Class 10 Science · Chapter 13

Our Environment

298 Class 10 Science questions on Our Environment from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 15 of 15

1. Q281 CBSE 2017
   List ​any ​two natural ecosystems.
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   A forest and a pond are two natural ecosystems.

   Any two natural ecosystems, for example a forest and a pond. (A lake, a grassland, a river, a sea or a desert would also be correct.)

   Step-by-step solution →
2. Q282 CBSE 2017
   List ​any ​two ​abiotic ​components of an ​ecosystem.
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   Temperature and water (rainfall) are two abiotic components of an ecosystem.

   Two abiotic components of an ecosystem: (1) temperature; (2) water (rainfall). Any other non-living physical factor — light, soil, air (wind) or minerals — is also correct.

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3. Q283 CBSE 2017
   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
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   The producer (plants) had 10,000 J of energy.

   $10000$ J. By the ten per cent law only about a tenth of the energy at one trophic level reaches the next, so the deer had $10\times 100=1000$ J and the plants (producers) had $10\times 1000=10000$ J.

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4. Q284 CBSE 2017
   In the following ​food chain, ​plants ​provide $500$ J ​of energy to rats. How much energy will be available ​to ​hawks from ​snakes ? Plants $⟶$ Rats $⟶$ Snakes $⟶$ ​Hawks
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   Hawks receive 5 J of energy from the snakes.

   $5$ J. By the ten per cent law the snakes receive $\frac{10}{100}\times 500=50$ J from the rats, and the hawks receive $\frac{10}{100}\times 50=5$ J from the snakes.

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5. Q285 CBSE 2017
   In ​the ​following food chain, 20,000 J of energy was available to the plants. How much ​energy would be available to ​man in ​this chain ? Plants ​→ Sheep → Man
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   200 J of energy would be available to man.

   $200$ J of energy would be available to man. By the ten per cent law, the sheep receive $\frac{10}{100}\times 20,000=2,000$ J, and man receives $\frac{10}{100}\times 2,000=200$ J.

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6. Q286 CBSE 2017
   Name two natural ecosystems.
   Show answer

   A forest and a pond are two natural ecosystems.

   Any two natural ecosystems, for example a forest and a pond. (Lakes, grasslands, deserts, rivers and seas are also natural ecosystems; gardens, crop fields and aquariums are human-made ecosystems.)

   Step-by-step solution →
7. Q287 CBSE 2017
   Give two ​examples ​of ​decomposers ? ​State their important role ​in ​nature.
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   Decomposers such as bacteria and fungi turn dead remains and wastes into simple substances that replenish the soil and keep the environment clean.

   Examples: bacteria and fungi (for instance, soil bacteria, and fungi such as mushrooms and bread mould). Role: Decomposers break down the dead remains and waste products of plants and animals, converting complex organic substances into simple inorganic substances. These go into the soil and are used again by plants, so decomposers replenish the soil with nutrients; by clearing away dead remains and wastes they also keep the environment clean.

   Step-by-step solution →
8. Q288 CBSE 2017
   Mention ​three harmful ​effects of using polythene bags on the ​environment. ​Suggest an effective ​alternative to ​these bags.
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   Polythene bags are non-biodegradable, choke drains and can kill animals that swallow them; reusable jute or cotton bags are a good alternative.

   Harmful effects of polythene bags on the environment: 1. Polythene is non-biodegradable, so discarded bags are not broken down by bacteria and fungi; they pile up as litter in soil and water bodies for a very long time. 2. They choke drains and sewers, causing waterlogging, and mosquitoes breed in the stagnant water. 3. Stray animals such as cows swallow them with the food waste thrown away in them; the bags can block the digestive tract and kill the animals. Effective alternative: reusable jute or cotton cloth bags. (Paper bags are also biodegradable, but they tear easily and are usually used only once.)

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9. Q289 CBSE 2017
   We often see domestic waste decomposing in the bye ​lanes ​of our residential colony, besides many ​empty plastic bottles, wrappers etc. lying here and ​there. Suggest any two ​arguments to make the residents realise that the improper disposal of waste may be harmful to their ​own as well as ​community health.
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   Rotting waste breeds flies and rats that spread disease; plastic chokes drains and holds water where mosquitoes breed, harming residents and the community.

   (1) The domestic waste decomposing in the open gives off a foul smell and becomes a breeding ground for houseflies, cockroaches and rats. Flies carry germs from it to uncovered food, spreading diseases such as cholera, typhoid and diarrhoea to the residents and their neighbours. (2) Plastic bottles and wrappers are non-biodegradable, so they stay in the lanes for a very long time. They choke the drains, so that dirty water overflows and stagnates, and they hold rainwater in which mosquitoes breed, spreading diseases such as malaria and dengue through the colony; burning them in the open gives off harmful gases. Since these carriers of disease and the blocked drains can affect any house in the colony, careless disposal of waste harms the residents’ own health as well as the health of the community.

   Step-by-step solution →
10. Q290 CBSE 2017
    What ​are decomposers ​? State ​the role ​of decomposers ​in the ​environment.
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    Decomposers are bacteria and fungi that break down dead remains and wastes; they clean the environment and return nutrients to the soil.

    Decomposers are micro-organisms, mainly bacteria and fungi, that break down the complex organic substances present in the dead remains and waste products of plants and animals into simple inorganic substances. Role in the environment: 1. They break down dead remains and wastes, so these do not pile up; they act as the cleaners of the environment. 2. The simple inorganic substances they release go into the soil and are taken up again by plants, so nutrients are returned to the soil and recycled, which keeps the soil fertile.

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11. Q291 CBSE 2017
    What is ozone ? Name ​the ​chemicals that ​damage the ​ozone ​layer.
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    Ozone (${\text{O}}_3$) is a three-atom oxygen molecule that shields the Earth from UV radiation; chlorofluorocarbons (CFCs) damage the ozone layer.

    Ozone (${\text{O}}_3$) is a molecule formed by three atoms of oxygen. In the higher levels of the atmosphere it forms the ozone layer, which shields the surface of the earth from the harmful ultraviolet (UV) radiation of the Sun. The chemicals that damage the ozone layer are chlorofluorocarbons (CFCs), synthetic chemicals used as refrigerants and in fire extinguishers (and as propellants in aerosol sprays).

    Step-by-step solution →
12. Q292 CBSE 2017
    With the help of ​an example of ​a ​food chain, prove that the ​flow ​of energy in ​the ​biosphere is unidirectional.
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    In the chain grass, grasshopper, frog, snake, energy moves only forward, with about $10\%$ passed on, and never flows back.

    Example: grass $\to$ grasshopper $\to$ frog $\to$ snake. The grass captures about $1\%$ of the solar energy falling on its leaves and stores it as food. This energy passes to the grasshopper when it eats the grass, then to the frog and then to the snake - always in the direction of the arrows - and only about $10\%$ of it reaches each next level (for example $10000$ J $\to$ $1000$ J $\to$ $100$ J $\to$ $10$ J); the rest is used in life processes and lost as heat. The energy captured by the grass does not go back to the Sun, and the energy that has passed to the grasshopper never comes back to the grass: within the chain energy passes only from the eaten to the eater, and the heat lost at each step cannot be used by the plants, which need sunlight to make food. So, as energy moves from one trophic level to the next, it is no longer available to the previous level: the flow of energy is unidirectional.

    Step-by-step solution →
13. Q293 CBSE 2017
    How ​can you help ​in reducing the ​problem of waste disposal ? Write ​any ​two methods.
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    Segregate waste at home and compost the biodegradable part; reduce non-biodegradable materials by using cloth or jute bags instead of polythene.

    Any two of the following: 1. Segregate waste at home: put biodegradable waste (kitchen waste, peels, leaves) and non-biodegradable waste (plastic, glass, metal) in separate dustbins, and turn the biodegradable part into manure by composting. 2. Reduce the use of non-biodegradable materials: carry a cloth or jute bag instead of using polythene bags, and avoid disposable plastic articles. 3. Reuse and recycle: use articles such as bottles, jars and paper again, and send paper, glass, metal and plastic for recycling.

    Step-by-step solution →
14. Q294 CBSE 2017
    Give reason to ​justify ​the following ​:

    1. (a)The flow of energy ​in every food web is unidirectional.
    2. (b)The ​decomposers ​play an important role in an ecosystem.
    Show answer

    Energy captured by producers never returns and is lost as heat at each level; decomposers recycle nutrients and clean the environment.

    (a) The energy of a food web comes from the Sun and is trapped by the producers. The energy captured by the producers does not go back to the Sun, and the energy passed to the herbivores does not come back to the producers; as it moves through the trophic levels it is no longer available to the previous level. At each level much of the energy is used in life processes and lost as heat, which plants cannot use to make food, and only about 10 per cent passes to the next level. So energy moves in one direction only. (b) Decomposers (bacteria and fungi) break down the complex organic substances of dead plants, dead animals and wastes into simple inorganic substances, which go into the soil and are used again by plants. They thus recycle nutrients and replenish the soil, and they also clean the environment of dead remains and wastes.

    Step-by-step solution →
15. Q295 CBSE 2017
    Mr. Kumar, the incharge of “Eco-Club” of a school felt the ​need of organising an “Awareness Campaign” for the residents of the nearby areas to make them realise the necessity of segregating the biodegradable and non-biodegradable ​wastes. He went from door-to-door with his students and gave arguments to explain the people about the importance of disposal of their household waste judiciously. He also informed them about ​the prosecutional provisions ​in the cases where garbage ​is thrown at ​places other than the specified bins.

    1. (a)List two advantages of disposing the waste after ​segregating it in two categories.
    2. (b)List two ​arguments given by Mr. Kumar.
    3. (c)Write two values exhibited by Mr. Kumar.
    Show answer

    Segregation allows composting and recycling and cuts pollution; Mr. Kumar warned of disease and punishment and showed environmental concern and social responsibility.

    (a) Two advantages: (i) Biodegradable waste can be turned into compost (manure) or biogas, and non-biodegradable waste such as plastic, glass and metal can be reused or recycled, which is not possible with mixed waste. (ii) Less waste reaches open dumps and landfills, so there is less pollution of soil, water and air, and the waste is easier and safer to handle. (b) Two arguments (any two of these): (i) Carelessly thrown or mixed garbage breeds flies, mosquitoes and germs that spread diseases, so judicious disposal protects everyone’s health. (ii) Non-biodegradable wastes such as polythene bags last for a long time, choke drains, harm animals and pollute the soil, and are far easier to recycle when kept separate. (iii) Throwing garbage anywhere other than the specified bins is punishable under the law. (c) Two values: concern for the environment (environmental awareness) and a sense of social responsibility; leadership and concern for public health are also shown.

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16. Q296 CBSE 2017
    You have been selected to talk ​on “ozone layer and its ​protection” in the school assembly on ‘Environment Day.’

    1. (a)​Why should ozone ​layer be protected to save the environment ?
    2. (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.
    Show answer

    The ozone layer absorbs most of the Sun's harmful UV radiation, so it must be protected; avoid CFC products and service cooling appliances properly.

    (a) The ozone layer, high in the atmosphere, shields the surface of the earth from the ultraviolet (UV) radiation of the Sun by absorbing most of it. UV radiation is highly damaging to organisms: it is known to cause skin cancer in human beings, and it can also damage the eyes and harm plants and other living things. If the ozone layer is thinned, more UV reaches the earth, so the layer must be protected to protect life and the environment. (b) Two ways: (1) Avoid products that contain chlorofluorocarbons (CFCs): use CFC-free refrigerators and air-conditioners, and avoid aerosol sprays and fire extinguishers that contain CFCs or other ozone-depleting gases. (2) Have refrigerators and air-conditioners serviced and disposed of properly so that their cooling gases do not leak into the air, and spread awareness about the harm caused by CFCs among family and friends.

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17. Q297 CBSE 2017
    Your mother always thought 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.

    1. (a)How would you explain to your mother about fruit juices ​getting contaminated with pesticides ?
    2. (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.
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    Pesticides sprayed on crops stay on fruits and enter them via soil and water, so juice is contaminated; the phenomenon is biological magnification.

    (a) Pesticides are sprayed on crops, fruit trees included, to protect them from pests and diseases. Some of the pesticide stays on the fruits, and some is washed down into the soil and water bodies, from where plants absorb it along with water and minerals, so it also gets inside the fruits. Juice made from such fruits therefore contains the pesticide. Pesticide that seeps down through the soil can also contaminate ground water, and if such water is used in making the juice, it adds pesticide to the juice as well. Many pesticides are not biodegradable, so they are not broken down, and washing the fruit removes only part of what is on its skin. (b) The phenomenon is biological magnification. Non-biodegradable chemicals such as many pesticides enter a food chain through the plants. They are not broken down or excreted, so they get accumulated in each organism, and because an organism eats large amounts of food from the level below, their concentration increases progressively at each trophic level. Human beings are at the top of many food chains, so the maximum concentration of these chemicals can build up in our bodies, and beyond a limit it damages our organs.

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18. Q298 CBSE 2017
    Some children wanted to collect the waste scattered in ​the park and burn it at ​the corner. Praveen ​checked ​them, and asked them to classify the waste in two categories and ​dispose ​separately in the green and blue dust bins placed in the park.

    1. (i)Write the criteria of separating ​the waste in two categories.
    2. (ii)Write two advantages of segregating the waste from the environmental ​point of view.
    3. (iii)Write two values exhibited by Praveen.
    Show answer

    Waste is sorted into biodegradable and non-biodegradable; this allows composting, recycling and no burning; Praveen showed environmental concern and civic responsibility.

    (i) The waste is separated on the basis of whether it can be broken down by biological processes (by decomposers such as bacteria and fungi). Biodegradable waste, such as fruit peels, fallen leaves, grass cuttings and left-over food, goes into one bin (usually the green one); non-biodegradable waste, such as polythene, plastic bottles, glass and metal cans, goes into the other (usually the blue one). (ii) Advantages: 1. The biodegradable waste can be composted into manure (or used for biogas), returning nutrients to the soil. 2. The non-biodegradable waste can be reused or recycled, so less of it stays in the soil and water or goes to landfills; and neither kind needs to be burnt, so no smoke or harmful gases are released into the air. (iii) Values shown by Praveen: concern for the environment, and a sense of responsibility as a citizen (civic sense), shown by guiding the other children; awareness of proper waste management.

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