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Chapter 12

Composition and Structure of the Atmosphere

Class 9 - Total Geography Morning Star


Short Answer Questions

Question 1

What is known as atmosphere?

Answer

The blanket of air surrounding the Earth is known as the atmosphere.

Question 2

State the gaseous composition of the atmosphere.

Answer

The atmosphere is a mixture of many gases and tiny solid particles. Atmosphere contains-

  1. 78% nitrogen gas
  2. 21% oxygen gas
  3. The remaining 1% of air is made up of Carbon dioxide, Water Vapour, Helium, Hydrogen, Argon etc.

Question 3

Name the four layers of the atmosphere.

Answer

The four layers of the atmosphere are-

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Question 4

What is known as troposphere?

Answer

The troposphere is the lowermost and densest layer of the atmosphere. Its height varies from 18 km at the equator to 8 km at the poles.

Question 5

Mention the chief characteristics of stratosphere.

Answer

The chief characteristics of stratosphere are-

  1. The air is thin, cold and dry. The temperature is about -55°C.
  2. The Ozone layer lies within the stratosphere. Ozone is generally found between the altitudes of 20 and 50 km.
  3. Ozone absorbs the ultraviolet solar radiation coming from above. The insolation received from the Sun is equal to that lost by it. That is why the temperature of the layer is constant. In the higher levels, however, temperature increases with height.
  4. The lower layer of the stratosphere has a virtual absence of water vapour and has constant temperature conditions, therefore, it is ideal for flying jet aircraft.
  5. Temperature rises from -60°C at the base of the stratosphere to 0°C at stratopause.
  6. The upper limit of the stratosphere is known as stratopause.

Question 6

In which layer of atmosphere do all the weather conditions occur?

Answer

All the weather conditions occur in the troposphere.

Question 7

Name the constituent gases of atmosphere which scientists consider responsible for climate change.

Answer

The constituent gases of atmosphere which scientists consider responsible for climate change are Carbon dioxide, Methane, Chlorofluorocarbons, Ozone and Water Vapour.

Question 8

What is known as Ozone Layer?

Answer

Ozone layer is a layer in the stratosphere of the atmosphere which keeps temperature constant in the lower levels and absorbs ultraviolet rays of the Sun.

Question 9

What is leading to depletion of Ozone Layer in the atmosphere?

Answer

Many chemicals like Chlorine, Bromine and Chlorofluorocarbons are leading to depletion of Ozone Layer in the atmosphere. Chlorofluorocarbon compounds escape into the atmosphere and finally break down in the Stratosphere. They produce Chlorine atoms which destroy the Ozone layer.

Sulphur dioxide given out during volcanic eruptions, solar storms and human activities also lead to depletion of Ozone layer.

Question 10

What is known as Global Warming?

Answer

The rise in average mean temperature of the Earth on account of enhanced concentration of greenhouse gases in the atmosphere is known as global warming.

Question 11

Name important Greenhouse gases.

Answer

Some important Greenhouse gases are Carbon dioxide, Methane, Chlorofluorocarbons, Ozone and Water Vapour.

Explain the following terms/processes

Question 1

Global Warming

Answer

The rise in average mean temperature of the Earth on account of enhanced concentration of greenhouse gases in the atmosphere is known as global warming.

Question 2

Greenhouse Effect

Answer

The greenhouse gases in the atmosphere allow the near infrared rays from the Sun to penetrate the Earth but do not allow the heat radiated by the heated Earth to penetrate back into space. This adds to the heat already available on the Earth.

This increase in temperature due to the concentration of the greenhouse gases is known as the greenhouse effect.

Question 3

Normal Lapse Rate of Temperature

Answer

The troposphere is characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gain.

Question 4

CFCs

Answer

Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of Carbon, Chlorine, and Fluorine. They are regarded as the main reason for the Ozone Hole near Antarctica. CFC gases are used in refrigerators, aircraft and air conditioners.

Structured Questions

Question 1(a)

Define atmosphere. Name the four layers of atmosphere.

Answer

The blanket of air surrounding the Earth is known as the atmosphere.

The four layers of the atmosphere are-

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Question 1(b)

Mention any two functions of the atmosphere.

Answer

Two functions of the atmosphere are-

  1. It protects the Earth from the harmful ultraviolet and infrared rays of the Sun.
  2. It helps in retaining the necessary warmth on the Earth.

Question 1(c)

Give a reason for each of the following:

(i) We find it difficult to breathe when we climb mountains.

(ii) The atmosphere is the most dynamic entity.

(iii) All the weather phenomena takes place in the troposphere.

Answer

(i) We find it difficult to breathe when we climb mountains because the layers of atmosphere become thinner at high altitudes. This means that there is less pressure to push the air into the lungs and a lower percentage of Oxygen in the air. This makes it harder to breath.

(ii) The atmosphere is the most dynamic entity because of its composition. Large masses of air are being moved up and down and across the surface of the Earth.

(iii) The troposphere is characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gain. This temperature variation is responsible for many turbulences which result in all weather phenomena taking place in the troposphere.

Question 1(d)

Draw a well labelled diagram of the structure of the Earth's atmosphere.

Answer

Below diagram shows the structure of the Earth's atmosphere:

Draw a well labelled diagram of the structure of the Earth's atmosphere. Composition and Structure of Atmosphere, Total Geography ICSE Class 9 Solutions.

Question 2(a)

Describe the structure of the atmosphere.

Answer

The atmosphere is a mixture of many gases and tiny solid particles. Atmosphere contains-

  1. 78% nitrogen gas
  2. 21% oxygen gas
  3. The remaining 1% of air is made up carbon dioxide, water vapour, helium, hydrogen, argon etc.
  4. Some particles like pollen from plants, dust, ash from meteorites and volcanic eruptions, smoke from fire and salt particles from the sea are also present in the lower layer of the atmosphere.

Question 2(b)

Explain the factors responsible for depletion of Ozone in atmosphere.

Answer

The factors responsible for depletion of Ozone in atmosphere are-

  1. Chemicals like Chlorine and Bromine
  2. Chlorofluorocarbon gases used in refrigerators, aircraft and air conditioners. CFC compounds escape into the atmosphere and finally break down in the stratosphere, producing Chlorine atoms which destroy the Ozone layer.
  3. Sulphur dioxide given out during volcanic eruptions, speeds up destructive chemical reactions.
  4. Solar storms consist of coronal mass ejections and solar flares associated with explosions on the surface of the Sun. They also cause Ozone layer depletion.
  5. Human activities also result in Ozone layer depletion. Due to bitterly cold Antarctic winter, the stratospheric ice clouds promote the production of chemically active Chlorine and Bromine. This leads to Ozone destruction when sunlight returns in the Antarctic spring.

Question 2(c)

State any three factors that lead to Global Warming.

Answer

Three factors that lead to Global Warming are-

  1. Destruction of Ozone layer
  2. Greenhouse effect in the atmosphere
  3. Deforestation

Question 2(d)

Draw a well labelled diagram to explain the Greenhouse Effect.

Answer

Below diagram shows the Greenhouse Effect:

Draw a well labelled diagram to explain the Greenhouse Effect. Composition and Structure of Atmosphere, Total Geography ICSE Class 9 Solutions.
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