MP Board Class 8th Science Solutions Chapter 18 Pollution of Air and Water
MP Board Class 8th Science Pollution of Air and Water NCERT Textbook Exercises
What are the different ways in which water gets contaminated?
Different ways of water contamination:
- Discharge or dumping of domestic wastes and sewage into water bodies.
- Surface runoff by water after rains.
- Faulty drainage system.
- Discharge from chemical factories directly into the river.
- Discharge from laboratories and hospitals into the river.
- Disposal of dead bodies of animals and human beings into the rivers.
At an individual level, how can you help to reduce air pollution?
Air pollution can be reduced by
- planting more and more trees.
- using smokeless stoves and LPG.
- using smokeless fuel like CNG in vehicles.
- avoiding the use of fossil fuels like coal and petroleum.
- saying ‘No’ to plastic bags.
- avoiding smoking.
- not burning dry leaves etc., but putting them in compost pits to make manure.
Clear, transparent water is always fit for drinking. Comment.
Clear, transparent water is not always fit for drinking. It may have harmful micro-organisms and dissolved impurities in it. such water may cause water borne diseases like cholera, typhoid and jaundice.
You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Measures to supply clean water are given below:
- The water is first filtered.
- Water is then purified by chlorination. It is done by adding chlorine tablets to the water as per specification. Bleaching powder may also be used to kill the germs if any, present in water.
- This water after proper cleaning is supplied to the residents through pipelines.
- There should be no leakage in the pipes through which water runs.
Explain the differences between pure air and polluted air.
- Pure air has about 78% nitrogen, 21% oxygen and 0.03% carbon dioxide. It does not contain dust particles and smoke in it.
- Polluted air has pollutants like dust and carbon particles, smoke and harmful gases like sulphur dioxide, nitrogen dioxide, excess carbon dioxide and carbon monoxide in it.
Explain circumstances leading to acid rain. How does acid rain affect us?
When fossil fuels like coal and petroleum are burnt, they produce air- polluting gases like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. When these acids drop down with rain water, the rain water becomes acidic. Thus, acid rain is caused mainly due to mixing of sulphuric acid in rain water.
Harmful effects of Acid Rain:
- Acid rain results in the corrosion of the marble of the buildings, monuments and statues made of marble, slate or limestone.
- It increases the corrosion of metals.
- It is harmful to aquatic life.
- It damages the leaves of plants and trees.
- It affects adversely the vegetation and reduces reproduction.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
Describe the ‘Green House Effect’ in your own words.
In a green house, the heat of sun is allowed to get in but is not allowed to get out of it. The trapped heat of the sun warms the green house. The trapping of radiations of the sun by carbon dioxide layer to keep the earth’s atmosphere warm is known as green house effect. Besides, carbon dioxide, the other green house gases are methane, nitrous oxide, Water vapour and CFCs. In the absence of green house effect, the life would not have existed on earth due to low temperatures. But now it threatens life. Carbon dioxide is one of the gases responsible for this effect.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Today, global warming has appeared as one of the most severe threat to the human kind. On one hand, carbon dioxide is added in the atmosphere due to human activities, on the other, as forest areas are also decreasing day by day, it leads to an increase in the amount of C02 in the atmosphere. This accumulation of C02 forms a thick blanket in the atmosphere. This blanket traps heat and does not allow it to escape into the space. As a result average temperature of the earth’s atmosphere is gradually increasing.
This is termed as global warming. Global warming can create the melting of icebergs, resulting in rise in the sea level causing the flooding of many coastal areas. Global warming can also bring about climatic changes. It could also result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. So, we must be aware of this problem and take every possible step to tackle it. Global warming has become a major concern for governments worldwide. Many countries have reached an agreement to reduce the emission of greenhouse gases.
Describe the threat to the beauty of the Taj Mahal.
Over the past 2 decades, India’s most famous tourist attraction, the Taj Mahal located in Agra, has become a matter of concern. Experts have warned that pollutants in air are discolouring its white marble. So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected.
The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain corrodes the marbles of the monument. The phenomenon is also called “Marble cancer’. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble.
The Supreme Court has taken several steps to save the Taj. It has ordered the industries to switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquified Petroleum Gas). Moreover, the automobiles should switch over to unleaded petrol in the Taj zone.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Agriculture relies on the use of chemical fertilizers to improve the crop yields. All these chemicals dissolve in water and run into water bodies from the fields. These seep into the ground and pollute the ground water. Lot of algae in the ponds grow and keep the ponds green. This is caused due to excessive quantities of chemicals like nitrates and phosphates which are present in fertilizers. These act as nutrients for algae to flourish. When these algae die, they serve as food for decomposers like bacteria. They use up a lot of oxygen. This results in a decrease in the oxygen level which is harmful for the survival ‘of other organisms. class can divide itself into two groups, with each group looking at a different area. For example, one group can find out whether there is an environment club in the school. What are its objectives? What is its calendar of events? How can you become a member? If your school does not have such a club, you even think of starting one along with a few of your friends.
MP Board Class 8th Science Pollution of Air and Water NCERT Extended Learning – Activities and Projects
In some cities, a pollution check has been made compulsory for vehicles. Visit a petrol pump in order to learn about the process of conducting a pollution check. You may systematically record your findings in the following areas:
Average number of vehicles checked per month.
Time taken to check each vehicle. Pollutants checked for.
The process of testing.
Permissible levels of emission of various gases.
Measures taken if the emitted gases are above the permissible limits.
How frequently is a pollution check required?
Conduct a survey in your school to investigate various environment related activities that have been undertaken. The class can divide itself into two groups, with each group looking at a different area. For example, one group can find out whether there is an environment club in the school. What are its objectives? What is its calendar of events? How can you become a member? If your school does not have such a club, you even think of starting one along with a few of your friends.
Organise a field visit to a river in or around your town with the help of your teachers. Observations followed by discussion could focus on:
The history of the river.
Role of the river in meeting the town water needs.
Sources of pollution.
Effects of pollution on the people living by the riverside as well as those living far away.
Find out with the help of your teachers and the internet (if possible) whether there are any international agreements to control global warming. Which are the gases covered under these agreements?
MP Board Class 8th Science Pollution of Air and Water NCERT Intext Activities and Projects
You may have covered your nose while passing a brick kiln emitting smoke or started coughing while walking on a busy road (Fig 18.1). On the basis of your experience, compare the quality of air at the places given below:
A park and a busy road.
A residential area and an industrial area. A busy traffic intersection at different times of the day e.g. early morning, afternoon and evening.
A park is full of fresh air, whereas a busy road is very polluted because of fumes, smokes, dust and sound. A residential area is also polluted but compared to an industrial area, it is almost negligibly polluted. Industrial area is extremely polluted with chemical pollutants, toxic gases, etc. In the early morning, the traffic intersection is free from any pollutants, but in the afternoon it becomes very polluted due to smokes left out by vehicles, etc. In the evening, the place is extremely polluted. A village is usually not polluted whereas a town has polluted air, polluted water and lot of other pollutions like sound pollution etc.
Prepare a table using the pollutants mentioned above. You may even add more data to the following table.
You have various options of commuting to your school such as walking, going by bicycle, travelling by bus or other public transport, using a car individually, travelling by car pool. Discuss in your class the impact of each of these options on the quality of air.
Going on foot or by bicycle will not cause any type of pollution. Travelling by bus, other public transport system or by car pool will cause pollution upto an extent, while using a car individually will cause more pollution.
Try to collect samples of water from a tap, pond, river, well and lake. Pour each into separate glass containers. Compare these for smell, acidity and colour. Complete the following table.
MP Board Class 8th Science Pollution of Air and Water NCERT Additional Important Questions
A. Short Answer Type Questions
What are the different sources responsible for the depletion of atmospheric oxygen?
The sources are:
- Burning of fuel which consume oxygen gas.
- Excessive use of various pesticides like DDT.
What was the aim of the Ganga Action Plan?
Its aim was to reduce the pollution level in the Ganga river.
How would the disposal of garbage, etc., affect the living organisms in the river?
Disposal of garbage into the rivers pollute the river water. When garbage rots, it produces poisonous and toxic gases so that living organisms cannot breathe and die ultimately.
What will happen if we drink polluted water?
If we drink polluted water, we may suffer from the water borne diseases such as jaundice, dysentery, hepatitis, cholera, etc.
How can water be made fit for drinking?
- Drinking water can be boiled before drinking. It kills the harmful bacteria present in it.
- It can also be. purified by adding potassium permanganate (Lai Dawai) or bleaching powder.
- In cities alum and chlorine gas is added to purify water.
B. Long Answer Type Questions
What is atmosphere?
The atmosphere is the protective blanket of gases surrounding the earth. It is a mixture of gases. The composition is very important for the survival of living things on the earth. The atmosphere contains N2, O2, CO2, noble gases, water vapour and dust particles. The composition of atmosphere depends upon place, season and altitude, etc.
What are the major pollutants of air? Name these.
The major air pollutants are:
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
- Suspended Particulate Matter (SPM)
- Chlorofluorocarbons (CFCs)
How is acid rain harmful to us?
Acid fain is harmful in a number of ways:
- Acid rain removes important calcium and Magnesium nationals from the soil and upsets the balance of nutrients in the soil. This ‘Sheets crops’.
- Aquatic life is affected by acid rain. There are many aquatic organisms that cannot survive due “to increased acidity of water.
- Acid rain damages buildings by corroding building materials like cement, marble and steel.
What is global warming? How is it caused?
Increasing temperature of the earth is called global warming. The radiation of the sun, reaching the earth is not being consumed. This is due to the deforestation. The level of CO2 has increased and thus global warming has also increased. CO2 is absorbed by the plants for photosynthesis. So reduced number of plants increases the amount of carbon dioxide in the environment. This cuases accumulation of carbondioxide and increases temperature.