Science Textbook Solutions for Class 8 Science Chapter 8 - Pollution


Important points to remember :

  1. Contamination  of  natural  environment  that  will  be  harmful  to  ecosystems  is  called as pollution. 
  2. Many problems have been arisen on the earth due to human interference  in the nature. Industrialization,  increasing population, mining, transportation, indiscriminate  use of pesticides and fertilizers are causing pollution on the earth. 
  3. Factors affecting natural functions of ecosystem and causing harmful effects on abiotic and biotic factors are called as pollutants. 
  4. Pollutants make the environment poisonous and unhealthy. Pollutants  may be natural  or manmade. 
  5. Worst ever industrial accident had been occurred in Bhopal on the night of                2nd Dec.1984. 
  6. Eight thousand people had been died due to accidental gas leakage.  acids mix with rain drops and snowflakes and come down as rain, called as acid rain.
  7. Water  is said to  be  polluted  when  it becomes  unclean  and poisonous due  to mixing  of natural  or artificial  unwanted material,  when it becomes  harmful to living organisms due to decreased oxygen content. 
  8. Soil is said to be polluted  when there  are changes in its physical  biological  and chemical properties and its fertility decreases due to either natural or manmade reasons. 


Question 1: Following are some statements about pollution which type of pollution do those express?
A. Fog seems to be appearing in Delhi during day hours.
Answer : Air pollution.

B. Many times, vomiting and dysentery occurs after eating 'pani puri'
Answer : water pollution

C. Problem of sneezing occurs sometimes during visit to garden.
Answer : Air pollution

D. Crop does not grow up in some areas.
Answer : soil pollution.

E. People living in the busy squares face the problems like short breathing and other respiratory problems.
Answer : Air pollution


Question 2: Read the passage and identify the sentences expressing types of pollution.
Nilesh is a student of std. VIII and lives in urban area.  It takes about an hour to go to the school by bus. He faces the heavy traffic of two wheelers, four wheelers, rickshaws, buses while going to school. He is facng the problem of asthma since to stay away from urban area. Since then, his mother sent him to the village of his maternal uncle. Nilesh saw th heaps of garbage of many places in village. Foul smell of human and animal wastes was present at many places. Blackish water with foul smell was flowing in a stream. He devleoped some abdominal disease with in few days.
Answer :
Nilesh is a student of std. VIII and lives in urban area.  It takes about an hour to go to the school by bus. He faces the heavy traffic of two wheelers, four wheelers, rickshaws, buses  (Air pollution) while going to school. He is facing the problem of asthma (Air pollution) since to stay away from urban area. Since then, his mother sent him to the village of his maternal uncle. Nilesh saw the heaps of garbage in many places in village. Foul smell of human and animal wastes (Air and soil pollution) was present at many places. Blackish water with foul smell (Water pollution) was flowing in a stream. He devleoped some abdominal disease (Water pollution) with in few days.


Question 3: Match the pairs from  'A' and  'B' columns and explain the effect of pollution on human health.
  Column  'A'                           Column 'B'
1. Water containing cobalt  a. Mental                                                                    retardednes
2. Methane gas                       b. Paralysis
3. Water containing lead    c. Inflammation                                                      of lungs.
4. Sulphur dioxide               d. Skin cancer
5. Nitrogen dixoide              e. Irritation of .                                                        eyes
Answer :
1. Water containing cobalt b. Paralysis

2. Methane gas  - d. Skin cancer

3. Water containing lead - a. Mental retardedness

4. Sulphur dioxide - e. Irritation of eyes

5. Nitrogen dixoide - c. Inflammation of lungs


Question 4: True or false
A. Water does not get polluted by washing the cloths in running water of river. - False

B. More the use of electric appliances, more wil be the pollution. - True


Question 5: Answer the following.
A. What is pollution ?
Answer : Pollution is any undesirable change that takes place in the environment which is harmful to both living and non-living things.

B. What are pollutants 
Answer : Pollutants are the harmful chemicals and substances that cause pollution. For example, nitrogen oxides, sulphur oxides, carbon monoxide, pesticides etc.

C. What is acid rain
Answer : Gases such as sulphur dioxide, sulphur trioxide and nitrogen dioxide, when present in air, combine with the water droplets present in the atmosphere to form acid droplets. These droplets remain suspended in air and fall down on the earth along with rain, thereby making the rain acidic. Such rain is called acid rain.

D. What is green house effect ?
Answer : The increase in the average temperature of the earth’s surface due to the increase in concentration of greenhouse gases such as carbon dioxide, methane, etc. is called greenhouse effect.

E. Which are visible pollution known as you ?
Answer :.Pollutants which are visible to our naked eyes are called visible pollutants. For example, sewage, plant and animal wastes, pesticides, plastic, sand etc.

F. Which are invisible pollutions ?
Answer : Invisible pollutants are pollutants which are not visible to our naked eyes. For example, fungi, viruses, bacteria, gases like carbon monoxide, nitrogen dioxide etc.


Question 6: Answer the following 
A. Give are examples of each of water, soil and air pollution from your residential area.
Answer : The water pollution is due to the discharge of wastewater from the industrial and commercial waste.

Some of the examples of water pollution are septic tanks and pit latrines. The air pollution is due to the release of chemicals & particulates into the atmosphere.

Some of the common pollutants includes of sulfur dioxide, carbon monoxide, nitrogen oxides and chlorofluorocarbons.

Examples of soil pollution are petroleum hydrocarbons in soil and pesticides.

B. How does the pollution occur due to vehicles ?  Give the names of vehicles causing least pollution.
Answer : The petrol and Diesel spread unburn sulpher and nitrous oxide which mixes and be the cause of pollution . it is very harmful to us . the CNG is the best fuel for avoiding from pollution . it has taken the place of petrol and Diesel because it spread more less nitrous and sulpher oxide.

C. What are natural reasons for water pollution.
Answer : Following are the some natural reasons
1. Aquatic weeds· Depletion in O2 level· Changes in natural qualities of water
2. Decomposing matter· Decomposing bodies of plant, animals
3. Mud/sludge ·  River current and its diversion
4. Soil erosion ·  Many biotic and abiotic factors are added to water due to soil erosion.
5. Microbes like fungi and bacteria· grow on organic matter decaying in water.
6. Algae ·  Excessive algal growth pollutes water
7. Nematodes :·  Soil nematodes flow in with rain.

D. Suggest four preventive measures for air pollution.
Answer : Preventive measures of air pollution
1.  Smoke emerging from factories contains harmful particles. Hence, pollution controlling machinery should be used. Ex. Arresters, filters.
2.  Proper  disposal of  stinking  waste generated in cities.
3. Control on atomic  tests, chemical weapons, etc.
4. Control / ban over CFC production.

E. Explain relation between green house effect and global warming.
Answer : The greenhouse effect is a natural process traps heat in the atmosphere - global warming tends to be when additional greenhouse gases are released into the atmosphere and this causes a warming event.
Carbon dioxide (CO2) and other greenhouse gases act like a blanket, absorbing IR radiation and preventing it from escaping into outer space. The net effect is the gradual heating of Earth's atmosphere and surface, a process known as global warming.

F. Construct two slogans each on air, water and soil pollution.
Answer :
1. air - Look around, walk around, breathe clean air and don’t litter the ground.

2. air- Air pollution is not a joke. Air pollution will maje you choke.

3. water- Save water , the world is in your hands.

4. water- Water water everywhere, try to save it if you care.

5. soil- Whatever is affixed to the soil belongs to the soil.

6. soil No food without soil.


Question 7: Classify the following pollutions into natural and manmade categories.
Sewage, dust, pollen grains, chemical fertilizers, vehicular smoke, algae, pesticides, waste of animals and birds.
Answer :
Sewage - Man made
Dust - Natural
Pollen grains - Natural
Chemical fertilizers - Man made
Vehicular smoke - Man made
Algae - Natural
Pesticides - Man made
Waste of animal and plants - Natural


# Can you Tell
1. Where do you see the pollution around you? 
Answer : Everywhere

2. How does the pollution occur?
Answer : Air pollution occurs when things that aren't normally there are added to the air. A common type of air pollution happens when people release particles into the air from burning fuels. ... These can take part in further chemical reactions once they are in the atmosphere, creating acid rain.

3. Why is it said that air is homogenous mixture of different gases? 
Answer : Air is said to be Homogeneous mixture of different gases because it contains different gases like Nitrogen ,oxygen, carbon dioxide, argon, etc. This is said to be homogeneous mixture because the constituent cannot be distinguished unlike heterogeneous mixture.

4. Which  different  hazardous gases are released  through fuel combustion?
Answer : Gases released into the atmosphere by fuel combustion process are: CO2, SO2, H2O, N2, O2, CO, NOx, PAHs (polycyclic aromatic hydrocarbons), VOCs (volatile organic compounds), dioxins, furans.


# Can you Recall
1. What is importance of ozone layer?
Answer : Ozone is a gas in the atmosphere that protects everything living on the Earth from harmful ultraviolet (UV) rays from the Sun. Without the layer of ozone in the atmosphere, it would be very difficult for anything to survive on the surface. (Think of a very bad sunburn, only much worse!) Plants cannot live and grow in heavy ultraviolet radiation, nor can the plankton that serve as food for most of the ocean life. The ozone layer acts as a shield to absorb the UV rays, and keep them from doing damage at the Earth's surface.

2. What are reasons for depletion in ozone layer?
Answer : Causes for Ozone Layer Depletion

  1. Sunspots.
  2. Stratospheric winds.
  3. Volcanic eruptions.
  4. CFCs.
  5. Halons.
  6. Carbon Tetrachloride.
  7. Methyl chloroform.
  8. Methyl bromide.


3. What is meant by soil erosion? 
Answer : Soil erosion is defined as the wearing away of topsoil. Topsoil is the top layer of soil and is the most fertile because it contains the most organic, nutrient-rich materials. One of the main causes of soil erosion is water erosion, which is the loss of topsoil due to water.

4. What are reasons for depletion in soil fertility?
Answer : The basic causes of soil erosion are the result of human activities such as deforestation, overgrazing and poor soil management. Removal of more nutrients by crops than added through manures or fertilizers is called as nutrient mining or depletion.

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