Ecosystem–Structure and Function Questions in English

(C) In most ecosystems,the Sun is the primary source of energy for all producers (plants,algae,and cyanobacteria) to perform photosynthesis.
However,in deep sea-hydrothermal vent ecosystems,sunlight cannot penetrate the water column.
In these environments,chemosynthetic bacteria derive energy from the oxidation of inorganic chemicals (like hydrogen sulfide) released from hydrothermal vents.
Therefore,these ecosystems are independent of solar energy.

(A) In ecological succession,the process starts with pioneer species and proceeds through various seral stages. The final stage of succession is known as the climax community. This community is stable,mature,and in near equilibrium with the environment of that area. Therefore,option $A$ is the correct definition.

(C) The natural reservoir of phosphorus is rock,which contains phosphorus in the form of phosphates.
When rocks are weathered,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 option is $C$.

(A) Robert Costanza and his colleagues have put very price tags on nature's life-support services. According to their estimates,the global ecosystem services are worth $33$ trillion $US$ dollars a year. Out of the total cost of various ecosystem services,the soil formation accounts for about $50\%$ of the total value. Other services like recreation and nutrient cycling account for less than $10\%$ each.

(C) The total quantity of global carbon is distributed across various reservoirs.
According to the $NCERT$ textbook,approximately $71\%$ of the total global carbon is found dissolved in the oceans.
The remaining carbon is present in the atmosphere,terrestrial ecosystems,and fossil fuels.
Therefore,the correct option is $C$.

(D) In an ecosystem,the energy flow follows a specific trophic structure.
$1$. Primary producers (autotrophs) are organisms like plants that produce their own food.
$2$. Primary consumers (herbivores) are organisms that feed directly on primary producers.
$3$. Secondary consumers (primary carnivores) are organisms that feed on primary consumers.
Since herbivores consume plants (primary producers) directly,they are classified as primary consumers.

(C) The $PAR$ (Photosynthetically Active Radiation) constitutes less than $50\%$ of the total incident solar radiation.
Plants capture only $2-10\%$ of the $PAR$ to perform photosynthesis and synthesize organic food.
Therefore,the correct option is $C$.

(B) In an ecosystem,there are primarily $2$ types of food chains:
$1$. Grazing Food Chain $(GFC)$: This food chain starts with producers (green plants) and moves to herbivores and then to carnivores.
$2$. Detritus Food Chain $(DFC)$: This food chain begins with dead organic matter (detritus) and is decomposed by decomposers (fungi and bacteria).

(A) The vertical distribution of different species occupying different levels in an ecosystem is known as $Stratification$.
For example,trees occupy the top vertical strata or layer of a forest,shrubs the second,and herbs and grasses occupy the bottom layers.

(A) The $PAR$ (Photosynthetically Active Radiation) constitutes less than $50$ percent of the total incident solar radiation.
Plants are capable of capturing only $2-10$ percent of this $PAR$ to perform photosynthesis.
This captured energy sustains the entire ecosystem.

(D) Primary succession occurs in areas where no living organisms ever existed.
Examples of such areas include newly cooled lava,bare rock,and newly created ponds or reservoirs.
Since all the given options represent environments where life is starting from scratch without any pre-existing soil or organic matter,they are all correct examples of primary succession.

(B) In the standard representation of the global carbon cycle,carbon is stored in various reservoirs.
$Y$ represents the biological remains of marine organisms,specifically $Plankton$,which settle on the ocean floor.
Over millions of years,these organic remains undergo geological processes to form $Z$,which consists of $Limestone$ and $dolomite$ (calcium and magnesium carbonates).
Therefore,the correct identification is $Y=$ Plankton and $Z=$ Limestone and dolomite.

(B) Biogeochemical cycles are broadly classified into two types: Gaseous cycles and Sedimentary cycles.
$1$. Gaseous cycles: The reservoir for these elements is the atmosphere or hydrosphere (e.g.,Nitrogen,Carbon,Oxygen cycles).
$2$. Sedimentary cycles: The reservoir for these elements is the Earth's crust (lithosphere). These elements are released from rocks through weathering and are typically less mobile than gaseous elements.
Examples of sedimentary cycles include the Phosphorus cycle and the Sulphur cycle.
Therefore,the correct option is $B$.

(C) : Grasshoppers are herbivores that feed directly on green plants (producers),therefore they are classified as primary consumers. This statement is correct.
$R$: Fishes and birds occupy various trophic levels depending on their diet. While some may be top carnivores,many are primary or secondary consumers. Therefore,the statement that they are included in top carnivores as a general rule is incorrect. Thus,$A$ is correct and $R$ is incorrect.

(D) Assertion $(A)$: The statement is incorrect. According to the $NCERT$ textbook,$71\%$ of the total global carbon is dissolved in the oceans,not $80\%$.
Reason $(R)$: The statement is correct. Carbon constitutes $49\%$ of the dry weight of organisms and is the second most abundant element in living organisms after oxygen.

(B) In a nutrient cycle,the reservoir acts as a storage pool for nutrients.
Its primary function is to maintain the balance of nutrients in the ecosystem by releasing them when there is a deficit in the cycling pool (the biotic and abiotic components actively involved in the cycle).
For example,in the phosphorus cycle,the Earth's crust acts as the reservoir,releasing phosphorus through weathering to meet the needs of living organisms when the available supply is low.

(D) According to the $NCERT$ textbook on Ecosystems,carbon cycling occurs through the atmosphere,ocean,and through living and dead organisms.
Approximately $71\%$ of the total global carbon is found dissolved in the oceans.
The atmospheric reservoir contains only about $1\%$ of the total global carbon.
Therefore,the correct distribution is $1\%$ in the atmosphere and $71\%$ in the oceans.

(C) $PAR$ stands for Photosynthetically Active Radiation.
It represents the spectral range of solar radiation from $400 \ nm$ to $700 \ nm$ that photosynthetic organisms are able to use in the process of photosynthesis.
While the total solar radiation reaching the Earth's surface is significant,only a portion of it falls within this specific wavelength range.
Scientific studies indicate that less than $50\%$ of the total incident solar radiation is $PAR$.

(D) Foundation species are organisms that play a major role in creating,modifying,or maintaining the physical structure of an ecosystem. By doing so,they significantly influence the environmental conditions and the availability of resources for other species,thereby contributing to the overall properties and stability of the ecosystem. Examples include corals in coral reefs or trees in a forest.

(C) In a marine aquatic ecosystem,the upper layer is known as the photic zone or euphotic zone,where sunlight can penetrate.
This region supports primary productivity through photosynthesis.
Phytoplankton (microscopic algae) are the primary producers found in this layer.
Zooplankton (microscopic animals) feed on these phytoplankton and are also abundant in the upper layers.
Therefore,both phytoplankton and zooplankton are characteristic of the upper layer of a marine ecosystem.

(B) The food chain that begins with dead organic matter and involves microorganisms (decomposers) breaking down this matter is called the $Detritus$ $food$ $chain$ $(DFC)$.
In this chain,the primary source of energy is dead organic matter (detritus) rather than living producers.
Microorganisms like bacteria and fungi act as decomposers,breaking down the complex organic compounds into simpler inorganic substances.
Therefore,the correct option is $B$.

(B) The bulk of $CO_2$ fixation on Earth occurs in the oceans. Although terrestrial ecosystems like tropical rainforests are highly productive,the vast surface area of the oceans,combined with the photosynthetic activity of phytoplankton,accounts for approximately $40\%$ of the total global carbon fixation.

(A) In a pond ecosystem,the trophic levels are organized based on energy flow.
$1$. The first trophic level consists of producers,which are the $Phytoplankton$.
$2$. The second trophic level consists of primary consumers,which feed on the producers. In a pond,$Zooplankton$ act as the primary consumers.
$3$. Therefore,$Zooplankton$ represent the second trophic level,making them the second most important level in terms of energy transfer from producers to higher consumers.

(B) Biogeochemical cycles are broadly classified into two types: Gaseous cycles and Sedimentary cycles.
$1$. Gaseous cycles: The reservoir for these elements is the atmosphere or hydrosphere (e.g.,Nitrogen,Oxygen,Carbon).
$2$. Sedimentary cycles: The reservoir for these elements is the Earth's crust (lithosphere). Phosphorus and Sulfur are classic examples of sedimentary cycles because their primary reservoir is rock/soil.

(D) Primary succession is the process of ecological succession that occurs in an area where no community previously existed.
This includes environments such as newly cooled lava,bare rock,or sand dunes where soil formation has not yet occurred.
In contrast,secondary succession occurs in areas where a pre-existing community has been destroyed (e.g.,after a fire or flood),as the soil is already present.

(D) In an ecosystem,the flow of energy starts from producers (plants).
Primary consumers are organisms that feed directly on producers.
Since producers are plants,organisms that eat plants are known as herbivores.
Therefore,primary consumers are herbivores.

(A) In ecological succession,the climax community represents the final,stable stage of an ecosystem that remains relatively unchanged unless disturbed.
While factors like soil type,nutrient availability,and biotic interactions influence the rate of succession,the ultimate nature and composition of the climax community are primarily determined by the regional climate (temperature and precipitation patterns).
Thus,climate is the most significant factor that dictates the potential vegetation of a climax community.

(D) In the world's oceans,the primary producers (autotrophs) are predominantly microscopic organisms.
Although large seaweeds exist,the vast majority of the biomass of autotrophs is contributed by free-floating microscopic algae,cyanobacteria,and nanoplankton,which form the base of the marine food web.
These organisms are collectively known as phytoplankton.
Therefore,the correct option is $D$.

(A) In an ecosystem,the trophic level is determined by the position an organism occupies in a food chain.
Bamboo is a plant,which is a producer.
Producers are autotrophs that synthesize their own food through photosynthesis.
In any food chain,producers always occupy the first trophic level $(T_1)$.
Therefore,bamboo plants belong to the first trophic level $(T_1)$.

(D) To ensure the restoration of a degraded ecosystem, it is essential to reduce the factors that cause instability and promote resilience.
An ecosystem that is highly stable and highly resilient is better equipped to recover from disturbances.
Stability refers to the ability of an ecosystem to remain unchanged despite disturbances, while resilience refers to the capacity of an ecosystem to recover after a disturbance.
Therefore, to restore an ecosystem, we must aim for $High \text{ stability}$ and $High \text{ resilience}$ by stopping activities that degrade these properties.

(C) The global carbon cycle involves the movement of carbon between the atmosphere,biosphere,and oceans.
Oceans act as the largest reservoir of carbon in the biosphere.
Approximately $70\%$ of the total global carbon is dissolved in the oceans.
Therefore,the correct option is $C$.

(C) Photosynthetically Active Radiation $(PAR)$ is the spectral range of solar radiation from $400 \ nm$ to $700 \ nm$ that photosynthetic organisms are able to use in the process of photosynthesis.
Plants capture only a small portion of the total solar radiation reaching the Earth's surface.
Out of the total solar radiation,less than $50\%$ is $PAR$.
Even out of this $PAR$,plants capture only $2-10\%$ to perform photosynthesis.

(A) The mass of living material (biomass) present at a particular trophic level at a particular time is known as the $Standing \ crop$.
It is measured as the mass of living organisms (biomass) or the number in a unit area.
$Standing \ state$ refers to the amount of inorganic nutrients present in the soil at a given time,not the living biomass.

(B) Secondary succession is the process of ecological succession that occurs in areas where a previously existing community has been cleared or destroyed by natural or human-induced disturbances,such as deforestation,fire,or floods.
Unlike primary succession,which begins on bare,lifeless areas (like bare rocks or cooled lava) where soil is absent,secondary succession occurs in areas where soil is already present and may contain seeds or spores.
Because the soil is already formed and nutrient-rich,secondary succession proceeds much faster than primary succession.

(D) Hydrarch succession (succession in water) proceeds through several stages:
$1$. Phytoplankton stage
$2$. Rooted submerged stage (e.g.,$Vallisneria$,$Hydrilla$)
$3$. Rooted floating angiosperm stage (e.g.,$Nymphaea$,$Trapa$)
$4$. Free-floating plant stage (e.g.,$Azolla$,$Pistia$)
$5$. Reed-swamp stage
$6$. Marsh-meadow stage
$7$. Scrub stage
$8$. Forest stage
Therefore,the second stage,which is the rooted submerged stage,is represented by plants like $Vallisneria$.

(D) The natural reservoir of phosphorus is rocks. Phosphorus is a major constituent of biological membranes,nucleic acids,and cellular energy transfer systems. Many animals also need large quantities of this element to make shells,bones,and teeth. The natural reservoir of phosphorus is rock,which contains phosphorus in the form of phosphates. When rocks are weathered,minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants.

(B) Ecological succession is the gradual and predictable change in the species composition of a given area.
It leads to the establishment of a stable community that is in equilibrium with the environment,known as the climax community.
Primary succession occurs in areas where no living organisms ever existed,and it is a very slow process.
Therefore,option $B$ is the correct statement.

(B) Nutrient cycles are broadly classified into two types: Gaseous and Sedimentary.
$1$. Gaseous cycles: The reservoir for these nutrients exists in the atmosphere. Examples include $Carbon$ and $Nitrogen$ cycles.
$2$. Sedimentary cycles: The reservoir for these nutrients is located in the Earth's crust (rocks/soil). Examples include $Sulfur$ and $Phosphorus$ cycles.
Therefore,the correct pairing is Gaseous ($Carbon$ and $Nitrogen$) and Sedimentary ($Sulfur$ and $Phosphorus$).

(D) In deep-sea hydrothermal vent ecosystems, sunlight cannot penetrate the water, making photosynthesis impossible.
Instead, the primary producers are $Chemosynthetic$ bacteria.
These bacteria derive energy from the oxidation of inorganic chemicals, such as hydrogen sulfide $(H_2S)$, which are released from the hydrothermal vents.
This process is known as chemosynthesis, which forms the base of the food chain in these extreme environments.

(A) An agro-ecosystem is a human-managed ecosystem designed for agricultural production.
$1$. Unlike natural ecosystems,agro-ecosystems are characterized by low genetic diversity because they typically involve monoculture (growing a single crop species).
$2$. They are not characterized by ecological succession,as they are maintained in an early successional stage by human intervention.
$3$. Weeds and soil organisms are present in agro-ecosystems,though their populations may be managed or altered.
Therefore,the most distinct feature among the options is low genetic diversity.

(B) In $Tropical \text{ rain forests}$, the vegetation is highly stratified due to intense competition for sunlight. Plants are arranged in distinct vertical layers based on their height, which include the emergent layer, canopy layer, understory, and forest floor. This vertical stratification allows different species to coexist by utilizing light at different levels.

(A) The biomass of an ecosystem refers to the total mass of living organisms in a given area at a specific time.
Forest ecosystems,particularly tropical rainforests,contain massive amounts of vegetation (trees,shrubs,and plants) which contribute to a very high standing crop biomass compared to aquatic ecosystems like ponds or lakes,or terrestrial grasslands.
Therefore,the forest ecosystem has the highest biomass among the given options.

(C) For an ecosystem to be self-sustaining,it must maintain a balance where essential nutrients and materials such as oxygen,carbon dioxide,water,and nitrogen are continuously recycled between the biotic components (organisms) and the abiotic environment. This process of nutrient cycling ensures that resources are not depleted,allowing the ecosystem to function independently.

(D) The main source of energy for an ecosystem is the radiant energy or light energy derived from the sun.
$50\%$ of the total solar radiation that falls on Earth is Photosynthetically Active Radiation $(PAR)$.
The light energy is converted into chemical energy in the form of sugar by photosynthesis.
The chemical equation is: $6H_2O + 6CO_2 + \text{Light} \to C_6H_{12}O_6 + 6O_2$.
Plants utilize only $2-10\%$ of the incident $PAR$ for the process of photosynthesis.

(B) In a typical food chain,the number of organisms decreases as we move from the producer level to the higher trophic levels (consumers).
Producers (plants) occupy the first trophic level and are present in the highest number to support the energy requirements of the entire ecosystem.
While decomposers (bacteria and fungi) are numerous,they are generally considered to exist outside the linear structure of a standard food chain.
Therefore,among the components of a food chain,producers have the largest population.

(C) Zooplankton.
Zooplankton are primary consumers in aquatic food chains that feed upon phytoplankton.
Therefore,they occupy the second trophic level in a lake ecosystem.

(A) The total incident solar radiation consists of various wavelengths of light.
Photosynthetically active radiation,commonly known as $PAR$,represents the spectral range of solar radiation from $400 \ nm$ to $700 \ nm$ that photosynthetic organisms are able to use in the process of photosynthesis.
Out of the total incident solar radiation reaching the Earth's surface,approximately $50 \%$ constitutes $PAR$.

(N/A) An ecosystem is defined as an interacting unit that includes both the biological community as well as the non-living components of an area. The living and the non-living components of an ecosystem interact amongst themselves and function as a unit,which is evident during the processes of nutrient cycling,energy flow,decomposition,and productivity.
The two main components of an ecosystem are:
$1$. Biotic component: This includes the living organisms within an ecosystem,such as producers,consumers,and decomposers.
- Producers: These are autotrophs (e.g.,plants and algae) that synthesize their own food using sunlight via photosynthesis.
- Consumers: These are heterotrophs that depend on producers directly or indirectly for food (e.g.,primary,secondary,and tertiary consumers).
- Decomposers: These include microorganisms like bacteria and fungi that obtain nutrients by breaking down dead organic matter.
$2$. Abiotic component: These are the non-living physical and chemical factors of an ecosystem,such as light,temperature,water,soil,air,and inorganic nutrients.

(N/A) Sedimentary cycles have their reservoirs in the Earth's crust or rocks.
Nutrient elements are found in the sediments of the Earth.
Elements such as sulphur,phosphorus,potassium,and calcium have sedimentary cycles.
Sedimentary cycles are very slow.
They take a long time to complete their circulation and are considered as less perfect cycles.
This is because during recycling,nutrient elements may get locked in the reservoir pool,thereby taking a very long time to come out and continue circulation.
Thus,it usually goes out of circulation for a long time.

(N/A) The carbon cycle is an important gaseous cycle which has its reservoir pool in the atmosphere. All living organisms contain carbon as a major body constituent. Carbon is a fundamental element found in all living forms. All biomolecules such as carbohydrates,lipids,and proteins required for life processes are made of carbon. Carbon is incorporated into living forms through a fundamental process called 'photosynthesis'. Photosynthesis uses sunlight and atmospheric carbon dioxide to produce a carbon compound called 'glucose'. This glucose molecule is utilized by other living organisms. Thus,atmospheric carbon is incorporated in living forms. Now,it is necessary to recycle this absorbed carbon dioxide back into the atmosphere to complete the cycle. There are various processes by which carbon is recycled back into the atmosphere in the form of carbon dioxide gas. The process of respiration breaks down glucose molecules to produce carbon dioxide gas. The process of decomposition also releases carbon dioxide from dead bodies of plants and animals into the atmosphere. Combustion of fuels,industrialization,deforestation,volcanic eruptions,and forest fires act as other major sources of carbon dioxide.