NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem

Last Updated: August 30, 2024Categories: NCERT Solutions

Multiple Choice Questions
Long Answer Type Questions: NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem
NCERT Exemplar For Class 12 Science

NCERT Exemplar for Class 12 Biology Chapter 14

The NCERT Exemplar for Class 12 Biology helps students deepen their knowledge of the Ecosystem topic. SimplyAcad provides this exemplar to cover all areas and sections of Chapter 14 in the biology textbook. Subject experts have created a variety of questions, including MCQs, very short, short, and long answer types. These questions help students become familiar with different exam patterns, giving them an advantage in their studies.

Students can easily access the NCERT Exemplar for Class 12 Biology below, helping them perform exceptionally well in their upcoming 12th board exams.

Additionally, SimplyAcad offers detailed NCERT exemplars for all chapters in Class 12 Science.

Multiple Choice Questions

Question 1

Decomposers like fungi and bacteria are:

i. autotrophs

ii. heterotrophs

iii. saprotrophs

iv. chemo-autotrophs.

Choose the correct answer:

(a) i and iii,
(b) i and iv
(c) ii and iii,
(d) i and ii

Ans: (c) ii and iii

Question 2

The process of mineralisation by microorganisms helps in the release of:

a. inorganic nutrients from humus
b. both organic and inorganic nutrients from detritus
c. organic nutrients from humus
d. inorganic nutrients from detritus and formation of humus.

Ans: (d) inorganic nutrients from detritus and formation of humus

Question 3

Productivity is the rate of production of biomass expressed in terms of:

i. (kcalm-3)yr-1
ii. g-2yr-1
iii. g-1yr-1
iv. (kcalm-2)yr-1

(a) ii,
(b) iii,
(c) ii and iv,
(d) i and iii

Ans: (c) ii and iv

Question 4

An inverted pyramid of biomass can be found in which ecosystem?

a. Forest
b. Marine
c. Grassland
d. Tundra

Ans: (b) Marine

Question 5

Which of the following is not a producer?

a. Spirogyra
b. Agaricus
c. Volvox
d. Nostoc

Ans: (b) Agaricus

Question 6

Which of the following ecosystems is most productive in terms of net primary production?

a. Deserts
b. Tropical rain forests
c. Oceans
d. Estuaries

Ans: (b) Tropical rain forests

Question 7

Pyramid of numbers is:

a. Always upright
b. Always inverted
c. Either upright or inverted
d. Neither upright nor inverted.

Ans: (c) Either upright or inverted

Question 8

Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis?

a. Less than 1%
b. 2-10%
c. 30%
d. 50%

Ans: (b) 2-10%

Question 9

Among the following, where do you think the process of decomposition would be the fastest?

a. Tropical rainforest
b. Antarctic
c. Dry arid region
d. Alpine region

Ans: (a) Tropical rainforest

Question 10

How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

a. 1%
b. 10%
c. 40%
d. 90%

Ans: (b) 10%

Question 11

During the process of ecological succession the changes that take place in communities are:

a. Orderly and sequential
b. Random
c. Very quick
d. Not influenced by the physical environment.

Ans: (a) Orderly and sequential

Question 12

Climax community is in a state of:

a. non-equilibrium
b. equilibrium
c. disorder
d. constant change.

Ans: (b) equilibrium

Question 13

Among the following bio-geo-chemical cycles which one does not have losses due to respiration?

a. Phosphorus
b. Nitrogen
c. Sulphur
d. All of the above

Ans: (d) All of the above

Question 14

The sequence of communities of primary succession in water is:

a. phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees.
b. phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees.
c. free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees.
d. phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Ans: (d) phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Question 15

The reservoir for the gaseous type of biogeochemical cycle exists in:

a. stratosphere
b. atmosphere
c. ionosphere
d. lithosphere

Ans: (b) atmosphere

Question 16

If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be:

a. scavenger
b. tertiary producer
c. tertiary consumer
d. secondary consumer

Ans: (c) tertiary consumer

Question 17

Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100mm?

(a) Grassland
(b) Shrubby forest
(c) Desert
(d) Mangrove

Ans: (c) Desert

Question 18

The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called:

a. Pelagic zone
b. Benthic zone
c. Lentic zone
d. Littoral zone

Ans: (d) Littoral zone

Question 19

Edaphic factor refers to:

a. Water
b. Soil
c. Relative humidity
d. Altitude

Ans: (b) Soil

Question 20

Which of the following is an ecosystem service provided by a natural ecosystem?

(a) Cycling of nutrients
(b) Prevention of soil erosion
(c) Pollutant absorption and reduction of the threat of global warming
(d) All of the above

Ans: (d) All of the above

Very Short Answer Type Questions

Question 1

Name an organism found as a secondary carnivore in an aquatic ecosystem.

Solution:

Shark

Question 2

What does the base tier of the ecological pyramid represent?

Solution:

Producers

Question 3

Under what conditions would a particular stage in the process of succession revert back to an earlier stage?

Solution:

A particular stage in the succession process would revert to an earlier stage in the event of natural or human-induced disruptions.

Question 4

Arrange the following as observed in vertical stratification of a forest: Grass, Shrubby plants, Teak, Amaranths.

Solution:

Teak → Amaranths → Shrubby plants → Grass

Question 5

Name an omnivore which occurs in both the grazing food chain and the decomposer food chain.

Solution:

Crow

Question 6

Justify the pitcher plant as a producer.

Solution:

Photosynthesis is carried out by the pitcher plant, which contains chlorophyll. It solely eats insects to get nitrogen from them. As a result, the pitcher plant is a producer.

Question 7

Name any two organisms which can occupy more than one trophic level in an ecosystem.

Solution:

Sparrow: When it feeds on grains, it is a primary consumer, but when it eats worms and insects, it becomes a secondary consumer.
Human: When it eats grains and pulses, it is a primary consumer; however, when it eats lamb, it is a secondary consumer.

Question 8

In the North East region of India, during the process of jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation. How would you explain the regrowth of forests in ecological terms?

Solution:

Forest regeneration is an example of ecological succession in this circumstance. After forest clearing, the conditions become xerarch, which then progresses to mesarch as the forest grows.

Question 9

Climax stage is achieved quickly in secondary succession as compared to primary succession. Why?

Solution:

After primary succession, soil becomes available. It creates perfect conditions for the growth of larger plants. When compared to primary succession, secondary succession occurs more swiftly. Hence, climax is furthermore reached more rapidly.

Question 10

Among bryophytes, lichens, and ferns, which one is a pioneer species in a xeric succession?

Solution:

Lichens

Question 11

What is the ultimate source of energy for ecosystems?

Solution:

Sun

Question 12

Is the common edible mushroom an autotroph or a heterotroph?

Solution:

Heterotroph

Question 13

Why are oceans least productive?

Solution:

Solar radiation is scarce in the oceans, particularly in the deep waters. Because of the same reason, oceans are the least productive.

Question 14

Why is the rate of assimilation of energy at the herbivore level called secondary productivity?

Solution:

Secondary productivity refers to the rate at which consumers create new organic matter. Consumers obtain raw resources from producers for this reason, which is facilitated via assimilation. Because of the same reason, the rate of energy assimilation at the herbivore level is referred to as secondary productivity.

Question 15

Why are nutrient cycles in nature called biogeochemical cycles?

Solution:

Nutrients are cycled through both biotic and abiotic components. The term ‘bio’ refers to biotic elements, whereas ‘geo’ refers to abiotic elements. As a result, biogeochemical cycles are used to describe nutrient cycles in nature.

Question 16

Give any two examples of xerarch succession.

Solution:

The two examples of xerarch succession are bare rock and sand.

Question 17

Define self-sustainability.

Solution:

A self-sustainable system is one that is self-sustaining and does not require any external input. The system’s ability to sustain itself is known as self-sustainability. Natural ecosystems are self-sustaining.

Question 18

Given below is a figure of an ecosystem. Answer the following questions.

i. What type of ecosystem is shown in the figure?
Solution: Desert ecosystem

ii. Name any plant that is characteristic of such an ecosystem.
Solution: Bushes, acacia, etc.

Question 19

What is common to earthworm, mushroom, soil mites, and dung beetle in an ecosystem?

Solution:

They are all referred to as detritivores since they are the major consumers in a detritus food chain

Short Answer Type Questions: NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem

Question 1

Organisms at a higher trophic level have less energy available. Comment.

Ans: Only 10% of the total energy ingested by a species at one trophic level is accessible to the organism at the next trophic level, as per the 10% rule. As a result, only 10% of the energy a producer turns into biomass is available to the primary consumer. Likewise, the secondary consumer has access to only 10% of the energy utilized by the first consumer. Due to this reason, higher trophic level species have less energy available.

Question 2

The number of trophic levels in an ecosystem are limited. Comment.

Ans: The number of trophic levels in every ecosystem can reach a maximum of five, in which case the food chain would appear like this:

Producer → Primary Consumer → Secondary Consumer → Tertiary consumer → Quaternary Consumer

Assume that the producer is able to capture 100 units of energy. The producer will use 90 of these units, while the primary consumer will have access to 10 of them. Finally, the quaternary consumer will have access to only 0.001 units, which is an insignificant amount of energy. As a result, no ecosystem can support additional trophic levels.

Question 3

Is an aquarium a complete ecosystem?

Ans: Aquariums are man-made ecosystems with their own set of constraints. Producers cannot have a limitless supply of inorganic materials in the confined space of an aquarium. A significant number of producers is required to support even a small number of consumers, which is not achievable in a tiny aquarium. Food must be provided for the aquarium’s fish, and the aquarium must be cleaned on a regular basis. Because an aquarium isn’t self-sustaining, it can’t be considered a complete ecosystem.

Question 4

What could be the reason for the faster rate of decomposition in the tropics?

Ans: Decomposition is primarily an oxygen-dependent process. This also necessitates the use of ambient temperature and moisture. Decomposition is accelerated when debris is high in nitrogen and water-soluble compounds. Each of these conditions can be found in a tropical climate. As a result, decomposition occurs more quickly in the tropics.

Question 5

Human activities interfere with the carbon cycle. List any two such activities.

Ans: The two actions that disrupt the carbon cycle are as follows:

(a) Forest clearing: Less green cover slows carbonification, causing the carbon cycle to be disrupted.

(b) Burning Fossil Fuels: Burning fossil fuels releases carbon into the atmosphere, increasing the percentage of carbon dioxide in the atmosphere. It also has an impact on the carbon cycle.

Question 6

Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.

Ans: At a specific trophic level, about 90% of the energy ingested by an organism is wasted as heat energy. Just 10% is left over for the organism at the next trophic level. By the time it reaches the highest trophic level, the energy accessible is a minuscule fraction of the energy converted by the producer. As a consequence, energy transmission through various trophic levels is non-cyclic and unidirectional.

Question 7

Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs, what are microbes referred to as? How do the microbes fulfill their energy requirements?

Ans: Productivity, decomposition, energy flow, and nutrient cycling are all necessary components of any ecosystem. Plants and animals both contribute to productivity. While some microorganisms have a role in productivity, like algae and chemosynthetic bacteria, others, like algae and chemosynthetic bacteria, are autotrophs. Heterotrophic microorganisms make up the majority of the population. Parasitic bacteria get their nourishment from the host they live in. Saprotrophs are a type of microorganism that feeds on other bacteria. They eat detritus and are hence a vital part of the detritus food chain.

Question 8

Poaching of tigers is a burning issue in today’s world. What implication would this activity have on the functioning of the ecosystem of which the tigers are an integral part?

Ans: Tigers are tertiary consumers, meaning they are at the top of the forest food chain. Tertiary consumers play a crucial role in regulating the populations of secondary and primary consumers. If all tigers were eliminated, there would be no predators left to control the herbivore population. As a result, herbivores would overgraze, quickly depleting the producers and disrupting the entire ecosystem.

In the absence of producers, herbivores would eventually starve to death. This will completely devastate the ecosystem.

Question 9

In relation to energy transfer in the ecosystem, explain the statement “10 kg of deer’s meat is equivalent to 1 kg of lion’s flesh”.

Ans: It is known that only 10% of the energy consumed at one trophic level can be used at the next. At the primary consumer level, 10 kg of deer meat equals 10 kg of biomass. 90% of it is absorbed by the deer for its own consumption. The lion will have access to the leftover 10%, or 1 kg. As a result, it is correct to declare that 10 kg of deer meat equals 1 kg of lion meat.

Question 10

Primary productivity varies from ecosystem to ecosystem. Explain.

Ans: The biomass generated per unit area by photosynthesis over time is referred to as primary productivity. It is the quantity of biomass produced by green plants in a given habitat in simple terms. The number of plants differs from one ecosystem to the next. The number of plants in tropical rainforests is higher than in deserts. As a result, primary productivity in tropical rainforests would be substantially higher than in deserts. This demonstrates that primary productivity differs by ecosystem.

Question 11

Sometimes due to biotic/abiotic factors, the climax remains in a particular seral stage (pre climax) without reaching climax. Do you agree with this statement? If yes, give a suitable example.

Ans: A sere refers to the full succession of communities which shift in a given location (s). All biotic and abiotic elements play an important part in this shift, allowing a community to achieve its climax. If the community’s biotic and abiotic conditions are insufficient to support climax, this might stay in a given seral stage without attaining the climax. Table Top Mountain, with its sparse vegetation, is an instance of a community in the seral stage. Just mosses and ferns might be found in the community at the tabletop mountain’s peak. In time, this would pave the way for taller plants.

Question 12

What is an incomplete ecosystem? Explain with the help of a suitable example.

Ans: An incomplete ecosystem is the one that is missing certain biotic or abiotic components. An ecology that isn’t complete can’t be self-sustaining. The aquarium is a good example of a partially completed ecosystem. Even though there are producers and consumers in the aquarium, there are no decomposers. Due to a shortage of decomposers, the aquarium should be cleaned frequently and maintained regularly.

Question 13

What are the shortcomings of ecological pyramids in the study of ecosystems?

Ans: The following are some of the problems with ecological pyramids:

α. It ignores the fact that the same species might be found in two or more trophic levels.

β. It is dependent on a simple food chain assumption. A simple food chain, on the other hand, does not occur in nature. It’s the natural world’s intricate food web.

χ. The decomposers are not included in the food pyramid. Decomposers, on the other hand, are essential components of the nutrient cycle.

Question 14

How do you distinguish between humification and mineralisation?

Ans: The detritus food chain includes both humification and mineralisation. Decomposition results in the production of inorganic compounds from organic matter, whereas humification results in the formation of a dark-colored amorphous material termed humus. Mineralisation, unlike humifaction, results in the full breakdown of organic molecules into inorganic compounds.

Question 15

Fill in the trophic levels (1, 2, 3 and 4) in the boxes provided in the figure.

Ans:

Producer
Primary Consumer
Secondary Consumer
Tertiary Consumer

Question 16

The rate of decomposition of detritus is affected by abiotic factors like the availability of oxygen, pH of the soil substratum, temperature, etc. Discuss.

Ans: Living creatures are responsible for decomposition, albeit the rate of decomposition is regulated by a variety of abiotic variables. Because this is an oxygen-intensive mechanism, the rate of decomposition is influenced by the supply of oxygen. If there is more oxygen available, decomposition will proceed more quickly. The rate of decomposition is higher in warm weather than in cold weather. pH has an impact on the pace of decomposition. The rate of breakdown in neutral soil is higher than in acidic soil.

Long Answer Type Questions: NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem

Question 1

A farmer harvests his crop and expresses his harvest in three different ways.

a. I have harvested 10 quintals of wheat.
b. I have harvested 10 quintals of wheat today in one acre of land.
c. I have harvested 10 quintals of wheat in one acre of land, 6 months after sowing.

Do the above statements mean one and the same thing? If your answer is yes, give reasons. And if your answer is ‘no’ explain the meaning of each expression.

Ans: Different statements imply different things.

The first statement merely reflects the amount of biomass generated, but not the time or region over which it was produced.
The second statement reveals the quantity and area of the product, but not the time it took to make it.
The third statement is complete as it demonstrates the quantity, area, and duration.

The third statement’s data can be utilized to estimate primary productivity on the farm in terms of biomass produced.

Question 2

Justify the following statement in terms of ecosystem dynamics. “Nature tends to increase the gross primary productivity, while man tends to increase the net primary productivity”.

Ans:

Gross primary productivity (GPP) is the rate at which organic matter is produced in an ecosystem. Net Primary Productivity (NPP) is calculated by subtracting respiratory losses (R) from GPP.

Nature provides various biotic and abiotic factors that help increase GPP, naturally boosting gross primary productivity. However, humans must optimize the use of the biomass produced. This includes methods like harvesting crops and picking fruits at the right time.

If fruits remain on the tree for too long, they cause more respiratory losses, which reduces NPP. By picking fruits at the right time, humans can maximize net primary productivity.

Question 3

Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer.

A young forest
A natural old forest
A shallow polluted lake
Alpine meadow

Ans:

A young forest can be seen as a community that hasn’t yet reached its climax. This means the forest has a lower tree density, which leads to lower primary productivity. On the other hand, an old, mature forest represents a community that has reached its peak. Such forests are typically filled with tall trees and dense foliage, resulting in higher primary productivity.

In contrast, a shallow polluted lake may have few producers. Pollution likely harmed the environment, reducing the number of producers and overall productivity in the pond.

As a result, this pond may have a low primary productivity. An alpine meadow is a grassy area with few or no trees. Primary productivity is lower when there are fewer trees. In light of the foregoing, it is reasonable to conclude that the natural ancient forest does have the highest degree of primary productivity.

Question 4

What are the three types of ecological pyramids? What information is conveyed by each pyramid with regard to structure, function, and energy in the ecosystem?

Ans: Below given are the three types of ecological pyramids:

Pyramid of Number: This pyramid shows the number of individuals at each trophic level. Producers occupy the bottom, followed by primary consumers, secondary consumers, and so on. Usually, the base of the pyramid is large. However, in some cases, this pyramid can be inverted.
Pyramid of Biomass: This pyramid represents the biomass (measured in dry weight) at each trophic level. Producers form the base, followed by primary consumers, secondary consumers, and so forth. Typically, the base of the pyramid is large. However, in some cases, the pyramid can be inverted.
Pyramid of Energy: This pyramid shows the energy consumed at each trophic level. Producers occupy the bottom of the pyramid, followed by primary consumers, secondary consumers, and so on. In most cases, the base of the pyramid is broad, reflecting the large amount of energy available at the producer level. This pyramid cannot be inverted.

In any type of pyramid, a specific trophic level demonstrates a functional level. A single organism can exist on multiple levels. The flow of energy would always be from prey to predator. The amount and availability of energy varies at different levels and reduces at subsequent levels.

Question 5

Write a short note on the pyramid of numbers and pyramid of biomass.

Ans:

Pyramid of Numbers: A graphical representation of the number of creatures at each trophic level is called a pyramid of numbers. Because the producers are always more numerous than the other trophic levels in an ecosystem, this is an upright pyramid. Charles Elton proposed the pyramid of numbers in 1927. The number of species engaged in each rung of the food chain varies dramatically, as Charles found out. The number of predators at the peak of the trophic structure decreases significantly as the links of the trophic structure progress.
Pyramid of Biomass: A biomass pyramid is a graphical representation of the biomass present in a unit of land at various trophic levels. It also shows the relationship between biomass and trophic level, evaluating the biomass obtainable at any particular time in each trophic degree of an energy network.

The changed biomass pyramid and the upstanding biomass pyramid are the two types of biomass pyramids. In a lake biological system, the mass of phytoplankton, the major producers, would constantly be lower than that of the mass of heterotrophs including fish and creepy crawlies, demonstrating the rearranging pyramid of biomass. The pyramid takes on an odd structure as the biomass estimation grows larger, with tertiary shoppers appearing at the top.

Question 6

Given below is a list of autotrophs and heterotrophs. With your knowledge about the food chain, establish various linkages between the organisms on the principle of ‘eating and being eaten’. What is this inter-linkage established known as?

Algae, hydrilla, grasshopper, rat, squirrel, crow, maize plant, deer, rabbit, lizard, wolf, snake, peacock, phytoplankton, crustaceans, whale, tiger, lion, sparrow, duck, crane, cockroach, spider, toad, fish, leopard, elephant, goat, Nymphaea, Spirogyra.

Ans: The term “food web” refers to the interconnection of many creatures. With the above list of creatures, the following two food webs are possible.

Question 7

“The energy flow in the ecosystem follows the second law of thermodynamics.” Explain.

Ans:

According to the second law of thermodynamics, the entropy of an isolated system never decreases; such a system naturally moves toward thermodynamic equilibrium. In this state, the system adopts the configuration with the highest entropy. To synthesize the molecules needed by an ecosystem, a constant supply of energy is necessary.

The law of thermodynamics dictates that energy flow in an ecosystem is always unidirectional. A reverse flow of energy would disrupt the system’s balance. Producers capture solar energy and serve as conduits, passing energy to the next trophic levels. Because maintaining alignment with the law of thermodynamics is challenging, energy never moves from a higher trophic level to a lower one.

Question 8

What will happen to an ecosystem if:

a. All producers are removed;
b. All organisms of herbivore level are eliminated; and
c. All top carnivore population is removed.

Ans:

a. All producers are removed: When all producers are removed from an ecosystem, the primary consumers are left hungry. Because of hunger, all of the primary consumers would perish. This means there would be no food for secondary and tertiary consumers, who will be gratified in due course. The ecosystem would come to an end as a result of this.
b. All organisms of herbivore level are eliminated: If all herbivores are destroyed from an ecosystem, predators will have no food. Due to a scarcity of food, all of the carnivores might eventually starve to death. In the absence of herbivores, plant populations will grow exponentially. However, if there aren’t enough other biotic components, the biogeochemical cycle will come to a standstill. This will bring the ecosystem to a close.
c. All top carnivore population is removed:Herbivore populations would explode if top carnivores were destroyed. Overgrazing would then threaten the survival of green plants.

Question 9

Give two examples of artificial or man-made ecosystems. List the salient features by which they differ from natural ecosystems.

Ans: Two examples of artificial ecosystems are Crop fields and an aquarium.

Natural Ecosystems	Man-made Ecosystems
(i) Natural ecosystems are the ones that do not involve human intervention.	(i) Man-made ecosystems are the ones that involve human intervention.
(ii) Numerous natural ecosystems are being spanned over huge areas.	(ii) These are the ecosystems which span within a limited area.
(iii) Replenishment of nutrients happens via biogeochemical cycles.	(iii) Replenishment of nutrients is done by humans.
(iv) There is an equilibrium between the producers and consumers population.	(iv) There remains an imbalance in the producers and consumers population.
(v) Natural ecosystems are self-sustaining.	(v) Man-made ecosystems are not self-sustaining.

Question 10

The biodiversity increases when one moves from the pioneer to the climax stage. What could be the explanation?

Ans: The food availability for customers determines a community’s biodiversity. If a community’s flora is diverse, this could sustain a wider range of consumer kinds.

The much more typical plants in a pioneer colony include bryophytes, lichens, and pteridophytes. Such plants don’t really generate adequate biomass to support a diversified fauna.

As a result, biodiversity would be restricted at this time. Gymnosperms and angiosperms proliferate once the community reaches its peak. The biomass produced by these plants is sufficient to support a diversified fauna. As a consequence, biodiversity is currently expanding.

Question 11

What is a biogeochemical cycle? What is the role of the reservoir in a biogeochemical cycle? Give an example of a sedimentary cycle with a reservoir located in the earth’s crust.

Ans:

The biogeochemical cycle, or nutrient cycling, is the process of exchanging nutrients between different parts of an ecosystem. This cycle prevents nutrient waste by continuously renewing them in ecosystem reservoirs.

Reservoir Function: A nutrient can become inadequate when its outflow and influx are out of balance. The reservoir compensates for nutrient deficiencies, such as nitrogen, by supplying the necessary amounts.

Phosphorus Cycle: The phosphorus reservoir exists in the earth’s crust. The phosphorus cycle exemplifies a sedimentary cycle. Rocks naturally store phosphorus in the form of phosphates. When rocks weather, low concentrations of phosphates mix into the soil solution. Plant roots then absorb phosphorus from this soil solution. Plants supply phosphates to both primary and secondary users.

Question 12

What will be the P/R ratio of a climax community and a pioneer community? What explanation could you offer for the changes seen in the P/R ratio of a pioneer community and the climax community?

Ans:

A community’s P/R ratio is the proportion of gross output to communal respiration. This ratio can be equal to one, less than one, or greater than one.

In a pioneer community, the P/R ratio can vary—it may be less than or greater than one. However, in a climax community, the P/R ratio is consistently 1.

In a pioneer community, two scenarios are possible:

(a) When gross output is high and there are fewer consumers, respiratory loss decreases As a result, the P/R ratio exceeds 1.

(b) When the decomposer population is large, leading to higher decomposition rates, gross productivity falls below respiratory losses. In this case, the P/R ratio drops below 1.

In a climax community, the P/R ratio is 1. This occurs due to the stability of the community. The graph below shows the P/R ratio at various stages of community succession, with the primary community at the top and the climax community at the base.

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