NCERT Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Questions

In Text Questions

Question 1.
Why are some substances biodegradable and some non-biodegradable ? (CCE 2011)
Answer:
Biodegradable substances are substances of organic origin which can be broken down by enzymes of saprophytes, e.g., garbage, sewage, livestock waste, agriculture waste. Non-biodegradable substances are man-made substances which cannot be degraded by saprophytes because they lack the enzymes to do so e.g., waste plastic and polythene articles.

Question 2..
Give any two ways in which biodegradable substances would affect the environment.
(CBSE Delhi 2007, AI 2009 C)
Answer:

  1. Stink: Within a day or so waste biodegradable substances begin to stink and produce foul gases.
  2. Pests and Pathogens: The decaying biodegradable substances become breeding places of flies and many other pests. They also contain a number of pathogens. Flies and other pests carry the germs to all the places visited by them resulting in spread of diseases.

Question 3.
Give any two ways in which non-biodegradable substances would affect the environment. (CBSE AI 2009 C)
Answer:

  1. Dumping Area: Dumping of non-biodegradable substances on a piece of land converts the same into barren land. It is also called landscape pollution.
  2. Biological Magnification: Pesticides, heavy metals and other chemicals enter water and food chains. They accumulate in toxic proportions and harm all kinds of living organisms. Their concentration also increases with rise in trophic level. Human beings are harmed the most because man lies at the top of every food chain.

Question 4.
What are trophic levels ? Give an example of a food chain and state the trophic levels in it.
Answer:
(a) Trophic Levels. They are steps or divisions of food chain which are characterised by particular methods of obtaining food, e.g., producers (T1), herbivores (T2), primary carnivores (T3), etc.

NCERT Solutions for Class 10 Science Chapter 15 Our Environment image - 1
(b) Flow of Energy Through Food Chain. Energy enters a food chain through producers. Producers or green plants trap solar energy and convert it into chemical energy of food during photosynthesis. From producers energy passes into herbivores. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes into primary carnivores, again with a lot of dissipation. Only about 10% of herbivore energy is passed into body mass of primary carnivores. From primary carnivores, nearly 10% energy passes into secondary carnivores and so on. It is ultimately lost as heat.

Question 5.
What is the role of decomposers in the ecosystem ?
Answer:
Ecosystem is a self-contained ecological system which consists of a distinct biotic community and the physical environment, both interacting and exchanging materials between them. It is a structural and functional unit of biosphere. Ecosystem is an open system which requires a regular input of energy and circulation of matter for its sustenance. Different ecosystems are in contact with one another. Though they are distinct, but exchange of materials can occur amongst them. Ecosystem can be small (e.g., rotting piece of wood) or large (e.g., forest, ocean), temporary (e.g., rain fed pond) or permanent (e.g., lake, forest), natural or artificial.
Natural Ecosystems: They are ecosystems which develop in nature without human support. Natural ecosystems are of two types, terrestrial and aquatic. Terrestrial ecosystems occur over land. They are of three major types -— desert, grassland and forest. Aquatic ecosystems are found in water bodies, e.g., ponds, lakes, rivers (fresh water), estuaries, marine (salt water).
Artificial Ecosystems: They are ecosystems which have been p/g. 5.7. An aquarium. created and are maintained by human beings. Artificial ecosystems are also called man-made or anthropogenic ecosystems. Agroecosystem is the largest man-made ecosystem. Garden is a common artificial ecosystem maintained by most institutes. It has various types of plants grown and maintained by gardener — grass, trees, flower bearing plants like Rose, Jasmine, Sunflower. A number of animals become residents and visitors of the garden. Aquarium is another artificial ecosystem.

Question 6.
What is ozone and how does it affect any ecosystem ?
Answer:
Definition of Ozone: Ozone is a triatomic molecule made up of three atoms of oxygen, O3.
Effect:

  1. Protection against ultraVoilet rays if present in stratosphere,
  2. Ozone dissipates the energy of ultraviolet rays by undergoing dissociation following by reassociation
    NCERT Solutions for Class 10 Science Chapter 15 Our Environment image - 2

If present in the atmosphere of ecosystem, it is highly toxic causing injury to mucous membranes, eye irritation and internal haemorrhages in animals and humans. It harms plants by destroying photosynthetic cells producing necrosis.

Question 7.
How can you help in reducing the problem of waste disposal ? Give any tivo methods.
Answer:
Waste disposal is becoming the biggest problem of all local bodies. It is consuming a big chunk of their revenues. Even then the points of collection are turning into stinking areas. Transport of waste to disposal site is seldom perfect. There is stink all the way. A lot of waste is thrown on the roads by the vehicles carrying the waste.
The quantity of waste can be reduced if you form the habit of separation of waste into biodegradable and non-biodegradable parts.

  1. Non-biodegradable Waste. Most often the non-biodegradable waste is recycled. It is taken away by rag pickers.
  2. Biodegradable Waste. Biodegradable waste is putressible. It can be composted or vermicomposted to prepare compost for your kitchen gardens. The technique can also be used in schools and other institutions. Some institutes in big cities have installed incinerators for disposal of combustible components of waste. Hospital waste is being compulsorily incinerated to reduce contamination and spread of diseases.

NCERT Chapter End Exercises

Question 1.
Which of the following groups contains only easily biodegradable items ?
(A) Grass, flower and leather
(B) Grass, wood and plastic
(C) Fruit peels, cake and lime juice ,
(D) Cake, wood and grass.
Answer:
(A), (C), (D).

Question 2.
Which of the following constitute a food chain
(A) Grass, wheat and mango
(B) Grass, goat and human
(C) Goat, cow and elephant
(D) Grass, fish and goat.
Answer:
(B).

Question 3.
Which of the following are environment friendly practices ?
(A) Carrying cloth bags to put purchases in while shopping
(B) Switching off unnecessary lights and fans
(C) Walking to school instead of getting your mother to drop you on her scooter
(D) All the above.
Answer:
(D).

Question 4.
What will happen if you kill all the orgainsms in one trophic level ?
Answer:
Higher Trophic Level. All the organisms will be starved and die. Lower Trophic Level. The organisms will increase in number much beyond the carrying capacity of the enviroment. They will become weak and fall easy prey to various diseases, ultimately resulting in decline in population. The ecosystem may get converted into a desert.

Question 5.

  1. Will the impact of removing all the organisms in a trophic level be different for different trophic levels ?
  2. Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?

Answer:

  1. Yes. Impact of removing all the organisms of a trophic level depends upon the trophic level. Removal of producers will kill all the consumers. Killing of carnivores will increase the number of herbivores which in turn will eat up all the producers. They would themselves die of starvation. However, if herbivores are removed, all the carnivores of the area will die. The plants which are dependent upon animals for pollination will fail to reproduce and die ultimately. Others would persist and increase in number, again much beyond the carrying capacity of the environment.
  2. No. Removal of all the organisms of a trophic level will disturb the ecosystem – killing of higher trophic level organisms and explosion in populations of lower level organisms. Higher number of lower trophic level organisms will adversely affect the ecosystem by consuming whole or major part of their prey.

Question 6.
What is biological magnification ? Will the levels of this magnification be different at different levels of the ecosystem ?
Answer:
Definition: Biological magnification is increase in the concentration of a chemical per unit weight of the organisms with the successive rise in trophic level. In one study it was found that concentration of harmful chemical like DDT will increase 80,000 times the concentration present in water.
Levels of Magnification at Different Levels of Ecosystem. Levels of biomagnification of a chemical will be different at different levels of ecosystem. In one study it was found that concentration of a pesticide was 0.002 ppm in water, 0.05 ppm in plankton, 2.4 ppm in fish and 16.0 ppm in fish eating bird.
NCERT Solutions for Class 10 Science Chapter 15 Our Environment image - 3

Question 7.
What are the problems caused by the nonbiodegradable waste we generate ?
Answer:

  1. Volume: Being non-biodegradable, the volume of these wastes will not decrease by natural process of decomposition.
  2. Land Use: They have to be dumped over land. The land becomes unfit for any other purpose.
  3. Heavy Metals: Heavy metals present in industrial wastes (e.g., copper, lead, chromium, nickel, mercury) remain in the soil indefinitely. Slowly they pass into vegetation and crops harming both humans and animals.
  4. Pesticides and Other Toxins: They pollute underground water, surface water and soil. The chemicals enter food chain and become concentrated, harming animals and humans.
  5. Rag Pickers: In the process of removing recyclable materials from solid wastes, the rag pickers are exposed to many diseases and toxins.
  6. Recycling: Recycling of materials produces only’inferior quality products. Recycling of polythene and plastic is accompanied by release of carcinogenic toxins like dioxins and furans.

Question 8.
If all the waste we generate is biodegradable, will this have no impact on the environment ?
Answer:
The impact on the environment will depend upon the system of collecting, transporting and disposal of biodegradable waste. If it is regular and clean, the impact will be little in urban areas. Only some effect will be observed at disposable site which will emit foul gases and expose the sanitary workers to contamination. The same can also be reduced by increased use of machines and wearing of protective gear by the sanitary workers.

Question 9.
Why is damage to the ozone layer a cause of concern What steps are being taken to limit this damage ?
Answer:
Cause of Concern: Ozone layer present in the stratosphere has thinned out by about 8% over the equator and more so over the antarctica where a big ozone hole appears every year.
This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing increased number of skin cancers, cataracts and reduced immunity in human beings. There is increased incidence of blinding of animals, death of young ones, reduced photosynthesis, higher number of mutations and damage to articles.
Steps to Limit Damage:

  1. Ban on production and use of halons.
  2. Ban on production and use of chlorofluorocarbons.

Selection Type Questions

Alternate Response Type Questions
(True/False, Right(√)/Wrong (x), Yes/No)

Question 1.
Wastes are of two types, biodegradable and non-biodegradable.
Question 2.
Non-biodegradable articles are the ones which cannot be digested.
Question 3.
Ozone is formed in stratosphere by action of ultravoilet radiations on oxygen.
Question 4.
Earth is kept warm due to green house flux.
Question 5.
Rag pickers remove reusable articles.
Question 6.
Pyrolysis is aerobic combustion while incineration is anaerobic combustion.
Question 7.
Biodegradable wastes should be separated and kept in blue colour bins for garbage collectors.
Question 8.
Food web ensures survival of all types of trophic levels.

Matching Type Questions

Question 9.
Match the articles in columns I and II (single matching) :

Column I Column II
(a) Hawk (i) Producer
(b) Hare (ii) Top carnivore
(c) Grass (iii) Green house gas
(d) Carbon dioxide (iv) Herbivore

Question 10.
Match the contents of columns I, II and III (double matching)

Column I Column II Column III
(a)    Ecosystem

(b)    Producers

(c)    Omnivores

(d)    Persistent pesticide

(i) Food chain 

(ii) Abiotic components

(iii) Transducer

(iv) Plant food

p.  Food energy

q.  Biomagnification

r. Animal food

s. Biotic components

Question 11.
To what trophic level (T1, T2, T3, T4) do the following belong (key or check list items)
NCERT Solutions for Class 10 Science Chapter 15 Our Environment image - 4

Question 12.
Match each stimulus with appropriate response :

Activity Deforestation (A) Increase runoflf (B) Destruction of wild life (C)
(i) Hunting

(ii) Felling of trees

(iii) Litter Collection

Fill In the Blanks

Question 13. Waste substances that are broken down by microbes are called ………. : ………… .
Question 14. Gardens and crop fields are ………………. ecosystems.
Question 15. Microorganisms are called ……………… as they break down the complex organic remains into simple inorganic substances.
Question 16. Decrease in ozone in stratosphere is linked to release of synthetic chemicals like ……………… .
Question 17. Improvement in life style often results in increased generation of …………. : ………… material.

Answers:
NCERT Solutions for Class 10 Science Chapter 15 Our Environment image - 5

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Short Answer Questions

Question 1.
Why is improper disposal of wastes a curse to environment ?
Answer:
An improper disposal of wastes means addition of pollutants into environment —air, water, soil. They will harm living beings, human assets and human beings. For example, passage of sewage into water body will cause eutrophication, stink, development of sludge, killing of animals and source of water borne pathogens.

Question 2.
Write the common food chain of a pond ecosystem.
Answer:
NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment image - 1
Question 3.
What are the advantages of cloth bags over plastic bags during shopping ?
Answer:
Advantages of Cloth Bags

  1. Cloth bags are stronger and more durable as compared to plastic bags.
  2. They are washable.
  3. They are reused time and again.
  4. Cloth bags do not pollute environment.
  5. They are made of biodegradable material which can also be recycled.

Question 4.
Why are crop fields known as artificial ecosystems ?
Answer:
Crop fields are known as artificial ecosystems because they are raised, maintained, nourished and reaped by human beings.

Question 5.
Differentiate between biodegradable and non-biodegradable substances. Give examples.
Answer:

Biodegradable Wastes Non-biodegradable Wastes
1. Origin. They are biological in origin. They are commonly man-made.
2. Degradability. The wastes are degraded by microorganisms. They are not degraded by microorganisms.
3. Accumulation. They do not accumulate in nature. They pile up and accumulate in nature.
4. Biomagnification. The biodegradable wastes do not show biomagnification. The soluble non-degradable wastes enter food chains and undergo biomagnification.
5. Resource. The wastes can be converted into resource. Some wastes can be recycled.
Examples. Garbage, livestock wastes, sewage. Examples. Plastic, polythene, glass, nickel, cadmium, several pesticides.

Question 6.
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) Biosphere (also environment)
(b) Trophic level.
(c) Abiotic factors.
(d) Consumers (also heterotrophs)

Question 7.
Explain the role of decomposers in the environment. (CCE 2011)
Answer:
Decomposers are saprophytes which feed on organic remains by a process of external digestion and absorption of solubilised materials, e.g., many bacteria, fungi. In the process they perform the following functions :

  1. Cleansing the earth of organic remains and continuously creating space for newer generations of organisms.
  2. Release of minerals from organic remains. The phenomenon is called mineralisation. The released minerals become available to plants for utilization in synthesis of new organic matter. Decomposers, therefore, take part in biogeochemical recycling.

Question 8.
Select the mismatched pair in the following and correct it.
(a) Biomagnification: Accumulation of chemicals at the successive trophic levels of a food chain.
(b) Ecosystem: Biotic component of environment.
(c) Aquarium: A man-made ecosystem.
(d) Parasites: Organisms which obtain food from other living organisms.
Answer:
(b) Ecosystem: It is an ecological system consisting of a distinct biotic community and the physical environment (consisting of a number of abiotic factors) both interacting and exchanging materials between them.

Question 9.
We do not clean ponds or lakes but an aquarium needs to be cleaned. Why ?
Answer:
An aquarium is an artificial system which is also incomplete due to absence of producers, food chains and decomposers. There is no recycling and self cleaning. However, a pond or a lake is a self sustained, natural and complete ecosystem where there is perfect recycling of nutrients.

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Long Answer Questions

Question 10.
Indicate the flow of energy in an ecosystem. Why is it undirectional ? Justify. (CCE 2014)
Answer:
An ecosystem does not have its own source of energy. It receives the same from sun. Green plants or producers trap the solar energy and change it into chemical form during synthesis of food. Herbivores obtain energy from the food they take. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes to primary carnivores. However, only about 10% of herbivore energy is passed into body mass of primary carnivores.
The rest is dissipated. From primary carnivores the energy passes into secondary carnivores (10%), etc. It is ultimately lost as heat.
NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment image - 2
Since energy available decreases at every tophic level, very little of it is available at higher trophic levels. There is dissipation of energy at every step of its transfer and transformation. Hence it cannot flow in the reverse direction i.e., energy flow is unidirectional from sun to plants, plants to animals, animals to animals, organic remains to decomposers and dissipation as heat.

Question 11.
What are decomposers ? What will be the consequences of their absence in an ecosystem ?
Answer:
Definition: Decomposers or microconsumers are saprophytes which obtain their nourishment from organic remains by secreting digestive enzymes over the latter and absorbing the solubilised substances.
Absence of Decomposers:

  1. Organic remains will pile up leaving no space for new living beings,
  2. Biogeochemical cycling will stop so that raw materials will not be available to plants for manufacture of more food,
  3. In the absence of food, all living beings will die of starvation.

Question 12.
Suggest any four activities in daily life which are ecofriendly.
Answer:

  1. Use of cloth bags instead of polythene or plastic bags.
  2. Separation of biodegradable and non-biodegradable in green and blue coloured bins.
  3. Use of compact fluorescent lamps instead of incandescent lamps.
  4. Harvesting of rain water and preventing wastage of resources.

Question 13.
Give two differences between food chain and food web.
Answer:

Food Chain Food Web
1. Units. It consists of a single unit of food relations. It is a complex formed by several units of food relations.
2. Sequence. It is a straight sequence of organisms. It is a network of many linkages among the connected food chains.
3. Populations. It has a maximum of 4-6 populations of different species. A food web consists of numerous populations of different species.
4. Food. Only one type of organism is used as food by a particular type of organism. An organism can use two to several types of organisms as food.
5. Disturbance. A disturbance in food chain is difficult to overcome. A disturbance is overcome after some time.
6. Endangered Species. It does not help in restoring population of endangered species. Rather it may decline further. A food web helps in increasing population of endangered species.

Question 14.
Name the wastes which are generated in your house daily. What measures would you take for their disposal ?
Answer:
Wastes :

  1. Vegetable and fruit peels and rind, stale food, food leftovers, used tea leaves.
  2. Milk pouches, polythene bags, empty cartons.
  3. Waste paper (newspaper, bags, envelopes), packing paper, empty bottles, torn cloth pieces, etc.
  4. Dust and other sweepings.

Disposal :

  1. Separation into biodegradable and non-biodegradable, recyclable and non-recyclable wastes.
  2. Recyclable wastes (waste paper, cloth, polythene or plastic bags, cartons, bottles, cans, etc.) can be given to rag pickers for recycling.
  3. Preparation of compost or vetmicompost from kitchen wastes for home garden (kitchen garden).
  4. In the absence of kitchen garden, the household garbage and other wastes can be given to waste collectors for disposal.

Question 15.
Suggest suitable mechanisms for waste management in fertilizer industries.
Answer:
Fertilizer industries produce mainly two types of wastes (a) Gaseous (b) Effluents. Additionally they may release heat and fuel waste if coal is being used as a source of energy.

  1. Gaseous Wastes: They are passed through wet scrubbers to dissolve the pollutant gases.
  2. Effluents: The effluents of the industry are tested for chemicals present in them. The same can be retrieved and made available to the market. Hot effluents are cooled. Acidic or alkaline nature can be corrected. Heavy metals and toxins can be separated. Only treated and harmless effluents are allowed to be discharged into surrounding environment.

Question 16.
What are the by products of fertilizer industries ? How do they affect the environment.
Answer:
The most common by product of fertilizer industries are axides of nitrogen and sulphur. They pass into atmosphere and spread to all nearby places. The gases have a corrosive effect on several items besides being harmful to living beings. They also give rise to acid rain. Acid rain is highly destructive to forests, crops and aquatic biota.

Question 17.
Explain some harmful effects of agricultural practices on the environment.
Answer:

  1. Soil: Fertilizer added to soil not only changes the chemistry of the soil but also kills many useful microbes.
  2. Ground Water: A part of fertilizer always leaches down into soil and reaches ground water. It raises the salt content of ground water.
  3. Eutrophication: Run-off from fields sprayed with fertilizer reaches water bodies. It results in their eutrophication.
  4. Pesticides: Pesticides sprayed over crops reach water bodies killing the biota. Persistent pesticides undergo biomagnification and prove highly harmful to higher organisms.
  5. Ground Water: Continued use of ground water in agriculture has resulted in lowering of water table at most of the places.
  6. Irrigation: It causes water-logging and salination of soils.
  7. Genetic Erosion: Use of only selected high yielding varieties has resulted in genetic erosion of the crop plants.
  8. Damage to Nature: Natural ecosystems and habitats have been damaged during clearing land for agriculture.

Value Based Questions in Science for Class 10 Chapter 15 Our Environment

Question 1.
Why have the railway vendors been switching over from re-usable glasses to plastic cups, then clay cups and now paper cups while we stress greater role for renewable articles.
Answer:
There is no denying the fact that reusable articles are ecofriendly. However, they are also liable to get contaminated, especially when railway vendors do not have time and resources to sterilise them. Therefore, railways switched over to disposable articles. Reusable glasses were replaced with disposable plastic cups. However, plastic cups are not biodegradable. Their disposal posed a big problem. They could not be burnt as burning produced toxic gases. The dumping place became sites of breeding flies, mosquitoes and others. The practice was, therefore, discontinued and replaced by clay cups or kulhads. However, making lakhs of kulhads daily removed top fertile soil from several hundred acres of land. The clay cups also required dumping places. Ultimately, disposable paper cups have come to stay with the vendors. The waste cups are recyclable as well as can be burnt without causing problem of dumping.

Question 2.
Hospital waste is not allowed to be mixed with municipal trash and garbage. Neither it is dumped separately. How is it disposed off and why ?
Answer:
Hospital waste is highly contaminated and can be a source of several diseases wherever it is dumped or disposed off. It also contains infected, cancerous and other waste tissues that can be source of several diseases. Therefore, hospital wastes are collected in separate bags and taken to incinerators for disposal. In incinerators the articles are burnt at 850°C under aerobic conditions. Smoke and grit are precipitated to avoid air pollution. Only ash and unburnt metallic materials are left. They are disposed off in land fills.

Question 3.
Most Australians develop skin problems as they grow old. Why ?
Answer:
Australia lies near Antarctica in the zone where ozone hole appears every year. More high energy ultraviolet rays (UV – B) reach the earth in the area of ozone hole. UV radiations cause skin cancers, mutations and cataracts besides reducing immunity. Therefore, most Australians come to have skin problems as they grow old.

Question 4.
Mahi’s father is a manufacturer who purchases raw materials from only one firm and sells the finished product to another single firm. While studying the difference between food chain and food web Mahi noted that his father is following a faulty practice which must be stopped. He also tried to convince his father about it.
What is the fault in the business of Mahi’s father and how has Mahi got this idea ?
Answer:
In a food chain, members of one trophic level are eaten by members of higher trophic level. A disease or scarcity due to drought that kills members of one trophic level, affects the population of both lower trophic level (very high number, glut) as well as higher trophic level (starvation and death). By anology, Mahi found that any problem in the supplier firm or purchaser firm will ruin his father’s business. Therefore, like a food web, there should be a few alternative sources of raw material supply as well as sale of finished products.
You plan to organise a compaign on “Harmful effects of smoking on human health” in your neighbourhood areas and guide them.

Question 5.
(a) List any three reasons that you will give to convince the people about harmful effects of smoking on human health.
(b) List any three values that are indicated with such approach. (CCE 2014)
Answer:
(a)

  1. Smoking causes cancer of oral cavity and lungs, bronchitis, emphysema, gastric ulcers and heart disease.
  2. Tobacco smoke is equally harmful to nonsmokers who live along with the smoker. They develop respiratory problems and CO toxicity.
  3. Smoking is a wasteful, rather harmful drain on the resources of the family.
  4. Smoke is irritant to nonsmokers.

(b) Values:

  1. To protect the residents from the harmful effect of smoking .
  2. It will educate your classmates and others in the compaign not to indulge in smoking despite peer pressure.
  3. Participants in the compaign will be able to spread the message to their families and acquaintances. Ecoclub of your school is organising a debate on the topic “Nature’s fury unleashed by human greed (Uttarakhand disaster) “.

Question 6.
(a) List three arguments that you will use to convince the audience that humans are responsible for this disaster.
(b) List three values that will be inculcated with this debate. (CCE 2014)
Answer:
(a) Nature’s Fury: Humans are responsible for excessive landslides and floods in the hilly areas due to following reasons :

  1. Building dams to store water and generate electricity. However, the geology of hills is usually unstable.
    Seepage from dams make the hills prone to excessive landslides and earthquakes.
  2. Hills attract a large number of tourists. Roads are build up and a great deal of construction activity is carried out along the roads to accomodate tourists.
  3. Trees are cut off for construction activity and roads. Debris of construction sites is often thrown into gorges and channels near the roads and buildings.
  4. A lot of garbage and other wastes are generated by tourists and the locals. However, there is no system for their proper disposal.

(b) Values:

  1. It is important to know the features of our environment and surroundings.
  2. No human activity should disturb the balance of nature.
  3. Trees are life line against disturbances in nature. They should not be felled unless protective measures have been taken.
  4. There should be proper and scientific method for disposal of wastes.
    You have been asked to talk on “Ozone layer and its protection” in the school assembly on ‘Envrionment Day’.

Question 7.
(a) Why should ozone layer be protected to save the environment ?
(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 envronment. (CBSE Delhi 2017)
Answer:
Ozone layer is present in the stratosphere roughtly 23-25 km above the equator and 10-16 km above the poles. It protects the earth by filtering out the harmful UV radiations,. However, due to release of ozone depleting substances (ODS), ozone layer has thinned out by 8% over the equator. A big hole appears every year in August-September over Antarctica. This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing increased number of skin cancers, cataracts and reduced immunity in human beings. There is also increased incidence of blinding of animals, death of young ones, reduced photosynthesis, higher number of mutations and damage to articles.
The remedy lies in banning the use of ozone depleting substances like halons and chlorofluorocarbons (CFCs).
All the classmates and the public in general should be made aware of the consequences of depletion of ozone layer, causes of depletion as well other aspects of degradation of environment. This could be done by

  1. Arranging poster making competition as well as exhibition highlighting the effects of ozone layer depletion,
  2. Conducting street plays about the harmful effects of our tampering with envronment and how to remedy the situation.

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Short Answer Questions

Question 1.
Why is improper disposal of wastes a curse to environment ?
Answer:
An improper disposal of wastes means addition of pollutants into environment —air, water, soil. They will harm living beings, human assets and human beings. For example, passage of sewage into water body will cause eutrophication, stink, development of sludge, killing of animals and source of water borne pathogens.

Question 2.
Write the common food chain of a pond ecosystem.
Answer:
NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment image - 1
Question 3.
What are the advantages of cloth bags over plastic bags during shopping ?
Answer:
Advantages of Cloth Bags

  1. Cloth bags are stronger and more durable as compared to plastic bags.
  2. They are washable.
  3. They are reused time and again.
  4. Cloth bags do not pollute environment.
  5. They are made of biodegradable material which can also be recycled.

Question 4.
Why are crop fields known as artificial ecosystems ?
Answer:
Crop fields are known as artificial ecosystems because they are raised, maintained, nourished and reaped by human beings.

Question 5.
Differentiate between biodegradable and non-biodegradable substances. Give examples.
Answer:

Biodegradable Wastes Non-biodegradable Wastes
1. Origin. They are biological in origin. They are commonly man-made.
2. Degradability. The wastes are degraded by microorganisms. They are not degraded by microorganisms.
3. Accumulation. They do not accumulate in nature. They pile up and accumulate in nature.
4. Biomagnification. The biodegradable wastes do not show biomagnification. The soluble non-degradable wastes enter food chains and undergo biomagnification.
5. Resource. The wastes can be converted into resource. Some wastes can be recycled.
Examples. Garbage, livestock wastes, sewage. Examples. Plastic, polythene, glass, nickel, cadmium, several pesticides.

Question 6.
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) Biosphere (also environment)
(b) Trophic level.
(c) Abiotic factors.
(d) Consumers (also heterotrophs)

Question 7.
Explain the role of decomposers in the environment. (CCE 2011)
Answer:
Decomposers are saprophytes which feed on organic remains by a process of external digestion and absorption of solubilised materials, e.g., many bacteria, fungi. In the process they perform the following functions :

  1. Cleansing the earth of organic remains and continuously creating space for newer generations of organisms.
  2. Release of minerals from organic remains. The phenomenon is called mineralisation. The released minerals become available to plants for utilization in synthesis of new organic matter. Decomposers, therefore, take part in biogeochemical recycling.

Question 8.
Select the mismatched pair in the following and correct it.
(a) Biomagnification: Accumulation of chemicals at the successive trophic levels of a food chain.
(b) Ecosystem: Biotic component of environment.
(c) Aquarium: A man-made ecosystem.
(d) Parasites: Organisms which obtain food from other living organisms.
Answer:
(b) Ecosystem: It is an ecological system consisting of a distinct biotic community and the physical environment (consisting of a number of abiotic factors) both interacting and exchanging materials between them.

Question 9.
We do not clean ponds or lakes but an aquarium needs to be cleaned. Why ?
Answer:
An aquarium is an artificial system which is also incomplete due to absence of producers, food chains and decomposers. There is no recycling and self cleaning. However, a pond or a lake is a self sustained, natural and complete ecosystem where there is perfect recycling of nutrients.

NCERT Exemplar Solutions for Class 10 Science Chapter 15 Long Answer Questions

Question 10.
Indicate the flow of energy in an ecosystem. Why is it undirectional ? Justify. (CCE 2014)
Answer:
An ecosystem does not have its own source of energy. It receives the same from sun. Green plants or producers trap the solar energy and change it into chemical form during synthesis of food. Herbivores obtain energy from the food they take. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes to primary carnivores. However, only about 10% of herbivore energy is passed into body mass of primary carnivores.
The rest is dissipated. From primary carnivores the energy passes into secondary carnivores (10%), etc. It is ultimately lost as heat.
NCERT Exemplar Solutions for Class 10 Science Chapter 15 Our Environment image - 2
Since energy available decreases at every tophic level, very little of it is available at higher trophic levels. There is dissipation of energy at every step of its transfer and transformation. Hence it cannot flow in the reverse direction i.e., energy flow is unidirectional from sun to plants, plants to animals, animals to animals, organic remains to decomposers and dissipation as heat.

Question 11.
What are decomposers ? What will be the consequences of their absence in an ecosystem ?
Answer:
Definition: Decomposers or microconsumers are saprophytes which obtain their nourishment from organic remains by secreting digestive enzymes over the latter and absorbing the solubilised substances.
Absence of Decomposers:

  1. Organic remains will pile up leaving no space for new living beings,
  2. Biogeochemical cycling will stop so that raw materials will not be available to plants for manufacture of more food,
  3. In the absence of food, all living beings will die of starvation.

Question 12.
Suggest any four activities in daily life which are ecofriendly.
Answer:

  1. Use of cloth bags instead of polythene or plastic bags.
  2. Separation of biodegradable and non-biodegradable in green and blue coloured bins.
  3. Use of compact fluorescent lamps instead of incandescent lamps.
  4. Harvesting of rain water and preventing wastage of resources.

Question 13.
Give two differences between food chain and food web.
Answer:

Food Chain Food Web
1. Units. It consists of a single unit of food relations. It is a complex formed by several units of food relations.
2. Sequence. It is a straight sequence of organisms. It is a network of many linkages among the connected food chains.
3. Populations. It has a maximum of 4-6 populations of different species. A food web consists of numerous populations of different species.
4. Food. Only one type of organism is used as food by a particular type of organism. An organism can use two to several types of organisms as food.
5. Disturbance. A disturbance in food chain is difficult to overcome. A disturbance is overcome after some time.
6. Endangered Species. It does not help in restoring population of endangered species. Rather it may decline further. A food web helps in increasing population of endangered species.

Question 14.
Name the wastes which are generated in your house daily. What measures would you take for their disposal ?
Answer:
Wastes :

  1. Vegetable and fruit peels and rind, stale food, food leftovers, used tea leaves.
  2. Milk pouches, polythene bags, empty cartons.
  3. Waste paper (newspaper, bags, envelopes), packing paper, empty bottles, torn cloth pieces, etc.
  4. Dust and other sweepings.

Disposal :

  1. Separation into biodegradable and non-biodegradable, recyclable and non-recyclable wastes.
  2. Recyclable wastes (waste paper, cloth, polythene or plastic bags, cartons, bottles, cans, etc.) can be given to rag pickers for recycling.
  3. Preparation of compost or vetmicompost from kitchen wastes for home garden (kitchen garden).
  4. In the absence of kitchen garden, the household garbage and other wastes can be given to waste collectors for disposal.

Question 15.
Suggest suitable mechanisms for waste management in fertilizer industries.
Answer:
Fertilizer industries produce mainly two types of wastes (a) Gaseous (b) Effluents. Additionally they may release heat and fuel waste if coal is being used as a source of energy.

  1. Gaseous Wastes: They are passed through wet scrubbers to dissolve the pollutant gases.
  2. Effluents: The effluents of the industry are tested for chemicals present in them. The same can be retrieved and made available to the market. Hot effluents are cooled. Acidic or alkaline nature can be corrected. Heavy metals and toxins can be separated. Only treated and harmless effluents are allowed to be discharged into surrounding environment.

Question 16.
What are the by products of fertilizer industries ? How do they affect the environment.
Answer:
The most common by product of fertilizer industries are axides of nitrogen and sulphur. They pass into atmosphere and spread to all nearby places. The gases have a corrosive effect on several items besides being harmful to living beings. They also give rise to acid rain. Acid rain is highly destructive to forests, crops and aquatic biota.

Question 17.
Explain some harmful effects of agricultural practices on the environment.
Answer:

  1. Soil: Fertilizer added to soil not only changes the chemistry of the soil but also kills many useful microbes.
  2. Ground Water: A part of fertilizer always leaches down into soil and reaches ground water. It raises the salt content of ground water.
  3. Eutrophication: Run-off from fields sprayed with fertilizer reaches water bodies. It results in their eutrophication.
  4. Pesticides: Pesticides sprayed over crops reach water bodies killing the biota. Persistent pesticides undergo biomagnification and prove highly harmful to higher organisms.
  5. Ground Water: Continued use of ground water in agriculture has resulted in lowering of water table at most of the places.
  6. Irrigation: It causes water-logging and salination of soils.
  7. Genetic Erosion: Use of only selected high yielding varieties has resulted in genetic erosion of the crop plants.
  8. Damage to Nature: Natural ecosystems and habitats have been damaged during clearing land for agriculture.

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