Ecosystem–Structure and Function Questions in English

(B) Primary succession refers to the process of ecological succession that occurs in areas where no living organisms have previously existed. These are barren,soilless,and uninhabited regions,such as newly cooled lava,bare rock surfaces,sand dunes,or newly created ponds and reservoirs. Since there is no pre-existing soil or organic matter,the process starts with the formation of soil by pioneer species.

(B) The sulphur cycle is a sedimentary cycle,meaning its primary reservoir is the earth's crust,where sulphur is found in rocks and minerals.
In contrast,the carbon cycle is a gaseous cycle,and its primary reservoir is the atmosphere,which contains carbon in the form of carbon dioxide $(CO_2)$.

(A) In a sedimentary cycle,the elements are circulated through the Earth's crust.
The main reservoirs for these cycles are soil and rocks.
Examples of sedimentary cycles include the sulphur cycle and the phosphorus cycle.
Therefore,the Earth's crust acts as the primary reservoir for these nutrients.

(C) Succession is the process of change in the species structure of an ecological community over time.
Secondary succession occurs in areas where life existed previously but was destroyed (e.g.,abandoned farm lands,burned or cut forests).
In a buried or cut forest,the soil is already present,rich in humus,and often contains seeds,spores,or underground stems (rhizomes).
Because the soil and nutrients are already available,the process of colonization and community development is much faster compared to primary succession on bare rock or newly cooled lava,which requires soil formation first.

(D) Homeostasis,also known as the state of equilibrium or the balance of nature,is maintained in an ecosystem through various control mechanisms. These include the carrying capacity of the environment,self-regulation,and feedback systems that ensure the stability of the ecosystem.

(C) In ecological succession,the entire sequence of communities that successively change in a given area is called a sere. The individual transitional communities that appear during this process are known as seral communities or seral stages.

(B) Organisms that feed on dead organic matter are known as decomposers or detritivores.
In a Detritus Food Chain $(DFC)$,the dead organic matter (detritus) acts as the $1^{st}$ trophic level.
The organisms that feed on this detritus (detritivores) occupy the $2^{nd}$ trophic level.
Decomposers are heterotrophic organisms,primarily bacteria and fungi,that break down complex organic matter into simple inorganic substances through the secretion of extracellular enzymes.
They play a crucial role in nutrient cycling within the ecosystem.

(D) Autotrophs are organisms that can synthesize their own organic food from inorganic raw materials using energy from sunlight or chemical reactions.
They serve as the primary producers in an ecosystem.
They occupy the first trophic level and form the base of the food chain.
Therefore,all the given statements are correct.

(B) In a pond ecosystem,the producers are phytoplankton.
Primary consumers are organisms that feed directly on producers.
Zooplankton,such as small crustaceans (water fleas,Cyclops),are herbivores that feed on phytoplankton.
Therefore,zooplankton act as the primary consumers in a pond ecosystem.
Other examples of primary consumers in this ecosystem include mosquito larvae,tadpoles,snails,and certain small fish.

(D) The components of an ecosystem are broadly classified into two main categories:
$1$. Biotic components: These include all living organisms within the ecosystem,such as producers (plants),consumers (animals),and decomposers (microorganisms).
$2$. Abiotic components: These include all non-living physical and chemical factors that influence the ecosystem,such as air,water,soil,solar radiation,and temperature.

(A) Benthos are organisms that live at the bottom of a water body,such as a lake or pond.
In the context of a pond ecosystem,these organisms often function as primary consumers or decomposers residing in the deep benthic zone.

(B) In an ecosystem,the trophic structure is organized as follows:
$1$. Producers occupy Trophic level-$I$.
$2$. Herbivores are organisms that feed directly on producers,thus they are Primary consumers and occupy Trophic level-$II$.
$3$. Primary carnivores feed on herbivores,thus they are Secondary consumers and occupy Trophic level-$III$.
$4$. Secondary carnivores (or top carnivores) occupy Trophic level-$IV$ or higher.
Therefore,'Primary consumers' and 'herbivores' refer to the same ecological group.

(D) Biogeochemical cycles are broadly classified into two types: gaseous and sedimentary.
$1.$ Gaseous cycles: The reservoir for these elements is the atmosphere or hydrosphere. Examples include the nitrogen cycle $(III)$ and the carbon cycle $(IV)$.
$2.$ Sedimentary cycles: The reservoir for these elements is the Earth's crust (soil and rocks). Examples include the sulphur cycle $(I)$ and the phosphorus cycle $(II)$.
Therefore, nitrogen and carbon cycles are gaseous cycles.

(B) Lithosere is a type of xerosere that begins on bare rock surfaces.
The initial substratum lacks water and organic matter,containing only minerals in an unweathered state.
Lichens are the pioneer species that colonize these bare rocks,initiating the process of primary succession.

(A) Primary succession in water,also known as hydrarch succession,follows a specific sequence of stages:
$1$. Phytoplankton stage: The pioneer species are small phytoplanktons.
$2$. Submerged plant stage: Rooted submerged hydrophytes appear.
$3$. Submerged free-floating plant stage: Free-floating angiosperms appear.
$4$. Reed-swamp stage: Plants like sedges and grasses appear.
$5$. Marsh-meadow stage: The area becomes more terrestrial.
$6$. Scrub and Forest stage: Finally,trees dominate the area.
Therefore,the correct sequence is: $Small \ phytoplanktons \rightarrow Rooted \ hydrophytes \rightarrow Free-floating \ angiosperms \rightarrow Sedges \rightarrow Grasses \rightarrow Trees$. Note: Option $A$ is the closest logical progression provided in the choices,though standard $NCERT$ sequences often list rooted hydrophytes before free-floating stages depending on the specific depth and conditions.

(A) The structure of an ecosystem is characterized by the organization of its biotic and abiotic components.
Key features of ecosystem structure include:
$1$. Species composition: Identification and enumeration of plant and animal species.
$2$. Stratification: The vertical distribution of different species occupying different levels.
$3$. Energy flow,nutrient cycling,and primary production.
Natality,mortality,and sex ratio are characteristics of a population,not an ecosystem structure.
Therefore,stratification is the correct answer.

(C) Another name for nutrient cycling is the biogeochemical cycle.
The movement of nutrient elements through various components (abiotic and biotic) of an ecosystem is known as nutrient cycling or the biogeochemical cycle.

(A) Stability is the ability of an ecosystem to resist change or remain in its original state despite unfavourable factors.
Resilience is the capacity of an ecosystem to recover or regain its original structure and function after being disturbed or damaged.
Since the ecosystem is easily damaged,it has low stability.
Since it can recover after the damaging effect stops,it has high resilience.
Therefore,the correct answer is low stability and high resilience.

(A) In a pond ecosystem,producers include phytoplankton (e.g.,diatoms,Chlorella,Spirogyra,Chlamydomonas,etc.),free-floating macrophytes (e.g.,Lemna,Azolla),suspended macrophytes (e.g.,Utricularia,Hydrilla),submerged plants (Vallisneria),floating-leaved plants (e.g.,Nelumbo),and emergent plants (Sagittaria),etc.
Since diatoms are photosynthetic organisms that convert solar energy into chemical energy,they function as producers in the aquatic food chain.

(B) Hydrarch succession,or hydrosere,is the process by which a pond ecosystem gradually transitions into a terrestrial community.
In the reed-swamp stage,the water body becomes shallow (approximately $0.3-1.0 \ m$ deep),allowing amphibious plants to thrive.
$Sagittaria$ is a characteristic plant of the reed-swamp stage.
$Juncus$ is associated with the sedge-meadow stage.
$Salix$ represents the woodland stage.
$Trapa$ is found in the rooted-floating stage.

(B) In a lake,the ecosystem is divided into zones such as the littoral zone,limnetic zone,and profundal zone.
In the $Limnetic$ zone,which is the open water area away from the shore,light penetration is sufficient for photosynthesis.
The primary producers in this zone are mainly phytoplanktonic algae,such as diatoms,green algae,and blue-green algae.
In contrast,the $Profundal$ zone is the deep,dark region where light is insufficient for photosynthesis,and organisms here depend on organic matter falling from the upper zones.

(B) Stratification refers to the vertical distribution of different species occupying different levels in an ecosystem.
In a forest ecosystem,particularly in tropical rainforests,stratification is highly complex and well-defined.
It typically consists of five vertical layers: the subterranean layer,the forest floor,the herbaceous layer,the shrub layer,and the tree canopy layer.

(C) An ecosystem is composed of biotic (living) and abiotic (non-living) components. The biotic component includes producers,consumers,and detritivores. Producers are essential for energy fixation (photosynthesis),while detritivores are essential for nutrient cycling and decomposition. Therefore,producers and detritivores are considered the absolutely essential functional components of the ecosystem.

(B) In the phosphorus cycle of a terrestrial ecosystem:
$1$. $A$ represents the process of Decomposition,where organic matter (detritus) is broken down into inorganic nutrients.
$2$. $B$ represents the process of Weathering,which releases phosphorus from rock minerals into the soil.
$3$. $C$ represents Producers (plants),which take up phosphorus from the soil.
$4$. $D$ represents the Soil solution,which acts as the reservoir for inorganic phosphorus.
Therefore,the correct identification is $A-$Decomposition,$B-$Weathering,$C-$Producer,$D-$Soil.

(A) The components of an ecosystem are broadly classified into two categories: Biotic and Abiotic components.
$1$. $A$ represents the Biotic component,which includes living organisms like producers,consumers,and decomposers $(C)$.
$2$. $B$ represents the Abiotic component,which includes non-living factors like soil,water,gases,and solar radiation.
$3$. Producers (autotrophs) are further classified based on their energy source into $D$ (Photoautotrophs) and $E$ (Chemoautotrophs).
Therefore,the correct sequence is $A-$Biotic,$B-$Abiotic,$C-$Decomposers,$D-$Photoautotrophs,$E-$Chemoautotrophs.

(A) Stratification refers to the vertical distribution of different species occupying different levels in an ecosystem.
It is most pronounced in tropical rainforests due to the high diversity of plant species and their varying heights,which create distinct layers such as the emergent layer,canopy,understory,and forest floor.
This vertical layering allows for the efficient utilization of light and resources among different organisms.

(C) The nutrient reservoir acts as a buffer in the ecosystem.
It meets the deficit that arises due to an imbalance in the rate of influx (input) and efflux (output) of nutrients within the system.

(D) An agroecosystem is a man-made ecosystem that covers vast areas of land globally for agricultural purposes.
It is the largest man-made ecosystem because it involves extensive land use for crop production,livestock,and associated management practices.
Unlike zoos,gardens,or aquariums,which are small-scale and localized,agroecosystems span millions of hectares worldwide.

(B) Plants capture only $2-10\;\%$ of $PAR$ (Photosynthetically Active Radiation) for the synthesis of organic matter. This corresponds to approximately $1-5\;\%$ of the total incident solar radiation.

(C) The amount of living material present in different trophic levels at a given time is known as the standing crop.
It is measured as the mass of living organisms (biomass) or the number of organisms in a unit area.
It is not always represented as dry weight only; it can be measured as fresh weight or number as well.
Therefore,the statement that it is 'always represented as dry weight only' is incorrect.

(C) The functional aspects of an ecosystem include energy flow,decomposition,and nutrient cycling. Species composition is a structural aspect of an ecosystem,not a functional one.

(A) Ecological succession is defined as the gradual and predictable change in the species composition of a given area. It is an orderly and sequential process that leads to the development of a stable climax community.

(B) According to Robert Costanza's estimates for ecosystem services,the cost distribution is as follows: Soil formation accounts for approximately $50\%$ of the total value. Nutrient cycling accounts for less than $10\%$ (approximately $6\%$),while Climate regulation and Habitat for wildlife each account for approximately $6\%$. Therefore,the statement that Nutrient cycling accounts for $10\%$ is incorrect as it is less than $10\%$.

(B) Ecological succession is a gradual and predictable change in the species composition of a given area. During this process,as the community structure evolves from pioneer species to a climax community,the physical and biological environment changes significantly. This includes changes in the types and diversity of decomposers present in the ecosystem,as they adapt to the changing availability of organic matter and nutrient cycling requirements at different seral stages.

(B) The global ecosystem is broadly divided into $2$ basic categories to facilitate its study:
$(i)$ Terrestrial ecosystem: Includes forests,grasslands,and deserts.
$(ii)$ Aquatic ecosystem: Includes ponds,lakes,wetlands,rivers,and oceans.

(D) sparrow acts as a primary consumer when it feeds on seeds,grains,or fruits,as it directly consumes plant products.
It acts as a secondary consumer when it feeds on insects or small worms,which are primary consumers.
Therefore,a sparrow occupies both the primary consumer and secondary consumer trophic levels depending on its diet.

(A) In ecological succession,the initial seral stages (pioneer communities) are characterized by simple food webs,low species diversity,and low biomass compared to the climax community. As succession progresses,diversity and biomass increase,and niche specialization becomes more pronounced.

(D) Biogeochemical cycles are broadly classified into two types: gaseous cycles and sedimentary cycles.
In gaseous cycles,the reservoir for the element is the atmosphere or hydrosphere (e.g.,Carbon,Nitrogen,Hydrogen,Oxygen).
In sedimentary cycles,the reservoir for the element is the Earth's crust (e.g.,Phosphorus,Sulfur).
Therefore,Phosphorus is the odd one out as it represents a sedimentary cycle.

(B) Ecological succession is the process of change in the species structure of an ecological community over time.
Primary succession occurs in areas where no living organisms previously existed,such as bare rock or sand dunes.
Because these areas lack soil and organic matter,the process of soil formation and colonization by pioneer species is extremely slow.
Consequently,it can take several thousand years for primary succession on sand dunes to reach a stable climax community.
In contrast,secondary succession (as seen in burnt forests,flooded lands,or abandoned farmlands) occurs much faster because soil and some organic matter are already present.

(C) In Xerarch succession (succession on bare rock),the sequence of communities is as follows:
$1$. Pioneer species: Lichens.
$2$. Transitional communities: Mosses $\rightarrow$ Herbs $\rightarrow$ Shrubs.
$3$. Climax community: Forest.
Therefore,the correct sequence of transitional communities is Bryophytes (Mosses) $\rightarrow$ Herbs $\rightarrow$ Shrubs.

(D) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
It is considered a self-sufficient unit.
It involves the cyclic exchange of materials between living beings and the environment.
It requires a continuous input of energy (usually solar energy) to maintain its structure and function.
However,an ecosystem is not characterized solely by a 'major' vegetation type; it can be characterized by both minor and major vegetation types depending on the scale and complexity of the ecosystem.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment. It consists of both biotic components (producers,consumers,and decomposers) and abiotic components (inorganic substances,organic compounds,and climatic factors).

(D) Artificial aquatic ecosystems are those created or maintained by human intervention.
$1$. Large dams and reservoirs are constructed by humans for water storage and power generation.
$2$. Canals are man-made waterways.
$3$. Fishery tanks and aquaria are specifically designed and maintained by humans for aquatic life.
Therefore,all the options listed are examples of artificial aquatic ecosystems.

(A) An ecosystem is characterized by both structural and functional aspects.
Structural aspects include species composition,stratification,and diversity.
Functional aspects include productivity,decomposition,energy flow,and nutrient cycling.
Therefore,productivity is a functional aspect,not a structural one.

(C) The functional aspects of an ecosystem include energy flow,nutrient cycling,and homeostasis. Homeostasis refers to the ability of an ecosystem to maintain a stable internal environment despite external changes. Species composition,inorganic nutrients,and topography are considered structural aspects of an ecosystem.

(A) Stratification refers to the vertical distribution of different species occupying different levels in an ecosystem.
Tropical rain forests exhibit the most complex and well-developed stratification due to high biodiversity,abundant rainfall,and favorable temperatures,which allow for distinct layers such as the emergent layer,canopy,understory,and forest floor.
Therefore,the correct option is $A$.

(C) Key industry animals are those organisms that convert plant matter into animal biomass.
Since herbivores consume producers (plants) and serve as the primary source of energy for higher trophic levels,they are referred to as key industry animals.

(B) In an ecosystem,energy is lost at each trophic level due to respiration.
For producers,the respiratory loss is approximately $20\%$.
For herbivores,the respiratory loss is approximately $30\%$.
For carnivores,the respiratory loss is approximately $60\%$.
Therefore,the correct sequence is $20\%, 30\%, 60\%$.

(C) Earth is considered an open system regarding energy because it receives solar radiation and radiates heat back into space.
However,it is considered a closed system regarding matter because the amount of matter (elements) on Earth remains essentially constant,with negligible exchange with outer space.

(B) The provided image illustrates the 'submerged free-floating plant' stage of hydrarch succession.
In the sequence of hydrarch succession,the submerged free-floating plant stage is followed by the 'reed-swamp' stage,where emergent plants like Typha and Sagittaria begin to dominate.