Class 7 Geography Chapter 4 Question Answers - Air

Q1. How can the level of oxygen remain constant in the atmosphere?
Ans: Oxygen which is available in the atmosphere is generated by the plants through its photosynthesis process. Green plants use carbon dioxide to make their food and release oxygen.
The amount of carbon dioxide released by humans or animals seems to be equal to the amount used by the plants which make a perfect balance. Hence, only plants play an important role to make the balance of oxygen in the atmosphere. If we cut trees, then this balance gets disturbed.

Q2. Name the five layers of atmosphere.
Ans: Starting from the earth’s surface, five layers of atmosphere are:

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere

Q3. How is balance of gases disrupted in the atmosphere?
Ans: There are many reasons which affect our atmosphere negatively. The balance of atmosphere needs to be balance of gases which are released by human beings. Due to the industrialization use of coal, fuel etc., is raising day by day.
Apart from this, burning of the fields, forests, wood, leaves etc., heat and smoke affect the atmosphere. All these releases gases on our atmosphere is disrupted and as a result imbalance of atmospheric gases is increasing day by day and living beings are facing man-made diseases.

Q4. Why do the astronauts wear special protective space suits?
Ans: On the moon, there is no air and hence no air pressure. Astronauts have to wear special protective space suits filled with air when they go to the moon. If they do not wear these space suits, the counter-pressure exerted by the body of the astronauts would make the blood vessels burst. The astronauts would bleed.

Q5. What is insolation? What are its effect?
Ans: An important factor that influences the distribution of temperature is insolation. The amount of insolation decreases from the equator towards the poles. Therefore, the temperature decreases in the same manner.

Q6. Describe the composition of the atmosphere.
Ans: The composition of gases in the atmosphere can be classified as Nitrogen (78%), Oxygen (21%), Argon (0.93%), Carbon dioxide (0.03%) and water vapor (0.1%). In the atmosphere, nitrogen and oxygen are found in plentiful ratio. Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities.
Apart from these gases, tiny dust particles are also present in the air. Nitrogen is the most plentiful gas in the air. When we inhale, we take some amount of nitrogen into our lungs and exhale it. Composition of the atmosphere can be understood from the following pie chart.


Q7. What are the effects of global warming?
Ans: The effects of global warming can be summarized as under:
(i) Due to the global warming, snow and ice begin to melt and thus sea level rises. Therefore, floods occur in the coastal areas. With the increase in the global warming, the water in the ocean warms up and it heats up the surrounding air, creating hurricanes and sea storms.
(ii) Due to the global warming, changes occurred in weather patterns and this affected as a serious public health. With the increase in the rainfall, waterborne diseases are likely to spread.
(iii) Due to the global warming, many places may face conditions of droughts. As a result food shortage may occur.
(iv) Due to the global warming, as more carbon dioxide is trapped in the atmosphere, breathable air becomes harder to come by. Thus, global warming may cause respiratory diseases.
(v) Due to the global warming, wild animals’ life may be in danger.
(vi) Due to the global warming, supply of freshwater may be disrupted.

Q8. Describe the structure of the atmosphere.
Ans: The whole atmosphere is divided into five layers. These include:
(i) Troposphere: This layer is most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, food and hailstorm occur in this layer.
(ii) Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50km. This layer is almost free from clouds and weather phenomena. This is most ideal for flying aeroplanes. It contains a layer of ozone gas.
(iii) Mesosphere: This is the third layer of the atmosphere. It extends upto the height of 80 km.
(iv) Thermosphere: Temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission.
(v) Exosphere: It is the uppermost layer of the atmosphere. This layer has very thin air, light gases like helium and hydrogen float into the space from here.