7 Class. Ch 4.Air Around Us.

7 Class. Geography

Chapter 4. Air Around Us.

Keywords :

Global Warming : a gradual increase in the overall temperature of the earth's atmosphere.

Immunity : amount of water vapors in the atmosphere

monsoons : seasonal reversal of the wind direction according to the change in the season

photosynthesis : plants observes Co2 in the presence of sunlight and turn that energy into food
Something to Know -

Tick the correct options :

1.in the normal lapse rate temperature decreases at the rate of 1 degree with every

(a) 165 m ascend

(b) 175 m ascend

(d) 195 m ascend

2. Which layer is safe for flying air crafts

(a) troposphere

(b) stratosphere

(d) thermosphere

3. The role of ionparticles in the atmosphere is to

(e) absorb ultraviolet rays

(b) enable wireless communication

(d) enable rainfall

4. Which one of the following in the main cause of global warming?

(a) air pollution

(b) water pollution

(d) land degradation

5. Smog causes

(a) breathing problems

(b) purification of air

(d) reduction in temperature

B. fill in the blanks :

1. Atmosphere is mainly composed of three major gases nitrogen.oxygen and carbon dioxide.

2. Gases like argon, helium, methane, etc, are present in small amounts in the air.

3. All weather phenomena occur in the troposphere.

4. Amospheric conditions over a long period of time and on a larger area is called climate.

5. The normal air pressure to level is 1013 milibar.

C. Match the following :

1. Mono oxide gas. b. Most harmful gas present in the atmosphere.

2. Weather. e. Atmospheric conditions for a specific place covering a short period of time.

3. Barometer d. An instrument to measure atmospheric pressure.

4. Atmospheric Pressure a.Weight or pressure exerted by the air

5. Rainfall c.The falling of water drops on the earth's surface.

D. Answer the following questions in brief.

1. Name the layers of the atmosphere.

Ans. The layers of the atmosphere are -

Troposphere

Stratosphere

Mesosphere

Thermosphere

2. How do plants absorb nitrogen?

Ans. Plants absorb nitrogen through the soil.

3. What is the importance of water vapours in the atmosphere?

Ans. Water vapour in the atmosphere causes of rainfall and snowfall.

2 .Name the different variables of atmosphere.

Ans. Atmosphere consists of three major gases - nitrogen, oxygen and carbon dioxide. Water vapours and dust particles are also important components of the atmosphere.

5. What type of climate does India have?

Ans. India has monsoonal climate.

E. Answer the following questions.

1. What is the importance of carbon dioxide and oxygen for living beings?

Ans. Carbon dioxide is an important gas in maintaining the life cycle of plants over the earth.The carbon dioxide gas absorbs heat of the sun and warms up the lower atmosphere of the earth's surface.

All living organisms in inhale oxygen from the surrounding air to stay alive. Hence oxygen is known as a life supporting gas.

2. Name three major sources of pollutants in the air. Also state the ill - effects of these air pollutants.

Ans. Playing automobiles in cities release gaseous pollutants like carbon monoxide, sulphur dioxide and lead particles causing air pollution which in turn is a cause of several diseases. The smoke particles when combined with fog from smog, causing serious health problems.

3. What is the importance of ozone gas? Why is global warming a threat to life on the earth?

Ans. In the absence of the ozone gas in the atmosphere, life would have been impossible on the surface of the earth. The carbon dioxide has a property to observe heat, it increases temperature of the atmosphere which in tern increases the temperature over the earth's surface. This is the cause of global warming which will decrease the life support system over this planet.

4. How is rainfall caused? Explain it with the help of a diagram.

Ans. As the hot air rises, it reaches high in the atmosphere where it cools down due to the presence of low temperature there. Thus, the water present in the form of water vapours condenses into tiny droplets of water or crystals of ice. In due course of time, these tiny particles join together and form clouds. Due to further cooling these tiny condensed droplets join together to form large droplets.

These droplets become so heavy that the air cannot hold them and hence fall down as rainfall or snowfall.

5. Write the difference between weather and climate.

Ans. Weather : Weather refers to the state of atmosphere that includes its temperature, pressure and humidity for a specific place and for a short period of time.

Climate : Climate refers to the state of atmospheric condition that includes temperature, rainfall, pressure over a long period of time and covers a large area.

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