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 9 of 15

1. Q161 CBSE 2024
   Write an aquatic ​food chain with four ​tropic levels. Name the ​primary and tertiary consumer present ​in this food ​chain.
   Show answer

   In $\text{Phytoplankton}\to \text{Zooplankton}\to \text{Small fish}\to \text{Large fish}$, zooplankton are the primary and large fish the tertiary consumer.

   Food chain: Phytoplankton → Zooplankton → Small fish → Large fish. Primary consumer: zooplankton, which feed on the producers at the second trophic level. Tertiary consumer: large fish, at the fourth trophic level. Any other correct aquatic chain of four levels is equally valid, provided each organism feeds on the one before it. The printed "tropic levels" means trophic levels.

   Step-by-step solution →
2. Q162 CBSE 2024
   Explain ​why ​a ​garden ​is ​called ​an ecosystem.
   Show answer

   A garden is an ecosystem because its living and non-living components interact with one another.

   A garden is called an ecosystem because it has living (biotic) components, namely plants such as grasses, trees, rose, jasmine and sunflower, animals such as insects, frogs and birds, and decomposers in the soil, together with non-living (abiotic) components such as sunlight, air, water, temperature, soil and minerals, and these interact. The plants use sunlight, water and minerals to make food, animals depend on the plants and on one another for food, decomposers return nutrients to the soil, and all their activities are affected by the abiotic factors. A garden is therefore a human-made ecosystem.

   Step-by-step solution →
3. Q163 CBSE 2024
   Explain with the help of a terrestrial food chain 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 ?
   Show answer

   Pesticides pass from soil to plants along $\text{Grass}\to \text{Goat}\to \text{Human being}$ and, being non-biodegradable, are most concentrated in humans at the top.

   Pesticides and other chemicals used to protect crops are washed down into the soil. Plants absorb them from the soil along with water and minerals, and they then pass along the terrestrial food chain Grass (crops) → Goat → Human being: the goat eats the contaminated grass, and human beings eat the goat's meat (and the crops themselves). These chemicals are not degradable, so they are not broken down and they accumulate progressively at each trophic level; this is called biological magnification. Human beings occupy the top level of the food chain, so the maximum concentration of these chemicals accumulates in our bodies.

   Step-by-step solution →
4. Q164 CBSE 2024
   Use of pesticides to protect our crops ​affect ​organisms ​at various trophic levels ​especially human beings. ​Name the phenomenon ​involved and ​explain how does it happen.
   Show answer

   Biological magnification: non-degradable pesticides enter the food chain and build up at each trophic level, reaching the maximum in human beings.

   The phenomenon is biological magnification. Pesticides used on crops are washed down into the soil or into water bodies. From the soil and water they are absorbed by plants along with water and minerals, and from water bodies they are taken up by aquatic plants and animals — this is how they enter the food chain. As these chemicals are not degradable, they get accumulated progressively at each trophic level, since each organism takes in the chemical from all the food it eats from the level below. Human beings occupy the top level in the food chain, so the maximum concentration of these chemicals gets accumulated in our bodies.

   Step-by-step solution →
5. Q165 CBSE 2024
   Study the picture given below showing three food chains (a), (b) ​and (c) and answer the following questions : (i) Name the type ​of ecosystems that exist in food ​chains (b) and (c). (ii) The ​first trophic level in all food chains are producers. Why ? What percentage of solar energy do these producers ​capture for their use ? (iii) Why are the arrows shown in the diagram in one direction ​only and not vice versa ? Justify.

   Show answer

   Chain (b) is a grassland and (c) a pond ecosystem; producers come first and capture about 1% of solar energy; arrows show one-way energy flow.

   (i) Food chain (b) — grass, grasshopper, frog, snake, eagle — belongs to a grassland ecosystem; food chain (c) — plant, scorpion-like animal, fish, crane — belongs to a pond (aquatic) ecosystem. (ii) Producers form the first trophic level because only green plants (and blue-green algae) can make their own food from simple inorganic substances by photosynthesis, using sunlight; every other organism depends on them, directly or indirectly, for food and energy. These producers capture about $1\%$ of the solar energy that falls on their leaves. (iii) The arrows show the direction in which energy (food) passes — from the organism that is eaten to the one that eats it. The flow of energy is unidirectional: the energy captured by producers does not go back to the Sun, and the energy passed to herbivores does not come back to the producers; at each level much of it is lost as heat and is no longer available to the level before. So the arrows point one way only, not vice versa.

   Step-by-step solution →
6. Q166 CBSE 2024
   Differentiate between biodegradable ​and non-biodegradable wastes. We generate ​a lot ​of ​non-biodegradable wastes ​in our daily life. Write any two harmful effects ​caused by these wastes ​if not disposed ​off properly.
   Show answer

   Biodegradable wastes are broken down by decomposers, non-biodegradable ones are not; the latter pollute soil and water and enter food chains.

   Biodegradable wastes are broken down by biological processes, by decomposers such as bacteria and fungi, into simple substances that return to the soil (for example vegetable peels, paper, cotton cloth). Non-biodegradable wastes are not broken down by biological processes and persist in the environment for a long time (for example polythene bags, plastics, glass, many pesticides). Two harmful effects of non-biodegradable wastes not disposed of properly: (1) They accumulate, littering land, clogging drains and polluting soil and water. (2) Harmful chemicals among them, such as pesticides, enter food chains and build up at each trophic level (biological magnification), reaching the highest concentration in organisms at the top, including human beings.

   Step-by-step solution →
7. Q167 CBSE 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 ?
   Show answer

   A food chain is a single series, a food web a network of chains; fewer deer means more grass and fewer tigers.

   Food chain: a single straight series of organisms in which each feeds on the one before it, so food energy passes along one path and each organism occupies one trophic level. Food web: a network of many food chains linked together, in which an organism may eat, and be eaten by, several kinds of organisms, so energy has many alternative paths. In the chain grass → deer → tiger, grass is at the first trophic level and the tiger at the third. If the deer population decreases, the population of grass (first trophic level) will increase, because fewer deer feed on it, and the population of tigers (third trophic level) will decrease, because they get less food.

   Step-by-step solution →
8. Q168 CBSE 2024
   Plants $\to$ Deer $\to$ 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.
   Show answer

   Removing deer makes plants increase and lions starve; in a food web the impact on lions is less, as they have other prey.

   On removing the deer (second trophic level): the plants (first trophic level) are no longer eaten, so their number increases; the lions (third trophic level) lose their only food, so they starve and their number decreases, and they may die out. In a food web the impact on the lions would not be the same; it would be much less severe. A food web is a network of interconnected food chains, so the lions can feed on other herbivores (for example zebra or buffalo) and survive.

   Step-by-step solution →
9. Q169 CBSE 2024
   What are ​decomposers ? Explain how ​the ​decomposers

   1. (i)keep the environment clean, ​and also
   2. (ii)​replenish ​the soil nutrients.
   Show answer

   Decomposers are bacteria and fungi that break down dead remains into simple inorganic substances, keeping the environment clean and returning nutrients to the soil.

   Decomposers are micro-organisms, such as bacteria and fungi, that break down the dead remains and waste products of organisms, that is, complex organic substances, into simple inorganic substances. (i) By breaking down the dead bodies of plants and animals and their wastes, decomposers remove them from the surroundings; without them dead matter and wastes would keep piling up, so they keep the environment clean. (ii) The simple inorganic substances released by decomposition go into the soil, where they are absorbed by plants and used once more; in this way the nutrients locked up in dead matter are returned to the soil, replenishing it.

   Step-by-step solution →
10. Q170 CBSE 2024
    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?
    Show answer

    Ozone (${\text{O}}_3$) shields Earth from UV radiation; CFCs deplete it; UNEP's 1987 agreement froze CFC production at 1986 levels.

    Gas X is ozone (${\text{O}}_3$). Function: At the higher levels of the atmosphere, the ozone layer shields the surface of the Earth from the ultraviolet (UV) radiation of the Sun, which is highly damaging to organisms (for example, it causes skin cancer in human beings). Chemical: Chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers, are linked to the decrease in ozone. Measures: In 1987 the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels, and it is now mandatory for all manufacturing companies to make CFC-free refrigerators throughout the world.

    Step-by-step solution →
11. Q171 CBSE 2024
    What ​does a food chain represent ? “The number ​of ​trophic ​levels in a food chain is limited.” ​Give an example stating ​reason to justify this ​statement.
    Show answer

    A food chain shows how food and energy pass from producers to consumers; only $10\%$ passes on at each step, limiting trophic levels.

    A food chain represents the sequence of organisms, each feeding on the one before it, through which food and energy pass from the producers to the consumers; each step of the chain is a trophic level. Example: Grass $\to$ Grasshopper $\to$ Frog $\to$ Snake. Reason: at each step only about 10 per cent of the energy taken in by one trophic level reaches the next; the rest is lost as heat to the environment or used up in the organism's own life processes. So if the grass stores 10,000 J, the grasshoppers get about 1,000 J, the frogs about 100 J and the snakes only about 10 J, and a fifth level would get only about 1 J. Since so little usable energy remains after four trophic levels, food chains generally consist of only three or four steps, so the number of trophic levels is limited.

    Step-by-step solution →
12. Q172 CBSE 2023
    Study ​the given figure of a Food ​web ​and ​identify ​the ​primary consumer in the ​food web:

    1. (a)Mice and Bear
    2. (b)Rabbit and Cat
    3. (c)Rabbit and Fox
    4. (d)Mice and Rabbit
    Show answer

    (d) Mice and Rabbit

    Step-by-step solution →
13. Q173 CBSE 2023
    Choose the ​option giving ​correct matching the ​items ​given ​in ​Column – I & II.

    Items to be matched

    Column – I	Column – II
    A. Physical environment	(i) Ozone layer depletion
    B. Exposure to UV radiation	(ii) Bacteria and Fungi
    C. Chlorofluoro Carbon compounds	(iii) Abiotic components
    D. Decomposers	(iv) Skin Cancer

    1. (a)A – (iii), B – (i), C – (iv), D – (ii)
    2. (b)A – (iii), B – (iv), C – (i), D – (ii)
    3. (c)A – (iii), B – (iv), C – (ii), D – (i)
    4. (d)A – (iii), B – (i), C – (ii), D – (iv)
    Show answer

    (b) A – (iii), B – (iv), C – (i), D – (ii)

    Step-by-step solution →
14. Q174 CBSE 2023
    These consists of two statements – Assertion (A) and ​Reason (R). Answer this question ​selecting ​the appropriate ​option ​given ​below :

    Assertion (A): The energy which passes to the herbivores does not come back to autotrophs.

    Reason (R): The flow of energy in a food chain is unidirectional.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).
    2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).

    Step-by-step solution →
15. Q175 CBSE 2023
    These consists of two ​statements ​– Assertion (A) ​and Reason (R). Answer this ​question ​selecting the appropriate option ​given below :

    Assertion (A): An ecosystem consists of biotic components and abiotic components.

    Reason (R): Biotic and abiotic components play important roles for the sustenance of life and work independently in all ecosystems.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).
    2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (c) Assertion (A) is true, but Reason (R) is false.

    Step-by-step solution →
16. Q176 CBSE 2023
    List two ​reasons ​to show ​that ​the existence ​of decomposers ​is ​essential in an ecosystem.
    Show answer

    Decomposers recycle nutrients to the soil for plants and clear dead remains and wastes, keeping the environment clean.

    Two reasons why decomposers are essential in an ecosystem: 1. They break down the complex organic substances in dead plants, dead animals and their wastes into simple inorganic substances, which go back into the soil and are used again by plants. In this way nutrients are recycled and the soil is replenished. 2. By breaking down dead remains and wastes, they clear them away and so clean the environment; without decomposers, dead bodies and wastes would keep piling up.

    Step-by-step solution →
17. Q177 CBSE 2023
    1. (i)State the essential function performed by ozone at the higher ​levels of the ​atmosphere.
    2. (ii)Why was there a ​sharp drop in the ​amount of ozone ​in the ​atmosphere in 1980’s.
    Show answer

    Ozone shields the Earth's surface from harmful UV radiation; CFCs freed chlorine atoms that destroyed ozone, causing the 1980s drop.

    (i) At the higher levels of the atmosphere, ozone (${\text{O}}_3$) shields the surface of the earth from the ultraviolet (UV) radiation of the Sun by absorbing much of it. This radiation is highly damaging to organisms; in human beings it is known to cause skin cancer. (ii) The sharp drop in the 1980s has been linked to synthetic chemicals called chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers. Released CFCs reach the ozone layer, where UV radiation breaks them down and sets free chlorine atoms, which break ozone molecules down; each chlorine atom can destroy many ozone molecules.

    Step-by-step solution →
18. Q178 CBSE 2023
    State two reasons why ​human-made materials ​like plastics ​persist for ​a long ​time in ​the environment.
    Show answer

    Decomposers have no enzyme for plastics, and the ordinary temperature and pressure of the environment are too mild to break them down.

    (i) Enzymes are specific in their action: a particular enzyme is needed to break down a particular substance. The common decomposers (bacteria and other saprophytes) have no enzymes that can act on plastics, so plastics are not broken down by biological processes; they are non-biodegradable. (ii) Plastics can be acted upon by physical processes such as strong heat and high pressure, but the ambient conditions of our environment (the ordinary temperature and pressure of soil, water and air) are too mild to break them down. So plastics are not removed from the environment and persist in it for a very long time.

    Step-by-step solution →
19. Q179 CBSE 2023
    Why is ​damage to ​the ozone layer ​a cause for concern ​? What ​steps are being taken ​to ​limit this damage ?
    Show answer

    Damage to the ozone layer, linked to CFCs, lets in more harmful UV; CFC production is being frozen and CFCs replaced.

    Ozone at the higher levels of the atmosphere shields the surface of the earth from the ultraviolet (UV) radiation of the Sun. UV radiation is highly damaging to organisms: for example, it causes skin cancer in human beings. Damage to the ozone layer lets more UV radiation reach the surface, so it is a cause for concern. The loss of ozone has been linked to CFCs (chlorofluorocarbons), used as refrigerants and in fire extinguishers. Steps: in 1987 the United Nations Environment Programme (UNEP) forged an agreement (the Montreal Protocol) to freeze CFC production at 1986 levels; manufacturers are now required to make CFC-free refrigerators, and CFCs are being replaced by substitutes that do far less damage to the ozone layer.

    Step-by-step solution →
20. Q180 CBSE 2023
    “Although gardens ​are created by man ​but they ​are considered to be an ecosystem.” ​Justify ​this statement.
    Show answer

    A garden has interacting living and non-living components, so although it is human-made it is an ecosystem.

    An ecosystem is made up of all the interacting living organisms of an area together with the non-living parts of their environment. A garden has both: producers (grasses, trees, flowering plants), consumers (insects, frogs, birds) and decomposers (bacteria and fungi of the soil), along with soil, water, air, sunlight and temperature. These interact: plants make food using sunlight, animals feed on the plants, and decomposers return nutrients to the soil for the plants to use again. So although it is made and looked after by people, a garden is an ecosystem, a human-made (artificial) one.

    Step-by-step solution →