Lakhmir Singh & Manjit Kaur: Pollution of Air and Water - 2 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.26. What is meant by water pollution? What are the different ways in which water gets polluted?

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

Water gets polluted in the following ways:

• Water can be contaminated by human waste or sewage.
• 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.
• Some industries and power plants releases hot water into the rivers. Hot water can also be considered as a pollutant.
• The excessive use of pesticides and fertilizers in agriculture also causes water pollution.

(b) State the harmful effects of water pollution.

Pollution is not a distant phenomenon anymore. It is affecting the quality of our day to day lives. Following are harmful effects of water pollution:

• The chemicals such as arsenic, lead and fluorides discharged by the industries are very toxic to plants and animals.
• The hot water released by certain industries raises the temperature of the water body. It adversely affects the plants and animals living in it.
• The 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 aquatic organisms.
• Water contaminated with sewage may contain bacteria, viruses, fungi and parasites which can cause diseases like cholera, typhoid and jaundice.

Q.27. (a) What is air? Write the names of various constituents of air.
(b) What is air pollution? What are the main sources of air pollution?

(a) 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.

(b) Polluted air is contaminated with the substances like smoke, dust and other harmful substances called pollutants.

These pollutants can come from natural sources or from human activities. Following are the main sources of air pollution:

• The natural sources of air pollution are smoke and dust arising from forest fires or volcanic eruptions.
• The pollutants can also be added from the human activities.
• These are from automobile exhausts, power plants, factories and burning of firewood and dung cakes.
• The pollutants like Sulphur dioxide and Nitrogen dioxide when present in polluted air causes acid rain.
• The gas called carbon monoxide enters the air by the incomplete burning of fuels such as petrol and diesel. It is a very poisonous gas which reduces the oxygen carrying capacity of blood.
• The Chlorofluorocarbons which are used in the refrigerators, air conditioners and aerosol sprays also act as air pollutants. They are responsible to deplete the ozone layer in the atmosphere.

Q.28. What is smog? How is smog formed? What are its harmful effects?

• A thick fog- like layer in the atmosphere which is made up of smoke and is called smog. The smoke released is released into the atmosphere due to various activities like automobile exhausts, power plants, factories and burning of firewood and dung cakes etc., The smoke may contain the oxides of nitrogen which combines with other air pollutants and fog to form smog. The smog is very harmful in the following ways.
• The smog is very harmful and causes breathing difficulties such as asthma, cough and wheezing in children.
• Smog reduces visibility which may result in road accidents.

Q.29. What is acid rain? How is acid rain caused? What are the harmful effects of acid rain?

• The industries such as oil refineries, rubber processing, automobiles 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 rainwater acidic. This is called Acid rain. Following are the harmful effects of acid rain:
• Acid rain is very harmful for fish and other animals. It makes the water acidic and causes them to absorb the aluminum that makes its way from soil into lakes and streams.
• Increased acidity of water due to acid rain adversely affects the growth and reproduction ability of fishes.
• It damages buildings, monuments, and statues.

Q.30. What is global warming? What are the likely harmful effects of global warming?

• 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. Due to increase in the amount of carbon dioxide in the atmosphere, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.
• Global warming has become a major concern for governments worldwide. Many countries have reached an agreement to control the situation by reducing the emission of greenhouse gases. Following are the harmful effects of global warming:
• Global warming can cause sea levels to rise dramatically. It has resulted in flooding of coastal areas in many places.
• It could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals.
• It has caused an increase in the melting of polar icecaps which has resulted in the rise of sea level more quickly over the last century.
• There has to be check on the emission of greenhouse gases at the present level. This may cause the temperature to rise by more than 2 degrees by the end of the century which is very dangerous.

Q.31. Which of the following is not a greenhouse gas?
(a)  carbon dioxide
(b)  nitrous oxide
(c) methane

(d) nitrogen

Correct Answer is option (d)

Carbon dioxide is the gas which is responsible for greenhouse effect. Some other gases like methane, nitrous oxide and water vapors also contribute towards this process.

Q.32. Which of the following air pollutant reduces the oxygen-carrying capacity of blood to a large extent?
(a) carbon dioxide
(b) nitrogen monoxide
(c) carbon monoxide
(d) sulphur dioxide

Correct Answer is option (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.

Q.33. The constituent of polluted air which contributes in producing acid rain is:
(a) nitrogen
(b) sulphur dioxide
(c) oxygen
(d) argon

Correct Answer is option (b)

The source of Sulphur dioxide in the air is the fossil fuels combustion in the power plants, industries and motor vehicles emissions. It is a very harmful pollutant when present in the atmosphere. It can cause the respiratory problems, including permanent lung damage.

Q.34. The Kyoto Protocol is associated with one of the following. This one is:
(a) reduction in the use of chlorofluorocarbons.
(b) reduction in the emission of greenhouse gases
(c) reduction in the cutting of forest trees
(d) reduction in pollution of fresh water sources

Correct Answer is option (b)

Global warming has become a major concern for governments worldwide. Many countries have reached an agreement to control the situation by reducing the emission of greenhouse gases.

Q.35. Which of the following will be reduced in air in a city forest when a lot of dust and fly ash in emitted by a coal-based factory in the vicinity?
(a) nitrogen
(b) carbon dioxide
(c) oxygen
(d) water vapour

Correct Answer is option (c)

The various air pollutants discharged by motor vehicle and by the burning of fossil fuel in a factory are carbon dioxide, carbon monoxide, nitrogen oxides and smoke. It results in the decrease in the amount of oxygen in the air.

Q.36. Which of the following disease cannot be caused by drinking of river water contaminated with untreated sewage?
(a) cholera
(b) typhoid
(c) tuberculosis
(d) diarrhea

Correct Answer is option (c)

The water contaminated with sewage may contain bacteria, viruses, fungi and parasites which cause diseases like cholera, typhoid and diarrhea.

Q.37. Which of the following statement about ozone is correct?
(a) it is essential for breathing
(b) it absorbs ultraviolet rays
(c) its proportion in air is about 3%
(d) it is mainly responsible for global warming

Correct Answer is option (d)

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

Q.38. Drinking water can be made absolutely safe by adding some:
(a) aspirin tablets
(b) iodine tablets
(c) chlorine tablets
(d) chlorophyll tablets

Correct Answer is option (c)

Chlorination can be done by adding chlorine tablets or bleaching powder into water. Only specific number of chlorine tablets should be used.

Q.39. The excessive use of one of the following in agriculture can cause the death of fish in a pond by oxygen starvation. This one is:
(a) fertilizers
(b) manures
(c) pesticides
(d) herbicides

Correct Answer is option (a)

The 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.40. Which of the following is usually not a water pollutant?
(a) sewage
(b) fertilizer
(c) fly ash
(d) pesticide

Correct Answer is option (c)

Fly ash is the air pollutant which is produced by the insufficient burning of fuels which enters into the atmosphere causing air pollution.

Q.41. Which of the following are used in electric water filters to kill all the harmful micro-organisms present in tap water and make it absolutely safe for drinking?
(a) infrared radiation
(b) gamma radiation
(c) visible radiation
(d) ultraviolet radiation

Correct Answer is option (d)

Ultraviolet radiations kill bacteria and viruses and are used in electric water filters to make water safe for drinking.

Q.42. Which of the following is not an air pollutant?
(a) sulphur dioxide
(b) sewage
(c) CFCs
(d) SPM

Correct Answer is option (b)

The harmful substances like sewage, toxic materials, silt etc., when gets mixed with water, causes water pollution. The gases like carbon dioxide, carbon monoxide, Sulphur dioxide, nitrogen dioxide and chlorofluorocarbons are the major pollutants of air.

Q.43. Which of the following air pollutant is capable of preventing photosynthesis in plants?
(a) CFCs
(b) nitrogen oxides
(c) dust
(d) carbon monoxide

Correct Answer is option (c)

Dust reduces the photosynthesis in plants due which causes a decrease in energy production in plants causing the plants to suffer.

Q.44. One of the following does not contribute in producing acid rain. This one is:
(a) nitrogen dioxide
(b) nitrogen monoxide
(c) carbon monoxide
(d) sulphur dioxide

Correct Answer is option (c)

The air pollutants such as 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. This is called Acid rain.

Q.45. Which of the following will reach the earth in greater amounts if the number of chlorofluorocarbons released into the air increases?
(a) infrared rays
(b) X-rays
(c) gamma rays
(d) ultraviolet rays

Correct Answer is option (d)

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.

High Order Thinking Skills (HOTS)

Q.46. The farmers use large amounts of a substance P in the fields to increase the crop yield. The excess of P dissolves in water and runs into a lake. The substance P causes rapid growth of tiny green water plants Q in the lake which cover the whole lake like a green sheet. When the plants Q die, the organisms called R decompose them by utilizing S dissolved in lake water. The amount of dissolved Sin water decreases too much due to which the fish living in lake suffocate and die. What are P, Q, R and S?

The substance P is Fertilizer. The 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.

The substance Q is Algae, R is Bacteria and S is oxygen.

Q.47. At many places the wastewater containing human excreta from homes and carried in big underground pipes is dumped into a river as such which pollutes the river water.
(a) What is the common name of such wastewater?
(b) Name five types of harmful organisms contained in it.
(c) Name any five human diseases caused by drinking river water contaminated with such wastewater.

(a) The common name of such wastewater is Sewage. The harmful substances like sewage, toxic materials, silt etc., when gets mixed with water, causes water pollution.
(b) Sewage water contains bacteria, viruses, protozoa, fungi and parasites(worms) which may cause diseases like cholera, typhoid and jaundice. The bacteria present in the fecal matter of mammals are indicates the quality of water. If water has these bacteria, it means that it has been contaminated by fecal matter. If such water is used by us, it can cause various infections.
(c) Drinking river water contaminated with such wastewater can result into diseases such as Cholera, Typhoid, Diarrhea, Dysentery and Jaundice.

Q.48. Match the items given in column I with one or more items given in column II:

(i) Prevents photosynthesis – (d) Dust in air

Dust reduces the photosynthesis in plants due which causes a decrease in energy production in plants causing the plants to suffer.

(ii) Damage ozone layer – (e) CFCs

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.

(iii) Produce acid rain – (f) Sulphur dioxide

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. This is called Acid rain.

(iv) Kill fish by deoxygenating water – (b) Excess fertilizer in fields

The 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 including fish.

(v) Causes water borne diseases – (a) Sewage dumped in river

Sewage water contains bacteria, viruses, protozoa, fungi and parasites(worms) which may cause diseases like cholera, typhoid and jaundice.

(vi) Leads to global warming in air – (c) Carbon dioxide in air

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.49. State one way in which the air pollution caused by the burning of fossil fuels in transport and industry can kill the fish living in a lake and one way in which the water pollution caused by an agricultural activity can kill fish living in the same lake.

Fossil fuels burn in the air to produce gases such as Sulphur dioxide and nitrogen dioxide. 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. This is called Acid rain. Acid rain caused by the burning of fossil fuels makes the lake water too much acidic which kills the fish.

The 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 including fish.

Q.50. The incomplete combustion of firewood in homes produces a very poisonous gas X. When inhaled, gas X combines with the substance Y present in blood and reduces the capacity of blood to carry gas Z causing respiratory problems and suffocation. What are X, Y and Z?

The incomplete combustion of firewood in homes produces a very poisonous gas X which is known as Carbon monoxide. When inhaled, Carbon monoxide combines with the substance Y known as Haemoglobin which is present in blood. Carbon monoxide combines with the haemoglobin of our blood. It reduces the oxygen carrying capacity of blood causing respiratory problems and suffocation. Hence, the substance Z is Oxygen.