organism that feeds on soil.
– Saprophage/Detritivore: Feeds on dead organic matter (detritus). Earthworms are also detritivores, but their primary mode of feeding involves ingesting soil containing detritus.
– Coprophage: Feeds on faeces.
– Necrophage: Feeds on dead animals (carrion).

By ingesting soil, earthworms play a crucial role in soil formation, aeration, drainage, and nutrient cycling. They break down organic matter, mix soil horizons, and excrete nutrient-rich casts, significantly improving soil fertility and structure.

50. The term ‘biotope’ refers to

The term ‘biotope’ refers to

a set of general physical conditions excluding chemical and biological conditions in a given geographic area

a homogeneous set of physical and chemical conditions in a given geographic area at a particular time

a homogeneous set of both biological and chemical conditions in a given geographic area

a particular type of biological assemblage in a given geographic area

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A biotope is an area of uniform environmental conditions that provides a habitat for a specific assemblage of plants and animals. It is defined by its homogeneous set of physical and chemical characteristics, distinct from the living community (biocenose) that inhabits it.

– Biotope refers to the non-living environment or habitat.
– It is characterized by homogeneous physical and chemical conditions (e.g., temperature, humidity, soil type, pH, salinity).
– The living community inhabiting a biotope is called a biocenose or biotic assemblage.
– An ecosystem comprises both the biotope and the biocenose.

The concept of biotope is central to the study of ecology, particularly in habitat classification and conservation. Understanding the characteristics of a biotope helps predict the types of organisms that can thrive there and assess the impact of environmental changes.