Ecosystem–Structure and Function Questions in English

(A) Primary succession is the process of biological community development in an area where no living organisms previously existed,such as on newly cooled lava,bare rock,or sand dunes. Since the lava surface is devoid of any soil or pre-existing life,the colonization by pioneer species (like lichens) marks the beginning of primary succession.

(C) Ecological succession is the gradual and predictable change in the species composition of a given area.
In primary succession,the process starts in areas where no living organisms ever existed,such as bare rocks.
The first group of organisms to colonize such a barren area are the pioneer species,which are typically lichens or mosses.
These pioneer species act as producers,as they are autotrophic and begin the process of soil formation and energy fixation,thereby establishing the foundation for subsequent communities.
Therefore,producers are the first to be established at the primary level of succession.

(C) Hydrarch succession is the process of ecological succession that begins in water or areas with abundant moisture.
In this process,the plant community gradually evolves from an aquatic environment towards a mesophytic (moderate moisture) environment.
Therefore,the correct option is $C$.

(C) In ecological succession,the first organisms to colonize a bare area are known as pioneer species.
On bare rocks,the process of succession begins with the colonization of lichens.
Lichens secrete acids that help in the weathering of rocks,which leads to the formation of soil.
This soil then supports the growth of bryophytes and subsequently other higher plants.

(D) Ecological succession is the gradual and predictable change in the species composition of a given area.
$1$. Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
$2$. Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
$3$. Hence,in both cases,the final climax community is a forest,which represents a mesic (moderate water) condition.

(C) $Pioneer$ $Species$ refers to the first organisms to colonize a previously barren or unoccupied area,such as bare rock,thereby initiating the process of ecological succession.
These species modify the environment,making it more suitable for subsequent species to inhabit.
For example,$Lichens$ are typically the $Pioneer$ $Species$ on bare rocks.

(B) In a hydrarch succession (succession in aquatic areas), the process proceeds from hydric (aquatic) to mesic (moderate) conditions.
$1$. The pioneer species are usually small organisms like $Phytoplankton$.
$2$. These are followed by $Rooted \text{ } submerged \text{ } plants$.
$3$. Next, $Free-floating \text{ } plants$ appear.
$4$. Then, $Rooted-floating \text{ } angiosperms$ (like $Nymphaea$) occur.
$5$. This is followed by the $Reed-swamp \text{ } stage$, $Marsh-meadow \text{ } stage$, $Scrub \text{ } stage$, and finally the $Forest \text{ } (climax \text{ } community)$.
Therefore, the correct sequence is $Phytoplankton \rightarrow Rooted \text{ } submerged \text{ } plants \rightarrow Free-floating \text{ } plants \rightarrow Rooted-floating \text{ } angiosperms$.

(C) Hydrarch succession refers to the series of successional stages that occur in water bodies,starting from aquatic environments and progressing towards terrestrial ones.
In this process,the final stable community that is established is the climax community.
For hydrarch succession,the climax community is typically a forest.
Therefore,the correct option is $C$.

(A) In $hydrarch$ $succession$ (succession in aquatic areas),the process begins in $phytoplankton$ and progresses through various stages like $submerged$ $plant$ stage,$floating$ $plant$ stage,$reed-swamp$ stage,$marsh-meadow$ stage,and $scrub$ stage.
Ultimately,these stages lead to the formation of a $mesic$ (terrestrial) forest ecosystem.
Therefore,the final climax community in $hydrarch$ $succession$ is a $terrestrial$ ecosystem.

(D) Secondary succession occurs in areas where a previously existing community has been cleared (e.g., abandoned farmlands, burned forests).
It is dependent on several factors:
$1$. Invasion of species: The arrival and establishment of new species.
$2$. Soil conditions and water availability: Since the soil is already present, the nutrient status and moisture content significantly influence the rate and type of succession.
$3$. Environmental conditions: Climatic factors like temperature and rainfall play a crucial role in determining the climax community.
Therefore, all these factors are essential for secondary succession.

(D) Nutrient cycles are broadly classified into two types: Gaseous cycles and Sedimentary cycles.
$1$. Gaseous cycles: The reservoir for these nutrients is the atmosphere or hydrosphere (e.g.,Carbon,Nitrogen,and Oxygen cycles).
$2$. Sedimentary cycles: The reservoir for these nutrients is the Earth's crust (lithosphere). Phosphorus,sulfur,and calcium cycles are examples of sedimentary cycles.
Therefore,the Phosphorus cycle is a sedimentary cycle.

(D) The maintenance of nutrient levels in the atmosphere and the biosphere is regulated by various environmental factors.
$1$. Factors like temperature,soil composition,humidity,and $pH$ influence the rate of nutrient cycling and decomposition.
$2$. Atmospheric gases,climate,and the decomposition of organisms (which releases nutrients back into the cycle) are essential for maintaining the balance of nutrients.
$3$. Therefore,both sets of factors mentioned in options $B$ and $C$ play a critical role in nutrient regulation.
$4$. Thus,the correct answer is $D$.

(C) The total global carbon is distributed across various reservoirs,including the oceans,terrestrial biosphere,and the atmosphere.
According to the $NCERT$ textbook on Ecosystems,the atmosphere contains approximately $1\, \%$ of the total global carbon.
Oceans contain $71\, \%$ of the global carbon,while the rest is found in the terrestrial biosphere and fossil fuels.

(A) The natural reservoir of phosphorus is rock. During the process of weathering,minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. Unlike the carbon cycle,there is no significant respiratory release of phosphorus into the atmosphere. Therefore,the correct answer is rock,which is a major component of the Earth's crust (mountains/sedimentary rocks).

(B) In biogeochemical cycles,carbon is primarily exchanged through the atmosphere in the form of $CO_2$.
Phosphorus is a sedimentary cycle,meaning its primary reservoir is the Earth's crust (rocks),and it has negligible atmospheric input compared to carbon.
Sulfur also has a significant atmospheric component (e.g.,$SO_2$,$H_2S$),but phosphorus is distinctly known for its lack of a significant gaseous phase in its cycle.
Therefore,phosphorus has a much lower atmospheric input than carbon.

(A) Robert Costanza and his colleagues have put very price tags on nature's life-support services.
Researchers have put an average price tag of $33$ trillion $US$ dollars a year on these fundamental ecosystem services,which are largely taken for granted.
This value is significantly higher than the global Gross National Product $(GNP)$ which is around $18$ trillion $US$ dollars.

(A) Eugene Pleasants Odum $(E. P. Odum)$ is widely recognized as the father of ecosystem ecology. He was an American biologist who emphasized the study of ecosystems as functional units of nature. His textbook,'Fundamentals of Ecology',played a crucial role in establishing ecosystem ecology as a distinct field of study.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
Ecosystems are broadly classified into two types: Natural and Artificial (Man-made).
Natural ecosystems include forests,grasslands,and lakes,which operate by themselves without any significant human interference.
An artificial or man-made ecosystem is created and maintained by human beings for their specific needs,such as agriculture or aquaculture.
Therefore,a crop field is an example of an artificial ecosystem.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
Among the given options, the ocean is the largest ecosystem on Earth.
It covers approximately $71\%$ of the Earth's surface and contains a vast diversity of life forms, making it the most extensive aquatic ecosystem.

(A) Decomposers are organisms that break down dead or decaying organic matter. In an ecosystem,the primary decomposers are saprophytic organisms,specifically bacteria and fungi. They secrete digestive enzymes onto the dead organic material to break it down into simpler inorganic substances,which are then absorbed. Therefore,the correct answer is $A$.

(A) food chain typically represents the flow of energy from producers to consumers (herbivores,carnivores,etc.).
Decomposers (saprotrophs) are organisms that break down dead organic matter and are generally considered part of the detritus food chain or a separate functional group in an ecosystem,rather than being a direct link in the standard grazing food chain.
Therefore,in the context of standard textbook classifications for grazing food chains,decomposers are often excluded from the primary sequence of producers and consumers.

(C) In an ecosystem,primary consumers are organisms that feed directly on producers (plants).
Plant parasites (herbivores) are organisms that derive their nutrition directly from plants.
Producers are autotrophs,not consumers.
Animal parasites feed on other animals (secondary or tertiary consumers).
Cockroaches are omnivores,feeding on both plant and animal matter.
Therefore,plant parasites are classified as primary consumers.

(C) In an ecosystem with a simple food web or food chain,there is low species diversity.
Because there are fewer alternative pathways for energy flow,these systems are less resilient to external changes.
If a change occurs at any one trophic level (such as a significant increase or decrease in the population of a species),it directly impacts the other levels.
Consequently,the food chain is likely to be disrupted or destroyed,leading to an imbalance in the ecosystem.

(D) The number of organisms at any trophic level in an ecosystem is determined by several ecological factors:
$1$. The availability of food and energy from the lower trophic level directly limits the population size of the current level.
$2$. The presence of predators at higher trophic levels regulates the population of the lower trophic levels through top-down control.
$3$. Producers are the primary source of energy for the entire ecosystem,and their productivity dictates the energy available for all subsequent levels.
Therefore,all these factors play a crucial role in determining the number of organisms at a specific trophic level. Hence,the correct option is $D$.

(A) In marine ecosystems,nitrogen $(N_2)$ is often the limiting nutrient for primary productivity because it is present in low concentrations in the photic zone. While terrestrial and forest ecosystems also require nitrogen,marine environments are specifically characterized by nitrogen limitation in vast open ocean areas,making it a critical limiting factor for phytoplankton growth.

(A) The species that invades a bare area and initiates the process of ecological succession is known as the $Pioneer$ species.
In primary succession,these are typically lichens or mosses that can survive on bare rock.
These species help in soil formation and create conditions suitable for the growth of subsequent species.

(A) In primary succession,the process starts on bare rock where no soil exists. Lichens are the pioneer species that colonize these bare rocks. They secrete acids to dissolve the rock,which helps in the process of weathering and soil formation. This creates a suitable environment for the growth of mosses and subsequently other plants.

(B) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
Ecosystems are broadly categorized into two types: Natural and Artificial (Man-made).
Natural ecosystems are those that operate by themselves under natural conditions without any major interference by humans,such as forests,grasslands,and ponds.
Artificial ecosystems are maintained by humans,such as crop fields and aquariums.
Therefore,a pond is a classic example of a natural ecosystem.

(A) An ecosystem is a dynamic unit where biotic and abiotic components interact.
$1$. The biotic community is constantly changing due to processes like succession,evolution,and migration.
$2$. Abiotic factors like climate,temperature,and nutrient availability also fluctuate over time.
$3$. Therefore,both biotic and abiotic components are dynamic,not static.
$4$. Since the question asks what is not static,and both biotic and abiotic components are dynamic,the most appropriate answer in the context of ecological change is the biotic community,which undergoes continuous transformation.

(A) Secondary succession is the process of ecological succession that occurs in areas where a previously existing community has been removed by a disturbance (e.g.,fire,flood,or deforestation) but the soil remains intact.
Because the soil is already present,secondary succession occurs much faster than primary succession.
For the formation of a grassland community in secondary succession,it typically takes approximately $50$ to $100$ years to reach a stable state.

(C) The sequence provided represents the stages of hydrarch succession (hydrosere).
$1$. Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
$2$. It starts with phytoplankton,moves through submerged,floating,and reed-swamp stages,and eventually leads to a forest (climax community).
$3$. This process describes how an aquatic habitat gradually transforms into a terrestrial forest ecosystem.

(B) In ecological succession,the pioneer species are the first organisms to colonize a previously barren area.
Lichens are known as pioneer species in $Lithosere$ (succession on bare rocks).
They secrete acids to dissolve rock,helping in the process of weathering and soil formation,which eventually allows other plants to grow.
Since $Lithosere$ is a type of $Xerosere$ (succession in dry areas),both are technically correct,but $Lithosere$ is the most specific and accurate term for succession starting on bare rocks.

(D) Micro-consumers,also known as decomposers or saprotrophs,are organisms that break down complex organic matter into simpler inorganic substances. They do not fit into the traditional trophic levels of primary,secondary,or tertiary consumers,which are typically reserved for macro-consumers (herbivores and carnivores). Therefore,they are classified separately from these categories.

(A) The living world on Earth is primarily driven by solar energy. Plants and photosynthetic bacteria capture a small fraction of the total solar radiation reaching the Earth. This specific portion of the solar spectrum,which is utilized by plants for photosynthesis,is known as $PAR$ (Photosynthetically Active Radiation). $PAR$ constitutes less than $50 \%$ of the incident solar radiation. Plants capture only $2-10 \%$ of this $PAR$ to synthesize food,which sustains the entire ecosystem.

(A) $1$. Secondary productivity is defined as the rate of formation of new organic matter by consumers.
$2$. $NPP$ (Net Primary Productivity) is the biomass available for consumption to heterotrophs (herbivores and decomposers),not just herbivores.
$3$. $GPP$ (Gross Primary Productivity) is the total rate of production of organic matter during photosynthesis,not the 'actual' productivity (which is $NPP$).
$4$. $A$ lion is a tertiary or top consumer,occupying the fourth or higher trophic level,not the secondary trophic level (which is occupied by primary consumers like herbivores).
Therefore,the correct statement is $A$.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
Option $A$ is correct as the ocean is a natural aquatic ecosystem.
Option $B$ is correct as a crop field is a man-made (artificial) ecosystem.
Option $C$ is incorrect because a desert is a natural terrestrial ecosystem,not an artificial one.
Option $D$ is correct as the ocean is the largest ecosystem on Earth.
Therefore,the odd one out is $C$.

(B) The atmosphere contains approximately $78 \%$ of nitrogen,making it the primary reservoir for the nitrogen cycle.
Phosphorus is a sedimentary nutrient,and its primary reservoir is the Earth's crust,specifically bedrocks and other geological deposits formed over past geological ages.

(B) Within biological communities,some species may be important in determining the ability of a large number of other species to persist in the community.
These crucial species are termed $Keystone$ $species$.
These species often have considerably low abundance and biomass compared to dominant species,but their removal or a decrease in their number causes serious disruption in the functions of the community.
$e.g.$,top predators,grey wolves in grasslands,or specific plant species that maintain ecosystem structure.

(A) Psammosere: The sequence of successional stages occurring on sand.
Lithosere: The sequence of successional stages occurring on bare rock.
Hydrosere: The various stages of biotic succession taking place in a water body are collectively termed as hydrosere.
Xerosere: The series of developmental stages of biotic succession in an arid (dry) area is termed as xerosere.

(D) food chain represents the flow of energy through an ecosystem and consists of producers,consumers,and decomposers.
Producers are typically plants (autotrophs).
Consumers are categorized based on their trophic levels:
$1$. Primary consumers (Herbivores) feed on plants.
$2$. Secondary consumers (Primary carnivores) feed on herbivores.
$3$. Tertiary consumers (Secondary carnivores) feed on primary carnivores.
$4$. Quaternary consumers (Top carnivores) are at the highest trophic level.
Since a food chain includes producers (plants) and various levels of consumers (herbivores and carnivores),the correct answer is 'All of these'.

(D) An ecosystem is defined as the structural and functional unit of the biosphere. It comprises all living organisms (biotic components) and their non-living (abiotic) environment. These components interact through food chains and chemical cycles,resulting in energy flow,biotic diversity,and material cycling,which together form a stable and self-supporting system.

(A) Producers are autotrophic organisms that are capable of manufacturing organic food from inorganic raw materials through the process of photosynthesis.
These organisms trap solar energy and convert it into chemical bond energy stored in organic compounds.
Therefore,green plants are known as producers in an ecosystem.

(B) In primary succession in water (hydrarch succession),the pioneer species are small phytoplanktons. These include organisms like diatoms,green flagellates,and single-celled colonial or filamentous green algae,which colonize the bare water body first.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and also with the surrounding physical environment.
$A$ pond is a classic example of a natural ecosystem because it is a self-sustaining unit that functions through the interaction of biotic components (like algae,fish,and microorganisms) and abiotic components (like water,sunlight,and dissolved minerals) without significant human intervention.
It is not a biome,as a biome is a large regional unit characterized by specific climate and vegetation (e.g.,desert,forest).
It is not an agroecosystem,as agroecosystems are man-made ecosystems (e.g.,crop fields).
It is not just a community,as a community refers only to the biotic component (all populations of different species in an area),whereas an ecosystem includes both biotic and abiotic factors.

(A) The Detritus Food Chain $(DFC)$ begins with detritus or dead organic matter. Detritivores and decomposers feed on it. As shown in the diagram,the chain starts with dead organic matter (detritus) which is consumed by organisms like earthworms,which are then consumed by higher trophic levels.

(C) $PAR$ stands for Photosynthetically Active Radiation.
The sun is the primary source of energy for all ecosystems on Earth.
Out of the total incident solar radiation,only $50\; \%$ is Photosynthetically Active Radiation $(PAR)$.
Plants capture only $2-10\; \%$ of the $PAR$,and this small amount of energy sustains the entire living world.
Therefore,there is a unidirectional flow of energy from the sun to producers and then to consumers.

(B) The lentic ecosystem refers to standing water bodies such as lakes,ponds,pools,puddles,ditches,and swamps. In contrast,running water ecosystems such as springs,streams,and rivers are referred to as lotic ecosystems.

(B) The amount of living matter (biomass) present in an ecosystem at a given time is referred to as the $Standing \ crop$.
It is measured as the mass of living organisms (biomass) or the number in a unit area.
$Biomass$ refers to the total mass of organisms,while $Standing \ state$ refers to the amount of inorganic nutrients present in the soil at a given time.

(B) Primary succession on bare rocks (lithosere) begins with the colonization of pioneer species.
$1$. Lichens are the pioneer species that secrete acids to dissolve rock,helping in soil formation.
$2$. Lichens are followed by small bryophytes (mosses) which further build up the soil layer.
$3$. This allows for the growth of herbaceous plants,followed by shrubs.
$4$. Finally,the area develops into a stable climax community,which is a forest.
Therefore,the correct sequence is: $Lichen \rightarrow Small \ bryophytes \rightarrow Herbs \rightarrow Shrubs \rightarrow Trees \rightarrow Forest$.

(D) The carbon cycle is a biogeochemical cycle by which carbon is exchanged among the biosphere,pedosphere,geosphere,hydrosphere,and atmosphere of the Earth.
It involves the movement of carbon through the atmosphere,oceans,and living and dead organisms.
It is estimated that $4 \times 10^{13} \text{ kg}$ of carbon is fixed in the biosphere through photosynthesis annually.