Important Questions for Class 12 Chapter 14: Ecosystem

An ecosystem is a functional unit of nature with constant interaction between living entities and also with their ambient physical environment. An ecosystem differs greatly in many aspects such as its size, from a small lake to a large forest or an ocean. Since it hugely varies and is complex and big, it is conveniently subdivided into two broad categories such as aquatic(pond, lakes, sea, ocean) and terrestrial(grassland, forest, desert). Some ecosystems are man-made and are referred to as artificial ecosystems.

The following important questions on the ecosystem will help you enhance your conceptual knowledge on the topic.

Very Short Answer Type Questions

Q.1. Give an example of a secondary carnivore found in an aquatic ecosystem.

A.1. Waterfowls and ducks

Q.2. The base tier of the ecological pyramid indicates?

A.2. It represents the producers

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

A.3. Reversion at an earlier stage is possible due to anthropogenic actions and natural disruptions such as flood, fire etc.

Q.4. Pick an omnivore that appears in both the decomposer and grazing food chain.

A.4. Crow, Cockroaches

Q.5. Why is pitcher plant called a producer?

A.5. Nepenthes or the pitcher plant is an insectivorous plant that has the potential of trapping solar rays for photosynthesis and is chlorophyllous. It is produced in the soil that lacks nitrogen. Hence they trap insects to compensate for the deficit of nitrogen.

Q.6. List two entities which are found in more than one trophic level in an ecosystem.

A.6. Sparrow and human beings.

Q.7. Justify why the climax phase is attained at a faster pace in secondary succession in comparison to the primary succession.

A.7. It is because of the availability of soil. Succession in primary succession begins from bare rocks which is a time-consuming process.

Q.8. In a xeric succession, which among these following species is a pioneer?
Fern, Lichens, Bryophytes.

A.8. Lichens followed by Bryophytes and then succeeded by ferns in the order.

Q.9. In an ecosystem, which is the ultimate source of energy?

A.9. Solar radiation

Q.10. Is the edible mushroom a heterotroph or an autotroph?

A.10. It is a heterotroph.

Q.11. What makes oceans the least productive?

A.11. It is because of the lack of sunlight with increasing depth. Oceans lack nitrogen, which is an important source of nutrient for plants. High salinity offered by oceans does not serve as a favourable condition for all plants. More importantly, the absence of soil is the reason why plants do not sustain.

Q.12. State why at the herbivore level, the rate of assimilation of energy is called as secondary productivity.

A.12. It is because the biomass available to the consumers for further consumption is formed by the autotrophs as a product of primary productivity.

Q.13. Why are nutrient cycles also referred to as biogeochemical cycles?

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

Q.14. List any two examples of xerarch succession.

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

Q.15. What is self-sustainability?

A.15. It maintains itself, with its own independent efforts.

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

a) Name the ecosystem

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


a) Tropical deciduous forest

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

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

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

Q.18. What is a 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. What are ecosystems?

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

Q.20. Give examples for the natural ecosystems and man-made or artificial ecosystems.

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

Short Answer Type Questions

Q.1. Availability of energy is less for entities at higher trophic levels. Why?

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

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

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

Q.3. Can we address an aquarium as a complete ecosystem?

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

Q.4. Why decomposition occurs at a faster rate in the tropics?

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

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

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

Q.6. Explain why the flow of energy at different levels in an ecosystem is unidirectional and non-cyclic.

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

Q.7. Plants → Autotrophs, Animals → Heterotrophs, Microbes → ? State how microbes accomplish their energy requirements.

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

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

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

Q.9. In the context of the transfer of energy in an ecosystem, what does ’10kg of deer’s meat is equivalent to 1 kg of lion’s flesh’ mean?
A.9. Only 10% of energy is passed from one to a higher trophic level. Hence if a lion hunts and eats a deer, 10kg of deer’s meat will make up for 1kg of lion’s meat.

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

Q.11. Describe the incomplete ecosystem with an example.

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

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

A.12. Following are the shortcomings:

  • A species can function at two or more trophic levels

  • These pyramids represent only simple food chains. But only complex food chains occur in nature.

  • Decomposers play a crucial role to maintain stability in an ecosystem which these pyramids do not account for.

Q.13. Differentiate between humification and mineralization.

A.13. Following is the difference:

Humification is the disintegration of soil which causes a collection of hummus, that is resistant to microbial activities and 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.

Q.14. Fill up for the tropic levels, labelled 1,2,3,4 in the given figure.
Trophic levels

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 decomposition affected by abiotic factors such as pH of the soil, availability of oxygen, temperature etc?

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

Q.16. What is the importance of the ecosystem?

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

Q.17. Define the Pyramid of Biomass?

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

Q.18. What is the Ecological Pyramid? 

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

Q.19. What are the three types of ecological pyramids?

A.19. The three types of ecological pyramids include:

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

Q.20. What are the aquatic ecosystem and the terrestrial ecosystem? Give examples.


Aquatic ecosystem–The ecosystems present in a body of water is called the Aquatic ecosystem.  There are two types of Aquatic ecosystem :

  1. Marine Ecosystem.
  2. Freshwater Ecosystem.

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

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

Long Answer Type Questions

Q.1. How does nature favour to raise the gross primary productivity while man tends to raise the net primary productivity?

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

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

A natural old forest, a young forest, alpine meadow, a shallow polluted lake.

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

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

A.3. The three types of pyramids are as follows:

  • Pyramid of numbers.

  • Pyramid of Biomass.

  • Pyramid of Energy.

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

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

A.4. As per the second law of thermodynamics, every activity that includes transformation includes wastage of energy in the form of heat and rise in disorganization excluding deep hydrothermal ecosystems. Out of the total PAR(Photosynthetically Active Radiation), only 2-10% is absorbed by organisms involved in photosynthesis to produce organic matter. Furthermore, the energy is utilized in metabolic activities, to form food and in storing biomass(very less). Biomass or the trapped energy is 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. Answer the following questions. Write the outcomes of the following events.
a) The consequence of eliminating all producers
b) The consequence of eliminating all entities at the herbivore level
c) The consequence of eliminating all top carnivore entities

A.5. a) It diminishes primary production in an ecosystem and hence unavailability of biomass to higher trophic levels b) It would result in an increase in primary productivity and biomass of producers. Carnivorous animals, due to unavailability of food, will not survive. c) There will be an increase in the herbivore population, resulting in over-grazing and hence desertification.

Q.6. Name two examples of man-made ecosystems. Write their salient features which distinguish them from natural ecosystems.

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

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

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

Q.8. Define producers, consumers and decomposers.


Producers: All autotrophs such as plants and other photosynthetic organisms that prepare their own food are called producers.

Consumers: All heterotrophs, including birds, animals, and other living organisms, which depend on producers and other organisms for food are called consumers. They are four different types of consumers:

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

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

Q.9. Explain the structure of the Ecosystem with the flowchart.

A.9. The structure of the ecosystem includes the living organisms and physical features of the environment, including the amount and distribution of nutrients in a particular habitat. It also provides information regarding the climatic conditions of that area.

Structure of the Ecosystem

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

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

Biotic Components include different life forms in an ecosystem. Based on nutrition, biotic components can be categorised into autotrophs, heterotrophs and saprotrophs (or 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. What is the Food Chain? Explain the different types of food chains in the ecosystem.

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

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

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