Class 10 Science · Chapter 13

Our Environment

141 Class 10 Science questions on Our Environment from the NCERT textbook, NCERT Exemplar and CBSE board papers 2024–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 3 of 8

1. Q41 Exemplar · Short Answer Questions
   Why are ​crop ​fields ​known ​as ​artificial ecosystems?
   Show answer

   A crop field is artificial because humans create and maintain it, choosing the crop, supplying inputs and removing the harvest.

   A crop field has both biotic and abiotic components and so is an ecosystem, but it is created and maintained entirely by human beings, and that is what makes it artificial. The land is ploughed, the natural vegetation is removed and one selected crop is sown in rows; irrigation replaces natural rainfall; manure and chemical fertilisers replace the nutrients that natural litter would have returned; weeds, insects, rodents and birds are killed, so the number of species and the food web are deliberately kept small and simple; and the crop is harvested and taken away, so the energy and minerals it holds leave the field instead of being recycled in it. If the farmer stops ploughing, sowing, irrigating and weeding, the crop disappears and wild vegetation takes over within a season or two. Because its composition and its very survival depend on continuous human effort, a crop field is called an artificial (man-made) ecosystem, like a garden, a park or an aquarium.

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2. Q42 Exemplar · Short Answer Questions
   Differentiate between biodegradable and ​non-biodegradable ​substances. Cite ​examples.
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   Biodegradable substances are broken down by decomposers and recycled; non-biodegradable ones, such as plastics, persist and accumulate.

   Biodegradable substances are those that decomposers — bacteria and fungi — can break down into simple substances; non-biodegradable substances are those that no decomposer can break down. The differences are: (i) Agent: biodegradable substances are broken down by the enzymes of microorganisms, non-biodegradable ones are not acted upon by any organism. (ii) Time: biodegradable substances decay in days to a few months, non-biodegradable ones remain for years or centuries. (iii) End products: biodegradation gives simple inorganic substances — carbon dioxide, water, nitrates, phosphates and minerals — which return to the soil, air and water and re-enter the nutrient cycle, whereas non-biodegradable substances accumulate as pollutants and, if toxic, are biomagnified up the food chain. (iv) Management: biodegradable waste can be composted or turned into biogas, while non-biodegradable waste can only be reduced, reused, recycled or landfilled. Examples — biodegradable: vegetable and fruit peels, leftover food, tea leaves, paper, cotton and jute cloth, wood, leaves, cow dung, sewage. Non-biodegradable: plastics and polythene bags, glass, metal cans, aluminium foil, thermocol, synthetic fibres, DDT, batteries and e-waste.

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3. Q43 Exemplar · Short Answer Questions
   Suggest one word for each of the following ​statements/ definitions

   1. (a)The ​physical and biological world where we live in
   2. (b)Each level of ​food chain where transfer of energy takes place
   3. (c)The physical factors like temperature, rainfall, wind ​and soil of an ​ecosystem
   4. (d)Organisms which ​depend on the producers either directly or indirectly for ​food
   Show answer

   The four words are environment, trophic level, abiotic components and consumers.

   (a) Environment; (b) Trophic level; (c) Abiotic components (abiotic factors); (d) Consumers.

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4. Q44 Exemplar · Short Answer Questions
   Explain the ​role of ​decomposers ​in ​the ​environment?
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   Decomposers break down dead matter, recycle nutrients, clean the environment and keep the soil fertile.

   Decomposers are saprophytic microorganisms — mainly bacteria and fungi — that break the complex organic matter of dead plants, dead animals and their excreta into simple inorganic substances. Their roles are: (i) Nutrient recycling: they release carbon dioxide, water, nitrates, phosphates and minerals into the soil, air and water, where producers absorb them again, so the same atoms are used over and over and the biogeochemical cycles keep running. (ii) Cleansing agents of nature: they clear away dead bodies, fallen leaves, excreta and other biodegradable waste that would otherwise pile up, and so make room for new organisms. (iii) Soil fertility: the humus they leave improves the texture, the water-holding capacity and the nutrient content of the soil — the principle used in composting and vermicomposting. (iv) They form the last link of every food chain and the bridge between the biotic and the abiotic world, since they return to the non-living environment the matter that the living world has taken from it.

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5. Q45 Exemplar · Short Answer Questions
   Select the mis-matched pair ​in the following ​and correct it.

   1. (a)Biomagnification — Accumulation of chemicals at the successive trophic levels of a food chain
   2. (b)​Ecosystem — ​Biotic components ​of ​environment
   3. (c)Aquarium — A man-made ecosystem
   4. (d)Parasites — Organisms which obtain food from other living organisms
   Show answer

   (b) Ecosystem — Biotic components of environment is mis-matched; an ecosystem includes the abiotic components as well.

   The mis-matched pair is (b) Ecosystem — Biotic components of environment. It is wrong because an ecosystem is not made of living things alone. Corrected: Ecosystem — all the living organisms (biotic components) of an area together with the non-living or abiotic components of the environment such as light, temperature, rainfall, wind, water, soil and air, the two interacting with one another as a self-supporting unit; for example a pond, a forest, a crop field or an aquarium. The other three pairs are correctly matched: (a) Biomagnification really is the accumulation of a non-biodegradable chemical at successive trophic levels of a food chain, (c) An aquarium really is a man-made ecosystem, and (d) Parasites really do obtain their food from other living organisms.

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6. Q46 Exemplar · Short Answer Questions
   We do ​not clean ponds ​or ​lakes, but an aquarium needs to ​be cleaned. Why?
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   A pond cleans itself through decomposers and water flow; an aquarium lacks these, so waste builds up and it must be cleaned by hand.

   A pond or a lake is a natural, complete and self-sustaining ecosystem. It contains producers (algae and water plants), consumers of every level and, above all, plenty of decomposers, and its water is renewed by rain and by streams. Dead plants and animals and the excreta of the fish are broken down by the decomposers into simple nutrients, which the producers absorb and use again, while the currents and rainwater dilute and carry away the rest. The nutrient cycle is therefore closed and nothing accumulates, so no one has to clean a lake. An aquarium is an artificial ecosystem made and maintained by man. It has only a few chosen plants and fish, an incomplete food web, too few decomposers and no natural inflow or outflow of water, and the fish are fed from outside. Uneaten food, fish excreta and dead matter therefore collect at the bottom, ammonia and other harmful substances build up, the water turns foul and cloudy and the dissolved oxygen falls, which would kill the fish. So the aquarium has to be cleaned and its water changed by hand — we do for it the work that decomposers and flowing water do for a pond by themselves.

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7. Q47 Exemplar · Long Answer Questions
   Indicate the flow ​of energy ​in an ​ecosystem. ​Why is it unidirectional? ​Justify.
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   Energy flows one way from the Sun up the trophic levels, losing about $90\%$ as heat at each step, so it cannot be recycled.

   Flow of energy: the Sun is the source. Green plants capture about $1\%$ of the sunlight falling on their leaves and convert it by photosynthesis into chemical energy, so the producers form the first trophic level ($T_1$). From them the energy passes to the herbivores ($T_2$), then to the small carnivores ($T_3$) and then to the top carnivores ($T_4$), while decomposers act on the dead matter of every level. At each transfer only about $10\%$ of the energy is stored at the next level — the ten per cent law — so $10000$ J at the producers leaves about $1000$ J at the herbivores, $100$ J at the small carnivores and $10$ J at the top carnivores. The remaining $90\%$ at each step is used up in respiration, movement and other life processes and is given off to the surroundings as heat. The flow is unidirectional because: (i) Energy enters the ecosystem at a single point, since only producers can trap solar energy; (ii) It moves only in the direction of feeding, producer to herbivore to carnivore, and never backwards; (iii) At every step a large part is converted into heat, which is dissipated into the atmosphere, and no organism can capture heat and rebuild it into food; and (iv) Therefore energy cannot be recycled the way carbon, nitrogen and water are — matter cycles, energy flows. Two consequences confirm it: food chains are short, usually of three or four links, because after four transfers only about $1$ J of the original $10000$ J is left; and the pyramid of energy is always upright. This is why every ecosystem needs a continuous fresh supply of solar energy.

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8. Q48 Exemplar · Long Answer Questions
   What ​are decomposers? ​What will ​be the consequence of ​their absence in an ​ecosystem?
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   Decomposers are bacteria and fungi that break down dead matter; without them waste piles up, nutrients stay locked and the ecosystem collapses.

   Decomposers are saprophytic microorganisms — mainly bacteria and fungi — that feed on the dead remains of plants and animals and on their excreta, breaking the complex organic matter down by their enzymes into simple inorganic substances such as carbon dioxide, water, nitrates, phosphates and minerals, and obtaining their own energy from the process. If they were absent from an ecosystem: (i) Dead bodies, fallen leaves and excreta would not be broken down and would go on piling up, leaving no room for new organisms and making the surroundings filthy and foul; (ii) The nitrogen, phosphorus, potassium, carbon and minerals held inside those dead bodies would stay locked in them and would never return to the soil, water and air; (iii) The nitrogen, carbon and phosphorus cycles, whose return arm is decomposition, would break, so matter would no longer be recycled; (iv) The soil, no longer replenished and forming no humus, would lose its fertility, its texture and its water-holding capacity; (v) The producers, starved of raw materials, could not grow, and since every food chain rests on the producers, the herbivores would starve and then the carnivores, so the whole ecosystem would collapse; and (vi) Sewage and other biodegradable waste would remain untreated, spreading pollution, foul odour and disease. In short, decomposers are the link that returns matter to the non-living environment, and without that link an ecosystem cannot go on working.

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9. Q49 Exemplar · Long Answer Questions
   Suggest ​any ​four ​activities ​in daily life ​which ​are eco-friendly.
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   Carry a cloth bag, segregate and compost waste, save electricity, and save water and travel wisely.

   Four eco-friendly activities for daily life (any four): (i) Carry a cloth or jute bag for shopping and refuse plastic carry bags, disposable plastic plates, cups and straws — one reusable bag replaces hundreds of polythene bags, which are non-biodegradable, choke drains, kill cattle that swallow them and give toxic fumes when burnt. (ii) Segregate household waste into biodegradable and non-biodegradable, compost the kitchen and garden waste in a pit or a vermicompost bed to make manure, and hand paper, glass, metal and plastic to a recycler — this returns the wet waste to the nutrient cycle and keeps the dry waste fit for recycling. (iii) Save electricity: switch off lights, fans and appliances when they are not needed, use LED or CFL lamps, dry clothes in the sun and use solar water heaters or cookers — most of our electricity comes from burning coal, a non-renewable fuel whose combustion pollutes the air. (iv) Save water and travel wisely: mend leaking taps, use a bucket instead of a running shower, reuse water from washing for the plants, harvest rainwater, and walk, cycle, car-pool or use public transport for short journeys — this conserves a limited resource and reduces vehicle exhaust. Other acceptable answers include planting and caring for trees, using both sides of paper, using rechargeable batteries, and not burning dry leaves or waste.

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10. Q50 Exemplar · Long Answer Questions
    Give ​two differences ​between ​food ​chain and ​food ​web.
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    A food chain is a single linear sequence that breaks easily; a food web is a stable network of interlinked chains.

    (i) Structure and number of food sources: a food chain is a single straight sequence of organisms in which each one is eaten by the next, so every organism has only one source of food, only one consumer and one trophic level — for example Grass $\to$ Grasshopper $\to$ Frog $\to$ Snake $\to$ Hawk. A food web is the network formed when many such chains of an ecosystem are interconnected, because most organisms eat several kinds of food and are eaten by several kinds of predator, so an organism may feed at more than one trophic level and the energy has many alternative paths. (ii) Stability: a food chain is fragile and rarely occurs alone — if any one member is removed, the chain breaks and the levels above it starve; a food web is stable, because if one prey species disappears its predators switch to an alternative food and the ecosystem continues to function. This is why food webs, and not isolated food chains, are what actually exist in nature.

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11. Q51 Exemplar · Long Answer Questions
    Name ​the ​wastes which are ​generated ​in your house daily. What ​measures would you take ​for ​their disposal?
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    Household waste is wet, dry or hazardous; segregate it, compost the wet part, recycle the dry part and never burn or dump waste.

    Wastes generated in a house daily: (i) Biodegradable (wet) waste — vegetable and fruit peels, leftover food, tea leaves, egg shells, spoilt food, garden leaves and flowers, cow dung. (ii) Non-biodegradable (dry) waste — plastic bags, wrappers, bottles and containers, glass bottles and broken glass, metal tins, aluminium foil, thermocol, rubber, synthetic cloth, and paper and cardboard (biodegradable, but better recycled). (iii) Hazardous and sanitary waste — used batteries, fused CFL and tube lights, expired medicines, broken thermometers, empty pesticide and paint tins, e-waste, used sanitary napkins and diapers. Measures for their disposal: (1) Reduce and reuse first — carry a cloth bag, avoid disposable plastic articles and over-packed goods, refill bottles and jars, use both sides of paper. (2) Segregate at source into three separate bins — green for wet waste, blue for dry recyclable waste, and a covered container for hazardous and sanitary waste. (3) Compost the wet waste in a compost pit or vermicompost bed, or give it to the wet-waste collection; it returns as manure for the plants, and where a biogas plant is available it also gives fuel gas. (4) Wash, dry and hand over the dry waste — paper, glass, metal and plastic — to the recycler so that it is made into new articles. (5) Deposit batteries, CFLs, medicines and e-waste only at authorised collection or take-back points, and wrap and dispose of sanitary waste separately as directed. (6) Send only the inert residue that is left to a properly built landfill. Never burn waste in the open, never throw it into drains, ponds or empty plots, and never leave it uncovered, since that breeds flies, mosquitoes and rats.

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12. Q52 Exemplar · Long Answer Questions
    Suggest ​suitable ​mechanism (s) ​for waste management ​in ​fertiliser ​industries.
    Show answer

    Reduce waste at source, treat the effluent, control gaseous emissions, recover and recycle materials and manage solid waste safely, with regular monitoring.

    A fertiliser plant makes three kinds of waste — liquid effluent (ammoniacal nitrogen, urea, nitrate, phosphate, fluoride, acids, oil), waste gases (ammonia, oxides of nitrogen and sulphur, fluorides, carbon dioxide, fertiliser dust) and solid waste (phosphogypsum, sludge, spent catalyst) — and each needs its own mechanism. (i) Reduce at source: closed modern process design, recovery of process condensate, leak-proof handling, separate storm-water drains and good housekeeping, so that less waste is made at all. (ii) Effluent treatment plant, in sequence: screening and equalisation, neutralisation with lime or acid, primary settling to remove solids and oil, steam or air stripping to drive off ammonia, biological treatment by activated sludge with nitrifying and denitrifying bacteria to remove the nitrogen, secondary clarification, and tertiary polishing by sand filtration and activated carbon. (iii) Recovery and recycling: condense and return the stripped ammonia, recover urea dust from the prilling tower, reuse the treated water as cooling and process water to reach zero liquid discharge, use phosphogypsum for cement and plaster board, recover sulphur from waste gas and send spent catalyst for metal recovery. (iv) Air-pollution control: cyclone separators, bag filters and electrostatic precipitators for dust; water, acid and alkali scrubbers to absorb ammonia, sulphur dioxide, oxides of nitrogen and fluorides; and a tall stack with continuous on-line monitoring. (v) Solid-waste management: dewater the sludge and store phosphogypsum on lined, impervious platforms with leachate collection, so rain cannot carry fluoride and heavy metals into the groundwater, and send only inert residue to a secure landfill. (vi) Monitoring and protection: regular testing of effluent and emissions against the prescribed standards, a green belt of trees around the plant, worker training and an emergency plan for ammonia leaks.

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13. Q53 Exemplar · Long Answer Questions
    What ​are ​the by-products ​of ​fertiliser industries? ​How ​do they affect the environment?
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    By-products are gases, liquid effluent and solid wastes; they cause acid rain, fluorosis, eutrophication and contamination of groundwater and soil.

    By-products of fertiliser industries: (i) Gases — ammonia, oxides of nitrogen, sulphur dioxide, carbon dioxide and carbon monoxide, fluorine compounds such as hydrogen fluoride from phosphatic plants, and fertiliser dust and particulates. (ii) Liquid effluent — ammoniacal nitrogen, urea, nitrates, phosphates, fluoride, acids and alkalis, oil and grease, suspended solids and traces of heavy metals such as cadmium from rock phosphate. (iii) Solids — phosphogypsum, sludge, spent catalyst and off-specification product. Their effects on the environment: (1) Sulphur dioxide and oxides of nitrogen dissolve in rain to form sulphuric and nitric acid, giving acid rain, which acidifies soils and lakes, damages crops, forests and aquatic life and corrodes marble buildings; oxides of nitrogen also help form photochemical smog. (2) Ammonia irritates the eyes, nose and lungs and is dangerous in a large leak; fluoride gases settle on fodder and cause fluorosis in cattle, with mottled teeth and stiff joints, and scorch the foliage of crops; dust and particulates cause respiratory disease. (3) Nitrate and phosphate in the effluent reach ponds, lakes and rivers and cause eutrophication — a heavy algal bloom grows and cuts off the light, and when it dies the decomposers consume the dissolved oxygen, so fish and other aquatic animals suffocate and the water body becomes foul. (4) Nitrate seeping into the groundwater makes drinking water unsafe and causes methaemoglobinaemia, the blue-baby disease, in infants, while fluoride causes dental and skeletal fluorosis. (5) Heaps of phosphogypsum and sludge occupy land and their leachate carries fluoride and cadmium into the soil and groundwater, from where cadmium can enter crops and the food chain. (6) Carbon dioxide adds to the greenhouse effect and nitrous oxide is both a powerful greenhouse gas and an ozone-depleting one. Almost every one of these is the product itself, escaped untreated, so recovery and effluent treatment cure the damage and save material at the same time.

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14. Q54 Exemplar · Long Answer Questions
    Explain some harmful ​effects ​of ​agricultural practices ​on the ​environment.
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    Fertilisers cause eutrophication and unsafe nitrate; pesticides are biomagnified; over-irrigation, groundwater use, monoculture and burning residue also damage soil, water and air.

    Harmful effects of agricultural practices: (i) Excess chemical fertiliser — the part the crop cannot absorb is washed into ponds, lakes and rivers and causes eutrophication, in which an algal bloom grows, dies and is decomposed, using up the dissolved oxygen so that fish die; nitrate also leaches into the groundwater and makes drinking water unsafe, causing the blue-baby disease in infants; and continued heavy use makes the soil acidic, kills earthworms and soil microorganisms and destroys the soil structure. (ii) Pesticides and weedicides — being non-biodegradable, their residues stay in the soil and water, are absorbed by plants and pass into the food chain. Since animals cannot excrete them, their concentration increases at every higher trophic level — biomagnification. Taking a ten-fold rise at each step, producers at $0.01$ ppm give herbivores $0.1$ ppm, small carnivores $1$ ppm and top carnivores $10$ ppm, while over the same three steps the available energy falls from $10000$ J to $10$ J: the residue rises exactly where the energy falls, and man, at the top of many chains, gets the largest dose. Pesticides also kill honey bees and other pollinators, earthworms, fish, birds and the natural predators of the pest, and the surviving pests become resistant. (iii) Over-irrigation with poor drainage — waterlogging and the accumulation of salts left behind by evaporation, so the soil becomes saline or alkaline and finally barren. (iv) Excessive withdrawal of groundwater by tube wells — the water table falls, wells dry up and sea water enters coastal aquifers. (v) Monoculture of high-yielding varieties and the clearing of forest and grassland — loss of agro-biodiversity, so that a single pest or disease can destroy the whole crop, along with habitat loss and soil erosion. (vi) Burning the crop residue — smoke, particulates and greenhouse gases in the air and the destruction of the soil's organic matter and microorganisms; paddy fields and cattle also release methane and nitrogenous fertiliser releases nitrous oxide, both powerful greenhouse gases. The remedies mirror the causes: apply fertiliser by soil test and use manure and biofertilisers, use biological pest control and integrated pest management, irrigate by drip or sprinkler with proper drainage, harvest rainwater, practise crop rotation and mixed cropping, and plough the stubble back into the soil.

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15. Q55 CBSE 2026
    Given below are some of the statements regarding ​our environment :

    1. (i)Change ​in our life-styles have resulted in greater amounts of waste material ​generation.
    2. (ii)Changes ​in attitude ​have resulted ​in use of more disposable things.
    3. (iii)Changes in packaging has resulted ​in much of our waste becoming non-biodegradable.
    4. (iv)Organic farming. Which amongst these is ​not leading to any damage of environment ?

    1. (a)(i), (ii), (iii)
    2. (b)(iv)
    3. (c)(i) and (iii)
    4. (d)(ii) and (iv)
    Show answer

    (b) (iv)

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16. Q56 CBSE 2026
    An ​ecosystem ​contains ​maximum ​number of ​:

    1. (a)Producers
    2. (b)Herbivores
    3. (c)Carnivores
    4. (d)Omnivores
    Show answer

    (a) Producers

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17. Q57 CBSE 2026
    Examine ​the given ​food chains ​to establish the ​correct one ​in an ​ecosystem ​:

    1. (a)Seed $⟶$ mouse $⟶$ snake $⟶$ deer
    2. (b)Algae $⟶$ small fish $⟶$ large fish $⟶$ hawk
    3. (c)Grasshopper $⟶$ frog $⟶$ snake $⟶$ elephant
    4. (d)Plants $⟶$ rabbit $⟶$ deer $⟶$ wolf
    Show answer

    (b) Algae $⟶$ small fish $⟶$ large fish $⟶$ hawk

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18. Q58 CBSE 2026
    Why do green plants ​occupy ​the first trophic ​level of any food ​chain ​? Pick out ​the right option from the following.

    1. (a)They are fixed at one place in the soil so they cannot move from place to place.
    2. (b)They are widely distributed.
    3. (c)There are more herbivores than carnivores.
    4. (d)They have the ability to make food using sunlight, by photosynthesis.
    Show answer

    (d) They have the ability to make food using sunlight, by photosynthesis.

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19. Q59 CBSE 2026
    Organisms of ​a ​higher ​trophic level which feed on ​several types of organisms belonging to a lower ​trophic level form the ​:

    1. (a)Food web
    2. (b)Ecosystem
    3. (c)Ecological pyramid
    4. (d)Food chain
    Show answer

    (a) Food web

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20. Q60 CBSE 2026
    Select ​the incorrect ​statement ​from the following :

    1. (a)Ozone is a molecule formed by three atoms of oxygen.
    2. (b)Ozone shields earth's surface from harmful infrared radiations.
    3. (c)CFC's are linked to decline of ${\text{O}}_3$ layer in our atmosphere.
    4. (d)Ozone at higher levels is a product of UV radiations acting on oxygen molecule.
    Show answer

    (b) Ozone shields earth's surface from harmful infrared radiations.

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