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Ecosystem Class 12 Important Questions And Answers MCQ PDF

Ecosystem Class 12:- Ecosystems consist of all the living entities and the physical environment and the surrounding with which they interact.It is a core concept.It consists of both of them that is the Biotic and the abiotic components of the environment.The term ecosystem is given by A.G Tansley in 1935.

Ecosystem Class 12
Ecosystem Class 12

Very Short Answer Type Questions – Ecosystem Class 12

Q.1. Name a secondary carnivore that lives in an aquatic ecosystem.

A.1. Ducks and Waterfowls. 

Q.2. What does the base tier of the ecological pyramid signify?

A.2. The base tier of the ecological pyramid represents the producers

Q.3. At which state in the process of succession relapse at an earlier stage is possible? 

A.3. Anthropogenic actions and natural disruptions such as flood, fire etc make reversion at an earlier stage  possible. 

 Q.4.Name an omnivore that is present in both the grazing and decomposer food chain.

A.4. Cockroaches and Crow. 

Q.5. Specify with proper reason why is pitcher plant called a producer?

A.5. Nepenthes or the pitcher plant is an insectivorous plant that traps solar rays for photosynthesis and is chlorophyllous. It mainly grows in the soil lacking nitrogen. Therefore they trap insects to make up for the lack of nitrogen.

Q.6. Name twp entities found in more than one trophic level in an ecosystem.

A.6.  Human beings and Sparrow. 

Q.7. Why is the climax phase attained at a faster pace in secondary succession when compared to the primary succession.

A.7. This is because of the of soil availability. Succession in primary successioni s a time-consuming process as itbegins from bare rocks .

Q.8.Which among these following species is a pioneer, in a xeric succession ?

 Bryophytes, Lichens, Fern. 

A.8. Lichens then Bryophytes and then  ferns in the order.

Ecosystem Class 12 QUiz

Q.9. What’s the ultimate source of energy in an ecosystem? 

A.9. Solar radiation. 

Q.10. Specify if the edible mushroom is a heterotroph or an autotroph?

A.10. AEdible mushroom  is a heterotroph.

Q.11. Why are oceans the least productive?

A.11. Oceans are the least productiveis because there is lack of sunlight with increasing depth. Oceans also lack nitrogen, which is an important source of nutrient for plants. Ocean water beaing highly saline does not serve as a favourable condition for all plants. Moreover, the absence of soil causes the lack of sustainibility in plants in the ocean. .

Q.12. Why is the rate of assimilation of energy at the herbivore level called as secondary productivity? 

A.12. This is due to the biomass available to the consumers for further consumption is produced by the autotrophs as a product of primary productivity.

Q.13. Specify with the proper reasoning why are the nutrient cycles are  also referred as the biogeochemical cycles?

A.13. The Nutrient molecules are passed from the environment to entities and back again to the environment in the  cyclic way, therefore the name where bio means living entities and the geo means air, water and rocks.

Q.14. Make a List any two of the examples of xerarch succession.

A.14. In the ecological communities, they are found in the remarkably dry conditions like the rock deserts and the sandy deserts.

Q.15. Define self-sustainability.

A.15. It maintains itself, with the own independent efforts of their.

Q.16. Observe the ecosystem and the answer the given questions:

Ecosystem Class 12

a)Write  the name the ecosystem

b) Give the name of the  plant which  is a characteristic of this ecosystem.


a)The  Tropical deciduous forest

b) The Diptherocarpus Jamun,  Palas Amia, Palas, Tectona in India.

Q.17. What do these living organisms share in the common: Soil mites, Earthworm, Mushroom, Dung beetle.

A.17. They all are the detritivores, primary consumers in the detritus food chain.

Q.18. Define biogeochemical cycle.

A.18. Biogeochemical cycles are defined as to the movement of nutrients and other essential elements between biotic and abiotic factors.

Q.19.Define ecosystems.

A.19.Ecosystem is defined as the community or the group of the living organisms living together in the physical environment by the concurrence with the non-living components.

Q.20. Write some of the examples for the natural ecosystems and the man-made or the artificial ecosystems.

A.20.The Forests,  desert ,tundra,grasslands, lakes, rivers and seas are the examples of natural ecosystems. Zoos, national parks, sanctuaries are the examples of man-made or the artificial ecosystems.

Short Answer Type Questions – Ecosystem Class 12

Q.1. The availability of the energy is less for the living organisms at the higher trophic levels. Why give the reason?

A.1. 10% energy flow law suggested by  the Lidman, is followed in the ecosystem. As per this law, only the 10% of the energy is available at the every trophic level is transferred to next trophic level. The remaining part is lost in  form of the heat(during respiration). As we approach the higher levels, the energy keeps declining which is available to entities. Therefore the topmost carnivore attains the least amount of the energy in the food chain.

Q.2. Why  the number of the trophic levels in an ecosystem limited?

A.2. There are not more than the 4-5 levels since the energy flow declines as we approach the higher levels as only 10% of the energy is passed from the one to the next progressive trophic level. The remaining energy is lost during the respiration and in the other crucial activities to the sustenance of the life. In the case there are the  more levels, the remaining energy will be limited to the extent which it furthermore would not be able to sustain the any trophic level through the energy flow. Therefore the levels are limited.

Q.3. Can we address the aquarium as the complete ecosystem?

A.3. An aquarium is an artificial ecosystem which is made by man. Ecosystem is said to be complete if it possesses all the biological and the physical components vital for the survival of the fishes. Therefore it is the complete ecosystem.

Ecosystem Class 12

Q.4. Why does the decomposition occurs at a faster rate in  tropical regions?

A.4. The decomposition is governed by the climatic factors therefore the favourable humidity and the temperature in the tropics facilitate  activities of the decomposers along with the soil rich in the dead remains supporting rapid rate of the decomposition.

Q.5. Write any two activities where the humans intervene with  carbon cycle.

A.5. The Massive burning of the fossil fuels for transport, energy and the deforestation.

Q.6. Give a reason why the flow of the energy at different levels in an ecosystem is unidirectional and they are non-cyclic.

A.6. The flow of the energy is one way and the non-cyclic( Plants →Herbivores→Carnivores→Top Carnivore). The energy which is transferred from 1st to the next trophic level decreases with the each passing level and they cannot flow in the reverse direction.

Q.7. Plants → Autotrophs, Animals → Heterotrophs, Microbes → ? Describe how the microbes fullfill their energy requirements.

A.7. The Microbes → Saprophytes. They are derive their energy from the remains of the dead organic matter of the animals and the plants, wherein digestion is extracellular.

Q.8. How would the issue of the ‘poaching of tigers’ affect the functioning of the ecosystem?

A.8. Tigers help in the maintaining ecological balance and form very important part of the food web. It regulates the extensive growth of the herbivores and helps in eliminating the sick, the old animals from the community, representing the health of forest. Therefore saving tigers is saving forests as tigers cannot survive in the places where they hunt(herbivores or trees) thereby the securing water and the food for all.

Q.9. In context of the transfer of the energy in an ecosystem, what does the ’10kg of deer’s meat is equivalent to 1 kg of the lion’s flesh’ mean?

A.9. Only the 10% of energy is passed from the one to a higher trophic level. Therefore if the lion hunts and eats a deer, the 10kg of the deer’s meat will make up for the 1kg of lion’s meat.

Q.10. Why does the primary productivity vary in the different ecosystems?

A.10. The rate at which the  plants(primary producers) utilize and store the solar rays for the formation of the chemical energy is referred to as the primary productivity. In ecosystems, producers vary and as the primary production is dependant on the plants, it varies in different ecosystems.

Q.11. What is an incomplete ecosystem? Give an example.

A.11. The Limited or the unavailability of the biotic and the abiotic components makes an ecosystem incomplete. For Example – The Benthic zone in an aquatic ecosystem

Q.12. In study of the ecosystem, what are the limitations of the ecological pyramids?

A.12. Following are the limitations of the ecological pyramids:

  • A species can function at the two or more the trophic levels
  • These pyramids represent only the simple food chains. But only the complex food chains occur in the nature.
  • The Decomposers play a very crucial role to maintain the stability in an ecosystem that these pyramids do not account for.

Q.13. Write a difference between the humification and the mineralization.

A.13. Following is the difference:

The humification is the disintegration of the soil which causes a collection of the hummus that is resistant to microbial activities and the decomposes at a slower rate.Mineralization is the process in which microbes degenerate humus further resulting in minerals and inorganic nutrients being discharged back into the soil.
Ecosystem Class 12

Q.14. Fill  the trophic levels, labelled 1,2,3,4 in the given figure.

Trophic levels
Ecosystem Class 12

A.14. 1 – Producers (First Trophic level – Plants) 2 – Primary Consumers (Second Trophic level – Herbivores) 3 – Secondary Consumers (Third Trophic level – Carnivores) 4 – Tertiary Consumers (Fourth Trophic level – Top Carnivores)

Q.15. Why is the rate of the decomposition affected by the abiotic factors such as the pH of the soil, the availability of the oxygen, temperature etc?

A.15. The pH of the soil affects the structure of the basophilic and the acidophilic microbes. The aerobic processes occur in the presence of the oxygen causing the complete degradation of the substance whereas the anaerobic processes occur in the absence of the oxygen, resulting in the incomplete degradation of the substance. The Microbes are unable to grow to their fullest at the higher temperatures but at low or the high temperatures, the stress-tolerant microbes flourish.

Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12

Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12 Ecosystem Class 12

Q.16. Write the importance of the ecosystem.

A.16. The ecosystem maintains the  balance in the environment. It provides the fresh air to breathe and the sequesters carbon to regulate the climate. It cycles the nutrients through the various biogeochemical cycles so that we have access to clean the drinking water without any the costly methods. It provides food and the shelter to a number of the living organisms. It also provides the raw materials for the different industrial and domestic purposes.

Q.17. Define the Pyramid of Biomass.

A.17. They are of three different types of ecological pyramids.  The Pyramid of the Biomass explains the relationship between the biomass and the trophic level of an energy community at the given time.

Q.18. Define the Ecological Pyramid.

A.18. An ecological pyramid is the graphical representation of the relationship between  different living organisms at the different trophic levels.

Q.19. Write the name of the three types of ecological pyramids?l.

A.19. Following are the three types of the ecological pyramids include:

  1. Pyramid of Number.
  2. Pyramid of Biomass.
  3. Pyramid of Energy.

Q.20. Define the aquatic ecosystem and the terrestrial ecosystem.Write some examples.


Aquatic ecosystem–The ecosystems present in the body of water is known as the Aquatic ecosystem.  They are of two types of the Aquatic ecosystem :

  1. Marine Ecosystem.
  2. Freshwater Ecosystem.

Terrestrial ecosystems–The ecosystems, that are exclusively land-based they are known as  the   Terrestrial ecosystems. There are four different types of the terrestrial ecosystems and they are distributed around the various geological zones.

  1. Desert Ecosystems.
  2. Forest Ecosystems.
  3. Tundra Ecosystems.
  4. Grassland Ecosystems.

Long Answer Type Questions

Q.1. How can we say that nature favour to the raise in the gross primary productivity while the man tends to raise the net primary productivity?

A.1. The energy in the ecosystem flows unidirectionally from the one to the next trophic level. The nature functions in the way so as to benefit the entities performing a specific activity. The plants conduct the photosynthesis. This is the plant’s primary activity as well as the gross primary productivity. This activity in the plants is dependent on the inputs and they produces to its maximum extent with an increase in the inputs. On the other hand, the humans depend on the plants. This is the part of their net primary productivity and this is not a matter of the concern for them if the specific plant has a low or the high gross primary productivity.

Q.2. In the context of the primary productivity, which the ecosystem would be more productive?

In the natural old forest, in the young forest, alpine meadow,  and the shallow polluted lake.

A.2. The ecosystem possesses more the producers will be more the productive. The young forests grow quicker than the older and the mature forests and therefore they are more productive in the terms of the primary productivity. The alpine meadows and the shallow polluted lakes will be the  less productive since they have the less number of the producers and the more dead matter.

Q.3. Describe the three types of the ecological pyramids. What data is propagated by the each pyramid in the association with function, structure and the energy in the ecosystem?

A.3. Following are the three types of pyramids :

  • Pyramid of numbers.
  • Pyramid of Biomass.
  • Pyramid of Energy.
AttributesPyramid of numbersPyramid of BiomassPyramid of Energy
StructureIt is the upright, denoting the number of the producers is maximum. The Herbivores are lesser when they are compared to the producers. The Primary carnivores are lesser compared to the secondary carnivores.Upright which denotes the biomass of the producers is maximum. As the tropic levels rise, a decline in the biomass is observed. The 10-20% of biomass is passed from the one to the next trophic level.They are Upright always. At the producer the level, energy flow is maximum. 10% of the energy transfers from the  one to the next, rest is scattered.
FunctionThe population at the higher trophic levels becomes the smaller as wastage of food takes place due to the various activities.The Reduction in the biomass represents the utilization and the wastage of biomass at the every levelMost energy is used in the respiration process.
EnergyTheir is No evidence.Biomass may represent the energy value.This will deals with the energy per unit area.
Ecosystem Class 12

Q.4. Describe how energy flow supports the second law of the thermodynamics in an ecosystem.

A.4. As per the second law of the thermodynamics, every activity which includes the transformation includes the wastage of energy in the form of heat and the rise in the disorganization excluding the deep hydrothermal ecosystems. Out of the total PAR(Photosynthetically Active Radiation), only the 2-10% is absorbed by the organisms involved in the photosynthesis to produce the organic matter. Furthermore, the energy is utilized in the metabolic activities, to form the food and in the storing biomass(very less). The Biomass or the trapped energy is the passed to the next trophic level as per the Lindeman’s law. 10% of the stored energy is transferred from one to the next consecutive trophic level.

Q.5. Write the answer of the following questions. Give the outcomes of the following events.

a) Consequence of the eliminating all the producers

b) Consequence of the eliminating all the entities at the herbivore level

c) Consequence of the eliminating all the top carnivore entities

A.5. a) It diminishes the primary production in an ecosystem and therefore the unavailability of the biomass to the higher trophic levels  

b) It would result in the increase in the primary productivity and the biomass of the producers. The Carnivorous animals, because of the unavailability of the food, will not survive. 

c) There will be the increase in the herbivore population, the resulting in over-grazing and therefore the desertification.

Q.6. Write the name of the two examples of the man-made ecosystems. Explain their salient features that distinguish them from natural ecosystems.

A.6. Following are the Examples of man-made ecosystems are – the  farmhouse and the aquarium. In these ecosystems, the maintenance of the biotic and the abiotic components occurs through the measures such as – the feeding, the cleaning, adequate oxygen supply to the fishes in the aquarium and the irrigation in crop or the farmhouse. In the  natural ecosystem, abiotic and the biotic components are maintained naturally such as – the nutrient cycle, prevention of the soil erosion, self-sustainability, the reduction of threat because of the global warming etc.

Q.7. What is the biogeochemical cycle? Write the  significance of the reservoir in this cycle, With a reservoir situated in the earth’s crust, give an example of the  sedimentary cycle.

A.7. The movement of the nutrient molecules through the different components of the ecosystem is called as a biogeochemical cycle. It is of two types of nutrient cycles – The Sedimentary and the gaseous. For the gaseous type of the cycle, the atmosphere is  reservoir(nitrogen cycle) and for sedimentary cycle – the crust of earth is the reservoir (phosphorous cycle). The function of reservoir is to be able to the compensate for the deficiency which takes place because of the inequality in the flow of the efflux and the influx. The Various environmental factors such as the temperature, moisture in the soil, pH etc govern the rate the  of liberation of the nutrients into the atmosphere. The phosphorus cycle is the example of the sedimentary type of cycle as it moves from the land and approaches the bottom of the seas and reverts to the land, whose natural reservoir is the crust of the earth. The Phosphorous is contained in the rocks in the form of the phosphates. The Soil erosion and the weathering cause them to enter water bodies. The Movements of the crustal plates lead to seafloor being uplifted and therefore the exposure of phosphates on the land surfaces. The Weathering over a period of time liberates phosphates, that are softened in soil and seeped by plant roots. The Herbivores and the other entities attain this element from producers. The Decomposition of the dead organisms and the waste products by phosphate-solubilizing bacteria release the phosphorous.

Q.8.What is the producers, consumers and the decomposers?

A.8.  Producers: All the autotrophs such as the plants and other photosynthetic organisms which prepare their own food they are known as producers.

Consumers: All the heterotrophs, including the birds, animals, and other living organisms, that depend on the producers and other organisms for food they are known as consumers. There are four different types of the consumers:

  1.  Primary consumers.
  2. Secondary consumers.
  3. Tertiary consumers.
  4. Quaternary consumers.

Decomposers: All the saprophytes, such as the fungi and the bacteria, that directly feed on the dead and the decaying organic matter they are known as decomposers.

Q.10. Describe the Biotic Components and the Abiotic Components of the Ecosystem with the suitable examples.

A.10. The Biotic and the Abiotic are the two Components, that are interrelated in an ecosystem.

The Biotic Components include the different life forms in an ecosystem. Based on the nutrition, biotic components can be categorised into the autotrophs, the heterotrophs and the saprotrophs (or the decomposers).

Abiotic Components includes the non-living component of an ecosystem. Air, water, soil, minerals, sunlight, temperature, nutrients, wind, altitude, turbidity are few examples of Abiotic Components.

Q.11. Define Food Chain. Write their different types of the food chains in the ecosystem.

A.11.  The food chain is defined as the network of links in the food web.  Which explains the flow of the  energy in an ecosystem. 

In this system, the producers are consumed by the predators – the primary and the secondary consumers and then the detritivores and finally by the decomposers. When many such individual food chains occur in the  ecosystem, it is collectively called as the Food Web. To some extent, both the food chains and food webs are similar to the each other.

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