Air Around Us
Atmosphere-
The earth is surrounded by a thin layer of air which extends up to several kilometres above the surface of the earth.
•As we move higher, the air gets rarer that is why mountaineers carry an oxygen cylinder with them while climbing a high mountain.
What is air made up of?
Major components of air are –
•Water vapour-Water evaporates to form water vapour and then by the process of condensation, water vapours condenses to form droplets.
•Oxygen- A most important component of air as
– Life on earth is possible because of this gas
– Supports burning.
•Nitrogen – The major part of air contains nitrogen
– It does not support burning.
•Carbon dioxide- Plants use carbon dioxide to prepare food.
– Excess of carbon dioxide may make us feel suffocated.
•Dust and smoke –The burning of fuel produces smoke which is harmful to the environment.
– Dust particles are always present in the air.
How does oxygen become available to animals and plants living in water and soil?
•Oxygen is dissolved in water, which helps animals and plants to breath inside the water.
•Animals form burrows and holes that make spaces available for air to move in and out of the soil .when it rains heavily, water fills in these holes and animals come out for respiration.
How is the oxygen in the atmosphere replaced?
The balance of oxygen and carbon dioxide is maintained through the exchange of these gases between plants and animals. Plants give oxygen for respiration to animals and in return take carbon dIoxide from animals for the process of photosynthesis.
EXERCISE
1. What is the composition of air?
Answer-
Air comprises of:
1- water vapour
2- Oxygen
3- Nitrogen
4- Carbon dioxide
5- Dust and smoke
2. Which gas in the atmosphere is essential for respiration?
Answer-
Oxygen is essential for respiration.
3. How will you prove that air supports burning?
Answer-
#Take a candle.
#Place it in on the table.
# Light the candle
# Now, cover the candle with a glass.
#We will find that the candle blows out after some time,.
We observe that oxygen in the air makes burning possible and when we put glass over it, oxygen supply cut off and candle blow out. Therefore, air supports oxygen.
4. How will you show that air is dissolved in water?
Answer-
Take some water in a glass. Heat it slowly. Before the water begins to boil, look carefully at the inner surface of the container. We can see bubbles inside it. This bubble comes from the air dissolve in water.
5. Why does a lump of cotton wool shrink in the water?
Answer-
Air is filled between the lump of cotton wool. When we keep wool in water, it shrinks because water is filled in that area by replacing air and this is a reason why lump of cotton wool shrink.
6. The layer of air around the earth is known as _____________.
Answer-
atmosphere.
7. The component of air used by green plants to make their food, is____________.
Answer-
carbon dioxide.
8. List five activities that are possible due to the presence of air.
Answer-
Activities that are possible due to air are:
1- Respiration
2- Water cycle
3- Generation of electricity with the help of windmill
4- Movement of sailing yachts
5- Photosynthesis
9. How do plants and animals help each other in the exchange of gases in the atmosphere?
Answer-
Plants and animals are interdependent on each other. Plants give oxygen to animals for breathing while taking carbon dioxide to make their food through the process of photosynthesis.
