Important Questions for CBSE Class 7 Science Our Environment Chapter 4 - Air

Very Short Answer Questions:                                                                    1 Mark

1. Fill in the blanks:

i. The ____ contains the gases which sustain life on this planet.

Ans: The troposphere contains the gases which sustain life on this planet.

ii. The ____ is free of clouds. 

Ans: The stratosphere is free of clouds.

iii. As we go up the layers of the atmosphere, the temperature _____. 

Ans: As we go up the layers of the atmosphere, the temperature decreases.

iv. When clouds condense and fall down in liquid form, it is called ___. 

Ans: When clouds condense and fall down in liquid form, it is called rain.

2. State true and false:

i. Bulk of the atmosphere is made from 78% nitrogen and 21% oxygen.

Ans: True

ii. The atmosphere provides protection to the earth and sustains life on the planet.

Ans: True

iii. Weather changes on an hourly basis.

Ans: True

iv. Air pressure exerts pressure on the moon.

Ans: False

3. Match the following:

Ans:

4. Choose the correct option:

i. _____ protects from the harmful sun rays. 

1. Carbon dioxide

2. Ozone 

3. Nitrogen

4. Oxygen

Ans: (b) Ozone

ii. _____ is the most important layer of the earth.

1. Thermosphere

2. Troposphere

3. Mesosphere

4. Stratosphere

Ans: (b) Troposphere

5. Define the following:

i. Monsoon 

Ans: Monsoon is a seasonal wind that blows over the Indian Ocean. It results in huge rainfall in the Indian subcontinent. It begins in June.

ii. Wind

Ans: A wind can be defined as the horizontal flow of air from a region with high pressure to a region with low pressure. The difference in air pressure causes this movement of the air.

Short Answer Questions: 2 Marks

6. What is the definition of atmosphere?

Ans: The atmosphere can be defined as follows:

• The atmosphere is a massive blanket of air surrounding the earth.

• It is composed of several gases like nitrogen, oxygen, and water vapour. 

• It gives us air for breathing, protects the earth from the harmful rays of sun, and also maintains its temperature. In simple words, the atmosphere is the component that helps life to sustain on the planet.

7. Define air pressure.

Ans: The atmosphere exerts pressure on the earth’s surface. This weight of air on the surface of the earth is defined as air pressure.

8. Tell the name of three types of rainfalls.

Ans: The three different types of rainfall are as follows:

• Convectional rainfall

• Orographic rainfall

• Cyclonic rainfall

9. What do you mean by weather? 

Ans: The state or condition of the atmosphere at a particular place at a particular time is called weather. It changes on an hourly and daily basis.

10. Which gas is responsible for greenhouse effect?

Ans: Carbon dioxide is the gas responsible for the occurrence of the greenhouse effect.

Short Answer Questions:                                                                     3 Marks

11. Why do wet clothes take a longer time to dry on a humid day?

Ans: Wet clothes dry when the water on them escapes into the atmosphere. On humid days, the water vapour content in the air is already quite high. This affects the rate of evaporation which means that only less quantity water is able to escape in the atmosphere from the wet clothes. As a result, the clothes take a longer time to dry on a humid day.

12. From the equator to poles the amount of insolation decreases, why?

Ans: The amount of insolation decreases from the equator to the poles because of the sun rays. This can be defined as follows:

• The rays of the sun cover a shorter distance while travelling to the equator as the equator is comparatively closer to the sun. These rays are also vertical. Consequently, the insolation is higher at the equator. 

• Simultaneously if moved towards the poles, the rays become more angled. These rays also have to travel a longer distance to reach the poles as the poles are located comparatively far from the sun.  As a result, the heat in the process. 

Thus, the amount of insolation received reduces from the equator towards the poles.

13. What are the main elements that make the atmosphere?

Ans: The main elements that make up the atmosphere are as follows:

• Nitrogen is the most abundant gas which makes up about $78$% of the atmosphere. 

• The next major element is oxygen which consists of $21$% of the total mass of air present in the atmosphere.

• Argon and carbon dioxide make up $0.93$% and $0.03$% respectively

• Apart from these, other elements helium, ozone, hydrogen, minute dust particles are found in minor quantities. 

(Image Will Be Updated Soon)

Figure 4.1: Main elements that make up the atmosphere

14. How do the bacteria help plants in getting nitrogen from the air?

Ans: For plants, nitrogen is a very essential element to survive. But plants cannot take nitrogen directly from the atmosphere. This is when bacteria play an important role in delivering nitrogen from the atmosphere to plants. They intake the atmospheric nitrogen, converts it into a usable form that is suitable for plants. In this way, plants get nitrogen due to the functions of the bacteria.

15. Why do astronauts wear special suits whenever they participate in interstellar travel?

Ans: When they go for interstellar travel there isn’t any kind of atmosphere or atmospheric pressure present there. In such a situation, the normal human bodies of astronauts would exercise counter pressure. This would result in the bursting of their blood vessels and consequent bleeding. Hence, to resist that pressure and avoid such disastrous circumstances, astronauts wear special suits whenever they participate in interstellar travel.

Long Answer Questions:                                                                             5 Marks

16. Write a short note on the pressure distribution present in the atmosphere.

Ans: Air pressure is applied on the surface of the earth by the weight of air. This air pressure is not even and varies from place to place. The distribution of air pressure can be explained as follows:

• The atmospheric pressure falls rapidly with the growing height in the atmosphere. At sea level, the air pressure is highest whereas it decreases with the increase in height. 

• The temperature of the air plays a crucial role in determining the pressure of the air at a particular place. The hotter the air, the less pressure it exerts. Hence, places with higher temperatures rise the temperature of the air and it rises upward. This helps to create a low-pressure area. Similarly, places with lower temperatures feel higher air pressure.

17. Define wind and mention different kinds of winds.

Ans: The movement of the air from high-pressure areas to low-pressure areas is defined as wind. 

The wind is divided into three major kinds:

• Permanent wind: These are winds which blow the whole year in the same direction. Westerlies, easterlies and trade winds are permanent winds.

• Seasonal winds: Winds that change their directions in different seasons are called seasonal winds. For example – Monsoon.

• Local Winds: Winds blowing in a certain area for a shorter period are called local winds. For example – Loo.

18. Explain the different kinds of layers of the atmosphere. 

Ans: Atmosphere is divided into the following five parts: 

• Troposphere: This is the first layer of the atmosphere. The air we breathe as well as other gases are present in the troposphere. The troposphere extends up to an average height of about $13$km. Every phenomenon related to weather takes place in this layer.

• Stratosphere: This comes after the troposphere. The stratosphere has its existence up to a height of about $50$km. Aeroplanes fly in the stratosphere as it is almost devoid of clouds and weather phenomena. This layer also contains ozone gas which protects the earth from fatal sun rays. 

• Mesosphere: Mesosphere extends at a height of $80$ km and it starts where the stratosphere ends. The meteorites that come from space burn up here after entering the atmosphere.

• Thermosphere: The temperature increases at a faster rate with a rise in height in this part of the atmosphere. As the ionosphere is present in this layer, it aids in radio transmission. It extends at altitudes between $90{\text{ - }}400$ km.

• Exosphere: It is the atmosphere's last and uppermost layer. It is filled with air. Hydrogen and helium are common here.

(Image Will Be Updated Soon)

Figure 4.2: Layers of the atmosphere

19. Why is the temperature of the cities higher than that of villages?

Ans: Temperature of the cities higher than that of villages because of the following reasons:

• Villages are the natural habitat of the people. Cities are the extended and modern version of the villages with a higher population. Hence, cities are very crowded with a larger rate of pollution. This pollution is caused due to gases emitted by vehicles and factories. These gases help in the rising of the temperature of the cities. 

• The asphalt of roads, buildings’ concrete metals also soak the heat in the day and release it during the night, increasing the temperature of the cities as compared to the villages.

• Also, the tall buildings present in the cities confines the hot and warm air and thus increase the temperature.

20. What is rainfall? What happens when excess rainfall takes place?

Ans: Rainfall can be defined as follows:

• Precipitation that falls on the surface of the earth in liquid form is termed rain. 

• It occurs due to the condensed gases which rise above the earth due to the high pressure of the wind and fall in the form of liquid droplets on the earth surface. 

• The rainfall on the earth takes place due to gravity. 

• Rainfall is also the main source of groundwater.

• When excess rainfall takes place, it results in the occurrence of floods.