Class 10 Science Chapter 13 Our Environment NCERT In-text Exercise Question Answer
The chapter 'Our Environment' helps students learn about ecosystems, food chains, and how human actions affect nature. Given below are the Class 10 Science Chapter 13 Our Environment question answers, which are designed by subject experts following the NCERT curriculum for better understanding.
Topic 13.1: Ecosystem and its components:
Q1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer:
Every step or level of the food chain is referred to as a trophic level. Energy transfer in the form of food occurs from one trophic level to another. Trophic levels can be broadly divided into Producers, Primary, Secondary, and Tertiary Consumers.
An example of a food chain:
Grass → Grasshopper → Frog → Snake → Eagle
Here, Grass is a producer, Grasshopper is the herbivore, Frog is the first carnivore, Snake is the second carnivore, and Eagle at the top is the third carnivore.
Q2. What is the role of decomposers in the ecosystem?
Answer:
Decomposers decompose the dead and decaying organisms' organic matter into simpler inorganic compounds. Decomposition aids in recycling nutrients back into the ecosystem, thus providing a constant supply of energy. Through the decomposition of dead organisms, they clean the environment and avoid the buildup of waste. The inorganic compounds released also enrich the soil, making it fertile for plant growth. Decomposers thus have an important role in sustaining the ecosystem's balance.
They also help in decomposing plant litter, like leaves and twigs, which aids in soil creation. Without decomposers, dead organic material would pile up, throwing the cycle of life off balance. Bacteria and fungi are the major decomposers, functioning well to decompose complex materials.
Topic 13.2: How do Our Activities Affect the Environment?
Q1. Why are some substances biodegradable and some non-biodegradable?
Answer:
Substances that can be broken down by biological processes are said to be biodegradable. In our environment, many of the substances are broken down easily by decomposers. Examples: Paper, vegetable peels, etc.
However, substances that cannot be broken down biologically but only by physical means are known as non-biodegradable substances. Example: Plastic.
Q2. Give any two ways in which biodegradable substances would affect the environment.
Answer:
Two ways in which biodegradable substances would affect the environment are:
1. These substances, on degradation, can produce a foul smell that affects the population living nearby. They may also become a breeding place for insects.
2. Many harmful greenhouse gases may evolve during degradation, leading to global warming.
Q3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
Any two ways in which non-biodegradable substances may affect the environment are:
1. The main problem caused is pollution. Non-biodegradable substances take many decades to degrade and hence remain in the environment, causing pollution.
2. They may render the soil infertile and hence affect the vegetation
Q4. What is ozone, and how does it affect any ecosystem?
Answer:
Ozone (O3) is a molecule made of three oxygen atoms. It affects the ecosystem in two ways, depending on its location:
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In the upper atmosphere (stratosphere), It forms a protective layer that absorbs harmful ultraviolet (UV) radiation. The depletion of this layer allows more UV rays to reach the Earth, harming living organisms.
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At ground level (troposphere) - It acts as a pollutant that harms the respiratory systems of humans and animals and damages plants and vegetation.
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Q5. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
Two methods used to reduce the problems of waste disposal are:
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Throwing biodegradable and non-biodegradable waste into separate dustbins so that recycling can be done easily.
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By putting the organic waste into compost pits dug in the ground, and preparing compost. This compost helps in increasing the fertility of the soil.
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Practising the 3 R's: Reduce, Reuse, and Recycle.
Chapter-end NCERT Exercise Science Our Environment Class 10 Question Answer
Solving the questions is important, as it makes students more confident and also decreases their stress. So, in this, we will cover all Class 10 Science Our Environment question answers.
Q1. Which of the following groups contains 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
Answer: (c) and (d)
Explanation:
Option (A)- Grass, flowers are biodegradable, but processed leather takes a very long time to decompose, so it is not fully biodegradable.
Option (B)- Grass, wood are natural and decompose easily, so they are biodegradable, but plastic is non-biodegradable.
Option (C)- Fruit peels, cake, and lime juice are all natural and easily decompose, so they are biodegradable.
Option (D)- Cake, wood, and grass are also natural materials that decompose easily and are biodegradable.
Hence, the correct option is (c) and (d).
Q2. Which of the following constitutes a food chain?
(a) Grass, wheat, and mango
(b) Grass, goat, and human
(c) Goat, cow, and elephant
(d) Grass, fish, and goat
Answer: (b) Grass, goat, and human
Explanation:
A food chain consists of different trophic levels.
(b) Grass → Goat → Human; constitute a food chain.
Here, the grass is a producer, the goat is the primary consumer, and the human is the secondary consumer.
Hence, the correct option is (b), Grass, goat, and human
Q3. Which of the following are environmentally 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 off on her scooter
(d) All of the above
Answer: (d) All of the above
Explanation:
All of the above-mentioned practices are environmentally friendly.
Hence, (d) All of the above is the correct answer.
Q4. What will happen if we kill all the organisms in one trophic level?
Answer:
If all the organisms of a trophic level are destroyed, the food chain will become unbalanced. The animals in the direct higher trophic level will die because of a lack of food, and the effect will follow. Also, the number of organisms in the direct lower trophic level will continue to grow, and this will destroy its direct lower level because of greater demand but lesser supply. So the entire food chain will collapse.
Q5. Will the impact of removing all the organisms in 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.
No, the organisms of any trophic level cannot be removed without causing any damage to the ecosystem.
Consider the following example:
Grass → Deer → Lion
1. If all the grass is removed, the deer will die out due to starvation, which in turn will wipe out the lions.
2. If the entire deer population is removed, the lions will die out due to starvation. The grasses will increase in number and turn the land into forests.
3. If all the lions are removed, the population of deer will keep on increasing, which in turn will eat all the grass, leaving the land barren.
Q6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer:
Biological Magnification is the rise in the concentration of toxic materials in the body of the organism at every trophic level.
Yes, the magnification levels are varied at various levels of the ecosystem. It is at the highest level of the food chain.
Since chemicals such as pesticides and DDT are not degradable, these collected progressively at every trophic level. Since human beings are at the top of any food chain, the highest concentration of these chemicals is collected in their bodies.
Q7. What are the problems caused by the non-biodegradable wastes that we generate?
Answer:
The non-biodegradable waste that we generate has the following problems for the environment:
1. Non-biodegradable wastes like pesticides reduce the fertility of soil as they penetrate it. The pH level of the soil becomes unsuitable for vegetation.
2. Non-biodegradable wastes like pesticides accumulate progressively at each trophic level and thus harm the organisms.
3. Non-biodegradable materials like plastics, when burning, release toxic chemicals into the environment, which leads to air pollution.
Q8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer:
If everything we throw away is biodegradable, it can still affect the environment if not dumped properly. It can cause a bad odour, impacting surrounding communities. It can also be a breeding ground for mosquitoes and other insects, which may lead to increased disease transmission. Proper dumping grounds must thus be established for effective waste management.
Composting is the best method of disposing of biodegradable waste, as it transforms waste into organic matter that can be utilized. Proper segregation of waste should be ensured by municipal authorities to allow recycling and composting. Public awareness campaigns can inform people about proper waste disposal. A well-maintained and clean environment leads to healthier and more sustainable living.
Q9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:
The ozone layer in the stratosphere is responsible for absorbing dangerous UV rays, which protects all living organisms. If the ozone layer gets depleted, higher exposure to UV radiation can cause severe health problems, such as skin cancer in human beings, and harm plants and animals. Thus, ozone layer damage is a significant environmental issue.
To minimise this harm, the manufacture of chlorofluorocarbons (CFCs), the cause of ozone depletion, was phased out in 1986. Global agreements such as the Montreal Protocol have been enforced to control ozone-depleting substances. Public awareness programs promote the use of environmentally friendly products. Researchers are also working on sustainable substitutes for toxic chemicals to save the ozone layer.
Important Questions from Class 10 Science Chapter 13 Our Environment
This chapter explains how different components of the environment interact and how human activities impact the ecosystem. Practising different questions given in the NCERT Solutions for Class 10 Science Chapter 13 Our Environment improves confidence.
Question 1: Which of the following is a non-biodegradable waste?
a) Vegetable peels
b) Paper
c) Plastic
d) Cotton
Answer: The correct answer is option c) Plastic
Explanation:
Paper, clipboards, metal containers like aluminum plants and human waste, and several plant products are classified under biodegradable substances. However, an example of a non-biodegradable substance could be plastic products.
Question 2: Due to depletion of the ozone layer, skin cancer in humans is caused by harmful
a) Infrared radiation
b) X-rays
c) gamma rays
d) UV radiation
Answer: The correct answer is option d) UV radiation
Explanation:
UV radiation is harmful to organisms as it can cause skin cancer in human beings. They can also damage the DNA of cells, leading to mutations and other health problems.
Question 3: The chemical formula of Ozone layer is _______
a) O4
b) O6
c) O5
d) O3
Answer: The correct answer is option d) O3
Explanation:
Ozone (O3) is a molecule formed by three atoms of oxygen. The higher-energy UV radiation reaction splits molecular oxygen (O2) into free oxygen (O). These atoms then combine with the molecular oxygen to form the Ozone layer.
Question 4: The major cause for the sharp drop in ozone in the atmosphere is
a) greenhouse gases
b) CFCs
c) Nitrogen gas
d) Hydrogen gas
Answer: The correct answer is option b) CFCs
Explanation:
Chlorofluorocarbons (CFCs) are synthetic chemicals used in refrigerators, air-conditioners, and fire extinguishers. They have been observed as a major cause for the sharp drop in ozone in the atmosphere.
Question 5: Primary producers capture about __ of the energy of sunlight that falls on their leaves.
a) 0.1%
b) 1%
c) 10%
d) 0.01%
Answer: The correct answer is option b) 1%
Explanation:
Primary producers that are green plants, also known as autotrophs, capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.
Question 6: In a food chain, the flow of energy is always
a) Unidirectional
b) Bidirectional
c) Circular
d) Random
Answer: The correct answer is option a) Unidirectional
Explanation:
Energy in an ecosystem always flows in one direction — from the Sun → producers → consumers → decomposers. It never flows backward. Once energy is used, it is lost as heat and cannot return to the Sun.
Question 7: The organisms that break down complex organic substances into simpler ones are called
a) Producers
b) Consumers
c) Decomposers
d) Parasites
Answer: The correct answer is option c) Decomposers
Explanation:
Decomposers (like bacteria and fungi) break down dead plants and animals into simpler substances. They help recycle nutrients back into the soil, maintaining ecosystem balance.
Question 8: The percentage of energy transferred from one trophic level to the next is approximately
a) 1%
b) 5%
c) 10%
d) 50%
Answer: The correct answer is option c) 10%
Explanation:
According to the 10% law of energy transfer, only about 10% of the energy is passed from one trophic level to the next. The remaining energy is lost as heat during metabolic activities.
Question 9: Which of the following is an example of a biological magnification?
a) Accumulation of oxygen in the atmosphere
b) Increase in population of herbivores
c) Increase in concentration of pesticides in a food chain
d) Recycling of nutrients in soil
Answer: The correct answer is option c) Increase in concentration of pesticides in a food chain
Explanation:
Biological magnification refers to the gradual increase in the concentration of harmful substances like pesticides at higher trophic levels of a food chain. This happens because these substances are non-biodegradable and accumulate in organisms over time.
Our Environment Science Class 10 CBSE Board PYQ
These Our Environment Class 10 CBSE Board PYQs highlight the importance of energy transfer, unidirectional flow, and eco-friendly practices. They are frequently asked in board exams and help students strengthen concepts for the NCERT Solutions Class 10 Science Chapter 13 Our Environment. Practising such questions improves confidence and ensures better exam preparation.
Question: If 10,000 J of energy is available at the producer level, how much energy will be available to the secondary consumers? Give reason to justify your answer.
Answer: If 10,000 joules of energy are present at the producer level, then the energy available to the secondary consumers is just 100 joules of energy.
This is because of the 10% law of energy transfer in a food chain, which states that only 10% of energy from one trophic level is transferred to the next, and the remaining 90% is lost in the form of heat or used by the organisms in different body functions.
Therefore, of 10,000 J at the producer level, 1000 J is available to the primary consumers, and 10% of this, i.e., 100 J, is available to the secondary consumers.
Question: "In a food chain, energy flow is unidirectional." Give two reasons for the given statement.
Answer:
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In a food chain, the energy always moves in one direction. It moves from the Sun to producers and from producers to consumers. This energy is not reused and can't travel backwards.
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In every trophic level, some energy is lost to the environment in the form of heat. Therefore, only a fraction of the energy is passed to the next level. This unidirectional transfer of energy from one organism to another causes the flow of energy in the food chain to be directional.
Question: Assertion (A): Use of jute bags for shopping reduces pollution.
Reason (R): Jute is biodegradable, and its bag may be reused as and when needed.
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Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
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Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
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Assertion (A) is true, but Reason (R) is false.
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Assertion (A) is false, but Reason (R) is true.
Answer: Assertion: The use of jute bags reduces pollution because they are an eco-friendly alternative to plastic bags. Jute is a natural material, and using jute bags helps in reducing the impact on the environment caused by the use and disposal of plastic bags.
Reason: Jute is biodegradable, which means that it can break down naturally in the environment, unlike plastic.
Hence, the answer is option 1) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
