Class 10 Science Chapter 15 Our Environment

Class 10 Science Chapter 15 Our Environment answer to each chapter is provided in the list so that you can easily browse throughout different chapters NCERT Class 10 Science Chapter 15 Our Environment and select need one.

Class 10 Science Chapter 15 Our Environment

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Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 15 Our Environment Solutions for All Subjects, You can practice these here.

Our Environment

Chapter – 15

Textual Questions and Answers:

Page no – 257 

Q.1. Why are some substances biodegradable and some non- biodegradable? 

Ans: The reason why some substances are biodegradable and some non-biodegradable is because the microorganisms like bacteria and decomposers like saprophytes have a specific role to play. They can breakdown only natural products like paper, wood, etc. but they cannot breakdown man-made products like plastics. Based on this, some substances are biodegradable and some non-biodegradable.

Q.2. Give any two ways in which biodegradable substances would affect the environment. 

Ans: (i) Biodegradable substances are decomposed by the action of microorganisms and decomposed materials are recycled through a geo-chemical cycle. 

(ii) Biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance soil fertility.

Q.3. Give any two ways in which non-biodegradable substances would affect the environment.

Ans: Non-biodegradable substances affect the environment in the following ways:

(a) They contaminate soil and water resources as they cannot be decomposed by micro-organisms.

(b) These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.

Page – 261 

Q.1. What are trophic levels? Give an example of a good chain and state the different trophic levels in it. 

Ans: Trophic level is the fundamental level occupied by an organism in food chain. Trophic literally means feeding, so trophic levels are the levels or positions at which species feed. Examples of trophic Levels include ‘herbivores’ and ‘decomposers’ 

An example of a food chain depicting various trophic levels is as follows:

3rd level carnivore                    Eagle

              ↑                                     ↑

2nd level carnivore                   Snake 

              ↑                                     ↑

1st level carnivore                     Frog

              ↑                                     ↑

      Herbivore                        Grasshopper

             ↑                                       ↑

     Producers                             Grass

Q.2. What is the role of decomposers in an ecosystem? 

Ans: Following is the role of a decomposer in the ecosystem:

(i) They act as a cleansing agent of the environment by decomposing the dead plants and animals.

(ii) They help in recycling the nutrients.

(iii) They provide space for new beings in the biosphere by decomposing the dead.

(iv) They help in putting back the various elements into water, soil and air for the reuse of producers like crop plants.

Page – 264 

Q.1. What is ozone and how does it affect any ecosystem? 

Ans: The stratospheric layer of the atmosphere contains an ozone layer

1. It acts as a protective shield to the earth from harmful UV- radiation.

2. Excess exposure to UV rays can lead to skin cancer and cataract. 

3. Thus the presence of ozone layer is essential to block the entry of harmful UV rays. 

Q.2. How can you help in reducing the problem of waste disposal? Give any two methods. 

Ans: The excessive waste material disposal due to modern industrialisation is becoming the major reason behind the current pollutions which is ruining our environment.

We have to control this excessive amount of waste material disposal, in order to save our environment.

Some of the prevention measures are:

(a) Using recyclable objects to generate the minimum possible waste materials.

Recyclable materials are also eco-friendly, that’s why it also reduces the pollution.

(b) We can use biodegradable waste materials for the biogas production which can be used as our domestic fuel. This will also save our money which we generally spend for purchasing household fuel substances such as LPG, Kerosine etc.


Q.1. Which of the following groups contain only biodegradable items? 

(a) Grass, flowers and leather.

(b) Grass, wood and plastic.

(c) Fruit-peels, cake and lime-juice.

(d) Cake, wood and grass.

Ans: (c) fruit-peels, cake and lime-juice. 

Q.2. Which of the following constitute a food-chain? 

(a) Grass, wheat and mango.

(b) Grass, goat and human.

(c) Goat, cow and elephant.

(d) Grass, fish and goat.

Ans: (b) Grass, goat and human. 

Q.3. Which of the following are environment-friendly practices?

(a) Carrying cloth-bags to put purchases in while shopping. 

(b) Switching off unnecessary lights and fans. 

(c) Walking to school instead of getting your mother to drop you on her scooter. 

(d) All of the above.

Ans: (d) All of the above. 

Q.4. What will happen if we kill all the organisms in one trophic level?

Ans: If we kill all the organisms in one trophic level, the transfer of food energy to next level will stop. there will be overpopulation of individuals belonging to the previous trophic level. The organisms of higher tropic level will also die. Hence, it will result in imbalance in the ecosystem.

Q.5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the Jun organisms of any trophic level be removed without causing any damage to the ecosystem? 

Ans: 1. If we remove producers from ecosystem, herbivores will not survive and the entire ecosystem collapse.  

2. Removing herbivores result in increase number of producers and carnivores would not get food. 

3. Removing carnivores result in increase of herbivores to unsustainable levels.  

4. If we remove decomposers from ecosystem waste material and animal dead remains would pile up and nutrients would not be available to the producers.  

5. Some or the other damage would be caused to the ecosystem if the organisms of any trophic level is removed.  

6. However impact of removing producers or decomposers would be serve as the whole ecosystem would collapse.  

7. Without plants sun’s energy cannot be converted to chemical energy which is the basis of life on earth.  

8. Without decomposers the nutrients cannot be recycled and made available to producers.

Q.6. What is biological magnification? Will the level of this magnification be different at different levels of the y ecosystem? 

Ans: Biological Magnification is a phenomenon which explains the increasing concentration of harmful chemicals like DDT with each increase in trophic level. From the soil the chemicals are absorbed by the plants. The primary consumers eat these plants and the harmful chemicals come to reside in their bodies. As these chemicals are not degradable, they accumulate in the bodies of the organisms and the top level of the food chain gets the highest concentration of these harmful chemicals. 

Most of the plants products which we eat are grown in fields in which pesticides and fertilisers have been used. These are absorbed by the plants and cannot be removed by washing or other means. As humans are at the top level of the food chain these chemicals get accumulated in our bodies and cause various disorders.

The level of biological magnification is different for different trophic levels of an eco system. 

Q.7. What are the problems caused by the non-biodegradable wastes that we generate? 

Ans: The non-biodegradable waste that we generate has the following problems on environment:

(i) Biological magnification- Non biodegradable wastes like pesticides enter into the food chain and accumulate with increase in trophic levels and thus harm the organisms.

(ii) These pesticides and chemicals also reduce the soil fertility when they penetrate into it, the soil either becomes too acidic or too alkaline.

(iii) Non-biodegradable materials like plastics/polythene bags when burned by Incineration also release toxic chemicals into the environment thus causing air pollution.

Q.8. If all the waste we generate is biodegradable, will this have no impact on the environment? 

Ans: Even if all the waste we generate is biodegradable, it will have an impact on the environment. This is because too much biodegradable waste can not be broken down into harmless simpler substances by the decomposes like micro-organisms at the right time. 

Q.9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 

Ans: The damage to the ozone layer is a cause for concern because:

  • It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
  • It can result in the death of many phytoplanktons that leads to increased global warming.

To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.

Multiple Choice Questions: 

Q.1. Which of the following constitutes a food chain? 

(a) Grass, wheat and mango.

(b) Grass, goats and human.

(c) Goat, cow and elephant.

(d) Grass, fish and goat.

Ans: (b) Grass, goats and human.

Q.2. In a food chain the initial organism is usually 

(a) Photosynthetic.

(b) Herbivore.

(c) Saprophytic.

(d) Parasitic.

Ans: (a) Photosynthetic.

Q.3. Which of the following represents a possible food chain found in a pond. 


(a) Green algae            fish              mosquito larvae.

(b) Fish                     Green algae    mosquito larvae 

(c) Mosquito larvae       fish              green algae 

(d) Green algae        mosquito larvae  fish

Ans: (d) Green algae   mosquito  larvae     fish

Q.4. Which of the following are decomposers of dead organisms? 

    Bacteria             Fungi              Viruses

(a) No                    yes                   yes

(b) Yes                   no                    yes

(c) Yes                   yes                   no

(d) Yes                   yes                   yes 

Ans: (c) Yes          yes                    no

Q.5. Which of the following is an artificial ecosystem? 

(a) Pond.

(b) Crop field.

(c) Lake.

(d) Forest.

Ans: (b) Crop field.

Q.6. Disposable plastic plates should not be used because 

(a) They are made of light weight materials. 

(b) They are made of toxic materials. 

(c) They are made of biodegradable materials.

(d) They are made of non-biodegradable materials. 

Ans: (d) They are made of non-biodegradable materials. 

Q.7. In a food chain, the third trophic level is always occupied by:

(a) Carnivores.

(b) Herbivores.

(c) Decomposers 

(d) Producers.

Ans: (a) Carnivores.

Q.8. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as: 

(a) Eutrophication.

(b) Biomagnification.

(c) Pollution.

(d) Accumulation.

Ans: (c) Pollution.

Q.9. If a grasshopper is eaten by a frog, then the energy transfer will be from. 

(a) Producer to decomposer. 

(b) Producer to primary consumer. 

(c) Primary consumer to secondary consumer 

(d) Secondary consumer to tarliery consumer. 

Ans: (c) Primary consumer to secondary consumer 

Q.10. An ecosystem includes: 

(a) All living organisms.

(b) Non-living objects.

(c) Both living organisms and non-living objects.

(d) All living organisms and input of sun’s energy. 

Ans: (c) Both living organisms and non-living objects.

Q.11. The decomposers in an ecosystem: 

(a) Convert inorganic material to simpler forms.

(b) Convert organic material to inorganic forms.

(c) Convert inorganic material into organic component.

(d) Do not break down organic compound. 

Ans: (b) Convert organic material to inorganic forms.

Q.12. What will happen deer is missing in the food chain given below. 

Grass → Deer → Tiger 

(a) The population of tigers increases.

(b) The population of grass decreased.

(c) Tigers will start eating grass.

(d) The population of tigers decreases and the population of grass increases. 

Ans: (d) The population of tigers decreases and the population of grass increases. 

Q.13. Organisms which synthesise carbohydrates from inorganic compounds by using radiant energy are called.

(a) Decomposers.

(b) Producers.

(c) Herbivores.

(d) Carnivores.

Ans: (b) Producers.

Q.14. Organism of a higher trophic level which feed on several types of organisms belonging to a number of lower trophic levels constitute the: 

(a) Ecosystem.

(b) Food web.

(c) Ecological pyramid.

(d) Food chain.

Ans: (b) Food web.

Q.15. In the following groups of materials, which group/groups contain only non-biodegradable materials? 

(i) Wood, paper, leather.

(ii) Polythene, detergent pvc.

(iii) Plastic, detergent, grass.

(iv) Plastic, bakelite, DDT.

(a) (iii) 

(b) (iv) 

(c) (i) and (iii) 

(d) (ii) and (iv) 

Ans: (d) (ii) and (iv) 

Q.16. Which of the following statement is incorrect?

(a) All green plants blue green algae are producers comperens. 

(b) Green Plants get their food from readymade organic comperens.

(c) Producers prepare their own food from inorganic compounds. 

(d) Plants convert solar energy into chemical energy. 

Ans: (b) Green Plants get their food from readymade organic comperens.

Q.17. Which of the following group of organisms are not constituents of a food chain? 

(i) Grass, lion, rabbit, wolf.

(ii) Plankton, man, fish, grasshopper.

(iii) Wolf, grass, snake, tiger 

(iv) Frog, snake, eagle, grass, grasshopper.

(a) (i) and (iii)

(b) (iii) and (iv) 

(c) (ii) and (iii) 

(d) (i) and (iv) 

Ans: (c) (ii) and (iii) 

Q.18. In the figure given alongside, the various trophic levels are shown in the form of a pyramid. At which trophic level the maximum energy is available? 

(a) T₄                          

(b) T₂

(c) T₁                          

(d) T₃

Ans: (c) T₁     

Q.19. One of the following is not a biodegradable material. This one is: 

(a) Cotton.

(b) Animal bones.

(c) Aluminium foil.

(d) Wood.

Ans. (c) Aluminium foil.

Q.20. Which of the following is not a non-biodegradable maternal? 

(a) Nylon socks.

(b) Plastic school bag.

(c) Jute carry bag.

(d) Polyester clothes.

Ans: (c) Jute carry bag.

Q.21. The use of one of the following will pollute the environment. This one is: 

(a) Paper carry bags.

(b) Cotton cloth carry bags.

(c) Nylon cloth carry bags.

(d) Jute carry bags.

Ans: (c) Nylon cloth carry bags.

Q.22. One of the following is not a consumer. This one is: 

(a) Giraffe.

(b) Antelope. 

(c) Algae.

(d) Alligator.

Ans: (c) Algae.

Q.23. Which of the following is not a producer? 

(a) Grass.

(b) Zooplankton.

(c) Phytoplankton.

(d) Paddy.

Ans: (b) Zooplankton.

Q.24. One of the following is a micro-consumer. This one is-

(a) Ant.

(b) Lice.

(c) Fungi.

(d) Mosquito.

Ans: (c) Fungi.

Q.25. Which of the following act as decomposers in an ecosystem? 

(a) Lactobacillus bacteria.

(b) Cyanobacteria.

(c) Putrefying bacteria.

(d) Rhizobium bacteria.

Ans: (c) Putrefying bacteria.

Q.26. One of the following helps in the recycling of materials in an ecosystem. This one is: 

(a) Autotrophs.

(b) Saprotrophs.

(c) Omnivores.

(d) Carnivores.

Ans: (b) Saprotrophs.

Q.27. In the food chain comprising of a snake, grass, insect and frog, the secondary consumer is:

(a) Insect.

(b) Snake.

(c) Frog.

(d) Grass.

Ans: (c) Frog.

Q.28. Sahara desert was formed over a period of time due to one of the following uncontrolled activities of man: 

(a) Excessive cutting down of forest plants and trees. 

(b) Excessive killing of large herbivores.

(c) Excessive killing of large carnivores.

(d) Excessive use of poisonous chemicals called herbicides. 

Ans: (c) Excessive killing of large carnivores.

Q.29. What provides the energy which then flows through a food chain? 

(a) Glucose.

(b) Oxygen.

(c) Respiration.

(d) Sunlight.

Ans: (d) Sunlight.

Q.30. Which pollutant released into the air during refrigeration and airconditioning is the greatest contributor to the depletion of ozone layer? 

(a) BHC.

(b) DDT.

(c) CFC.

(d) UNEP.

Ans: (c) CFC.

Q.31. In the food chain given below, if the amount of energy available at fourth trophic level is 5kj, what was the energy available at the producer level? 

Grass → Grasshopper → Frog Snake →Hawk

(a) 500 kj

(b) 50 kj 

(c) 5000 kj 

(d) 5 kj  

Ans: (c) 5000 kj.

Q.32. Which of the following limits the number of trophic levels in a food chain? 

(a) Insufficient food supply from producer level.

(b) Decrease in energy at higher trophic levels.

(c) Increase in the number of organisms at higher trophic levels.

(d) Accumulation of harmful chemicals at higher trophic levels. 

Ans: (b) Decrease in energy at higher trophic levels.

Q.33. What percentage of sun’s energy falling on the levels of green plants is utilised by the plants in the process of photosynthesis and stored as chemical energy of food? 

(a) 99 percent.

(b) 10 percent.

(c) 1 percent. 

(d) 20 percent.

Ans: (c) 1 percent. 

Q.34. The depletion of ozone layer in the upper atmosphere is mainly due to the emission of: 

(a) Unburnt hydrocarbons.

(b) Chlorofluorocarbons.

(c) Greenhouse gases.

(d) Ultraviolet radiations.

Ans: (b) Chlorofluorocarbons.

Q.35. In an ecosystem, the ten percent energy available for transfer from one trophic level to the next is in the form of: 

(a) Heat energy.

(b) Light energy.

(c) Chemical energy.

(d) Mechanical energy.

Ans: (c) Chemical energy.

Q.36. The flow of energy in an ecosystem is always : 

(a) Unidirectional.

(b) Bidirectional.

(c) Cyclic.

(d) Multidirectional. 

Ans: (a) Unidirectional.

Q.37. The excessive exposure of human to ultraviolet rays results in: 

(i) Damage to immune system.

(ii) Damage to lungs.

(iii) Skin cancer. 

(iv) Peptic ulcers.

(a) (i) and (ii) 

(b) (ii) and (iv) 

(c) (i) and (iii) 

(d) (iii) and (iv)

Ans: (c)  (i) and (iii) 

Q.38. Which of the following gets the minimum energy through the food chain in an ecosystem? 

(a) Carnivore.

(b) Large carnivore. 

(c) Producer.

(d) Herbivore.

Ans: (b) Large carnivore. 

Q.39. A food chain comprises of cat, seed-eating bird, plants, and dog. The organism which will have the maximum concentration of harmful pesticides coming through the food chain is most-likely to be: 

(a) Cat.

(b) Plants.

(c) Dog.

(d) Seed eating bird.

Ans: (c) Dog.

Q.40. An aquatic food chain comprises of the organisms like tadpoles, weeds, fish and water beetles. The organism gets the minimum energy through this food chain is:

(a) Water beetles.

(b) Tadpoles.

(c) Weeds

(d) Fish.

Ans: (d) Fish.

Q.41. Most of the water surface of a lake is covered with algae, This algae in a part of the food chain which also includes small fish, bird, larvae and big fish. Which of the following will obtain the maximum energy? 

(a) Big fish.

(b) Bird.

(c) Larvae.

(d) Small fish.

Ans: (c) Larvae.

Q.42. If the energy available at the producer level in a food chain is 150 J, how much energy will be transferred to tertiary consumer? 

(a) 15 J 

(b) 10 J 

(c) 1.50 J 

(d) 0.15 J 

Ans: (d) 0.15 J 

Q.43. If the energy trans ferred to a tertiary consumer in a food chain is 10 J, how much energy was available to the primary consumer? 

(a) 100J 

(b) 500J 

(c) 1000 J

(d) 5000 J 

Ans: (c) 1000 J

Q.44. In additions to wheat plants, a crop field ecosystem has organisms such as snake, peacock, eagle and mice. If the wheat plants are sprayed with pesticides periodically, which of the following will have the minimum concentration of pesticides in the body? 

(a) Snake.

(b) Eagle.

(c) Mice.

(d) Peacock.

Ans: (c) Mice.

Q.45. Which of the following in the best method to dispose of biological wastes from hospitals? 

(a) Landfill.

(b) Recycling.

(c) Incineration.

(d) Composting.

Ans: (c) Incineration.

Q.46. In an ecosystem: 

(i) The flow of energy is unidirectional 

(ii) The flow of materials is unidirectional.

(iii) The flow of materials is cyclic.

(iv) The flow of energy is cyclic.

(a) (i) and (ii) 

(b) (ii) and (iii)

(c) (i) and (iv)

(d) (i) and (iii) 

Ans: (d)  (i) and (iii) 

Q.47. The ten percent law is associated with 

(a) Transfer of energy from various trophic levels to decomposers ina food chain. 

(b) Transfer of ATP energy into muscular energy.

(c) Transfer of chemical energy from one organism to another. 

(d) Transfer of sun’s energy to the organisms called producers.

Ans: (c) Transfer of chemical energy from one organism to another. 

Q.48. The harmful chemical which is accumulating in human beings through food chain is: 

(a) Benzene hexachloride.

(b) DDT.

(c) Chlorofluorocarbon.

(d) Abscisic acid.

Ans: (b) DDT.

Q.49. O₂ is converted into O₃ by the action of:  

(a) Infrared radiations.

(b) Ultraviolet radiations.

(c) Gamma radiations.

(d) Cosmic radiations. 

Ans: (d) Ultraviolet radiations.

Q.50. Which of the following can not be added in a composting pit to prepare compost? 

(a) Sunflower plants.

(b) Fruit and vegetable peets.

(c) Flowers of plastic.

(d) Red worms.

Ans: (c) Flowers of plastic.

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