Our Environment Class 10 Important Questions and Answers

Important Questions for Class 10 Science Chapter 15 Our Environment covers each topic of the chapter. These questions aim at providing a better understanding of the chapter to the students and can be downloaded in PDF format. These important question bank help students in clearing their doubts so that they can score well in the exam.

While preparing for exams, students should practise these important questions of Class 10 Science to understand the concepts better. Solving important questions of Class 10 Science Chapter 15 will teach students time management skills and enhance their problem-solving skills. Also, students may come across a few of these questions in the board exam.

Important Questions for Class 10 Science Chapter 15 – PDF

1. What are the abiotic components of an ecosystem?

Answer: The non-living parts of an ecosystem are called abiotic components. Abiotic components include sunlight, water wind, temperature, altitude (height), soil, pH, and atmospheric gases.

2. How much energy of Sun can be converted into food energy by the green plants?

Answer: Energy flow in an ecosystem is unidirectional. Energy always flow from sun to the producers and then to the consumers. The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.

3. Why only 10% energy and mass is transferred to next level in a food chain?

Answer: When green plants are consumed by the herbivores (primary consumers) most of the energy is liberated as heat to the environment, some amount goes into digestion and some energy used for growth and reproduction. Only 10% of the food eaten is turned into its own body and made available for the next level of consumers.

4. What is meant by a trophic level?

Answer: (i) The group of organisms that occupy the same level in a food chain is called trophic level.

(ii) For example, in a grassland ecosystem, the different species of grasses are primary producers make up one trophic level.

(ii) Similarly different species of grass eating animals (herbivores) are at one trophic level.

5. Pick the biodegradable substances from the following:

Cotton, rubber, leather, radioactive material.

Answer: Biodegradable substances are those which can be breakdown or degraded by microorganisms such as bacteria and fungi. Cotton, rubber and leather are biodegradable substances in above given substances.

6. Pick the non-biodegradable, substances from the following:

Animal bones, wool, paper, glass.

Answer: Non-biodegradable substances are those which cannot be breakdown or degraded by microorganisms such as bacteria and fungi. Glass is no-biodegradable substance in above given substances.

7. Select from the following substances which have posed a threat to the environment:
Aerosols, consumers, bacteria, CFCs.

Answer: Aerosol and CFCs are substances that posed a threat to the environment

  • Aerosol is a substance enclosed under pressure and released as a fine spray by means of a propellant gas. For example, body deodorant, any of spray.
  • CFCs or Chlorofluorocarbons are a group of man-made compounds containing chlorine, fluorine and carbon. They are harmful and cause depletion of ozone layer.

8. Give the full form of CFC.

Answer: Full for of CFCs is chlorofluorocarbons, commonly known as Freon, CFCs are used in in air-conditioning, refrigeration, blowing agents in foams, insulations and packing materials, propellants in aerosol cans.

9. What happens during the first step of ozone formation in the atmosphere?

Answer: Ozone is formed naturally in the stratosphere layer of the atmosphere by a 2-steps reactive process. In the step-1, solar ultraviolet radiation (sunlight) breaks apart an oxygen molecule to form two separate oxygen atoms.

10. Choose one consumer each that belongs to the second and third trophic levels from the organisms given below:
Eagle, frog, tiger, rabbit, box.


  • Frog and rabbit belong to second trophic level as they are carnivores feed on plants or producers.
  • Eagle and tiger belong to third trophic level as they are carnivores feed on herbivores or primary consumers.

11. State 10% law. Explain with an example how energy flows through different trophic levels.

Answer: As we know that only 10% of energy is transferred from the first trophic level to the next and 90 % of the energy lost as heat to the surroundings. Let’s understand with an example.

Let’s assume that the plants or producers have 10 joules of energy, according to 10 % law, only 1 joule of energy will be available for transfer to next trophic level that is herbivores (deer) and 10 % of 1 joule that is 1.1 joule of energy is available for the carnivores (lion).

12. (a) How do autotrophs prepare their food?
(b) In the following food chain, 500J of energy is available to plant. How much energy will be available at I consumer and II consumer levels?
Plant → Sheep → Man

Answer: (a) Autotrophs prepare their food (carbohydrate) in presence of sunlight with the help of carbon dioxide and water. This process is called photosynthesis.

(b) According to 10% law, 10 % to 500J that is 50J is transferred to sheep (I consumer). Hence, 5J of energy is transferred to lion (II consumer) that is 10 % of 50 J.

13. Describe how ozone present in the atmosphere is important for sustaining the life on earth.

Answer: Ozone is a gas layer present in the stratosphere. This layer protects living beings on the Earth from harmful ultraviolet (UV) rays coming from the Sun. Without the layer of ozone in the atmosphere, it would be very difficult for anything to survive on the surface. Depletion of the ozone layer has consequences on humans, animals and plants.

14. Mention any one advantage of using disposable paper cups over disposable plastic cups. Mention of manner in which these paper cups do not adversely affect the environment.

Answer: Disposable paper cups are advantageous over plastic cups as paper cups are bio-degradable and can be recycled. Whereas, plastic is very harmful and is non-biodegradable as well as a curse to the eco-system so it is better to use disposable paper cups which can be recycled easily. Therefore, using paper cups does not adversely affects environment.

15. What would happen if a number of carnivores decreases in an ecosystem?

Answer: The following consequences may occur due to decreases in number of carnivores in an ecosystem:
(i) Population of herbivores will increase due to absence of its predator.
(ii) Autotrophs will disappear from earth due to overgrazing done by herbivores.
(iii) Both these factors may disturb the food chain and food webs thus affecting the ecosystem.

16. Explain how do decomposers help is recycling of materials in the ecosystem.

Answer: Decomposers such as bacteria and fungi break down dead plants and animal wastes in the process of decomposition. During decomposition complex substances converted into simple inorganic nutrients such as carbon and nitrogen. These nutrients are back into the environment so, that the producers can use them.

17. Name the radiations from the Sun that are absorbed by ozone layer. Mention one harmful effect caused by them.

Answer: The radiations from the Sun that are absorbed by ozone layer is ultraviolet (UV) radiation. UV radiation causes skin damage, in some cases the DNA damage causes genetic mutations. Prolonged exposure of UV radiation which can lead to skin cancer. Long exposure to eyes causes cataract.

18. Explain how making of “Kulhads” affects our environment.

Answer: Kulhads are made of soil. Use of earthen kulhads is not an environmentally friendly decision because for making enough kulhads upper layer of fertile soil is used. Loss of fertile soil can make land barren and unproductive. The removal of the layer of soil makes field to lose its fertility making it unfit for agriculture purpose.

19. What are top carnivores? Give two examples.

Answer: The top consumers are those predators which have no natural enemies. Top consumers are different in different food chains. Each food chain end with a top consumer. Some examples of top consumers are alligator, hawk, polar bear and lion or tiger.

20. Will the impact of removing all the organisms is a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?

Answer: Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels. Removing producers will affect herbivores heavily due to absence of food. They will die. Similarly, the carnivores would also die in absence of herbivores. Removing herbivores from the food chain, Producers would grow enormous; carnivores would not get food. Removing carnivores, the population of herbivores would increase to unsustainable levels.

No, the organisms of any trophic level cannot be removed without causing any damage to the ecosystem? It will disturb the food web and will create ecological imbalance.

21. Why is depletion of ozone layer a cause of concern?


  • Ozone layer is a high concentration of ozone molecules present in the stratosphere.
  • The main function of the ozone layer is to absorb the Sun’s ultraviolet radiation, hence protecting the Earth from its harmful effects.
  • Depletion of the ozone layer is a cause due to excessive use of CFCs or ammonia.
  • Damage of ozone layer is cause of concern because ultra violet radiation from the sun will reach the earth and will affect human beings, plants and animals.
  • After the Montreal Protocol, the Ozone layer is improving by the control use of CFCs and other harmful chemicals.

22. In a certain study conducted on occurrence of DDT along food chains in an ecosystem, the concentration of DDT in grass was found to be 0.5 ppm (parts per million), in sheep it was 2ppm and in man it was 10 ppm. Why was the concentration of DDT maximum in case of man?


  • DDT is an insecticide and is non-biodegradable compound.
  • Once this insecticide sprayed in the environment, it stays for very long time and through food chain into the organisms.
  • According to the concept of biomagnification, the maximum accumulation of a non-biodegradable pollutant is maximum in the highest trophic level.
  • Hence, DDT gets accumulates at each trophic level and since, man is at the highest trophic level, there is maximum accumulation of DDT observed in them.

23. “Energy flow in a food chain is unidirectional”. Justify this statement.


  • Sun is the only source of energy. Producers convert solar energy into chemical energy in the form of food.
  • The primary consumers (herbivores) depends on producers for food.
  • According to the energy transfer law, only 10% of energy is transferred from one trophic level to the other.
  • Therefore, the energy that is captured by the producers does not come back to the Sun and the energy transferred to the herbivores does not come back to the producers.
  • It just keeps on moving to the next trophic level in a unidirectional way.
  • That is why the flow of energy in the food chain is always unidirectional.

24. Show steps of food chains operating in:
(a) Forests
(b) Grasslands
(c) Ponds.

Answer: (a) In a forest the steps of food chain:
Trees (producers) → Deer (primary consumer) → Lion (top consumer).

(b) In a grassland the steps of food chain
Grasses (producers) → rabbit (primary consumer) → snake (secondary consumer) → owl (top consumer).

(c) In a pond the steps of food chain
Algae and aquatic plants (producers) → small fish (primary consumer) → big fish (secondary consumer) → shark (top consumer).

25. What are the problems caused by the non-biodegradable wastes that we generate?


  • Non-biodegradable waste such as plastics, aluminium cans and pesticides are inert substances. These persist in the environment for very long time.
  • This means that these substances require landfills for dumping.
  • Excess of fertilizers, pesticides and other chemicals cause soil infertility and also affects aquatic life.
  • Most of non-biodegradable chemicals are easily absorbed by the organisms causing biological magnification.

26. Name two natural ecosystems.    

Answer: Two natural ecosystems are:
(a) Temperate forest
(b) Tropical forest
(c) Grassland
(d) Ocean
(e) Lake.

27. What are decomposers? Write the role of decomposers in the environment.  

Answer: Decomposers are microorganisms that derive their nutrition from dead remains and waste products of organisms.
They play a vital role in our environment by breaking down the complex organic substance into simple inorganic substance which is made available for plants and other organisms. Hence they act as scavengers and not only keep the environment clean but also replenish the minerals.

28. (a) What is an ecosystem? List its two main components.
(b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.

Answer: (a) A self-sustaining functional unit consisting of living and non-living components is called ecosystem.
Components: Biotic components like plants and animals. Non-biotic components like soil, wind, light etc.

(b) A pond is a complete, natural and self-sustaining ecosystem whereas an aquarium is an artificial and incomplete ecosystem, without decomposers therefore it needs regular cleaning for proper running.

29. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day.’  
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.

Answer: (a) Ozone layer at the higher levels of the atmosphere, acts as a shield to protect earth from the harmful effects of the ultraviolet (UV) radiations; hence, it should be protected.
(b) (i) Urging the people to not to buy aerosol products with CFC that are available in the market.
(ii) Conducting poster making competition or street plays presenting the importance of ozone layer on earth.

30. Your mother always through that fruit juices are very healthy for everyone. One day she read in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health.    
(а) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit cause harm and damage to our organs.: Name the phenomenon and write about it.

Answer: (a) • Pesticides are the chemicals used to protect our crops from diseases and pests.
• These chemicals are washed down either into the soil or into water bodies.
• From the soil, they are absorbed by the terrestrial plants along with water and minerals.
• From the water bodies, they are absorbed by the aquatic plants.
• When the fruits of these plants are used to prepare fruit juices, they are contaminated with the pesticides.

(b) • The phenomenon is called biomagnification. It is the phenomenon in which certain harmful chemicals enter the food chain and get accumulated and increase in concentration at successive trophic levels.
• It is because they are not degradable.
• The maximum concentration of these chemicals is found in the top level consumers.

31. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer?  
Plants → Deer → Lion

Answer: 1,000,000 J of energy was available to the producer.

32. Why should biodegradable and non-biodegradable wastes be discarded in two separate dustbins?    

Answer: The biodegradable and non-biodegradable wastes must be discarded in two different dustbins because biodegradable wastes gets decomposed by the microorganisms whereas non-biodegradable wastes can be recycled and reused.

33. Name any two man-made ecosystems.    
 Agricultural/crop fields, aquaria, gardens,

34. We often use the word environment. What does it mean?  

Answer: It is the sum total of all external conditions and influences that affect the life and development of an organism, i.e. the environment includes all the physical or abiotic and biological or biotic factors.

35. Why are green plants called producers?    

Answer: Green plants can produce their own food by photosynthesis from inorganic compounds and hence are called producers.

36. What is ten per cent law? Explain with an example how energy flows through different trophic levels.    

Answer: Energy available at each successive trophic level of food chain is ten per cent of that at the previous level.
This is called ten per cent law. Thus, 90 per cent energy is lost to the surroundings at each trophic level. However, plants absorb only one per cent of radiant energy of the Sun during photosynthesis. This is explained as under:

Class 10 Science Chapter 15 Our Environment Important Question 36

37. What is ozone? How and where is it formed in the atmosphere? Explain how does it affect ecosystem.    

Answer: Ozone is an isotope of oxygen, i.e. it is a molecule formed by 3 atoms of oxygen.
O2 → O + O
O2 + O → O3 (Ozone)
Ozone exists in the ozone layer of stratosphere. At higher level o f atmosphere, O2 molecule breaks down to 2 oxygen atom. The oxygen atom then combines with the oxygen molecule to form ozone.

Ozone layer in the atmosphere prevents UV rays from reaching earth. Exposure to excess UV rays causes skin cancer, cataract and damages eye and immune system. It also decreases crop yield and reduces population of phytoplankton, zooplankton and certain fish larvae which are an important constituent of aquatic food chain. It also disturbs rainfall, causing ecological disturbance and reduces global food production. Thus, it affect the ecosystem.

39. “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.    

Answer: The energy flow through different steps in the food chain is unidirectional. The energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores, i.e. it moves progressively through various trophic levels. Thus energy flow from sun through producers to omnivores is in single direction only.

Pesticides are sprayed to kill pests on food plants. The food plants are eaten by herbivores and alongwith the food, pesticides are also eaten by the herbivores. Herbivores are eaten by carnivores and alongwith the herbivore animal, pesticide also enters the body of the carnivore. Man eat both plants and animals and pesticide alongwith food enters the body of human. Concentration of pesticides increases as we move upward in the food chain and the process is called bio-magnification.

40. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain.  

Answer: Ecosystem: It is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non-living constituents of the environment. Thus, an ecosystem is a self-sustaining system where energy and matter are exchanged between living and non-living components.

Main components of ecosystem:
Biotic Component: It means the living organisms of the environment-plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.
Abiotic Component: It means the non-living part of the environment-air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part of the abiotic environment.
An aquarium is an artificial and incomplete ecosystem compared to ponds or lakes which are natural, self-sustaining and complete ecosystems where there is a perfect recycling of materials. An aquarium therefore needs regular cleaning.

41. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer.    

Answer: CFC → Chloroflurocarbon

42. Which of the following are always at the second trophic level of the food chains?
Carnivores, Autotrophs, Herbivores

Answer: Herbivores are always at the 2nd trophic level.

43. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals? Name the phenomenon associated with it.
Insects, Hawk, Grass, Snake, Frog.    

Answer: Hawk will have highest concentration of non- biodegradable chemicals. The phenomenon is called biomagnification.

44. The first trophic level in a food chain is always a green plant. Why?    [AI 2015]

Answer: Only green plants can make their own food from sunlight. Green plants therefore, always occupy the 1st trophic level in a food chain.

45. What will be the amount of energy available to the organism of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules

Answer: 100 Joules of energy will be available to the organism of the 2nd trophic level.

46. (a) How can we help in reducing the problem of waste disposal? Suggest any three methods.    [
(b) Distinguish between biodegradable and nonbiodegradable wastes.  

Answer: (a) The three methods of waste disposal are:
(i) Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remoulded or reprocessed to new materials.
(ii) Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, left over food, grass clippings, human and animal waste can be converted into compost by burying this waste into ground and can be used as manure.
(iii) Incineration: Burning dawn many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed off in landfill.


Biodegradable wastesNon-biodegradable wastes
(i) These wastes can be broken-down into non-poisonous substances in nature by the action of microorganisms.(i) These wastes cannot be broken-down into non-poisonous substances by microorganisms.
(ii) They get recycled thus, do not need any dumping sites.(ii) They cannot be recycled thus, require dumping sites.

47. (a) What is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it.    
(b) With the help of an example explain that a garden is an ecosystem.
(c) Why only 10% energy is transferred to the next trophic level?

Answer: (a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.

(b) A garden comprises of different kind of flora and fauna such as grasses, flowering and nonflowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.

(c) Only 10% energy is transferred to the next trophic level because other 90 per cent is used for things like respiration, digestion, running away from predators.