1. Air And Properties Of Air -
ü Air is simply a mixture of different gases. The could of gas present around us on the planet earth is called as atmosphere.
ü Earth’s atmosphere consist of 78% Di-nitrogen gas, 21% Di-oxygen gas and 1% other gases that include Carbon Di-oxide, Carbon Mono-oxide, Helium etc.
ü The atmosphere extends up to several kilometers. It has layers namely Troposphere, Stratosphere, Mesosphere, Thermosphere, Ionosphere etc.
ü The air becomes thinner and thinner as we go high up from the surface of the earth. The first 10 km layer from surface of earth is called Troposphere. Clouds are present at the end of this layer.
ü The atmosphere is quite active due to the movement of air, with respect to the earth. Many gases interact with each other and several reactions occur in atmosphere.
ü The processes like cloud formation, thundering, rain etc., occur in the atmosphere.
ü Air is colourless, it has no colour and as well as taste.
ü Air is transparent i.e., we can see through it. It can not be seen but it can be felt.
ü Air occupies space. It fills all the space in a container which is otherwise empty and seems to be empty.
ü Air exerts pressure in all directions.
2. Uses Of Air -
ü Air exerts force on objects that come in its way. This property of air is quite useful. The air current makes the windmills to rotate.
ü Air helps in the movements of sailing yachts, sliders, parachutes and aircraft.
ü Air also helps in dispersal of seeds and pollen of flowers.
ü Compressed air is used in wheel cover of vehicles.
ü Nitrogen is used on a large scale to manufacture fertilizers.
ü Winnowing is possible only because of the air.
ü Air is also useful for playing several musical instruments.
ü Birds, bats and many insects fly in the air.
ü We cannot hear the sounds in the absence of air.
ü Various components of airplay various important roles.
3. Composition Of Air -
ü Water vapors - Air contains water vapors. When air comes in contact with a cool surface, it gets cooled and fog appears. The presence of water vapour in the air is important for the water cycle in nature.
ü Oxygen - The component of air that supports burning is called oxygen. Oxygen is necessary for the survival of all living beings. It is required in respiration. Percentage of oxygen in the air is around 20.95%.
ü Nitrogen - The major part of the air is nitrogen. It takes up four-fifth of the space (be around 78.11%) that air fills. Nitrogen does not support burning.
ü Carbon dioxide - Carbon dioxide makes up a small component (0.03%) of air around us. It causes a feeling of suffocation. All materials, when they burn consume oxygen and produce carbon dioxide. It is also produced along with water vapour during respiration. Plants need carbon dioxide for photosynthesis and to live.
ü Dust particles - Air contains dust particles. The presence of dust particles in air varies from place to place and time to time.
4. Breathing in Humans And In Plants -
ü Both animals and humans breathe by inhaling oxygen and exhaling carbon dioxide. this process is termed as respiration.
ü Plants respire through the process of photosynthesis. In this process, they take in carbon dioxide and give out oxygen as a waste, which we breathe in.
ü Photosynthesis is a biological process used by plants to prepare their food with the help of sunlight and energy. Carbon dioxide is taken in and oxygen is given out as a waste product in this process.
NCERT PRACTICE QUESTIONS
1. What is the composition of air?
Ans. - Air consist of water vapor, Oxygen, Nitrogen, Carbon dioxide, dust and smoke.
2. Which gas in the atmosphere is essential for respiration?
Ans. - Oxygen in the atmosphere is essential for respiration in humans while plants utilize carbon dioxide.
3. How will you prove that air supports burning?
Ans. - Cover the burning candle with glass cup, when air is blocked the candle goes off.
4. How will you show that air is dissolved in water?
Ans. - Heat the pan filled with water. Before they start boiling bubbles occur, these bubbles are due to air present in water. This experiment concludes air is present in the water.
5. Why does a lump of cotton wool shrink in water?
Ans. -The lump of cotton wool shrink in water because the air inside the cotton lumps are replaced by water which makes the layer stick together.
6. The layer of air around the earth is known as ___________.
Ans. - Atmosphere.
7. The component of air used by green plants to make their food, is ___________.
Ans. - Carbon dioxide.
8. List five activities that are possible due to the presence of air.
Ans. - 1.Photosynthesis 2.Cloud formation 3.Respiration 4.Transpiration 5.Winnowing
9. How do plants and animals help each other in the exchange of gases in the atmosphere?
Ans. - Plants in-take carbon dioxide to give out oxygen. This oxygen is used by animals for respiration, animals expel out carbon dioxide. This carbon dioxide is used by plants to prepare food.
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