Chapter 13: Our Environment

Important questions — the ones the board asked most (20)

1. Q1Short answer3 marksAsked: 2024

   The use of pesticides for the protection of our crops affects organisms at different trophic levels, especially human beings. Name the phenomenon involved and explain how it happens.

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 60 s

   Model answer · Biological magnification

   1. 1.The phenomenon involved is biological magnification (biomagnification).1 mark
   2. 2.Farmers use pesticides and other chemicals to protect crops from diseases and pests. These chemicals are washed down into the soil or into the water bodies.0.5 marks
   3. 3.From the soil, crop plants absorb these chemicals along with water and minerals. In water bodies, aquatic plants and animals take them up. This is how the chemicals enter the food chain.0.5 marks
   4. 4.These chemicals are non-biodegradable, which means they are not broken down. So they get accumulated progressively at each trophic level.0.5 marks
   5. 5.Human beings occupy the top level in any food chain, so the maximum concentration of these chemicals gets accumulated in our bodies.0.5 marks

   • Name the phenomenon first: "biological magnification (biomagnification)".
   • Say that the chemicals are absorbed "along with water and minerals" and so "enter the food chain".
   • Write that the chemicals are "non-biodegradable" and "get accumulated progressively at each trophic level", and that humans, at the top level, get the maximum concentration.

   Marks split as in the board’s published marking scheme

2. Q2Short answer3 marksAsked: 2023

   (a) (i) Why does a kitchen garden called an artificial ecosystem while a forest is considered to be a natural ecosystem ? (ii) While designing an artificial ecosystem at home, write any two things to be kept in mind to convert it into a self-sustaining system. Give reason to justify your answer. OR (b) (i) Construct a food chain of four trophic levels comprising the following : Hawk, snake, plants, rat. (ii) 20,000 J of energy was transferred by the producers to the organism of second trophic level. Calculate the amount of energy that will be transferred by organisms of the third trophic level to the organisms of the fourth trophic level.

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 110 s

   Model answer · artificial vs natural ecosystem

   1. 1.(a)(i) A kitchen garden is made and kept up by humans (sowing, watering, manuring, weeding), so it is artificial; a forest develops on its own and sustains itself without human help, so it is natural. OR (b)(i) Plants → Rat → Snake → Hawk.1 mark
   2. 2.(a)(ii) Include producers (green plants) to make food and oxygen by photosynthesis, and decomposers (soil microbes, earthworms) to break down wastes and return nutrients to the soil — with consumers to keep the food chain going, and enough sunlight and water. OR (b)(ii) By the 10% law, the second level passes 10% of 20,000 J = 2,000 J to the third level, and the third level passes 10% of 2,000 J = 200 J to the fourth level.2 marks

   Marks split from a structure derived from past papers (checked twice); not CBSE’s official scheme

3. Q3Long answer3 marksAsked: 2026

   14. Given below is a pyramid showing various trophic levels in an ecosystem : (a) From the organisms listed below, identify which one is to be placed at which trophic level ? Deer, Grass, Lion, Snake, Rabbit (b) Discuss the reason why primary consumers will have more energy as compared to secondary consumers ? (c) Why is the base of the pyramid broad ?

   

   Medha Ma’am

   Ask Medha’s AI teacher

   Watch it on the board · 60 s

   Model answer · trophic levels, energy pyramid

   1. 1.(a) Grass – producers (first trophic level); deer and rabbit – primary consumers (herbivores); snake – secondary consumer; lion – tertiary (top) consumer.1 mark
   2. 2.(b) Only about 10% of the energy at one level passes to the next; the rest is lost as heat and used in life processes. So secondary consumers get much less energy than primary consumers.1 mark
   3. 3.(c) The base is broad because producers are the most numerous and have the most energy, which supports the fewer organisms at each higher level.1 mark

   Marks split as in the board’s published marking scheme

4. Q4Short answer3 marksAsked: 2025

   33. What are decomposers? Give two examples. State how they maintain a balance in an ecosystem.

   How the model answer begins

   1. Decomposers are the microorganisms that break down the dead remains and waste products of organisms. They break down the complex organic substances into simple inorganic substances.

   The full answer from Medha Ma’am →
5. Q5Short answer3 marksAsked: 2024

   (A) Plants -> Deer -> Lion In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level? Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web? Justify. OR (B) A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

   How the model answer begins

   1. If all the deer, the organisms of the second trophic level (herbivores), are removed, the number of plants, the organisms of the first trophic level (producers), will increase, because no herbivores are left to eat them.

   The full answer from Medha Ma’am →
6. Q6Short answer3 marksAsked: 2024

   33. Study the given figure, in which three food chains (a), (b) and (c) are shown and answer the following questions : (i) Name the types of ecosystems in which food chains (b) and (c) exist. (ii) The first trophic level of each food chain is producers. Why ? What percentage of solar energy do these producers capture for their use ? (iii) Why are the directions of all arrows in the figure shown in only one direction, why can their direction not be reversed ? Justify.

   How the model answer begins

   1. (i) Food chain (b) exists in a terrestrial ecosystem, that is, a grassland.

   The full answer from Medha Ma’am →
7. Q7Short answer3 marksAsked: 2023

   Write one difference between biodegradable and non-biodegradable wastes. List two impacts of each type of the accumulated waste on environment if not disposed off properly.

8. Q8Short answer3 marksAsked: 2026

   (a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies ? What is this phenomenon known as ?

   How the model answer begins

   1. Plastic bags are non-biodegradable, that is, bacteria or other saprophytes cannot break them down. Because of this, they persist in the environment for a long time and cause pollution of the soil and water bodies when…

   The full answer from Medha Ma’am →
9. Q9Short answer3 marksAsked: 2025

   Mention the essential function performed by ozone at the higher levels of the atmosphere. How is it produced at the higher levels of the atmosphere ? Name the group of chemicals mainly responsible for the depletion of ozone layer in the atmosphere.

   How the model answer begins

   1. At the higher levels of the atmosphere, ozone (O3) shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms. For example, it is known to cause skin…

   The full answer from Medha Ma’am →
10. Q10Short answer3 marksAsked: 2025

    33. Some harmful chemicals get accumulated in human bodies through the food chain. Name this phenomenon. Explain the reason of maximum concentration of these chemicals found in our bodies.

    How the model answer begins

    1. This phenomenon is called biological magnification. Harmful chemicals such as pesticides get into our bodies through the food chain.

    The full answer from Medha Ma’am →
11. Q11Short answer3 marksAsked: 2025

    (a) "In a food chain energy flow is unidirectional." Give two reasons for the given statement. (b) If 10,000 J energy is available at the producer level, how much energy will be available to the secondary consumers ? Give reason to justify your answer.

    How the model answer begins

    1. Energy flow in a food chain is unidirectional because the energy that is captured by the autotrophs or producers from sunlight does not revert back to the solar input (sun). As it moves progressively through the various…

    The full answer from Medha Ma’am →
12. Q12Short answer3 marksAsked: 2025

    33. (a) "The flow of energy in a food chain is unidirectional". Give two reasons to justify this statement. (b) If 10,000 J of energy is available at the producer level, how much energy will be available to the secondary consumers ? Justify your answer with reason.

    How the model answer begins

    1. The flow of energy in a food chain is unidirectional because the energy that is captured by the autotrophs or producers does not revert back to the solar input. The energy which passes from producers to the next trophic…

    The full answer from Medha Ma’am →
13. Q13Short answer3 marksAsked: 2024

    Differentiate between food chain and food web. In a food chain consisting of deer, grass and tiger, if the population of deer decreases, what will happen to the population of organisms belonging to the first and third trophic levels ?

14. Q14Short answer3 marksAsked: 2023

    33. Explain how some harmful chemicals enter our bodies through the food chain. Why is the concentration of these harmful chemicals found to be maximum in human beings ?

15. Q15Short answer3 marksAsked: 2023

    How is ozone formed in the higher levels of the atmosphere ? “Damage to the ozone layer is a cause of concern.” Justify this statement.

    How the model answer begins

    1. At the higher levels of the atmosphere, ozone is formed by the action of high-energy ultraviolet radiation on oxygen. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms.

    The full answer from Medha Ma’am →
16. Q16Very short answer2 marksAsked: 2024

    Name the term used for the materials which cannot be broken down by biological processes. Give two ways by which they harm various components of an ecosystem.

    How the model answer begins

    1. Materials that are not broken down by biological processes are called non-biodegradable substances. Plastics are an example.

    The full answer from Medha Ma’am →
17. Q17Very short answer2 marksAsked: 2023

    26. How do harmful chemicals get accumulated progressively at each trophic level in a food chain ?

    How the model answer begins

    1. Harmful chemicals like pesticides are used to protect crops from diseases and pests, and these are not degradable. They are washed down into the soil or into water bodies, and from there are absorbed by plants and…

    The full answer from Medha Ma’am →
18. Q18Short answer2 marksAsked: 2026

    (i) Chlorofluorocarbons (CFCs) have been linked to depletion of ozone layer. In 1987, the United Nations Environment Programme (UNEP) succeeded in making an agreement. State this agreement. (ii) What is the role of ozone in our atmosphere ?

    How the model answer begins

    1. (i) In 1987 UNEP got an agreement (the Montreal Protocol) to freeze the production of CFCs at 1986 levels.

    The full answer from Medha Ma’am →
19. Q19Short answer2 marksAsked: 2026

    In the following food chain, 5 J of energy is available to man. Calculate, how much energy was available at the producer level. Why ? Plant ----> Goat ----> Man

    How the model answer begins

    1. By the 10 percent law, only about 10% of the energy at one level is passed to the next; the other 90% is used in respiration, growth and other life processes or lost as heat.

    The full answer from Medha Ma’am →
20. Q20Short answer2 marksAsked: 2026

    Explain why food chains generally consist of three or four steps.

13 more questions of this chapter, each with its model answer, in the Ask Medha app.

Objective questions with the board’s key (10)

1. 1. CBSE 2026

   Which of the following is NOT a 'biodegradable' group ?

   • (A) Vegetable peels, dead leaves, paper
   • (B) Cow dung, leather bag, water
   • (C) Polythene bag, rubber band, ball pen ✓
   • (D) Paper, fruit, bones

   Answer: (C)

2. 2. CBSE 2026

   Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level form the :

   • (A) Food web ✓
   • (B) Ecosystem
   • (C) Ecological pyramid
   • (D) Food chain

   Answer: (A)

3. 3. CBSE 2026

   In accumulation of toxic substances at higher trophic levels of an ecosystem through the food chain, which of the following organisms is affected the most ?

   • (A) Small aquatic plants
   • (B) Human beings ✓
   • (C) Small fish
   • (D) Large fish

   Answer: (B)

4. 4. CBSE 2026

   Assertion (A) : Natural replenishment of soil will not take place in absence of microbes. Reason (R) : Microbes, comprising of bacteria and fungi, break down dead remains and waste products of organisms, and they go into the soil.

   • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). ✓
   • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (A)

5. 5. CBSE 2026

   Assertion (A) : Ozone (O3) gas at higher levels of atmosphere is a product of UV radiation acting on Oxygen (O2). Reason (R) : The amount of ozone in the atmosphere began to drop sharply in 1980s.

   • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). ✓
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (B)

6. 6. CBSE 2026

   Given below are some of the statements regarding our environment : (i) Change in our life-styles have resulted in greater amounts of waste material generation. (ii) Changes in attitude have resulted in use of more disposable things. (iii) Changes in packaging has resulted in much of our waste becoming non-biodegradable. (iv) Organic farming. Which amongst these is not leading to any damage of environment ?

   • (A) (i), (ii), (iii)
   • (B) (iv) ✓
   • (C) (i) and (iii)
   • (D) (ii) and (iv)

   Answer: (B)

7. 7. CBSE 2026

   Assertion (A) : Highest percentage of pesticides is found in tertiary consumers in a food chain. Reason (R) : Chemicals / pesticides get accumulated progressively at each trophic level.

   • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). ✓
   • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (A)

8. 8. CBSE 2026

   In the given figure, identify the trophic level having maximum concentration of harmful chemicals.

   • (A) T1
   • (B) T5 ✓
   • (C) T4
   • (D) T3

   Answer: (B)

9. 9. CBSE 2026

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

   • (A) Availability of water
   • (B) Deficient food supply
   • (C) Decrease in energy at higher levels ✓
   • (D) Pollution in air

   Answer: (C)

10. 10. CBSE 2026

    Assertion (A) : There are generally a greater number of individuals at the lower trophic levels of an ecosystem. Reason (R) : The greatest number is of the producers.

    • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). ✓
    • (C) Assertion (A) is true, but Reason (R) is false.
    • (D) Assertion (A) is false, but Reason (R) is true.

    Answer: (B)

Questions parents and students ask

How many marks does "Our Environment" carry in CBSE Class 10 Science?

In the CBSE papers of 2023–2026, this chapter carried about 5 marks and about 3 questions a year; by marks it ranks 12 in Science.

Which are the most important (VVI) questions of "Our Environment"?

The 20 questions above are from the board’s real papers, each with the years it was asked; the most-asked come first with their full model answers. All 33 written questions of this chapter, with answers, are in the Ask Medha app.

Do the answers follow the board’s marking scheme?

Yes. CBSE publishes its marking schemes; every model answer here is written point by point to the marks the board’s own scheme gives, and checked by a second, independent model.