CBSE Class 8 - Science - CH 18 - POLLUTION OF AIR AND WATER

POLLUTION OF AIR AND WATER

NCERT Solution, Q & A

Q1: What are the different ways in which water gets contaminated?

Answer: Water gets contaminated in the following ways:

1. Various industrial units dispose off the chemicals in rivers. These chemicals are harmful and poisonous and contaminate water.
2. Water gets contaminated when sewage is disposed off (without any treatment) in rivers.
3. Ground water gets contaminated by harmful insectisides and pestisides sprayed by farmers and it becomes unfit for drinking.

Q2: At an individual level, how can you help reduce air pollution?


Answer: Air pollution should also be checked at individual level:

1. At at individual level, we can plant trees as trees reduce air pollution.
2. We can use public transportion and encourage car pooling so that air pollution can be reduced.
3. Instead of going by cars and scooters for short distances, we can go by foot or by bicycles.
4. By saying no to crackers we can minimise air pollution as well as noise pollution.
5. We should not burn garbage and dry leaves. The burning of dry leaves and garbage release green house gases which are responsible for global warming.

Q3: Clear, transparent water is always fit for drinking. Comment.

Answer: Transparent water is not always fit for drinking. It may contain harmful microorganisms and other pollutants. We should purify water before drinking. Water can be purified with the help of water purifier or by boiling it.


Q4: 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.

Answer: We can take following measures:

• Water should be treated properly to make it free from germs, chemical and physical impurities.
• Enforce laws to treat water and chemicals before disposing into water bodies.
• Proper maintenance of pipes supplying tap water to avoid any corrosion and leakage.
• Organize awareness programmes to keep water resources clean.

Q5: Explain the differences between pure air and polluted air.

Answer:

Pure Air	Polluted Air
(a) Free from harmful and poisonous gases	(a) Increased levels of harmful and poisonous gases.
(b) Fit for breathing and good for health	(b) Unfit for breathing and may cause diseases like asthma, cancer etc.
(c) Pure air is good for crop production and wild life.	(c) Polluted air is a threat to our ecosystem. It affects crops, wild life as well as aquatic life.

Q6: Explain circumstances leading to acid rain. How does acid rain affect us?

Answer: When harmful gases like sulphur dioxide and nitrogen dioxide, react with moisture present in air, they form nitric acid and sulphuric acid. These acids when drop down on earth along with rain, is called acid rain.

Acid rain causes skin irritation, inhibits germination of plants, causes corrosion to bridges and building. It changes the fertility of the soil, destroys plants and aquatic life.


Q7: Which of the following is not a greenhouse gas?

(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

Answer: (d) Nitrogen


Q8: Describe the ‘Green House Effect’ in your own words.

Answer: Green House effect is a process by which solar radiation is absorbed by green house gases and is transmitted to all directions. This increases the temperature of the surroundings and is responsible for global warming. Gases like CO₂ , Methane, ntirous oxide, water vapours trap heat radiation and are called greenhouse gases.

Green houses are often used for growing flowers, vegetables and plants (specially in cold region). Now because of increase in concentration of greenhouse gases in our envronment is adversely affecting the climate.

Green House Effect
credits:wikicommons

Q9: Prepare a brief speech on global warming that you have to make in your class.

Answer: Continuous increase in temperature of the earth due to increase levels of green house gases is known as Global warming. Global warming is one of the biggest concern worldwide. Scientists believe climate shifting, melting of glaciers  (eg. Gangotri glacier), sudden floods in coastal areas are due to global warming. The Kyoto Protocol is one such agreement made among the countries to reduce emission of green house gases.

Figure shows increase in earth's temperature in 2000-2009 when compared to 1951-180 data
image credits: wikicommons and NASA Earth Observatory

Q10: Describe the threat to the beauty of the Taj Mahal.

Answer: The industries located around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, were producing pollutants like sulphur dioxide and nitrogen dioxide, thus forming acid rain. It corroded the marble of Taj Mahal monument. The suspended particles and ash(soot) from Mathura refinery caused yellowish colour to Taj marbles. This is popularly called "Marble cancer phenomenon". Supreme Court has taken several steps to save Taj from pollution.

How Taj will look if it gets polluted at this rate?

Q11: Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer:  Excessive quantities of chemicals (fertilizers, weedicides, pesticides etc.) washed from the fields enter into ponds. These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in these ponds gets used up. This results in a decrease in the oxygen level which kills aquatic organisms.

Q12: What are the natural sources of air pollution?

Answer:  Following are few natural sources of air pollutions:

• Volcanic eruption
• forest fire
• sea salt sprays
• biological decay
• pollengrains and spores

Q13: What are anthropogenic sources of air pollution?

Answer: Man-made of anthropogenic sources of air pollutions are:

• Incomplete burning of fossil fuels, like petrol and diesel
• Gases like ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide
• CFCs or chlorofluorocarbons used in aerosols and refrigerant and propellent in aeroplanes.

Q14: How Sulphur dioxide is dangerous to our health?

Answer: It can cause irritation in eyes, lung cancer and asthma.


Q15: Why it is suggested to plant eucalyptus trees nearby sewage ponds?

Answer: We should plant eucalyptus trees near to sewage ponds. These trees absorb surplus waste water rapidly and release pure water vapour into the atmosphere.

Q16: What is potable water?

Answer: Water which is purified and fit for drinking is known as potable water.