Air - Class 6 ICSE

 


7. Air


[Composition of air]

Frequently Asked Questions (FAQ):

  1. Name the main gases of the air.

The main gases of air are nitrogen and oxygen.

  1. Name the most active constituent of the air.

The most active constituent of air is oxygen.

  1. What is meant by the term ‘humidity’?

The amount of water vapour in the air is known as humidity.

  1. Air is a mixture of gases. Give reasons.

Air is a mixture of gases because:

  • The composition of air is not constant and varies from place to place and from time to time.

  • The different components of air retain their identity.

  • The components of air can be readily separated by simple physical methods.

  • No energy is evolved or absorbed when a sample of air is obtained by mixing the components of gases in proper proportions.

  1. What is the percentage of oxygen in the air?

Oxygen accounts for about 21% of dry air.

  1. Why do living things need oxygen?

To generate energy to stay alive, by the process of respiration, living things need oxygen.

  1. Describe the process of respiration.  Why is it necessary for living things?

Respiration is the process by which living beings breathe in oxygen and use it to oxidise the digested food. Carbon dioxide and water vapour are formed during this process. 

Respiration is necessary for living beings because the energy released during this process keeps them alive.

  1. Which need more energy -  animals or plants? Give reasons.

Movement in plants is usually at cellular level.  So they need a comparatively less amount of energy.  Animals, on the other hand, need to move from place to place. So they require more energy. 

  1. Describe the process of respiration in plants. Why is it important for living beings?


To carry out various life processes,  plants get energy by the process of respiration. During this process glucose breaks down in the presence of oxygen to form carbon dioxide and water along with the release of energy. 

  1. Why do plants not photosynthesise during night?

Photosynthesis is the process by which solar energy is converted into chemical energy in plants. In the absence of sunlight, plants do not photosynthesize during night.

  1. Which process continues in plants day and night -  respiration or photosynthesis?  Give a reason.

In plants, respiration continues throughout day and night. Photosynthesis happens only  during the daytime as it needs sunlight.

  1. What is photosynthesis?  Why is it an important process for plants?

Photosynthesis is the process by which solar energy is converted into chemical energy in plants.

  1. Although photosynthesis occurs in plants, but it is also important for animals. Give reasons.

Photosynthesis, in plants, prepares all the energy that fuels living organisms. Animals obtain their energy directly or indirectly from plants. Hence, photosynthesis is important for animals also.

  1. Name the substance, in plants, that traps solar energy for the process of photosynthesis.

Chlorophyll traps energy of the sun for the process of photosynthesis.

  1. Why should one not sleep under a tree at night?

At night, in the absence of sunlight,  the tree will undergo only respiration, liberating carbon dioxide. There will be no photosynthesis. Hence no oxygen will be produced.  So, it is not safe for one to sleep under a tree at night.

  1. Write the chemical reaction of photosynthesis and respiration in plants.

Photosynthesis:

CO2 + H2O  ⎯⎯⎯⎯⎯⎯⎯> C6H12O6 + O2

(carbon dioxide) (water)       (sunlight)      (glucose) (oxygen)

Respiration:

C6H12O6 + O2  ⎯⎯⎯⎯⎯⎯⎯> CO2 + H2O + Energy

(glucose) (oxygen)                 (carbon dioxide) (water vapour)


  1. Differentiate between respiration and photosynthesis.


Respiration

Photosynthesis

1

It is the process of breaking down glucose to prepare carbon dioxide and water.

It is the process of preparing glucose in the presence of carbon dioxide and water.

2

Energy is produced (Exothermic reaction)

Energy is consumed (Endothermic reaction)

3

Happens all the time.

Happens only in the presence of sunlight.


  1. Define the following terms:

    1. Inhaled air The air we breathe in is called inhaled or inspired air.

    2. Exhaled air The air we breathe out is called exhaled or expired air. 

  2. Make a comparison of gases between inhaled and exhaled air.

Component

Inhaled Air

Exhaled Air

Oxygen

20.9%

17%

Carbon dioxide

0.034%

4%

Nitrogen

78.1%

78.1%

Water Vapour

Variable

Always high


  1. Which gas is released when something is burnt in the air?

  2. Name two industrial fuels that are used to give energy.

  3. What do you understand by the term ‘rusting’?

  4. What is air pollution?

  5. Describe how plants help in maintaining the balance between oxygen and carbon dioxide in the nature.

  6. How will you show experimentally that air and moisture are necessary for rusting?

  7. Fill in or the blanks. Choose the right words from the bracket:

    1. The composition of air is  not constant   at all places. (not constant/ constant)

    2. Carbon dioxide  reacts with lime water to form calcium carbonate. (oxygen/carbon dioxide)

    3.  Warm   air contains more water vapour than  cool   air. (cool/ warm)

    4. Burning of fuels produces  carbon dioxide . ( oxygen/ carbon dioxide)

    5. In the process of respiration,  carbon dioxide   is produced as a waste product. (oxygen/carbon  dioxide)

  8.  State whether true or false:

    1. About 78% oxygen is present in the air. False

    2. Air is invisible,  tasteless and odourless. True

    3. Carbon dioxide turns lime water milky. True

    4. The air we breathe is called exhaled air. False

    5. The process of breathing in and out is called respiration. True

    6. Photosynthesis occurs throughout day/night. False

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