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Page No 106:

Question 1:

Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest

Answer:

An artificial ecosystem is a man-made ecosystem e.g., crop field.

Hence, the correct answer is option (b).

Page No 106:

Question 2:

In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers

Answer:

A food chains always starts with plants or producers so they occupy the first trophic level. The plants in turn, are consumed by herbivores which occupy the second trophic level. Primary carnivores eat the herbivores and occupy third trophic level.

Hence, the correct answer is option (a).

Page No 106:

Question 3:

An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects

Answer:

An ecosystem consists of biotic components comprising living organisms and abiotic components (non-living constituents) comprising physical factors like temperature, rainfall, wind, soil and minerals.

Hence, the correct answer is option (c).

Page No 106:

Question 4:

In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 5 k J
(b) 50 k J
(c) 500 k J
(d) 5000 k J

Answer:

In an ecosystem, only 10 percent of the energy available at each trophic level is passed on to the next trophic level of the food chain. Thus, if 5 k J energy is available at fourth trophic level, 10 percent more that is, 50 k J energy will be available at third trophic level, 500 k J energy will be availabel at the second trophic level and 5000 k J energy will be available at the first trophic level or producer level.

Hence, the correct answer is option (d).

Page No 106:

Question 5:

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

Answer:

Biomagnification is the phenomenon of through which certain pollutants such as non-biodegradabale pesticides get accumulated in tissues in increasing concentration at successive trophic levels along the food chains.

Hence, the correct answer is option (c).



Page No 107:

Question 6:

Depletion of ozone is mainly due to
(a) chlorofluorocarbon compounds
(b) carbon monoxide
(c) methane
(d) pesticides

Answer:

Ozone depletion is due to ozone-depleting substances such as chlorofluorocarbon compounds.

Hence, the correct answer is option (a).

Page No 107:

Question 7:

Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores

Answer:

All green plants and certain bacteria can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun. So, they are called producers.

Hence, the correct answer is option (b).

Page No 107:

Question 8:

In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of
(a) heat energy
(b) light energy
(c) chemical energy
(d) mechanical energy

Answer:

10% energy refers to the average value for the amount of organic matter that is present at each step and reaches the next level of consumers. This organic matter is the source of chemical energy.

Hence, the correct answer is option (c).

Page No 107:

Question 9:

Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
(a) food web
(b) ecological pyramid
(c) ecosystem
(d) food chain

Answer:

Each organism of lower trophic level is generally eaten by two or more other kinds of organisms of higher trophic level which in turn, are eaten by several other organisms. So, instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.

Hence, the correct answer is option (a).

Page No 107:

Question 10:

Flow of energy in an ecosystem is always
(a) unidirectional
(b) bidirectional
(c) multi directional
(d) no specific direction

Answer:

In an ecosystem, the autotrophs capture the energy present in sunlight and convert it into chemical energy. So, energy flows from Sun to the autotrophs. From autotrophs, the energy goes to the herbivores and decomposers. From, herbivores, the energy is passed on to the organisms of the next trophic level and so on but it never flows backwards. So, the flow of energy in an ecosystem is always unidirectional.

Hence, the correct answer is option (a).

Page No 107:

Question 11:

Excessive exposure of humans to UV-rays results in
(i) damage to immune system
(ii) damage to lungs
(iii) skin cancer
(iv) peptic ulcers
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)

Answer:

UV-rays cause damage to DNA causing damage to immune system and skin cancer.

Hence, the correct answer is option (c).



Page No 108:

Question 12:

In the following groups of materials, which group (s) contains only non-biodegradable items?
(i) Wood, paper, leather
(ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass
(iv) Plastic, bakelite, DDT
(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)

Answer:

Non-biodegradable substances are those man-made materials like plastics, detergent, PVC, Bakelite, DDT, etc. which cannot be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time and harm the ecosystem.

Hence, the correct answer is option (d).

Page No 108:

Question 13:

Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy at higher trophic levels
(b) Sufficient food supply
(c) Polluted air
(d) Water

Answer:

Since only 10 percent of energy available at a trophic level is passed on to the next trophic level and rest energy is lost as heat, very little usable energy remains available after four trophic levels. So, decrease in energy at higher trophic levels limits the number of trophic levels in a food chain.

Hence, the correct answer is option (a).

Page No 108:

Question 14:

Which of the statement is incorrect?
(a) All green plants and blue green algae are producers
(b) Green plants get their food from organic compounds
(c) Producers prepare their own food from inorganic compounds
(d) Plants convert solar energy into chemical energy

Answer:

Green plants amke their food in the form of organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll. So, out of gievn four statements, option (b) is incorrect.

Hence, the correct answer is option (b).

Page No 108:

Question 15:

Which group of organisms are not constituents of a food chain?
(i) Grass, lion, rabbit, wolf
(ii) Plankton, man, fish, grasshopper
(iii) Wolf, grass, snake, tiger
(iv) Frog, snake, eagle, grass, grasshopper
(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iv)

Answer:

The groups of organisms in listed in (i) and (iv) constitute food chains:
(i) Grass   Rabbit Wolf  Lion
(iv) Grass  Grasshopper  Frog  Snake  Eagle

(ii) Three organisms (plankton, fish and man) constitute an aquatic food chain and grasshopper is a part of terrestrial food chain.
(iii) Three organisms (wolf, snake and tiger) are carnivores and grass is producer. Since there is no herbivore, a food chain cannot be constituted.

Hence, the correct answer is option (c).

Page No 108:

Question 16:

The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about
(a) 1 %
(b) 5 %
(c) 8 %
(d) 10 %

Answer:

The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy through photosynthesis.

Hence, the correct answer is option (a).

Page No 108:

Question 17:

In the given Figure 15.1 the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

(a) T4
(b) T2
(c) T1
(d) T3

Answer:

Since there is progressive decrease in the available energy along a food chain, producers or organisms at the first trophic level (shown as T1 in the given pyramid) have the maximum amount of available energy.

Hence, the correct answer is option (c).



Page No 109:

Question 18:

What will happen if deer is missing in the food chain given below?
Grass → Deer → Tiger
(a) The population of tiger increases
(b) The population of grass decreases
(c) Tiger will start eating grass
(d) The population of tiger decreases and the population of grass increases

Answer:

In the given food chain, grass is eaten by deer which in turn, is eaten by tiger. If deer is missing in the food chain, grass will not be eaten by it so, its population will increase whereas tiger will not be get its food and its population will decrease.

Hence, the correct answer is option (d).

Page No 109:

Question 19:

The decomposers in an ecosystem
(a) convert inorganic material, to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not breakdown organic compounds

Answer:

Decomposers are the microorganisms such as bacteria and fungi, that break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.

Hence, the correct answer is option (b).

Page No 109:

Question 20:

If a grasshopper is eaten by a frog, then the energy transfer will be from
(a) producer to decomposer
(b) producer to primary consumer
(c) primary consumer to secondary consumer
(d) secondary consumer to primary consumer

Answer:

A grasshopper consumes plants or producers, so it is a primary consumer. Frog eats grasshopper or primary consumer, so it is a secondary consumer. So, the transfer of energy will be from primary consumer to secondary consumer if a frog eats a grasshopper.

Hence, the correct answer is option (c).

Page No 109:

Question 21:

Disposable plastic plates should not be used because
(a) they are made of materials with light weight
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials

Answer:

Disposable plastic plates cannot be broken down by decomposers and remain in the environment for long. Since they are non-biodegradable, disposable plastic plates should not be used.

Hence, the correct answer is option (d).

Page No 109:

Question 22:

Why is improper disposal of waste a curse to environment?

Answer:

Improper disposal of waste is a curse to the environment because it not only pollutes the environment, soil, water and air but also has harmful effects on the other living organisms including humans. For example, if waste is dumped onto the ground, it will be a breeding place for many disease-causing organisms such as bacteria, viruses, etc. and their vectors such as mosquitoes, house flies etc. It will also cause soil and air pollution. 

Page No 109:

Question 23:

Write the common food chain of a pond ecosystem.

Answer:

Common food chain of a pond ecosystem is:

Phytoplanktons and aquatic plants → small aquatic animals (larvae, insects, shrimps, etc.) → fish → bird (heron)

Page No 109:

Question 24:

What are the advantages of cloth bags over plastic bags during shopping?

Answer:

Cloth bags are made up of plant-based fibres such as jute so, they are more advantageous over plastic bags during shopping for the following reasons:

  • ​They are made of natural fibres which are biodegradable so they are environmental-friendly or do not pollute environment.
  • They can be re-used multiple times and recycled.
  • They are stronger and durable than plastic bags.
  • They can be used for mutiple purposes and carrying more things.

Page No 109:

Question 25:

Why are crop fields known as artificial ecosystems?

Answer:

Artificial ecosystems are ecosystems which are created or maintained by humans. Crop fields are an example of artificial ecosystems because  plants grown in fields are selected by humans. Also, humans add chemicals such as manure, pesticides or herbicides in the fields to increase soil nutrients or control the organisms. Since humans manipulate both biotic and abiotic components of the crop fields, these are known as artificial ecosystems.

Page No 109:

Question 26:

Differentiate between biodegradable and non-biodegradable substances. Cite examples.

Answer:

Biodegradable substances are those substances that can be broken down by biological processes, e.g., paper, wood, vegetable peels. etc.
Non-biodegradable substances are those substances that cannot be broken down by biological processes, e.g., plastic, DDT, bakelite, etc.



Page No 110:

Question 27:

Suggest one word for each of the following statements/definitions
(a) The physical and biological world where we live in
(b) Each level of food chain where transfer of energy takes place
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
(d) Organisms which depend on the producers either directly or indirectly for food

Answer:

(a) Environment/Biosphere
(b) Trophic level
(c) Abiotic factors
(d) Consumers/Heterotrophs

Page No 110:

Question 28:

Explain the role of decomposers in the environment?

Answer:

Decomposers are organisms that break down the dead remains and waste products of organisms into simple inorganic substances that return to the soil. So, they help in cleaning the environment and constant re-cycling of the nutrients in the ecosystem.

Page No 110:

Question 29:

Select the mis-matched pair in the following and correct it.
 

(a) Biomagnification Accumulation of chemicals at the successive trophic levels of a food chain
(b) Ecosystem Biotic components of environment
(c) Aquarium A man-made ecosystem
(d) Parasites Organisms which obtain food from other living organisms

Answer:

The mis-matched pair is (b) and correct pair is:
(b) Ecosystem - Biotic and abiotic components of environment

Page No 110:

Question 30:

We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?

Answer:

An aquarium is an artificial and incomplete ecosystem i.e., it is a man-made ecosystem and it does not contain all the components of a natural ecosystem. For example, it does not contain soil and decomposers that break down the organic matter into simpler inorganic substances and act as cleaner. So, due to lack of cleaners, aquarium needs to be cleaned. In contrast, ponds or lakes are complete and natural ecosystem with all the components that keep them clean. So, they are self-sustaining ecosystems.

Page No 110:

Question 31:

Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.

Answer:

The flow of energy in an ecosystem occurs in the following manner:

Sun  Producers  Primary consumers Secondary consumers  Tertiary consumers

The flow of energy is unidirectional for the following two reasons:

  • Energy flows progressively through the various trophic levels and it is no longer available to the previous level because organisms are linked to each other through food relationships. 
  • Only 10% energy available at a trophic level is passed on to the next level and the energy available at each trophic level gets diminished progressively due to loss of energy at each level.

Page No 110:

Question 32:

What are decomposers? What will be the consequence of their absence in an ecosystem?

Answer:

Decomposers are organisms that break down complex organic matter of dead animals and plants into simpler inorganic substances. These inorganic susbstances return to the soil and become available to producers for their use. If decomposers are not present in the ecosystem, dead organisms and waste will pile up and nutrient re-cycling will not occur. In the absence of nutrient re-cycling, soil will not be replenished and will lack most of the nutrients required by producers to synthesise their food. This, in turn, will affect the flow of energy along a food chain.

Page No 110:

Question 33:

Suggest any four activities in daily life which are eco-friendly.

Answer:

  • Using paper/jute bag in place of plastic bags
  • Segregating bio-degradable and non-biodegradable wastes into separate bins
  • Using public transport for commuting, and walking or using cycle for short distances
  • Harvesting rain water
  • Switching off light/fans when not in use
  • Use of compost and vermi compost in place of fertilisers

Page No 110:

Question 34:

Give two differences between food chain and food web.

Answer:

Food Chain Food Web
It consists of a series of organisms linked to each other through their feeding relationship. It consists of a number of food chains interlinked to each other.
An organism at higher trophic level feeds on one organism occupying the lower trophic level, e.g., lion eating the deer. An organism occupying the higher trophic level can feed upon more than one organism of lower trophic levels of different food chains, e.g., lion eating deer or fox.

Page No 110:

Question 35:

Name the wastes which are generated in your house daily. What measures would you take for their disposal?

Answer:

Waste generated Measures taken for disposal
Kitchen waste (vegetable and fruit peels, stale food, leftover food, used tea leaves, etc.) Preparing compost, placing them near plants or trees for decomposition and return of nutrients to soil for use by the plants
Paper waste (newspaper, old books, paper envelopes, pamphlets, etc.) Sending for recycling
Plastic waste (plastic bags, milk pouches, containers, empty cartons, plastic toys, etc.)  Dumping in non-biodegradable bins for their safe disposal
Other household wastes (torn or old clothes, old electronic items, broken glass items, etc.) Clothes can be sold, re-used for cleaning, or can be donated. Borken glass items should be disposed carefully and old electronic items can be sold for recycling.

Page No 110:

Question 36:

Suggest suitable mechanism(s) for waste management in fertilizer industries.

Answer:

Suitable mechanisms for waste management in fertilizer industries:
Fertilizer industries generate soild waste, wastewater (contains organics, nitrates, alcohols, ammonia, phosphorous, heavy metals such as cadmium and suspended solids) and air pollutants (particulate matter, gaseous NH3, oxides of nitrogen, sulphur and carbon dioxide). So, the waste management mechanisms in fertilizer industries are:

  • Wastewater should be treated before its discharge into the surrounding water.
  • Soild waste should be dumped off at safe place by following safety measures.
  • Air pollution should be controlled e.g., by fitting certain adsorption equipment in chimneys to absorb harmful pollutants before the smoke is released into atmosphere.

Page No 110:

Question 37:

What are the by-products of fertiliser industries? How do they affect the environment?

Answer:

The byproducts of fertiliser industries are oxides of nitrogen and sulphur, other liquid chemicals and some solid waste material. The oxides of nitrogen and sulphur cause acid rain which is highly destructive to forests, crops, aquatic biota and historical buildings. Chemicals from liquid and soild wastes percolate through the soil causing soil pollution. It also causes decrease in soil fertility. Liquid chemicals, if discharged directly into a water body, will cause death of the aquatic animals.

Page No 110:

Question 38:

Explain some harmful effects of agricultural practices on the environment.

Answer:

Harmful effects of agricultural practices on the environment:

  • Soil pollution - Excessive cropping causes robbing of nutrients from the soil leading to loss of soil fertility. Also, over the time, it can lead to soil erosion and finally to desertification. Excessive use of fertilisers also changes soil chemistry and kills useful organisms.
  • Water pollution - Agricultural run off carries nutrients from fields to water and causes excessive growth of algae. This causes decreases in oxygen content in water leading to death of many aquatic organisms.
  • Lowering of water table - Excess drainage of groundwater for irrigation purposes has lowered down the water table. This results in acute water shortage at many places.
  • Biomagnification - The chemical pesticides are non-biodegradable thus, they accumulate in organisms in increasing amounts at each trophic level.
  • Damage to natural ecosystem or habitat - Clearing of forests for agriculture has resulted in loss of habitat to wildlife. Deforestation has also affected the water cycle and other nutrient recycling.



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