CHAPTER- 11 AIR AROUND US
Notes
1. During storms, the wind blows at a very high speed. Sometimes, it even uproots trees and blows away the upper parts of roofs.
2. Air is present all around us. Air has no color. We can see through it. It is transparent.
3. Atmosphere– Our Earth is surrounded by a thin layer of air. This layer extends several kilometers above the surface of the Earth and is called the atmosphere.
4. Water Vapour– Water vapour is present in the air. The presence of water vapour in the air is essential for the water cycle in nature.
5. Oxygen – The component of air that supports burning is called oxygen.
6. Smoke contains some gases and tiny dust particles, which are generally harmful.
- Dust particles are always present in the air.
- The amount of dust particles in the air keeps changing with time and place.
- When we breathe in through our nose, we take air inside. To prevent dust particles from entering the respiratory system, our nose has tiny hairs and mucus.
7. Animals that live in water use the oxygen dissolved in water for respiration.
EXERCISE
Question- 1. What is the composition of air?
Answer- Some water vapour, dust particles, and gases are present in the air. The air mainly contains nitrogen, oxygen, carbon dioxide, and several other gases. Nitrogen and oxygen together make up 99% of the air. The remaining 1% consists of carbon dioxide, some other gases, and water vapour.
Question- 2. Which gas in the atmosphere is essential for respiration?
Answer- Oxygen gas in the atmosphere is essential for respiration.
Question- 3. How will you prove that air supports burning?
Answer- Take two candles and cover one candle with a glass. After some time, one candle stops burning because during burning, oxygen is used up and carbon dioxide is released. After some time, no oxygen remains inside the glass, and the flame goes out. This proves that air supports burning.
Question- 4. How will you show that air is dissolved in water?
Answer- Take some water in a glass vessel. Heat it slowly. We observe that before the water starts boiling, air bubbles begin to rise to the surface. These bubbles are formed due to the air dissolved in the water.
Question- 5. Why does a lump of cotton wool shrink in water?
Answer- Air is present in a pile of cotton. When the pile of cotton is immersed in water, most of the air comes out and some part gets surrounded by water; therefore, it shrinks.
Question- 6. The layer of air around the earth is known as ________.
Answer- The layer of air around the earth is known as Atmosphere.
Question- 7. The component of air used by green plants to make their food, is ______.
Answer- The component of air used by green plants to make their food, is Carbon Dioxide.
Question- 8. List five activities that are possible due to the presence of air.
Answer- Five activities that are possible due to the presence of air:
1. Living beings use air for breathing (respiration).
2. Air helps in burning substances.
3. Windmills produce electricity with the help of air.
4. Plants use air (oxygen) to make food.
5. Air helps boats to sail and airplanes to fly.
Question- 9. How do plants and animals help each other in the exchange of gases in the atmosphere?
Answer- Plants and animals depend on each other. Animals breathe, for which they take in oxygen and release carbon dioxide. Plants take in carbon dioxide to make food and release oxygen. In this way, plants and animals help each other in the exchange of gases in the environment.