Important Questions of Class 10 Science Chapter 13, Our Environment

Our Environment Class 10 Important Questions: The important questions from Our Environment highlight that the environment consists of biotic (living organisms) and abiotic (non-living components) factors.

These components interact to form ecosystems, where energy flows through food chains and food webs. Understanding these interactions is crucial for maintaining ecological balance and sustaining life on Earth.

Our Environment ​Class 10 Important Questions with Answers

Our Environment Class 10 Important Questions with Answers help students understand the interaction between biotic and abiotic components in ecosystems. These questions focus on energy flow, ecological balance, and human impact on the environment.

Multiple Choice Question [1 Mark]

1. The decomposers in an ecosystem:
(A) Convert organic material to inorganic forms.
(B) Convert inorganic material to simpler forms.
(C) Convert inorganic material into the organic compound.
(D) Do not break down the organic compound.

Sol. (A) Convert organic material to inorganic forms.

2. The manufacturing of chlorofluorocarbons-free refrigerators is mandatory throughout the world. How does this help prevent ozone depletion?
(A) This will help convert oxygen molecules into ozone.
(B) This will help convert the CFCs into ozone molecules.
(C) This will reduce the production of CFCs from oxygen molecules.
(D) This will reduce the release of CFCs that reacts with ozone molecules.

Sol. (D) This will reduce the release of CFCs that reacts with ozone molecules

3. What is the order of the waste management hierarchy, from most to least favoured?
(A) Prevention → Recycle → Reuse → Disposal
(B) Prevention → Reuse → Disposal → Recycle
(C) Prevention → Disposal → Reuse → Recycle
(D) Prevention → Reuse → Recycle → Disposal

Sol. (D) Prevention → Reuse → Recycle → Disposal

4. Which of the following is not a component of the ecosystem?
(A) Abiotic factors
(B) Biotic factors
(C) Human beings
(D) None of the above

Sol. (D) None of the above

5. The process of removal of topsoil by water or wind is called:
(A) Deforestation
(B) Soil erosion
(C) Desertification
(D) Water pollution

Sol. (B) Soil erosion

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

(A) Producers to decomposers
(B) Producer to primary consumer
(C) Primary consumer to secondary consumer
(D) Secondary consumer to primary consumer

Sol. (C) Primary consumer to secondary consumer

7. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as:
(A) Eutrophication
(B) Pollution
(C) Biomagnification
(D) Accumulation

Sol. (C) Biomagnification

8. Identify the proper food chain:
(A) Grass → Frog → Insect → Snake
(B) Grass → Insect → Frog → Snake
(C) Insect → Frog → Grass → Snake
(D) Grass → Frog → Snake → Insect

Sol. (B) Grass → Insect → Frog → Snake

9. Which of the following is proper sequence of trophic levels?
(A) Producers → Herbivores → Top carnivores → Carnivores
(B) Top Carnivores → Carnivores → Herbivores → Producers
(C) Carnivores → Top Carnivores → Producers → Herbivores
(D) Herbivores → Carnivores → Producers → Top Carnivores

Sol. (B) Top Carnivores → Carnivores → Herbivores → Producers

10. Ozone forms by the combination of free oxygen atoms and oxygen molecules. How do free oxygen atoms form at higher levels of the atmosphere?
(A) By splitting molecular oxygen into free oxygen atoms in the presence of low-energy UV radiations.
(B) By splitting molecular oxygen into free oxygen atoms in the presence of high-energy UV radiations.
(C) By the combination of two molecular oxygen in the presence of high-energy UV radiations.
(D) By the combination of two free oxygen atoms in the presence of lower-energy UV radiation.

Sol. (B) By splitting molecular oxygen into free oxygen atoms in the presence of high-energy UV radiations

11. Why is the maximum concentration of pesticides found in human beings?
Sol. The pesticides are not biodegradable, they get accumulated progressively at each trophic level. As human beings occupy the topmost level in food chain, their concentration becomes maximum in our bodies.

12. Why are green plants called producers?
Sol. Green plants are called producers because they manufacture their own food with the help of CO2 and H2O in the presence of sunlight and chlorophyll.

 13. Bacteria and fungi are called decomposers. Why?
Sol. Bacteria and fungi are called decomposers because these microorganisms break down the complex organic matter present in dead plants and animals into simpler substances.

14. What is an ecosystem?
Sol. An ecosystem is defined as a structural and functional unit of the biosphere comprising of living organisms and their non-living environment.

 15. Name two natural and artificial ecosystem.
Sol.
Natural ecosystem: Forest, River
Artificial ecosystem: Aquarium, Garden

 16. Why are plastics non-biodegradable substances?
Sol. Plastics are non-biodegradable substances because they cannot be broken down by the action of enzyme, bacteria or decomposers.

 17. What do you mean by environment?
Sol. “Environment” can be defined as the physical and biological world where we live. It includes both biotic and abiotic compound.

18. Define a food web. Write its significance for ecosystem.
Sol. A system of interconnected food chains between various organisms so as to form a number of feeding connections amongst different organisms of a biotic community is called food web. A food web maintains ecological balance by maintaining the interdependence of different organisms.

 19. Differentiate between biodegradable and non-biodegradable substances.

Sol. Differences between biodegradable and non-biodegradable substances are:

20. Write two causes of depletion of ozone layer.
Sol. Two causes of depletion of ozone layer are:
(A) Use of CFCs in refrigerators and aerosol sprayers.
(B) Release of pollutant nitrogen monoxide by jets.

21. What do you mean by biological magnification?
Sol. Biomagnification is the process of increase in amount of some toxic, non-biodegradable substances such as DDT and heavy metals in successive trophic levels of a food chain. It results in accumulation of the highest concentration of these toxins in the topmost trophic level.

22. Write any four examples of abiotic components of an ecosystem.
Sol. The abiotic components of an ecosystem are:

1. Temperature

2. Soil

3. Rainfall

4. Minerals

23. Why are microorganisms like bacteria and fungi important in an ecosystem?
Sol. Microorganisms like bacteria and fungi are important in an ecosystem because they decompose or breakdown the dead remains of animals and plants. This releases the locked nutrients to be recycled in the ecosystem for reuse as raw materials by the producers.

24. Explain briefly about CFCs. Name two gases which have replaced CFCs.
Sol. CFCs (Chloroflurocarbons) are synthetic, harmful chemicals which are widely used in refrigerators and air conditioners, in aerosol sprayers, etc. Once released in the air, these harmful chemicals produce active chlorine which destroy the ozone by converting it into oxygen. CFCs are being replaced by Hydrofluorocarbons (HFCs) and hydrochloroflurocarbons (HCFCs).

25. What are decomposers? List two important roles they play in the environment
Sol. Decomposers are microorganisms including bacteria and fungi which decompose or break-down the complex organic compound present in dead plants and animals into simpler substances.

Role of decomposers in environment are:

• They help in decomposing dead bodies of plants and animals and hence act as cleansing agents of environment.

• They help in recycling of materials in the ecosystem to maintain its stability.

26. What is a food chain? Which of the following are always at the second trophic level of food chains among the carnivores, autotrophs and herbivores?
Sol. The sequential interlinking of organisms involving transfer of food energy from the producers, through a series of organisms with repeated eating and being eaten is called the food chain. A food chain involves a nutritive interaction between the living organisms of an ecosystem. Herbivores.

27. Differentiate between autotrophs, heterotrophs, and decomposers by giving one example of each.
Sol.

• Autotrophs: Organisms which can make their own food from carbon dioxide and water under the action of sunlight and in the presence of chlorophyll. Example: All green plants.

• Heterotrophs: Organisms which cannot make their own food by the process of photosynthesis and are dependent on others for food are called heterotrophs. Example: All animals.

• Decomposers: Organisms that decompose the complex molecule present in the dead remains of plants and animals are called decomposers. Examples: Bacteria and Fungi.

28. What is the role of the ozone layer in the atmosphere? How is it formed and explain how does it affect an ecosystem?
Sol. Ozone is a form of oxygen. It is a made up of three atoms of oxygen. It is highly poisonous. However, good amount of ozone is present in upper part of the atmosphere called stratosphere.

In the stratosphere, ozone is being photo-dissociated and generated simultaneously by absorption of harmful ultraviolet (UV) radiations coming from sun.
UV + O2 → O + O
O + O2 → O3

The two reactions are in equilibrium thereby maintaining a steady concentration of ozone in the stratosphere. Ozone layer is commonly called ozone blanket. It acts as a protective shield to protect all types of life from the harmful effect of UV radiation. Therefore, any thinning or depletion of ozone layer allows entry of high energy UV radiations into the earth's surface, thereby causing harmful effects on plants, animals and human beings.

The harmful effects of ozone depletion on man, animals and plants includes:
(i) Incidences of skin cancer and herpes.
(ii) Damage to eye sight, photoburning as well as increased incidences of cataract in eyes.
(iii) Increased embryonic mortality.
(iv) 10-25 % decline of photosynthesis in plants.
(v) Global warming.

29. Why the flow of energy in a food chain is unidirectional?
Sol. A food chain consists of series of populations which are related by eating and being eaten. There is a unidirectional flow of energy from Sun to producers and subsequently to series of different types of consumers, i.e., Solar radiations → Producers → Herbivores → Carnivores. It cannot pass in reverse direction. There is always a decrease in the flow of energy and content with rise in trophic level. As large quantity of energy is lost at each step as heat and is also used up in various metabolic activities.

30. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Sol. Trophic level is a step of food chain, at which transfer of food and energy takes place. The number of trophic levels is equal to the number of steps in the food chain.

The common example of food chain in a terrestrial ecosystem is:
Plants → Deer → Tiger

• Plants belong to the first trophic level of the food chain. They are the producers.

• Deer being a herbivorous animal, feeds upon plants and constitutes the second trophic level in the food chain as the primary consumer.

• Tiger is the secondary consumer occupying the third trophic level as it feeds upon deer.

Short Answer Type Question [3 Marks]

31. Differentiate between the food chain and the food web.
Sol.

32. Mention the advantages of paper bags over plastic bags.
Sol. The advantages of paper bags over plastic bags are:

(i) Paper bags can be recycled as they are biodegradable. Their recycling does not produce poisonous gases like recycling of plastic bags.
(ii) Once discarded, paper bags can be recycled again easily while plastic bags cannot be recycled easily as they clog machines and complicate the recycling processes.
(iii) Plastic bags kill thousands of marine animals every year as some animals confuse plastic bags with jellyfish which block the entrance to the stomach. Paper bags are a healthy, safe alternative to hazardous plastic bags.

33. Why are only 4 or 5 trophic levels present in each food chain?
Sol. The quantum of available energy in a food chain successively gets decreased at each trophic level. There is only 10 % flow of energy from one trophic level to the next higher level. Second law of thermodynamics says that transformation of energy from one form to the other is inefficient and involves dissipation of unavailable energy. This loss of energy at successive trophic levels restricts the size of food chain in an ecosystem to maximum 4 to 5 steps. Hence, only 4 to 5 trophic levels are present in each food chain.

34. Name the wastes which are generated in your house daily. What measures would you take for wastes disposal?
Sol. The types of waste generated in a house are:
(i) Kitchen waste like vegetable and fruit peel, used tea leaves etc.
(ii) Empty milk pouches, polythene bags, empty cartons, etc.
(iii) Waste paper (newspaper, paper bags, packing paper).
(iv) Used tooth picks and ear buds.
(v) Dust and other sweepings.

Measures for household waste disposal should be taken are as follows:
(i) Reuse of maximum possible materials.
(ii) Preparing compost from kitchen waste.
(iii) Segregation of biodegradable and non-biodegradable waste.

 35. What is meant by food chain? State the position of autotrophs and herbivores in food chain. Is it possible that the food chains have more than six trophic levels? Give reasons for your answer.
Sol. The sequence of living organisms in a community in which one organism consumes or feeds upon another organism to transfer food energy, is called a food chain. The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In fact, in a food chain, each step representing an organism forms a trophic level.

The position of producers (or autotrophs) in a food chain constitutes the first trophic level. They fix up sun's energy and make it available for consumers. The herbivores or primary consumers (which feed upon plants) constitutes the second trophic level in a food chain.

It is not possible that the food chains have more than six trophic levels. This is because of loss of 90 % energy at each trophic level and only 10 % energy is available at each successive level. In a food chain having more than six steps, energy available to the top carnivore will not be sufficient for their survival.

 36. Explain the phenomenon of ozone depletion. What are the factors responsible for it. What are its consequences?
Sol. Ozone depletion means the thinning of ozone layer in the atmosphere. Many chemicals mainly chlorofluorocarbons are responsible for ozone depletion. These are widely used as coolants in refrigerators and air conditioners; in fire extinguishers; in aerosol sprayer and as propellants. Once released in the air, these chemicals produce 'active chlorine' (Cl and ClO radicals) in the presence of UV radiations. These radicals, through chain reaction, then destroy the ozone by converting it into oxygen. A single active chlorine can deplete one lakh ozone molecules through chain reaction.

Thinning of ozone layer allows ultraviolet (UV) radiations to pass through it which then strike the earth and cause harmful effects on man, animals and plants.
(i) UV radiations increase incidences of skin cancer and herpes.
(ii) It causes damage to eyes resulting in dimming of eye sight.
(iii) Cause damage to immune system hence, lowering the body's resistance.
(iv) Harmful UV radiations increase mortality of developing embryo in the mother‟s uterus.
(v) These radiations decline the rate of photosynthesis in plants which ultimately increases the CO2 concentration leading to global warming.

 37. What practices can we follow to change our lifestyles so that less waste is generated?
Sol. The practices we can follow to change our lifestyles so that less waste is generated are:
(i) We can use only those materials which come packed in biodegradable packs such as paper, coir, jute, etc.
(ii) We can separate the waste generated into recyclable and non-recyclable parts.
(iii) We may reduce the use of certain products which are not so essential for our life.
(iv) We may recycle plastic, paper, glass and metal items.
(v) We can reuse certain things like paper, plastic container and glass bottles.

 38. Consider the food chain: Grass → Deer → Lion. What will happen if all the lions are removed from the above food chain?
Sol. If all the lions are removed, then there will be no predator control over the population of deer due to which its populations will greatly increase and deer will eat all grass. Over grazing will eliminate the grass and other green plants completely and turn the lush green forest into a desert area having no vegetation at all.

39. Which of the following are biodegradable and which non-biodegradable?
Glass bottle, Paper, Ball point pen refill, Hay, DDT, Wheat, Cake, Wood, Polythene bag, Jute bag, Cotton cloth, Grass, Vegetable peels
Sol.

• Biodegradable: Paper, Hay, Wheat, Cake, Wood, Jute bag, Cotton cloth, Grass, Vegetable peels.

• Non-biodegradable: Glass bottle, Ball point pen refill, DDT, Polythene bag.

40. Write down a food chain in
(a) in the sea
(b) that ends with humans
(c) that contains five links.

Sol.
(a) (Zooplankton) → (Phytoplankton) → (Small Fish) → (Big Fish) → (Carnivore) → (Large carnivore) → Algae → Protozoa

(b) (Producer) → (Herbivore) → (Omnivore) → (Primary consumer) → (Secondary consumer) → Plants → Goat → Man

(c) Plants → Grasshopper → Frog → Snake → Hawk →

Long Answer Type Question [5 Marks]

41. (a) Define trophic level. Draw the food chain with four trophic levels.
(b) What will happen if we kill all the organisms in one trophic level?

Sol.
(a) Trophic Levels – The various steps in a food chain at which the transfer of food takes place are called trophic levels. In a food chain, each step representing an organism forms a trophic level.

(Producer) → (Herbivore) → (Top carnivore) → (Carnivore)
Grass → Insect → Frog → Bird

(b) If we kill all the organisms in one trophic level, then the transfer of food (and energy) to the next trophic level will stop due to which the organisms of next trophic level will starve and die or migrate to other areas. The killing of all the organisms in one trophic level will also lead to the overpopulation of organisms in the previous trophic level.

These effects will cause an imbalance in the ecosystem. For example, if we kill all the herbivorous animals like deer, rabbits, etc., in a forest, then the carnivorous animals like lions, tigers, etc., will not get food. Due to this, the lions and tigers etc., will starve and die or migrate from forest and go towards human settlements and attack people. Moreover, in the absence of herbivores like deer, rabbits, etc., the population of the previous trophic level „plants‟ (or vegetation) will increase too much (because there are no deer or rabbits to eat them). All these effects will create an imbalance in the ecosystem.

42. Show how energy moves through an ecosystem. What causes it to be unidirectional? Explain.
Sol. Flow of energy in an ecosystem is as follows:

• Green plants in ecosystems capture about 1% of sunlight and convert it into food energy.

• Primary consumers lose most energy as heat, and only 10% is passed on to the next level.

• Due to energy loss, food chains usually have only three or four levels.

• There are more organisms at lower levels, with producers being the most numerous.
  
  

• Food chains are complex, often forming interconnected food webs instead of straight chains

• The flow of energy is unidirectional because the energy captured by autotrophs does not return to the Sun.

• Energy that is passed from autotrophs to herbivores does not go back to the autotrophs.

• As energy moves through the different trophic levels, it becomes unavailable to the previous level.

• Additionally, energy diminishes at each trophic level due to losses as it moves upward in the food chain.
  
  

43. Describe some of the negative environmental effects of agricultural practices.
Sol. Following are the harmful effects of agricultural practices on the environment:

• Soil degradation: Extensive cropping causes loss of soil fertility. Also, over time it can lead to soil erosion and finally to desertification.

• Pollution: Use of synthetic fertilisers and pesticides leads to soil, water and air pollution.

• Water shortage: Excess use of groundwater for agriculture lowers the water level. This results in acute water shortage at many places.

• Bio-magnification: The chemical pesticides, being non-biodegradable, accumulate in organisms in increasing amounts at each trophic level.

• Deforestation: Indiscriminate cutting of trees for agriculture has resulted in loss of habitat for wildlife. Thus, it also causes damage to the natural ecosystem

44. (a) In the following food chain, only 2J of energy was available to the peacocks. How much energy would have been present in Grass? Justify your answer. Grass → Grasshopper → Frog → Snake → Peacock
(b) In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer?
(c) What is ten per cent law? Explain with an example how energy flows through different trophic levels.
Sol. (a) In the given food chain, 20,000 J of energy must have been present in grass. This is because, as per the 10% law of energy transfer, only 10% of energy is transferred to the next trophic level.

(b) Plants → Deer → Lion
1,00,000 J of energy was available to the producer.

(c) 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: 1000 J as light

45. What are consumers? Name the four categories under which the consumers are further classified.
Sol. Consumers are the organisms which are unable to synthesise their own food. Therefore, they utilise materials and energy stored by the producers or eat other organisms. They are known as the heterotrophs. The consumers are of following categories:

(i) Primary or first-order consumers: These include the animals which eat plants or plant products. They are called herbivores or primary (first order) consumers. E.g., Cattle, deer, goat, rabbit, hare, rats, mice, grasshoppers etc.

(ii) Secondary or second order consumers: These include the animals which depend on primary consumers for their food. They are called primary carnivores or secondary (second order) consumers. Secondary consumers can be carnivores or omnivores. E.g., Cats, dogs, foxes, small fish, etc.

(iii) Tertiary or third order consumers: These are large carnivores (or top carnivores) which feed on primary and secondary consumers. These are termed as secondary carnivores or tertiary (third order) consumers. Common examples include shark and crocodile, wolves, lion, etc.

(iv) Quaternary or fourth order consumers: These are even larger carnivores which feed on secondary carnivores (tertiary consumers). E.g., Tigers, lions and eagles/hawks etc.

46. Case Study:
Ozone layer is present in the earth's atmosphere and shields the surface of the earth from ultraviolet (UV) radiation from the sun. There is 'bad' ozone formed in the lower atmosphere that harms plants and animals and also 'good' ozone found in the upper part of the atmosphere. It contains three oxygen atoms (O3) which are formed as a consequence of photochemical reactions in the environment.

(i) The good ozone is present in which layer of the atmosphere?
(a) Troposphere (b) Mesosphere (c) Stratosphere (d) Thermosphere
Sol. (c) Good ozone is found in the upper part of the atmosphere called the stratosphere.

(ii) The enhanced UV radiations would affect humans and other animals. It can cause:
(a) skin cancer in human beings.
(b) cataract in eyes of human beings.
(c) crop yield reduction.
(d) All of the above.
Sol. (d) UV radiations are highly damaging to plants, animals and human beings. It is known to cause skin cancer and cataract in eyes of human beings. It is also responsible for malfunctioning of immune system. It also causes significant damage to crops and plants.

(iii) Read the given statements regarding the ozone layer.
I. The amount of ozone in the atmosphere began to drop sharply in the 1960s.
II. Ozone is formed in the atmosphere as a result of photochemical reaction.
III. Harmful chemicals produce active chlorine in presence of UV radiations that destroys ozone layers.
IV. Ozone absorbs harmful UV radiations and X-rays emitted by sun.

Select the option that correctly identifies them as true (T) and false (F).

Sol. (b) Correct Statements: The amount of ozone in the atmosphere began to drop sharply in the 1980s. Ozone absorbs harmful UV radiations emitted by sun.

(iv) Which of the following compound causes depletion of ozone layer?
(a) Chlorofluorocarbons
(b) Methane
(c) Nitrous oxide
(d) All of these

Sol. (d) Ozone depleting substances (ODS) are the substances that deplete the ozone layer. Some examples of ozone depleting substances are chlorofluorocarbons, halogens, methane, nitrous oxide, carbon tetrachloride, etc.

 47. Read the passage carefully and answer the following questions.
After the examination, Rakesh with his friends went on a picnic to nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food, some friends collected the leftover food and plastic bags, etc. and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregated leftover food and peels of fruits from plastic materials and respectively dispose them off separately in green and red dustbins placed into corner of the park.

(a) In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the advantage of method suggested by Rakesh. (2 marks)
(b) How can we contribute in maintaining the parks and roads, neat and clean? (2 marks)

Sol.
(a) No, the burning of plastic is not an eco–friendly method of waste disposal because it releases a number of toxic chemicals that are harmful to humans, animals and plants as well as polluting the environment. Segregating the wastes and placing them in different bins (green for biodegradable and blue for non-biodegradable wastes) is an eco-friendly disposal.

(b) Parks and roads can be kept neat and clean by placing dustbins at selected places and telling people to throw the wastes only in the bins meant for them.

 48. Read the passage carefully and answer the following questions.
Each step or level of the food chain forms a trophic level. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level. We know that the food we eat acts as a fuel to provide us energy to do work. Thus, the interactions among various components of the environment involves flow of energy from one component of the system to another.

(a) Name the group of organisms which form in the first trophic level of all food chains. Why are they called so? (2 Marks)

(b) In the following food chain, only 5J of energy was available to the hawks. How much energy would have been present in Grass? Justify your answer.
Grass → Grasshopper → Frog → Snake → Hawk

Sol.
(a) Producers form the first trophic level of all food chains. They are called producers because they are autotrophic organisms which alone are able to manufacture organic food from inorganic raw materials by the process of photosynthesis. They capture sun‟s energy and convert it into chemical energy. The chemical energy is used in combining raw materials into organic food. This food is used up by themselves and rest enters the food chains as food for consumers.

(b) In the given food chain, 50,000 J of energy must have been present in grass. This is because, as per the 10% law of energy transfer, only 10% of energy is transferred to the next trophic level.

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