Selina Textbook Solutions: Composition and Structure of the Atmosphere

 Page 1


Composition and Structure of the Atmosphere 
Exercises 
I. Short Answer Questions. 
Question 1. 
What is known as atmosphere ? 
Answer: 
The blanket of air upto 1500 km surrounding the earth is known as atmosphere. 
Question 2. 
State the gaseous composition of the atmosphere. 
Answer: 
The atmosphere consists of 78% Nitrogen 21% oxygen and 1% other gases. 
Question 3. 
Mention any three functions of the atmosphere. 
Answer: 
1. Air has weight and exerts pressure. Being pressed down it always remains in 
contact with land and water. 
2. Due to their physical contact, exchange of gases between air, land and water 
takes place on a continuous basis. 
3. Soil absorbs oxygen and nitrogen due to this contact. Water vapours in air rise 
from oceans on account of evaporation. 
Question 4. 
Name the four layers of the atmosphere. 
Answer: 
Four layers of the atmosphere are : 
1. Troposphere 
2. Stratosphere, 
3. Mesosphere 
4. Thermosphere. 
Question 5. 
What is known as troposphere ? 
Answer: 
Troposphere is the lowest and densest layer of atmosphere touching the land surface. It 
extends from 8km to 18 km. in height 
Page 2


Composition and Structure of the Atmosphere 
Exercises 
I. Short Answer Questions. 
Question 1. 
What is known as atmosphere ? 
Answer: 
The blanket of air upto 1500 km surrounding the earth is known as atmosphere. 
Question 2. 
State the gaseous composition of the atmosphere. 
Answer: 
The atmosphere consists of 78% Nitrogen 21% oxygen and 1% other gases. 
Question 3. 
Mention any three functions of the atmosphere. 
Answer: 
1. Air has weight and exerts pressure. Being pressed down it always remains in 
contact with land and water. 
2. Due to their physical contact, exchange of gases between air, land and water 
takes place on a continuous basis. 
3. Soil absorbs oxygen and nitrogen due to this contact. Water vapours in air rise 
from oceans on account of evaporation. 
Question 4. 
Name the four layers of the atmosphere. 
Answer: 
Four layers of the atmosphere are : 
1. Troposphere 
2. Stratosphere, 
3. Mesosphere 
4. Thermosphere. 
Question 5. 
What is known as troposphere ? 
Answer: 
Troposphere is the lowest and densest layer of atmosphere touching the land surface. It 
extends from 8km to 18 km. in height 
Question 6. 
Mention the chief characteristics of stratosphere. 
Answer: 
There is total absence of water vapour in this layer. It extends upto a height of 50 km. 
The temperature remains constant up to – 55°C. 
Question 7. 
In which layer of atmosphere do all weather conditions occur ? 
Answer: 
Troposphere is the layer where all weather conditions occur in different forms. 
Question 8. 
Name the constituent gases of atmosphere which scientists consider responsible for 
climate change. 
Answer: 
Carbon dioxide and ozone are responsible for climate change, as carbon dioxide 
absorbs heat from sun and by radiation from the earth; ozone absorbs extremely hot 
ultra-violet rays controlling the ideal temperature conditions on the earth. 
Question 9. 
What is known as ozone layer ? 
Answer: 
Stratosphere contains sufficient amount of ozone which absorbs the extremely hot ultra-
violet rays of the sun. It is known as ozone layer. 
Question 10. 
What is leading to depletion of ozone layer in the atmosphere ? 
Answer: 
Excessive emission of carbon monoxide and CFCs from industries and vehicles take 
out the oxygen from ozone layer to form different compounds (oxides). In this way the 
depletion of ozone layer takes place. 
Question 11. 
What is known as Global Warming? 
Answer: 
Global Warming is the increase in temperature of earth due to enhanced concentration 
of Greenhouse gases (CFCs) in the atmosphere. 
Question 12. 
Name important Greenhouse gases. 
Answer: 
The main Greenhouse gases are CFCs (Chlorofluorocarbons) and nitrogen oxides 
which are emitted by fertilizers industries and transport engines along with carbon 
dioxide and methane. 
Page 3


Composition and Structure of the Atmosphere 
Exercises 
I. Short Answer Questions. 
Question 1. 
What is known as atmosphere ? 
Answer: 
The blanket of air upto 1500 km surrounding the earth is known as atmosphere. 
Question 2. 
State the gaseous composition of the atmosphere. 
Answer: 
The atmosphere consists of 78% Nitrogen 21% oxygen and 1% other gases. 
Question 3. 
Mention any three functions of the atmosphere. 
Answer: 
1. Air has weight and exerts pressure. Being pressed down it always remains in 
contact with land and water. 
2. Due to their physical contact, exchange of gases between air, land and water 
takes place on a continuous basis. 
3. Soil absorbs oxygen and nitrogen due to this contact. Water vapours in air rise 
from oceans on account of evaporation. 
Question 4. 
Name the four layers of the atmosphere. 
Answer: 
Four layers of the atmosphere are : 
1. Troposphere 
2. Stratosphere, 
3. Mesosphere 
4. Thermosphere. 
Question 5. 
What is known as troposphere ? 
Answer: 
Troposphere is the lowest and densest layer of atmosphere touching the land surface. It 
extends from 8km to 18 km. in height 
Question 6. 
Mention the chief characteristics of stratosphere. 
Answer: 
There is total absence of water vapour in this layer. It extends upto a height of 50 km. 
The temperature remains constant up to – 55°C. 
Question 7. 
In which layer of atmosphere do all weather conditions occur ? 
Answer: 
Troposphere is the layer where all weather conditions occur in different forms. 
Question 8. 
Name the constituent gases of atmosphere which scientists consider responsible for 
climate change. 
Answer: 
Carbon dioxide and ozone are responsible for climate change, as carbon dioxide 
absorbs heat from sun and by radiation from the earth; ozone absorbs extremely hot 
ultra-violet rays controlling the ideal temperature conditions on the earth. 
Question 9. 
What is known as ozone layer ? 
Answer: 
Stratosphere contains sufficient amount of ozone which absorbs the extremely hot ultra-
violet rays of the sun. It is known as ozone layer. 
Question 10. 
What is leading to depletion of ozone layer in the atmosphere ? 
Answer: 
Excessive emission of carbon monoxide and CFCs from industries and vehicles take 
out the oxygen from ozone layer to form different compounds (oxides). In this way the 
depletion of ozone layer takes place. 
Question 11. 
What is known as Global Warming? 
Answer: 
Global Warming is the increase in temperature of earth due to enhanced concentration 
of Greenhouse gases (CFCs) in the atmosphere. 
Question 12. 
Name important Greenhouse gases. 
Answer: 
The main Greenhouse gases are CFCs (Chlorofluorocarbons) and nitrogen oxides 
which are emitted by fertilizers industries and transport engines along with carbon 
dioxide and methane. 
Question 13. 
Name two chief characteristics of atmosphere. 
Answer: 
Atmosphere protects earth from harmful ultra-violet and infra-red rays of the sun. It 
controls the hydrological cycle and provide life giving gases. 
Question 14. 
What keeps the atmosphere in a dynamic state ? 
Answer: 
The atmosphere protects the earth from harmful ultraviolet and infrared rays of the sun. 
It has oxygen and nitrogen, the life sustaining gases. It helps in retaining the necessary 
warmth on the earth and helps in the circulation of water vapour as the source of 
rainfall. These functions of atmosphere keep it in a dynamic state. 
Question 15. 
What is called weather ? 
Answer: 
Weather is the physical condition or state of atmosphere (temperature, pressure, state 
of sky etc.) at a given locality or an area. 
II. Explain the following terms/processes in detail 
1. Global Warming 
2. Greenhouse Effect 
3. Normal Lapse Rate of Temperature 
4. CFCs 
Answer: 
? Global Warming : The temperature on the earth is rising. This phenomenon 
known as Global Warming is the result of enhanced concentration of Greenhouse 
gases in the atmosphere caused mainly by human activities. Consequences of 
Global Warming: 
1. Global temperature is likely rise by 2 to 5°C during the next century. Due to rise in 
temperature by 2 to 5°C, there is a chance of melting of ice caps on Earth’s poles. 
This melting of ice will result in the rise of the sea level. Large stretches of low 
lying areas will submerge and many island countries will face deep encroachment 
by sea water. Some may disappear altogether. 
2. As the increase in temperature will be uniform all over the surface of the world, 
there will be serious climatic changes. This will bring various changes in wind and 
rain patterns. 
3. Higher temperature will cause rise in transpiration, which in turn, will affect the 
groundwater table. 
Page 4


Composition and Structure of the Atmosphere 
Exercises 
I. Short Answer Questions. 
Question 1. 
What is known as atmosphere ? 
Answer: 
The blanket of air upto 1500 km surrounding the earth is known as atmosphere. 
Question 2. 
State the gaseous composition of the atmosphere. 
Answer: 
The atmosphere consists of 78% Nitrogen 21% oxygen and 1% other gases. 
Question 3. 
Mention any three functions of the atmosphere. 
Answer: 
1. Air has weight and exerts pressure. Being pressed down it always remains in 
contact with land and water. 
2. Due to their physical contact, exchange of gases between air, land and water 
takes place on a continuous basis. 
3. Soil absorbs oxygen and nitrogen due to this contact. Water vapours in air rise 
from oceans on account of evaporation. 
Question 4. 
Name the four layers of the atmosphere. 
Answer: 
Four layers of the atmosphere are : 
1. Troposphere 
2. Stratosphere, 
3. Mesosphere 
4. Thermosphere. 
Question 5. 
What is known as troposphere ? 
Answer: 
Troposphere is the lowest and densest layer of atmosphere touching the land surface. It 
extends from 8km to 18 km. in height 
Question 6. 
Mention the chief characteristics of stratosphere. 
Answer: 
There is total absence of water vapour in this layer. It extends upto a height of 50 km. 
The temperature remains constant up to – 55°C. 
Question 7. 
In which layer of atmosphere do all weather conditions occur ? 
Answer: 
Troposphere is the layer where all weather conditions occur in different forms. 
Question 8. 
Name the constituent gases of atmosphere which scientists consider responsible for 
climate change. 
Answer: 
Carbon dioxide and ozone are responsible for climate change, as carbon dioxide 
absorbs heat from sun and by radiation from the earth; ozone absorbs extremely hot 
ultra-violet rays controlling the ideal temperature conditions on the earth. 
Question 9. 
What is known as ozone layer ? 
Answer: 
Stratosphere contains sufficient amount of ozone which absorbs the extremely hot ultra-
violet rays of the sun. It is known as ozone layer. 
Question 10. 
What is leading to depletion of ozone layer in the atmosphere ? 
Answer: 
Excessive emission of carbon monoxide and CFCs from industries and vehicles take 
out the oxygen from ozone layer to form different compounds (oxides). In this way the 
depletion of ozone layer takes place. 
Question 11. 
What is known as Global Warming? 
Answer: 
Global Warming is the increase in temperature of earth due to enhanced concentration 
of Greenhouse gases (CFCs) in the atmosphere. 
Question 12. 
Name important Greenhouse gases. 
Answer: 
The main Greenhouse gases are CFCs (Chlorofluorocarbons) and nitrogen oxides 
which are emitted by fertilizers industries and transport engines along with carbon 
dioxide and methane. 
Question 13. 
Name two chief characteristics of atmosphere. 
Answer: 
Atmosphere protects earth from harmful ultra-violet and infra-red rays of the sun. It 
controls the hydrological cycle and provide life giving gases. 
Question 14. 
What keeps the atmosphere in a dynamic state ? 
Answer: 
The atmosphere protects the earth from harmful ultraviolet and infrared rays of the sun. 
It has oxygen and nitrogen, the life sustaining gases. It helps in retaining the necessary 
warmth on the earth and helps in the circulation of water vapour as the source of 
rainfall. These functions of atmosphere keep it in a dynamic state. 
Question 15. 
What is called weather ? 
Answer: 
Weather is the physical condition or state of atmosphere (temperature, pressure, state 
of sky etc.) at a given locality or an area. 
II. Explain the following terms/processes in detail 
1. Global Warming 
2. Greenhouse Effect 
3. Normal Lapse Rate of Temperature 
4. CFCs 
Answer: 
? Global Warming : The temperature on the earth is rising. This phenomenon 
known as Global Warming is the result of enhanced concentration of Greenhouse 
gases in the atmosphere caused mainly by human activities. Consequences of 
Global Warming: 
1. Global temperature is likely rise by 2 to 5°C during the next century. Due to rise in 
temperature by 2 to 5°C, there is a chance of melting of ice caps on Earth’s poles. 
This melting of ice will result in the rise of the sea level. Large stretches of low 
lying areas will submerge and many island countries will face deep encroachment 
by sea water. Some may disappear altogether. 
2. As the increase in temperature will be uniform all over the surface of the world, 
there will be serious climatic changes. This will bring various changes in wind and 
rain patterns. 
3. Higher temperature will cause rise in transpiration, which in turn, will affect the 
groundwater table. 
4. As the climatic belts shift from equator towards pole, the vegetation would also 
shift away from the equator. 
5. Insects and pests will increase in the warmer climatic conditions. Thus, pathogenic 
diseases will multiply. 
? Greenhouse Effect: Greenhouse are built in cold areas to grow the plants within 
it in warm temperature. But, due to Global Warming the whole earth is becoming a 
Greenhouse due to increase in temperature, which indirectly disturb the normal 
life on earth by challenging nature and nature will originate many unwanted 
problems of change in climate, radiation imbalance, diseases etc. 
The rate of absorption of solar radiation by earth and its emission back into space 
as infra-red waves balances the heat on earth. This phenomenon plays a very 
important role in maintaining surface temperature of earth. The carbon dioxide and 
other gases form a blanket around the globe which prevent the passage of infra-
red waves from earth back into space. Concentration of solar radiation produces 
much heat, making earth a very warm place. This phenomenon is similar to that of 
greenhouse in which the glass enclosed area gets heated up due to its insulation 
from the rest of the environment. Hence, warming of the atmosphere is due to the 
greenhouse effect. Hence, Global Warming is also known as Greenhouse Effect. 
? Normal Lapse Rate of Temperature : The decrease in Temperature is known as 
normal lapse rate, which is calculated as average decrease of 1°C for every 166 
metres altitude gained. The lapse rate works mainly in troposphere which results 
in various types of weather and climatic changes affecting the life on earth. 
? CFCs : (Chlorofluorocarbons) are organic compounds that contain carbon, 
chlorine, fluorine produced as volatile deriatives of methane and ethane which 
catalyze the conversion of ozone (O 3) into O 2, while O 3 is more powerful to absorb 
ultra-violet rays than that of O 2. So CFCs disturb the ozone layer which is so 
essential for earth. 
III. Long Answer Questions 
Question 1. 
Describe the structure of the atmosphere. 
Answer: 
In the atmosphere, there are concentric layers of air. Each layer has different density. 
The upper layers press down the lower one. So, the air of the lower layer is always 
heavier or denser, while the upper layers are thinner or less dense. In this way about 90 
per cent of the mass of air lies within a height of about 20 km from the surface of the 
earth. 
On the basis of the characteristics of temperature and air pressure there exist four 
thermal layers of the atmosphere. They are — Troposphere, Stratosphere, Mesosphere 
and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere. 
 
Page 5


Composition and Structure of the Atmosphere 
Exercises 
I. Short Answer Questions. 
Question 1. 
What is known as atmosphere ? 
Answer: 
The blanket of air upto 1500 km surrounding the earth is known as atmosphere. 
Question 2. 
State the gaseous composition of the atmosphere. 
Answer: 
The atmosphere consists of 78% Nitrogen 21% oxygen and 1% other gases. 
Question 3. 
Mention any three functions of the atmosphere. 
Answer: 
1. Air has weight and exerts pressure. Being pressed down it always remains in 
contact with land and water. 
2. Due to their physical contact, exchange of gases between air, land and water 
takes place on a continuous basis. 
3. Soil absorbs oxygen and nitrogen due to this contact. Water vapours in air rise 
from oceans on account of evaporation. 
Question 4. 
Name the four layers of the atmosphere. 
Answer: 
Four layers of the atmosphere are : 
1. Troposphere 
2. Stratosphere, 
3. Mesosphere 
4. Thermosphere. 
Question 5. 
What is known as troposphere ? 
Answer: 
Troposphere is the lowest and densest layer of atmosphere touching the land surface. It 
extends from 8km to 18 km. in height 
Question 6. 
Mention the chief characteristics of stratosphere. 
Answer: 
There is total absence of water vapour in this layer. It extends upto a height of 50 km. 
The temperature remains constant up to – 55°C. 
Question 7. 
In which layer of atmosphere do all weather conditions occur ? 
Answer: 
Troposphere is the layer where all weather conditions occur in different forms. 
Question 8. 
Name the constituent gases of atmosphere which scientists consider responsible for 
climate change. 
Answer: 
Carbon dioxide and ozone are responsible for climate change, as carbon dioxide 
absorbs heat from sun and by radiation from the earth; ozone absorbs extremely hot 
ultra-violet rays controlling the ideal temperature conditions on the earth. 
Question 9. 
What is known as ozone layer ? 
Answer: 
Stratosphere contains sufficient amount of ozone which absorbs the extremely hot ultra-
violet rays of the sun. It is known as ozone layer. 
Question 10. 
What is leading to depletion of ozone layer in the atmosphere ? 
Answer: 
Excessive emission of carbon monoxide and CFCs from industries and vehicles take 
out the oxygen from ozone layer to form different compounds (oxides). In this way the 
depletion of ozone layer takes place. 
Question 11. 
What is known as Global Warming? 
Answer: 
Global Warming is the increase in temperature of earth due to enhanced concentration 
of Greenhouse gases (CFCs) in the atmosphere. 
Question 12. 
Name important Greenhouse gases. 
Answer: 
The main Greenhouse gases are CFCs (Chlorofluorocarbons) and nitrogen oxides 
which are emitted by fertilizers industries and transport engines along with carbon 
dioxide and methane. 
Question 13. 
Name two chief characteristics of atmosphere. 
Answer: 
Atmosphere protects earth from harmful ultra-violet and infra-red rays of the sun. It 
controls the hydrological cycle and provide life giving gases. 
Question 14. 
What keeps the atmosphere in a dynamic state ? 
Answer: 
The atmosphere protects the earth from harmful ultraviolet and infrared rays of the sun. 
It has oxygen and nitrogen, the life sustaining gases. It helps in retaining the necessary 
warmth on the earth and helps in the circulation of water vapour as the source of 
rainfall. These functions of atmosphere keep it in a dynamic state. 
Question 15. 
What is called weather ? 
Answer: 
Weather is the physical condition or state of atmosphere (temperature, pressure, state 
of sky etc.) at a given locality or an area. 
II. Explain the following terms/processes in detail 
1. Global Warming 
2. Greenhouse Effect 
3. Normal Lapse Rate of Temperature 
4. CFCs 
Answer: 
? Global Warming : The temperature on the earth is rising. This phenomenon 
known as Global Warming is the result of enhanced concentration of Greenhouse 
gases in the atmosphere caused mainly by human activities. Consequences of 
Global Warming: 
1. Global temperature is likely rise by 2 to 5°C during the next century. Due to rise in 
temperature by 2 to 5°C, there is a chance of melting of ice caps on Earth’s poles. 
This melting of ice will result in the rise of the sea level. Large stretches of low 
lying areas will submerge and many island countries will face deep encroachment 
by sea water. Some may disappear altogether. 
2. As the increase in temperature will be uniform all over the surface of the world, 
there will be serious climatic changes. This will bring various changes in wind and 
rain patterns. 
3. Higher temperature will cause rise in transpiration, which in turn, will affect the 
groundwater table. 
4. As the climatic belts shift from equator towards pole, the vegetation would also 
shift away from the equator. 
5. Insects and pests will increase in the warmer climatic conditions. Thus, pathogenic 
diseases will multiply. 
? Greenhouse Effect: Greenhouse are built in cold areas to grow the plants within 
it in warm temperature. But, due to Global Warming the whole earth is becoming a 
Greenhouse due to increase in temperature, which indirectly disturb the normal 
life on earth by challenging nature and nature will originate many unwanted 
problems of change in climate, radiation imbalance, diseases etc. 
The rate of absorption of solar radiation by earth and its emission back into space 
as infra-red waves balances the heat on earth. This phenomenon plays a very 
important role in maintaining surface temperature of earth. The carbon dioxide and 
other gases form a blanket around the globe which prevent the passage of infra-
red waves from earth back into space. Concentration of solar radiation produces 
much heat, making earth a very warm place. This phenomenon is similar to that of 
greenhouse in which the glass enclosed area gets heated up due to its insulation 
from the rest of the environment. Hence, warming of the atmosphere is due to the 
greenhouse effect. Hence, Global Warming is also known as Greenhouse Effect. 
? Normal Lapse Rate of Temperature : The decrease in Temperature is known as 
normal lapse rate, which is calculated as average decrease of 1°C for every 166 
metres altitude gained. The lapse rate works mainly in troposphere which results 
in various types of weather and climatic changes affecting the life on earth. 
? CFCs : (Chlorofluorocarbons) are organic compounds that contain carbon, 
chlorine, fluorine produced as volatile deriatives of methane and ethane which 
catalyze the conversion of ozone (O 3) into O 2, while O 3 is more powerful to absorb 
ultra-violet rays than that of O 2. So CFCs disturb the ozone layer which is so 
essential for earth. 
III. Long Answer Questions 
Question 1. 
Describe the structure of the atmosphere. 
Answer: 
In the atmosphere, there are concentric layers of air. Each layer has different density. 
The upper layers press down the lower one. So, the air of the lower layer is always 
heavier or denser, while the upper layers are thinner or less dense. In this way about 90 
per cent of the mass of air lies within a height of about 20 km from the surface of the 
earth. 
On the basis of the characteristics of temperature and air pressure there exist four 
thermal layers of the atmosphere. They are — Troposphere, Stratosphere, Mesosphere 
and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere. 
 
Question 2. 
How does atmosphere govern life on earth ? 
Answer: 
Stratosphere absorbs the harmful ultra-violet rays of the sun and the troposphere 
regulates all weather conditions e.g. ideal temperature, rainfall and their impact on 
human life. 
Question 3. 
Explain the factors responsible for depletion of ozone in atmosphere. 
Answer: 
Various occupations related to industries, transport and fertilizer cause large amount of 
CFCs emission along with nitrogen oxide and methane have disturbed the ozone layer 
depleting the oxygen particles. Volcanic eruptions emit sulphur dioxide creating harmful 
chemical reactions which dismantle the ozone layer. 
Question 4. 
Give a description of the recent studies about Global Warming. 
Answer: 
The Global mean temperature has increased by 0.6°C in the 20th century. It is 
estimated to increase by 1.4° to 5.8°C by the year 2100 from 1990. This has affected 
abnormal weather conditions in various parts e.g. less rainfall in Africa and Gulf Coast 
of U.S.A., more rainfall in Asian tropical region and some areas may get no rainfall. 
Increasing melting of ice and glaciers resulted in rise of oceanic water level by 10 to 25 
cm. Warming of atmosphere will considerably increase its moisture carrying capacity. 
While the troposphere warms up, the stratosphe will cool down. 
It is the balance between radiation coming into the atmosphere and radiation going out. 
Any change in this balance can have rapid impact on life forms on earth because it will 
have an impact on the sensitivity, adaptability and vulnerability of the whole biospheric 
system. 
Climate change will bring about substantial changes in cereal production specially in the 
Tropics. Global freshwater conditions may worsen by 2025. 
Question 5. 
Why should we protect the atmosphere ? 
Answer: 
Atmosphere is necessary to sustain life on earth, because without atmosphere there 
would be no oxygen, no weather changes, rainfall etc, which are essential for activities 
of human life and ideal temperature on the earth. 
The atmosphere protects the earth from harmful ultraviolet and infrared rays of the sun. 
It has oxygen and nitrogen, the life sustaining gases. It helps in retaining the necessaiy 
warmth on the earth and helps in the circulation of water vapour as the source of 
rainfall. These functions of atmosphere keep it in a dynamic state.