Water-soluble inorganic nutrients moving down into soil horizons defines:
- Leaching
- Catabolism
- Humification
- Mineralisation
Explanation: By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
In a terrestrial ecosystem, a much larger fraction of energy flows through the:
- Aquatic food chain
- Grazing food chain
- Parasitic food chain
- Detritus food chain
Explanation: In a terrestrial ecosystem, a much larger fraction of energy flows through the Detritus Food Chain (DFC) than through the Grazing Food Chain (GFC).
The mass of living material at a particular trophic level is the:
- Standing crop
- Standing state
- Gross biomass
- Net biomass
Explanation: Each trophic level has a certain mass of living material at a particular time called the standing crop.
The phosphorus cycle is primarily an example of a:
- Gaseous cycle
- Sedimentary cycle
- Hydrological cycle
- Atmospheric cycle
Explanation: Phosphorus cycle is a sedimentary cycle as its main reservoir is rock, unlike gaseous cycles which have the atmosphere as their reservoir.
The reservoir for a gaseous type of nutrient cycle primarily exists in the:
- Earth's crust
- Atmosphere
- Living biomass
- Deep oceans
Explanation: For gaseous cycles like nitrogen and carbon, the reservoir exists in the atmosphere (or oceans for carbon).
The average price tag estimated by researchers for annual fundamental ecosystem services is:
- 33 billion dollars
- 100 billion dollars
- 1 trillion dollars
- 33 trillion dollars
Explanation: Robert Costanza and his colleagues put an average price tag of US $33 trillion a year on fundamental global ecosystem services.
Ecological succession starting on a completely bare rock is:
- Secondary succession
- Primary succession
- Climax succession
- Tertiary succession
Explanation: Succession that occurs in an area where no living organisms ever existed, like bare rock or newly cooled lava, is primary succession.
Ecological succession taking place in a water body is called:
- Hydrarch succession
- Psammarch succession
- Xerarch succession
- Litharch succession
Explanation: Hydrarch succession takes place in wet areas and the successional series progresses from hydric to the mesic conditions.
The entire sequence of communities that successively change in a given area is a:
- Sere
- Trophic level
- Climax
- Biome
Explanation: The entire sequence of communities that successively change in a given area are called sere(s).
Which of the following is considered a primary consumer?
Explanation: A rabbit is a herbivore, feeding directly on producers (plants), making it a primary consumer.
The standing state of nutrients in the soil heavily varies with seasons and the:
- Earth's magnetic field
- Phase of moon
- Type of ecosystem
- Time of day
Explanation: The amount of nutrients present in the soil (standing state) fluctuates depending on the season and the specific type of ecosystem.
The process of detritivores breaking down detritus into smaller particles is:
- Leaching
- Humification
- Catabolism
- Fragmentation
Explanation: Detritivores (e.g., earthworm) break down detritus into smaller particles in a process called fragmentation.
Which environmental conditions highly favor a high rate of decomposition?
- Warm and moist
- Cold and moist
- Hot and dry
- Cold and dry
Explanation: Warm and moist environments favor decomposition, whereas low temperature and anaerobiosis inhibit decomposition resulting in build-up of organic materials.
According to the 10 percent law, energy transferred between trophic levels is strictly:
- Chemical energy
- Light energy
- Kinetic energy
- Heat energy
Explanation: Energy is transferred from one trophic level to the next strictly in the form of chemical energy (biomass).
Unlike the carbon cycle, the global phosphorus cycle lacks a significant:
- Biological phase
- Sedimentary phase
- Atmospheric input
- Water phase
Explanation: There is no significant atmospheric release of phosphorus, and atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs.
The detritus food chain (DFC) begins with:
- Secondary consumers
- Primary consumers
- Primary producers
- Dead organic matter
Explanation: The detritus food chain begins with dead organic matter, which is processed by decomposers.
Net primary productivity (NPP) is gross primary productivity minus:
- Respiration losses
- Digestion losses
- Excretion losses
- Decomposition losses
Explanation: Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP = GPP - R).
In hydrarch succession, the pioneer species are usually minute:
- Phytoplankton
- Rooted hydrophytes
- Floating plants
- Submerged plants
Explanation: The pioneers in primary succession in water are small phytoplankton, which are later replaced by free-floating angiosperms.
Phosphorus is a major constituent of biological membranes, cellular energy transfer systems, and:
- Nucleic acids
- Lipids
- Carbohydrates
- Proteins
Explanation: Phosphorus is a critical component of nucleic acids (DNA and RNA), biological membranes (phospholipids), and cellular energy transfer systems (ATP).
The term 'Ecosystem' was first coined in 1935 by:
- A.G. Tansley
- E. Haeckel
- E.P. Odum
- R. Mishra
Explanation: Sir Arthur G. Tansley coined the term 'ecosystem' to recognize the integration of the biotic community and its physical environment.
What percentage of Photosynthetically Active Radiation (PAR) is captured by plants?
- One to two
- Two to ten
- Twenty to thirty
- Ten to twenty
Explanation: Plants capture only 2-10 percent of the PAR, and this small amount of energy sustains the entire living world.
Decomposition is faster if detritus is rich in nitrogen and:
- Water soluble sugars
- Chitin
- Lignin
- Cellulose
Explanation: Simple, water-soluble sugars and nitrogenous compounds provide quick energy and nutrients for decomposer microbes, accelerating decomposition.
The ecological pyramid of numbers for a parasitic food chain on a single tree is typically:
- Upright
- Irregular
- Inverted
- Spindle shaped
Explanation: A single tree (producer) supports many birds (herbivores), which in turn support even more parasites, making the pyramid of numbers inverted.
When natural rocks weather, minute amounts of phosphorus dissolve in soil solution primarily as:
- Phosphates
- Nitrates
- Sulfates
- Carbonates
Explanation: Weathering of rocks releases phosphorus slowly into the soil solution as phosphates, which are then absorbed by plant roots.
The rate of formation of new organic matter by consumers is:
- Gross productivity
- Tertiary productivity
- Secondary productivity
- Net productivity
Explanation: Secondary productivity is defined as the rate of formation of new organic matter by consumers.
The dark-coloured amorphous substance accumulating during decomposition is:
Explanation: Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action.
Humus serves as an excellent reservoir of nutrients primarily due to its:
- High solubility
- Colloidal nature
- Low molecular weight
- Crystalline nature
Explanation: Humus is colloidal in nature, giving it a high surface area and charge that allow it to hold onto water and essential nutrients tightly.
The specific species that invade a bare area are called:
- Seral species
- Pioneer species
- Dominant species
- Climax species
Explanation: The species that invade a bare area to initiate ecological succession are called pioneer species.
Ecological succession that takes place on bare rock or dry land is termed:
- Mesarch
- Hydrarch
- Halarch
- Xerarch
Explanation: Xerarch succession takes place in dry areas and the series progresses from xeric to mesic conditions.
In a grazing food chain, herbivores represent the:
- First trophic level
- Third trophic level
- Fourth trophic level
- Second trophic level
Explanation: Primary consumers (herbivores) feed directly on producers and thus occupy the second trophic level.
Vertical distribution of different species occupying different levels is called:
- Biomass distribution
- Trophic leveling
- Ecosystem stratification
- Ecological succession
Explanation: Stratification refers to the vertical arrangement of different species occupying different levels, such as trees, shrubs, and herbs in a forest.
The major natural reservoir for the phosphorus cycle is:
- Forest canopy
- Atmosphere
- Ocean water
- Rock deposits
Explanation: The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
A significant amount of carbon returns to the atmosphere as $CO_2$ primarily through:
- Fossilization
- Sedimentation
- Respiratory activities
- Photosynthesis
Explanation: Carbon returns to the atmosphere as $CO_2$ through the respiratory activities of the producers, consumers, and decomposers.
Secondary succession is generally much faster than primary succession because:
- No pioneers needed
- Soil is present
- Sunlight is intense
- More rain falls
Explanation: Since some soil or sediment is already present after the destruction of the previous community, secondary succession is much faster than primary succession.
The rate of decomposition is significantly slower if the detritus is rich in:
- Proteins and carbohydrates
- Water and salts
- Nitrogen and sugars
- Lignin and chitin
Explanation: Decomposition rate is slower if detritus is rich in lignin and chitin, and quicker if it is rich in nitrogen and water-soluble substances.
What is the primary source of energy for most ecosystems?
- Fossil fuels
- Solar radiation
- Geothermal heat
- Chemical bonds
Explanation: Except for the deep sea hydrothermal ecosystem, sun is the only source of energy for all ecosystems on Earth.
An earthworm acts on detritus primarily as a:
- Primary consumer
- Detritivore
- Secondary consumer
- Producer
Explanation: Earthworms are detritivores that help in the breakdown of detritus into smaller particles during fragmentation.
Which ecosystem typically has an inverted pyramid of biomass?
- Grassland ecosystem
- Forest ecosystem
- Marine ecosystem
- Desert ecosystem
Explanation: The pyramid of biomass in sea/ocean is generally inverted because the biomass of fishes far exceeds that of phytoplankton.
The climax community of both hydrarch and xerarch successions is a:
- Desert
- Marsh meadow
- Mesic forest
- Scrub forest
Explanation: Both hydrarch and xerarch successions lead to medium water conditions, converging to a stable mesic forest climax community.
Which ecological pyramid can never be inverted?
- Pyramid of species
- Pyramid of number
- Pyramid of biomass
- Pyramid of energy
Explanation: Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next, some energy is always lost as heat.
Excluding the Earth's lithosphere, which of the following acts as the largest global reservoir of actively cycling carbon, effectively regulating the concentration of atmospheric carbon dioxide?
- The terrestrial biosphere
- The atmospheric reservoir
- The oceanic reservoir
- The global permafrost
Explanation: About 71 percent of actively cycling carbon is found dissolved in the oceans. This massive oceanic reservoir plays a critical role in regulating the amount of carbon dioxide in the atmosphere.
The breakdown of complex organic matter by decomposers is:
- Fragmentation
- Humification
- Mineralisation
- Decomposition
Explanation: Decomposition is the process by which decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients.
Both hydrarch and xerarch successions ultimately lead to which community?
- Desert community
- Xeric community
- Hydric community
- Mesic community
Explanation: Both hydrarch (water) and xerarch (dry) successions lead to medium water conditions, converging to a mesic climax community.
Saprophytes (decomposers) are typically given which specific place in ecological pyramids?
- Top trophic level
- No specific place
- Second trophic level
- First trophic level
Explanation: Despite playing a vital role in the ecosystem, saprophytes are not given any place in ecological pyramids, which is a major limitation.
According to standard biogeochemical cycle estimates, approximately what percentage of the actively cycling global carbon is found dissolved within the Earth's oceans?
- 71 percent
- 30 percent
- 50 percent
- 95 percent
Explanation: About 71 percent of global carbon is dissolved in the oceans. This makes the oceanic carbon pool the largest active reservoir, serving to regulate atmospheric carbon dioxide levels.
In primary succession on rocks, the pioneer species are usually:
- Shrubs
- Mosses
- Lichens
- Grasses
Explanation: Lichens are usually the pioneer species on bare rock as they secrete acids to dissolve rock, helping in weathering and soil formation.
Biogeochemical cycles are mainly of two types: Gaseous and:
- Sedimentary
- Biological
- Atmospheric
- Hydrological
Explanation: Nutrient cycles are classified into gaseous (e.g., carbon, nitrogen) and sedimentary (e.g., sulfur, phosphorus) types based on their primary reservoirs.
Which of the following is completely ignored and NOT accommodated in ecological pyramids?
- Carnivores
- Herbivores
- Primary producers
- Food webs
Explanation: Ecological pyramids assume a simple, isolated food chain and do not accommodate the complex interconnections of a food web.
Secondary succession begins in areas where natural biotic communities have been:
- Frozen solid
- Newly formed
- Undisturbed
- Completely destroyed
Explanation: Secondary succession occurs in places like abandoned farm lands, burned or cut forests, where the previous biological community has been destroyed.
The amount of nutrients present in soil at any given time is the:
- Standing crop
- Mineral state
- Nutrient pool
- Standing state
Explanation: The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state.
The degradation of humus by some microbes releases inorganic nutrients via the process of:
- Humification
- Leaching
- Mineralisation
- Fragmentation
Explanation: Mineralisation is the final step of decomposition where microbes further degrade humus to release inorganic nutrients back into the soil.
The final, stable community in an ecological succession is the:
- Transitional community
- Seral community
- Pioneer community
- Climax community
Explanation: The climax community is the final stage of succession, which is in near equilibrium with the environment and remains relatively stable.
Fungi and bacteria in the detritus food chain act as:
- Primary producers
- Primary consumers
- Secondary consumers
- Decomposers
Explanation: Decomposers (saprotrophs) like fungi and bacteria secrete digestive enzymes that breakdown dead and waste materials.
The flow of energy in an ecosystem is strictly:
- Cyclic
- Bidirectional
- Unidirectional
- Multidirectional
Explanation: Energy flow is strictly unidirectional from producers to consumers and cannot revert back.
According to the standard NCERT curriculum used for UPSC, Robert Costanza estimated the price tag of nature's life-support ecosystem services. Which of the following accounted for the largest proportional contributor (roughly 50 percent)?
- Soil formation
- Climate regulation
- Nutrient cycling
- Habitat provision
Explanation: While primary scientific literature (Costanza's 1997 paper) lists nutrient cycling as the largest contributor, the standard Indian curriculum (NCERT Class 12 Biology) explicitly states that soil formation accounts for about 50 percent of the total ecosystem service value. For UPSC purposes, the NCERT text is the definitive answer key.
A network of interconnected food chains forms a:
- Biomass pyramid
- Energy pyramid
- Trophic level
- Food web
Explanation: The natural interconnection of food chains makes it a food web, allowing alternative pathways for energy flow.
In an aquatic ecosystem, the major conduit for energy flow is the:
- Grazing food chain
- Benthic food web
- Parasitic food chain
- Detritus food chain
Explanation: Unlike terrestrial ecosystems, the Grazing Food Chain (GFC) is the major conduit for energy flow in aquatic ecosystems.
The species composition of a climax community remains stable provided the:
- Nutrients are depleted
- Predators die
- Pioneers return
- Environment remains unchanged
Explanation: A climax community is in near equilibrium with the environment and its composition remains stable as long as the environment remains unchanged.
The ten percent law of energy transfer was proposed by:
- Raymond Lindeman
- Eugene Odum
- Arthur Tansley
- Charles Elton
Explanation: Raymond Lindeman (1942) proposed the 10 percent law, which states that only 10% of energy is transferred to the next trophic level.
Humans eating a varied diet of both plants and animals naturally occupy:
- No trophic level
- Only one level
- First trophic level
- Multiple trophic levels
Explanation: A given species may occupy more than one trophic level simultaneously. Humans are primary consumers when eating plants and secondary/tertiary when eating meat.