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NCERT Solutions for Class 12 Biology Chapter 16
Environmental Issues Class 12
Chapter 16 Environmental Issues Exercise Solutions
Exercise : Solutions of Questions on Page Number : 286
Q1 :
What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Answer :
Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other sources. It contains impurities
such as suspended solid (sand, salt, clay), colloidal material (fecal matter, bacteria, plastic and cloth fiber), dissolved
materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic wastes from
the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria. As a
result, the population of these micro-organisms in the water body increases. Here, they utilize most of the dissolved
oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river
water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic
algal, causing algal bloom. This causes deterioration of water quality and fish mortality.
Q2 :
List all the wastes that you generate, at home, school or during your Trips to other places, could you very
easily reduce? Which would be Difficult or rather impossible to reduce?
Answer :
Wastes generated at home include plastic bags, paper napkin, toiletries, kitchen wastes (such as peelings of
vegetables and fruits, tea leaves), domestic sewage, glass, etc.
Wastes generated at schools include waste paper, plastics, vegetable and fruit peels, food wrappings, sewage etc.
Wastes generated at trips or picnics include plastic, paper, vegetable and fruit peels, disposable cups, plates,
spoons etc.
Yes, wastes can be easily reduced by the judicious use of the above materials. Wastage of paper can be minimized
by writing on both sides of the paper and by using recycled paper. Plastic and glass waste can also be reduced by
recycling and re-using. Also, substituting plastics bags with biodegradable jute bags can reduce wastes generated at
home, school, or during trips. Domestic sewage can be reduced by optimizing the use of water while bathing,
cooking, and other household activities.
Non- biodegradable wastes such as plastic, metal, broken glass, etc are difficult to decompose because micro-
organisms do not have the ability to decompose them.
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, www.ncrtsolutions.in
Q3 :
Discuss the causes and effects of global warming. What measures need to be taken to control global
warming?
Answer :
Global warming is defined as an increase in the average temperature of the Earth's surface.
Causes of global warming: Global warming occurs as a result of the increased concentration of greenhouse gases
in the atmosphere. 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 excessive increase in the Earth's
temperature, leading to global warming. Global warming is a result of industrialization, burning of fossil fuels, and
deforestation.
Effects of global warming: Global warming is defined as an increase in the average temperature of the Earth's
surface. It has been observed that in the past three decades, the average temperature of the Earth has increased by
0.6ºC. As a result, the natural water cycle has been disturbed resulting in changes in the pattern of rainfall. It also
changes the amount of rain water. Also, it results in the melting of Polar ice caps and mountain glaciers, which has
caused a rise in the sea level, leading to the inundation of coastal regions.
Control measures for preventing global warming:
(i) Reducing the use of fossil fuels
(ii) Use of bio-fuels
(iii) Improving energy efficiency
(iv) Use of renewable source of energy such as CNG etc.
(v) Reforestation.
(vii) Recycling of materials
Q4 :
Match the items given in column A and B:
Column A Column B
(a) Catalytic converter (i) Particulate matter
(b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs (iii) High noise level
(d) Landfills (iv) Solid wastes
Answer :
Column A Column B
www.ncrtsolutions.in
NCERT Solutions for Class 12 Biology Chapter 16
Environmental Issues Class 12
Chapter 16 Environmental Issues Exercise Solutions
Exercise : Solutions of Questions on Page Number : 286
Q1 :
What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Answer :
Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other sources. It contains impurities
such as suspended solid (sand, salt, clay), colloidal material (fecal matter, bacteria, plastic and cloth fiber), dissolved
materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic wastes from
the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria. As a
result, the population of these micro-organisms in the water body increases. Here, they utilize most of the dissolved
oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river
water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic
algal, causing algal bloom. This causes deterioration of water quality and fish mortality.
Q2 :
List all the wastes that you generate, at home, school or during your Trips to other places, could you very
easily reduce? Which would be Difficult or rather impossible to reduce?
Answer :
Wastes generated at home include plastic bags, paper napkin, toiletries, kitchen wastes (such as peelings of
vegetables and fruits, tea leaves), domestic sewage, glass, etc.
Wastes generated at schools include waste paper, plastics, vegetable and fruit peels, food wrappings, sewage etc.
Wastes generated at trips or picnics include plastic, paper, vegetable and fruit peels, disposable cups, plates,
spoons etc.
Yes, wastes can be easily reduced by the judicious use of the above materials. Wastage of paper can be minimized
by writing on both sides of the paper and by using recycled paper. Plastic and glass waste can also be reduced by
recycling and re-using. Also, substituting plastics bags with biodegradable jute bags can reduce wastes generated at
home, school, or during trips. Domestic sewage can be reduced by optimizing the use of water while bathing,
cooking, and other household activities.
Non- biodegradable wastes such as plastic, metal, broken glass, etc are difficult to decompose because micro-
organisms do not have the ability to decompose them.
www.ncrtsolutions.in
, www.ncrtsolutions.in
Q3 :
Discuss the causes and effects of global warming. What measures need to be taken to control global
warming?
Answer :
Global warming is defined as an increase in the average temperature of the Earth's surface.
Causes of global warming: Global warming occurs as a result of the increased concentration of greenhouse gases
in the atmosphere. 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 excessive increase in the Earth's
temperature, leading to global warming. Global warming is a result of industrialization, burning of fossil fuels, and
deforestation.
Effects of global warming: Global warming is defined as an increase in the average temperature of the Earth's
surface. It has been observed that in the past three decades, the average temperature of the Earth has increased by
0.6ºC. As a result, the natural water cycle has been disturbed resulting in changes in the pattern of rainfall. It also
changes the amount of rain water. Also, it results in the melting of Polar ice caps and mountain glaciers, which has
caused a rise in the sea level, leading to the inundation of coastal regions.
Control measures for preventing global warming:
(i) Reducing the use of fossil fuels
(ii) Use of bio-fuels
(iii) Improving energy efficiency
(iv) Use of renewable source of energy such as CNG etc.
(v) Reforestation.
(vii) Recycling of materials
Q4 :
Match the items given in column A and B:
Column A Column B
(a) Catalytic converter (i) Particulate matter
(b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs (iii) High noise level
(d) Landfills (iv) Solid wastes
Answer :
Column A Column B
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