Question 1: What
are the different ways in which water gets contaminated?
Answer: Water
gets contaminated by the addition of:
(i) Agricultural chemicals: Farmers use excessive amounts of
pesticides and fertilizers to increase crop production. These chemicals get
carried away to the water bodies due to rains and floods which lead to water
pollution.
(ii) Industrial
wastes: Industries release harmful chemical wastes into water sources, thereby
polluting them.
(iii) Sewage wastes: Waste materials from kitchens, toilets,
and laundry sources are also responsible for contaminating water.
Question 2: At
an individual level, how can you help reduce air pollution?
Answer: An individual can reduce
air pollution by:
(i) Avoiding the use of cars as much as possible and by
using public transport whenever possible.
(ii) By not using vehicles for short distances.
(iii) By using clean fuels such as LPG and CNG instead of
diesel and petrol.
(iv) Always disposing the garbage properly and not burning
it.
(v) Controlling the emissions from vehicles and household
chimneys.
Question 3: Clear,
transparent water is always fit for drinking. Comment.
Answer: No.
Clear and transparent water is not always fit for drinking. Water might appear
clean, but it may contain some disease causing micro-organisms and other
dissolved impurities. Hence, it is advised to purify water before drinking.
Purification can be done by water purifying systems or by boiling the water.
Question 4: 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: To
ensure the supply of clean water to all residents the following steps must be
taken:
(i) The main water source must be built in clean
surroundings and should be maintained properly.
(ii) Chemical methods such as chlorination must be used for
purifying water.
(iii) The area around water pipes must also be clean.
Question 5: Explain
the differences between pure air and polluted air.
Answer: Pure
air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other
gases such as argon, methane, ozone, and water vapours are also present in
small quantities. When this composition of air is altered by the addition of
harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon
monoxide, and particulate matter, then the air is said to be polluted.
Question 6: Explain
circumstances leading to acid rain. How does acid rain affect us?
Answer: Burning
of fossil fuels such as coal and diesel releases a variety of pollutants such
as sulphur dioxide and nitrogen dioxide into the atmosphere. These pollutants
react with water vapours present in the atmosphere to form sulphuric acid and
nitric acid respectively. These acids come down with the rain, thereby
resulting in acid rain. Effects of acid rain:
(i) Acid rains damage crops.
(ii) Acid rains corrode buildings and structures especially
those made of marble such as Taj Mahal.
Question 7: Which
of the following is not a greenhouse gas? (a) Carbon dioxide (b) Sulphur
dioxide (c) Methane (d) Nitrogen
Answer: (d)
Nitrogen
Question 8: Describe
the ‘Greenhouse Effect’ in your own words.
Answer: Greenhouse
effect may lead to global warming, i.e., an overall increase in the average
temperature of the Earth. Greenhouse effect is caused by greenhouse gases.
Examples of greenhouse gases include carbon dioxide, methane, and water vapour.
When solar radiations reach the Earth, some of these radiations are absorbed by
earth and then released back to the atmosphere. Greenhouse gases present in the
atmosphere trap these radiations and do not allow heat to leave. This helps in
keeping our planet warm and thus, helps in human survival. However, an
indiscriminate increase in the amount of greenhouse gases can lead to excessive
increase in the Earth’s temperature leading to global warming.
Question 9: Prepare
a brief speech on global warming. You have to deliver the speech in your class.
Answer: Global warming is an increase in
the average temperature of the Earth’s surface. It occurs as a result of an
increased concentration of greenhouse gases in the atmosphere. The greenhouse
gases include carbon dioxide, methane, and water vapour. These gases trap solar
radiations released back by the Earth. This helps in keeping our planet warm
and thus, helps in human survival. However, an increase in the amount of
greenhouse gases can lead to an increase in the Earth’s temperature leading to
global warming.
Question 10: Describe
the threat to the beauty of the Taj Mahal.
Answer: Acid
rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on
the monument (that is completely made of marble), they react with marble to
form a powder-like substance that is then washed away by the rain. This
phenomenon is known as marble cancer. Also, the soot particles emitted from the
Mathura oil refinery located near Agra is leading to the yellowing of the
marble.
Question 11: Why
does the increased level of nutrients in the water affect the survival of
aquatic organisms?
Answer: An
increase in the level of nutrients in a water body leads to an excessive
increase in the population of algae in the water body. When these algae die,
they serve as food for decomposers. A lot of oxygen is utilised in this
process, consequently leading to a decrease in the level of oxygen dissolved in
the water body. This in turn causes fishes and other aquatic organisms to die.
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