Science STD 6 Chapter 11: Air Around Us - Exercises
1. What is the composition of air?
Air is a mixture of many gases. It mainly consists of nitrogen, oxygen, and a small amount of carbon dioxide and other gases. It also contains water vapour and dust particles.
2. Which gas in the atmosphere is essential for respiration?
Oxygen gas in the atmosphere is essential for respiration by all living organisms.
3. How will you prove that air supports burning?
To prove that air supports burning, you can conduct a simple experiment with two candles of the same size. Light both candles. Place an inverted glass tumbler over one of the candles. The candle under the glass tumbler will burn for a short time and then go off, while the other candle will continue burning. This shows that the air inside the tumbler was used up for burning, proving that a component of air (oxygen) supports combustion.
4. How will you show that air is dissolved in water?
To show that air is dissolved in water, take some water in a beaker and heat it slowly on a tripod stand. Before the water begins to boil, observe the sides of the beaker. You will see tiny bubbles forming on the inside surface. These bubbles are the air that was dissolved in the water, which is escaping due to the heat.
5. Why does a lump of cotton wool shrink in water?
A lump of cotton wool shrinks in water because the air trapped between its fibres is pushed out by the water. Since air occupies space, when it is removed, the cotton fibres move closer together, causing the lump to shrink.
6. The layer of air around the earth is known as .............
atmosphere
7. The component of air used by green plants to make their food, is .............
carbon dioxide
8. List five activities that are possible due to the presence of air.
Five activities possible due to the presence of air are:
- Flying a kite.
- Winnowing grains.
- Running a windmill to draw water or generate electricity.
- Sailing a boat with a sail.
- Birds, bats, and insects flying.
9. How do plants and animals help each other in the exchange of gases in the atmosphere?
Plants and animals are interdependent for the exchange of gases. Plants use carbon dioxide from the atmosphere to make food during photosynthesis and release oxygen. Animals and humans use this oxygen for respiration and release carbon dioxide. This process maintains a balance of oxygen and carbon dioxide in the atmosphere, allowing life to thrive.
Suggested Projects and Activities
1. On a clear glass window facing towards an open area, fix a small rectangular strip of paper... Do you notice a difference between the rectangular section that was left covered with paper and the rest of the glass window?
Outline: This activity is a long-term experiment to observe the presence of dust and other pollutants in the air. The covered part of the window will remain clean, while the exposed area will accumulate dust. This demonstrates that air contains dust particles and helps visualize air pollution. Repeating the activity at different times of the year can show how the amount of dust varies.
2. Observe the leaves of trees, shrubs or bushes planted by the roadside... Is there any difference in deposition of soot on leaves of trees near the roadside?
Outline: This activity is a comparative study of air pollution in different locations. Students will observe and compare the amount of soot on leaves of plants near a busy roadside versus those in a cleaner area like a garden. The leaves near the roadside will have a thicker layer of black soot, indicating that vehicles produce smoke and dust that pollute the air. The activity demonstrates the effects of air pollution and its localized impact.