Mix Examples- Ecosystem Questions in English

(C) To find the number of food chains,we trace all possible paths from the producer (Plant) to the top consumers:
$1$. Plant $\rightarrow$ Deer $\rightarrow$ Lion
$2$. Plant $\rightarrow$ Deer $\rightarrow$ Python $\rightarrow$ Frog
$3$. Plant $\rightarrow$ Goat $\rightarrow$ Lion
$4$. Plant $\rightarrow$ Goat $\rightarrow$ Python $\rightarrow$ Frog
$5$. Plant $\rightarrow$ Grasshopper $\rightarrow$ Frog
There are a total of $5$ distinct food chains in the given food web.

(D) During ecological succession,the community undergoes a series of sequential changes known as seral stages until it reaches a stable climax community.
$1$. $I.$ Changes in species diversity occur as pioneer species are replaced by more complex organisms.
$2$. $II.$ There is a gradual increase in the number of species and the total number of organisms as the habitat becomes more favorable.
$3$. $III.$ As the community matures,the total biomass increases significantly due to the accumulation of organic matter and the development of complex vegetation structures.
Therefore,all three statements are correct.

(C) Herbivores are primary consumers that depend primarily on plants for their nutritional requirements. If a single plant species is removed from a food web,the herbivores that rely on that specific plant will be forced to seek alternative food sources to survive.

(D) In the given food chain,trees are the producers. Birds feed on trees,lice are parasites on birds,and bacteria are hyper-parasites or decomposers feeding on lice. Since the size of the organisms decreases at each successive trophic level and the energy flows from a larger organism to a smaller parasitic organism,this is classified as a parasitic food chain.

(D) The sequence of hydrarch succession (Hydrosere) is as follows:
$1$. Phytoplankton stage
$2$. Submerged plant stage
$3$. Submerged free-floating plant stage
$4$. Reed swamp stage
$5$. Marsh meadow stage
$6$. Scrub stage
$7$. Forest stage
According to this sequence,the reed swamp stage is preceded by the floating stage (which includes both submerged free-floating and rooted floating plants).

(B) The pioneer community that establishes itself on a bare rock is Lichens. These are the first colonizers in primary succession on a bare rock surface. They secrete acids to dissolve rock,helping in the process of weathering and soil formation,which eventually allows other plants like mosses to grow. Examples include $Graphis$ and $Rhizocarpon$.

(D) Ecological succession is the process by which the structure of a biological community evolves over time.
In both primary and secondary succession,the community moves towards a stable climax community.
Succession occurring in dry areas (xeric) and succession occurring in water bodies (hydric) both eventually lead to a balanced environment with moderate moisture,known as mesic conditions.
Therefore,both xeric to mesic and hydric to mesic are correct pathways for succession.

(A) Carbon is a fundamental element for life and constitutes $49\;\%$ of the dry weight of organisms.
Out of the total global carbon,$71\;\%$ is dissolved in the oceans.
Therefore,the correct values are $49\;\%$ and $71\;\%$ respectively.

(B) In an ecosystem, primary consumers (herbivores) are the organisms that directly consume plant matter and convert it into animal biomass. Among the given options, the $Goat$ is a primary consumer (herbivore) that feeds on plants, whereas the others are either detritivores or carnivores.

(B) The amount of inorganic substances (such as $C, N, P, Ca$, etc.) present in an ecosystem at any given time is referred to as the $Standing \, state$.
Energy flow, nutrient cycling, and productivity are considered functional aspects of an ecosystem because they describe the processes and dynamics occurring within the system.
Therefore, the correct answer is $Standing \, state$ and $functional$.

(C) Statement $(A)$ is True: Stratification refers to the vertical distribution of different species occupying different levels in a community.
Statement $(B)$ is False: The correct relationship is $NPP = GPP - R$. Therefore,$GPP - R$ is Net Primary Productivity $(NPP)$,not Gross Primary Productivity $(GPP)$.
Statement $(C)$ is False: The rate of biomass production is called productivity,not decomposition.
Statement $(D)$ is True: The annual net primary productivity of the whole biosphere is approximately $170$ billion tons of organic matter,of which the oceans contribute only $55$ billion tons.
Thus,the correct sequence is $(A=T, B=F, C=F, D=T)$.

(A) The $DFC$ (Detritus Food Chain) begins with dead organic matter (detritus),not solar energy. In contrast,the $GFC$ (Grazing Food Chain) begins with producers that capture solar energy. Therefore,the statement that $DFC$ starts with solar energy is incorrect. $DFC$ is often connected to $GFC$ at some levels,and it relies on detritivores for the decomposition of organic matter. It is the primary pathway for energy flow in terrestrial ecosystems.

(D) food web is a complex network of interconnected food chains.
By providing multiple pathways for energy flow,it ensures that organisms have access to a greater variety of food sources.
This interconnectedness also helps in maintaining the stability of the ecosystem by increasing the overall availability and quantity of food resources at each trophic level.

(D) The correct match is $Omnivores - Cockroaches, Crows$.
$1$. Omnivores are organisms that consume both plant and animal matter.
$2$. Cockroaches and crows are well-known examples of omnivores as they feed on a wide variety of food sources including plant materials and small animals or organic waste.

(D) Primary succession is the process of ecological succession that occurs in an area where no community previously existed.
Based on the provided features:
$1$. Occur on newly cooled lava: Correct (Primary succession starts on bare rock).
$2$. Faster succession: Incorrect (Primary succession is very slow).
$3$. Progress to mesic condition: Correct (Succession generally leads to a stable climax community,which is often mesic).
$4$. Occurs on flooded land: Incorrect (This is usually associated with secondary succession or specific aquatic succession).
$5$. Slower succession: Correct (It takes a long time to build soil).
$6$. Changes in flora only: Incorrect (Succession involves changes in both flora and fauna).
Therefore,there are $3$ features associated with primary succession: $(1)$,$(3)$,and $(5)$.

(D) Phosphates are essential nutrients that circulate through the ecosystem.
They remain outside the natural cycle for a long period when they form insoluble compounds with metals (like calcium or iron) in the soil,or when they are sequestered in the skeletal structures (bones and teeth) of organisms,as these components do not decompose rapidly.

(D) The Assertion is incorrect because the successional process can occur in two ways: Primary succession and Secondary succession.
Primary succession occurs in areas where no living organisms ever existed (e.g.,bare rock,newly cooled lava).
Secondary succession occurs in areas where living organisms previously existed but were lost due to disturbances like fire,flood,or deforestation.
The Reason is also incorrect because areas where primary succession begins (like bare rock) are indeed supported by physical environmental conditions,although they may be harsh initially.

(C) In ecological succession,the climax community is the final stable stage that remains relatively unchanged unless disturbed. At this stage,the community is in equilibrium with the environment,meaning it does not significantly modify the environment,and the environment does not force the community to change. Therefore,the Assertion is correct.
However,the Reason is incorrect because the climax community is typically mesic (having moderate moisture conditions),not xerophytic. All successions,whether starting in water (hydrarch) or on bare rock (xerarch),eventually lead to a mesic climax community.

(D) During biotic succession,the environment becomes more stable and complex. As the ecosystem matures,species become more specialized to utilize specific resources,which leads to niches becoming narrower and more specific rather than broader. Therefore,the Assertion is incorrect.
Regarding the Reason,species diversity does increase during succession,but the total organic matter (biomass) also increases significantly as the community progresses toward a climax stage. Therefore,the Reason is also incorrect.

(D) During ecological succession,the nutrient availability generally increases because the accumulation of organic matter (humus) improves soil fertility and nutrient cycling.
Therefore,the Assertion is incorrect.
During succession,as the community becomes more complex and reaches a climax state,the $NCP$ (Net Community Productivity) generally decreases because a larger portion of the gross primary productivity is consumed by the community for respiration and maintenance.
Therefore,the Reason is also incorrect.
Thus,both Assertion and Reason are incorrect.

(A) Assertion $(A)$ is correct because food chains typically represent the flow of energy from producers to consumers,and decomposers are often omitted from these linear representations.
Reason $(R)$ is correct because decomposers (saprotrophs) break down dead organic matter from all trophic levels,including producers,herbivores,and carnivores.
Since decomposers operate at every level and are not restricted to a single linear path,they are excluded from the standard food chain models. Thus,the Reason correctly explains why they are excluded.

(C) In a hydrosere (succession in water),the sequence of stages is: Phytoplankton stage $\rightarrow$ Rooted submerged plant stage $\rightarrow$ Floating plant stage $\rightarrow$ Reed swamp stage $\rightarrow$ Sedge meadow stage $\rightarrow$ Woodland stage $\rightarrow$ Forest stage.
Therefore,the reed swamp stage is actually preceded by the floating plant stage,not followed by it. Thus,the Assertion is incorrect.
The Reason states that the sedge meadow stage has amphibious herbaceous plants,which is a correct biological fact.
Hence,the correct option is $C$.

(D) In a sedimentary cycle,the reservoir pool is the Earth's crust (lithosphere). The nutrients involved are typically non-gaseous in nature.
Examples of sedimentary cycles include the Phosphorus cycle $(II)$ and the Sulphur cycle $(I)$.
Carbon cycle $(III)$ and Nitrogen cycle $(IV)$ are examples of gaseous cycles where the reservoir pool is the atmosphere.

(D) According to David Tilman's long-term ecosystem experiments,a stable community should not show too much variation in productivity from year to year.
Therefore,the Assertion $(A)$ is incorrect.
$A$ stable community must be resilient to occasional disturbances (either natural or man-made).
Therefore,the Reason $(R)$ is also incorrect.
Thus,both Assertion and Reason are incorrect.

(D) $Eichhornia$ $crassipes$,commonly known as water hyacinth,is considered the world's most problematic aquatic weed.
It was introduced in India for its beautiful flowers but it grows very rapidly through vegetative propagation (offsets).
It causes environmental damage by clogging water bodies,depleting oxygen levels,and harming aquatic life,making it extremely difficult to eradicate.

(N/A) Coral reefs require specific environmental conditions to thrive,including high salinity,clear water,and a lack of excessive siltation.
In the regions from West Bengal to Andhra Pradesh,large rivers like the Ganges,Brahmaputra,Mahanadi,Godavari,and Krishna discharge massive amounts of fresh water and sediment (silt) into the Bay of Bengal.
This influx of fresh water lowers the salinity,and the high silt content increases turbidity,which blocks the sunlight necessary for the symbiotic algae (zooxanthellae) living within the coral polyps.
In contrast,the coastal regions of Tamil Nadu and certain other parts of the east coast have higher salinity,clearer water,and minimal freshwater inflow,providing the ideal conditions for coral reef development.

(A) The correct matching is as follows:
$P$. Herbivores are primary consumers that feed directly on plants,so $P-I$.
$Q$. Carnivores are secondary or tertiary consumers that feed on herbivores,making them indirectly dependent on plants,so $Q-II$.
$R$. Saprophytes (like Fungi) obtain nutrients from dead and decaying organic matter,so $R-III$.
Therefore,the correct sequence is $(P-I), (Q-II), (R-III)$.

(B) Pisaster is a genus of sea stars (starfish) found along the rocky intertidal zones of the Pacific coast of North America.
It is a classic example of a keystone species used in ecological studies.
In an experiment conducted by Robert Paine,when all starfish (Pisaster) were removed from an enclosed intertidal area,more than $10$ species of invertebrates became extinct within a year due to interspecific competition.

(C) In a pond ecosystem,decomposers are organisms that break down dead organic matter into simpler substances.
Among the given list:
$1$. Fungi: These are primary decomposers.
$2$. Bacteria: These are primary decomposers.
$3$. Flagellates: Some flagellates act as decomposers in aquatic environments.
Algae are producers,while floating and submerged plants are also producers.
Therefore,there are $3$ types of organisms (fungi,bacteria,and flagellates) that act as decomposers in this context.

(B) $P$ represents the process of photosynthesis,where plants use inorganic substances like $CO_2$ and $H_2O$ to synthesize organic compounds (glucose) using solar energy.
$Q$ represents the process of decomposition,where decomposers break down complex organic matter (dead remains of plants and animals) into simpler inorganic substances like $CO_2$,$H_2O$,and nutrients.

(B) In a terrestrial ecosystem,the primary producers are plants that grow on land.
$1$. Herbaceous plants: These are terrestrial producers.
$2$. Algae: These are primarily aquatic.
$3$. Woody plants: These are terrestrial producers.
$4$. Phytoplankton: These are aquatic producers.
$5$. Aquatic plants: These are aquatic producers.
Therefore,only Herbaceous plants and Woody plants are primary producers in a terrestrial ecosystem.
The total count is $2$.

(A) The food chain Grass $\rightarrow$ Goat $\rightarrow$ Human starts with producers (grass) that are consumed by herbivores (goat),which are then consumed by carnivores/omnivores (human).
This type of food chain,which begins with green plants (producers) and proceeds through herbivores to carnivores,is known as a Grazing food chain $(GFC)$.
In contrast,a Detritus food chain $(DFC)$ begins with dead organic matter.

(A) $1$. In a terrestrial ecosystem,the major conduit for energy flow is the detritus food chain $(DFC)$,not the grazing food chain $(GFC)$.
$2$. In an aquatic ecosystem,the grazing food chain $(GFC)$ is the major conduit for energy flow.
$3$. Therefore,the statement that 'much more energy flows through the grazing food chain than through the detritus food chain in a terrestrial ecosystem' is incorrect.
$4$. The detritus food chain is indeed connected to the grazing food chain at some levels (e.g.,organisms of the $DFC$ may become prey to the $GFC$ animals).
$5$. Organisms like cockroaches,crows,and humans are omnivores as they consume both plants and animals.
$6$. The natural interconnection of multiple food chains creates a complex network known as a food web.

(A) In an ecosystem,the trophic levels are defined based on the source of nutrition.
$T_1$ represents the producers (autotrophs).
$T_2$ represents the primary consumers (herbivores).
$T_3$ represents the secondary consumers (primary carnivores).
$T_4$ represents the tertiary consumers (secondary carnivores).
Detritivores (decomposers) feed on dead organic matter (detritus). In the context of energy flow models,they are often considered to operate at all trophic levels,but in standard ecological classification for food chains,they are frequently associated with the $T_1$ level or considered as a separate decomposer pathway. However,in many standard textbook contexts,detritivores are placed at the $T_1$ level because they derive energy from the breakdown of organic matter produced by primary producers.

(C) Omnivores are organisms that consume both plants and animals.
In an ecosystem,$T_1$ represents the producers (plants) and $T_2$ represents the primary consumers (herbivores).
Since omnivores consume both producers (plants) and primary consumers (herbivores),they feed on members of both $T_1$ and $T_2$ trophic levels.

(D) Carnivorous plants are unique because they are producers $(T_1)$ as they perform photosynthesis to synthesize their own food.
However,they also act as primary consumers $(T_2)$ because they trap and digest insects to supplement their nitrogen requirements in nutrient-poor soils.
Therefore,they occupy both the first trophic level $(T_1)$ and the second trophic level $(T_2)$.

(B) Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions. The correct sequence of stages is:
$1$. Phytoplankton stage
$2$. Submerged plant stage
$3$. Submerged free-floating plant stage
$4$. Reed-swamp stage
$5$. Marsh-meadow stage
$6$. Scrub stage
$7$. Forest stage (Climax community)
Thus,the correct sequence is Phytoplankton $\rightarrow$ Submerged plant stage $\rightarrow$ Submerged free-floating plant stage $\rightarrow$ Reed-swamp stage $\rightarrow$ Marsh-meadow stage $\rightarrow$ Scrub stage.

(D) Nutrient cycling is a fundamental process in an ecosystem.
$1$. Nutrients are never lost from the ecosystem; they are conserved and recycled repeatedly through biotic and abiotic components.
$2$. The movement of nutrient elements through the various components of an ecosystem is defined as nutrient cycling.
$3$. Since these cycles involve the movement of nutrients through living organisms (bio),geological processes (geo),and chemical processes (chemical),they are also known as biogeochemical cycles.
Therefore,all the given statements are correct.

(C) Statement $X$ is true because phosphorus is a sedimentary cycle,and its atmospheric input through rainfall is significantly lower compared to the carbon cycle,which relies heavily on atmospheric $CO_2$.
Statement $Y$ is false because the exchange of phosphorus between organisms and the environment is not negligible; it is a vital nutrient that cycles through food chains,decomposition,and weathering processes,although it lacks a significant gaseous phase.

(B) In the phosphorus cycle,phosphorus is released from rocks through weathering. This phosphorus enters the soil solution $(S)$. Producers (plants) absorb this dissolved phosphorus from the soil $(S)$ to incorporate it into their biomass $(Q)$. Consumers then feed on these producers $(R)$. Finally,decomposers break down the organic matter to return phosphorus to the soil. Based on the provided diagram:
- $P$ represents the rock reservoir.
- $Q$ represents the producers (plants) that incorporate phosphorus.
- $R$ represents the consumers.
- $S$ represents the soil solution.
Therefore,$Q$ represents the producers.

(A) The correct matches based on ecological data provided in the $NCERT$ textbook are:
- $a$. Carbon dissolved in oceans: $71 \%$ of the global carbon is found dissolved in oceans $(ii)$.
- $b$. Annual fixation of carbon through photosynthesis: Approximately $4 \times 10^{13} \ kg$ of carbon is fixed annually by photosynthesis $(iii)$.
- $c$. $PAR$ (Photosynthetically Active Radiation) captured by plants: Plants capture only $2$ to $10 \%$ of the incident $PAR$ $(iv)$.
- $d$. Productivity of oceans: The annual net primary productivity of the oceans is approximately $55$ billion tons $(i)$.
Therefore,the correct sequence is $(a) - (ii), (b) - (iii), (c) - (iv), (d) - (i)$.

(C) Statement $I$ is correct because energy flow in an ecosystem is always unidirectional,moving from the sun to producers and then to consumers,with energy being lost as heat at each trophic level.
Statement $II$ is incorrect because ecosystems are not exempted from the $2^{nd}$ law of thermodynamics. The $2^{nd}$ law states that energy transformation is never $100\%$ efficient,and some energy is always dissipated as heat,which is a fundamental principle governing energy flow in all ecosystems.

(D) Statement $(a)$ is correct: Cockroaches and crows are indeed omnivores as they consume both plant and animal matter.
Statement $(b)$ is correct: The Detritus Food Chain $(DFC)$ begins with dead organic matter,which is decomposed by decomposers.
Statement $(c)$ is correct: The mass of living material at a particular time at each trophic level is defined as the standing crop.
Statement $(d)$ is correct: Species composition and stratification are the two primary structural features of an ecosystem.
Since all four statements are correct,the total number of correct statements is $4$.

(C) The correct answer is $C$.
$1$. In a terrestrial ecosystem,the Detritus Food Chain $(DFC)$ is the major conduit for energy flow,whereas in an aquatic ecosystem,the Grazing Food Chain $(GFC)$ is the major conduit for energy flow.
$2$. $A$ food web consists of many interconnected food chains. Because of this complexity and the presence of alternative pathways for energy flow,a food web is significantly more stable than a simple food chain.
$3$. Therefore,the statement that 'Food web is less stable as compared to food chain' is incorrect.
$4$. Omnivores feed on multiple trophic levels,which creates cross-links between different food chains,thereby forming a food web.

(A) natural ecosystem is defined as a self-regulating and self-sustainable unit of nature.
It is self-sustainable because it contains all the necessary functional components: producers (to capture solar energy),consumers (to transfer energy),and decomposers (to recycle nutrients).
The presence of these components ensures the continuous flow of energy and the cycling of nutrients,which allows the ecosystem to maintain its structure and function independently.
Therefore,both the assertion and the reason are true,and the reason provides the correct explanation for why a natural ecosystem is self-sustainable.

(C) An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
$1$. Ecosystems can be classified as natural (e.g.,forests,rivers,oceans) or man-made/artificial (e.g.,crop fields,aquariums).
$2$. An aquatic ecosystem is one that exists in a body of water.
$3$. $A$ river,pond,and estuary are examples of natural aquatic ecosystems.
$4$. An aquarium is a man-made (artificial) structure designed to house aquatic organisms,making it both man-made and aquatic.
Therefore,the correct option is $C$.

(C) The flow of energy in an ecosystem follows the laws of thermodynamics.
$1$. The $1^{\text{st}}$ law of thermodynamics (Law of Conservation of Energy) states that energy can neither be created nor destroyed,only transformed from one form to another. Plants convert solar energy into chemical energy,and animals convert this chemical energy into kinetic or heat energy,which represents energy transformation.
$2$. The $2^{\text{nd}}$ law of thermodynamics states that energy transfer is never $100\%$ efficient; some energy is always lost as heat. In a food chain,energy is lost at each trophic level as heat during metabolic activities.
Since the statement describes the transformation of energy (1st law) and the conversion into heat (implying energy loss/entropy,2nd law),the entire process of energy flow in a food chain follows both laws of thermodynamics.

(C) Statement $(a)$ is correct: Net Primary Productivity $(NPP)$ is the amount of biomass available for consumption by heterotrophs (herbivores and decomposers).
Statement $(b)$ is correct: Secondary productivity is defined as the rate of formation of new organic matter by consumers (heterotrophs).
Statement $(c)$ is incorrect: The annual net primary productivity of the whole biosphere is approximately $170$ billion tons (dry weight) of organic matter. Of this,the productivity of the oceans is only $55$ billion tons,whereas land productivity is significantly higher.
Statement $(d)$ is correct: Warm and moist environments are ideal for the activity of decomposers,thus favouring the process of decomposition.

(A) Ecological succession is the gradual and predictable change in the species composition of a given area over a period of time.
It involves the development of a community from a pioneer stage to a climax community.
Since this process depends on the sequential colonization and replacement of species over long durations,time is a fundamental and crucial factor for ecological succession.

(C) The sparrow is an omnivorous bird. When it feeds on seeds,grains,or fruits,it acts as a primary consumer (herbivore) because it consumes producers directly. When it feeds on insects or small worms,it acts as a secondary consumer (carnivore) because it consumes primary consumers. Therefore,the sparrow can occupy both primary and secondary trophic levels depending on its diet.