Lakhmir Singh & Manjit Kaur: Pollution of Air and Water - 1 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.1. Name the gas present in atmosphere which is mainly responsible for causing global warming.

Carbon dioxide is the gas which is mainly responsible for causing global warming. Carbon dioxide traps heat and does not allow it to escape into space causing an increase in the average temperature of the earth’s atmosphere.

Q.2. Name two gases present in polluted air which can cause acid rain.

Sulphur dioxide and Nitrogen dioxide are the gases present in polluted air which causes acid rain.

Q.3. Name all the major pollutants of air.

The gases like carbon dioxide, carbon monoxide, Sulphur dioxide, nitrogen dioxide and chlorofluorocarbons are the major pollutants of air.

Q.4. Which air pollutant combines with the haemoglobin of our blood?

Carbon monoxide combines with the haemoglobin of our blood. It reduces the oxygen carrying capacity of blood.

Q.5. Name the various air pollutants discharged by motor vehicle exhausts.

The various air pollutants discharged by motor vehicle exhausts are carbon dioxide, carbon monoxide, nitrogen oxides and smoke.

Q..6. Which gas in the upper atmosphere prevents ultraviolet radiations of the sun from reaching the earth?

Ozone layer in the upper atmosphere prevents ultraviolet radiations of the sun from reaching the earth.

Q.7. Name any two diseases caused by drinking polluted water containing sewage.

Drinking of polluted water containing sewage causes diseases like cholera, typhoid and jaundice.

Q.8. Name any four toxic metals whose compounds are present in industrial wastes.

Arsenic, lead, mercury and fluorides are the toxic metals whose compounds are present in industrial wastes.

Q.9. Name any two types of chemicals used in agriculture which cause water pollution.

Pesticides and weedicides are the chemicals used in agriculture which cause water pollution.

Q.10. The use of excessive fertilizers in the fields lead to the deficiency of an important substance in the water of a nearby lake. Name the substance.

The use of excessive fertilizers in the fields lead to the deficiency of Oxygen in the water of a nearby lake. This may kill the aquatic organisms.

Q.11. What is Ganga Action Plan? When and why was it launched?

The plan to save the river Ganga was launched in 1985 is called the Ganga Action Plan. It was aimed to reduce the pollution levels in the river. Recent study by WWF – World wide fund for nature have found that Ganga is one of the most endangered rivers in the world. Large quantities of garbage, untreated sewage, dead bodies and many other harmful things are thrown directly into the river. The river is almost dead at many places where the pollution level is very high and the aquatic life cannot survive.

Q.12. Name any four pollutants which cause water pollution. State any three ways of controlling water pollution.

The harmful substances like sewage, toxic materials, silt etc., when gets mixed with water, causes water pollution. The pollutants which cause water pollution are:
Chemical waste from industries, sewage, silt, agricultural chemicals and garbage thrown into water.

Water pollution can be controlled in the following ways:

• Water should go through the sewage treatment plants before discharging into the water bodies.
• Use of pesticides and weedicides should be limited in order to prevent pollution.
• Industrial waste should be treated for harmful chemicals before discharging into the water bodies. Water treatment plants should be installed in all the industrial areas.
• We should save water consciously and should prevent the wastage of water. We must reuse, recycle and reduce the usage of water. We must try to reuse water. For example, water used for washing vegetables can be used to water plants in the garden.

Q.13. How do industries cause water pollution?

Industries cause water pollution in the following ways:

• Industries such as oil refineries, paper factories, textile and sugar mills and chemical factories discharge harmful chemicals into rivers and streams. These chemicals include arsenic, lead and flourides which are very toxic to plants and animals
• The soil is also affected by impure water which causes changes in acidity of soil and affects the growth of worms and plants etc.
• Some industries and power plants releases hot water into the rivers. Hot water can also be considered as a pollutant. It raises the temperature of the water body and adversely affects the plants and animals living in it.

Q.14. How can you help reduce air pollution at the individual level?

Pollution is not a distant phenomenon anymore. It is affecting the quality of our day to day lives. We must realize our responsibility and should start using the following environment- friendly processes:

• We should switch to cleaner fuels like CNG- Compressed natural gas and LPG- Liquified petroleum gas for both industries and automobiles.
• Automobiles should also use unleaded petrol.
• We should plant more trees which will help to control deforestation.
• Industrial waste should be treated for harmful chemicals before discharging into air the water bodies.
• We must switch to alternative fuels instead of fossil fuels. Alternative sources of energy can be solar energy, hydropower and wind energy.
• We must encourage the use a public transport, a bicycle or walking for short distances. This will help to reduce the use of fossil fuels.
• Burning of plant waste also causes pollution by the emission of smoke. Plant waste must be put in a compost rather than burning.

Q.15. Explain the difference between pure air and polluted air.

Pure air is a mixture of several gases that are invisible and odorless. It consists about 78% nitrogen, 21% is oxygen and less than 1% of Carbon dioxide and other gases like argon, methane and ozone and varying amount of water vapors. Polluted air on the other hand, is contaminated with the substances like smoke, dust and other harmful substances called pollutants. These pollutants can come from natural sources like smoke and dust arising from forest fires or volcanic eruptions. Pollutants can also be added from human activities. The sources of air pollution are automobile exhausts, power plants, factories and burning of firewood and dung cakes.

Q.16. What is ‘greenhouse effect’? State its importance for us.

The sun’s rays warms the surface of earth. A part of the radiation which falls on the earth is reflected back into the space and only a part of it is absorbed. This trapped radiation further warms the earth. The trapping of radiation by the earth’s atmosphere is known as Greenhouse effect. Life would not have been possible without this process. Carbon dioxide is one of the gases responsible for this effect. Some other gases like methane, nitrous oxide and water vapors also contribute towards this process.

Q.17. Name two greenhouse gases? Which one of them produces the maximum greenhouse effect?

The trapping of radiation by the earth’s atmosphere is known as Greenhouse effect. Life would not have been possible without this process. Carbon dioxide and methane are greenhouse gases. Carbon dioxide produces the maximum greenhouse effect.

Q.18. What depletes the ozone layer in the atmosphere? What are the harmful effects of the depletion of ozone layer on us?

Chlorofluorocarbons used in refrigerators, air conditioners and aerosol sprays are responsible to deplete the ozone layer in the atmosphere. Ozone layer protects us from harmful ultraviolet rays of the sun. There has been a depletion of ozone layer in the layers of atmosphere which has been caused by the chlorofluorocarbons and other atmospheric pollutants. This results in increase of ultraviolet radiations at ground level which gives rise to an increased risk of skin cancer.

Q.19. Name one source and one harmful effect of each of the following air pollutants:

(a) Sulphur dioxide

(b) Nitrogen oxides

(c) Carbon monoxide

(d) Chlorofluorocarbons (CFCs)

(a) The source of Sulphur dioxide in the air is the fossil fuels combustion in the power plants and other industries. It can also be produced by the motor vehicles emissions.

Sulphur dioxide is a very harmful pollutant when present in the atmosphere. It can cause the respiratory problems, including permanent lung damage.
(b) The source of nitrogen dioxide in the air is produced by the motor vehicles.

Nitrogen dioxide is a very harmful pollutant because it combines with other air pollutants and fog to form smog. The smog is responsible for causing breathing difficulties such as asthma, cough and wheezing in children.
(c) The source of carbon monoxide in the air is by the incomplete burning of fuels such as petrol and diesel.
Carbon monoxide is a very poisonous gas which reduces the oxygen carrying capacity of blood.
(d) The Chlorofluorocarbons are used in the refrigerators, air conditioners and aerosol sprays.

The Chlorofluorocarbons are responsible to deplete the ozone layer in the atmosphere. Ozone layer protects us from harmful ultraviolet rays of the sun. This results in increase of ultraviolet radiations at ground level which gives rise to an increased risk of skin cancer.

Q.20. Explain why, even clear, transparent and odourless water may not always be safe for drinking.

Even the clear, transparent and odourless water may not always be safe for drinking because it may contain pollutants. These pollutants include the chemicals which may be discharged from the Industries such as oil refineries, paper factories, textile and sugar mills and chemical factories. These chemicals include arsenic, lead and flourides which are very toxic to human beings, plants and animals. These pollutants can also be chemicals used in farming such as pesticides and weedicides. All these chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground and pollute ground water.

Q.21.

Explain why, hot water released by power plants and industries is considered a pollutant.

Answer:

Some industries and power plants releases hot water into the rivers. Hot water can also be considered as a pollutant. It raises the temperature of the water body and adversely affects the plants and animals living in it.

Q.22.

Why does the increased level of nutrients (or fertilizers) in the lake water affect the survival of aquatic organisms (like fish)?

Answer:

Some ponds or lakes have a lot of green algae growing in them. This is caused due to the excessive quantity of chemicals which are washed from the fields. These chemicals act as nutrients for these algae to grow. When these algae die, they act as a nutrient for decomposers like bacteria. As a result of this process, a lot of oxygen in the water gets used up causing the decrease of oxygen level. This affects the survival of aquatic plants which can also kill them.

Q.23.

Explain how the use of pesticides in agriculture causes water pollution.

Answer:

The use of pesticides in agriculture is responsible in causing the water pollution. It is also caused due to the excessive use fertilizers in the fields. These fertilizers act as nutrients for the algae to grow. When these algae die, they act as a nutrient for decomposers like bacteria. As a result of this process, a lot of oxygen in the water gets used up and leads to the deficiency of Oxygen in the water. This may kill the aquatic organisms.

Q.24. (a) Describe the threat to the Taj Mahal monument due to air pollution.
(b) State any two ways of controlling air pollution;

(a) Taj Mahal is India’s famous historical monument which is located in Agra. It has become a matter of concern to protect Taj Mahal due to the discoloration of its white marble. This is caused due to air pollution in Agra. The industries which are located in and around Agra such as Mathura Oil refinery, rubber processing, automobile and chemical industries have been responsible for the emission of air pollutants. These pollutants include Sulphur dioxide and nitrogen dioxide which reacts with water vapors in the atmosphere to form sulphuric acid and nitric acid. These acids combine with rain and makes the rain water acidic. Acid rain corrodes the marble of Taj Mahal. The suspended particles emitted by these industries have also contributed towards the yellowing of the marble.

(b) Several steps have been taken by Supreme court to protect Taj Mahal. The industries around Taj Mahal have been ordered to switch into clean fuels such as Compressed natural gas-CNG and Liquified petroleum gas- LPG. It has been advised that the automobiles should be switched over to unleaded petrol.

Q.25. (a) What is potable water? Name any two methods to make water safe for drinking.

(b) State two ways in which you conserve water at home by, preventing its wastage.

(a) The water which is safe for drinking without any risk of health problems is called potable water. Water can be made safe for drinking in the following ways:

• Household filters such as candle type filters can be used at homes to make the water safe for drinking.
• Boiling of water can be done before drinking at home. Boiling kills, the germs present in water and makes water safe for drinking.
• Chlorination can also be done for purifying water at home. It can be done by adding chlorine tablets or bleaching powder into water. Only specific number of chlorine tablets should be used.

(b)

• We should save water consciously and should prevent the wastage of water. We must reuse, recycle and reduce the usage of water.
• We must try to reuse water. For example, water used for washing vegetables can be used to water plants in the garden.
• We must try to save water by regularly checking the pipelines for any leakage or damage. We should always check for any open taps after using water supply.