Air
- A mixture of gases.
- One of the three states of matter.
- Present everywhere around us.
- Present in the soil and water as well.
- It has no color and it is transparent.
- We cannot see air but we can feel its presence around us.
- It occupies the entire available space.
What is air made up of?
Air is made up of a number of gases in various proportions. The major components of air are:- Water vapor: When air comes in contact with a cool surface, small droplets of water are formed on the surface. Water vapor present in the air when comes in contact with the cool surface, it immediately condenses into droplets of water. This shows that there is water vapor in the air. The presence of water vapor in air is important for the water cycle in nature.
- >Oxygen: an important component of air which supports life on Earth. Oxygen is the gas which supports combustion which means burning can take place only in the presence of oxygen. All the plants and animals take in / breathe in oxygen during the process of respiration. Aquatic animals (animals that live in water) take the oxygen dissolved in water for respiration while insects that live in the soil take the dissolved oxygen from the soil.
Place two candles each in two separate shallow trays and fill the trays with water. Light the candles and cover the burning candles with inverted glass jars of different sizes. Observe the burning candles and the level of water inside each of the inverted jar. The candle inside the smaller jar blows out faster and the level of water rises up. This is because the limited oxygen inside the jar was used by for burning the candle which blown off when there is no more oxygen inside the jar. The space inside the jar which was occupied by oxygen is then replaced by water. Oxygen supports combustion. Burning is not possible in the absence of oxygen.
Activity 2
Take some water in a container and look at its inner surface. There are no bubbles inside. Now heat it over low flame. As the water gets heated you can see tiny bubbles formed on the inner surface of the container. The air dissolved in water escapes out on heating and finally the water itself changes into vapor (its gaseous form) and goes out.
- Nitrogen: the major component of air which occupies nearly four-fifth of the atmospheric air. Nitrogen is a gas which does not support combustion i.e. burning.
- Carbon dioxide: A small part of the air is occupied by carbon dioxide. A majority of the gas is produced during the respiration process of plants and animals. When plant and animal products are burnt, carbon dioxide and other gases are produced.
- Dust and smoke: Smoke is produced by the burning of fuel. It contains small dust particles and few harmful gases. Dust particles are always present in the air and these can be seen in a beam of light entering into a dark room through a small opening.
How the atmosphere is getting oxygen?
All the green plants are capable of making their own food through a process called photosynthesis. During this process, oxygen is produced which is released into the air. However, plants use oxygen during respiration but they produce more oxygen than what they consume.Animals get the required oxygen from plants. While plants get carbon dioxide from the animals. Thus, the balance of oxygen and carbon dioxide in the atmosphere is maintained and both plants and animals are interdependent on each other.
Importance of air / wind
- Moving air is called wind.
- Wind helps in the movement of sail boats, yachts, gliders, parachutes etc.
- It also helps in the dispersal of seeds and pollen of flowers.
- It helps the birds and insects to fly.
- It helps the windmills to rotate. Windmills are used for drawing water from tube wells and also help in running flour mills. These are also used generate electricity which is known as wind energy.
- Air / wind plays an important role in water cycle in nature.
Exercises
- What is the composition of air? Ans. Air is composed of water vapor, oxygen, nitrogen, carbon dioxide, dust particles and smoke.
- Which gas is essential for respiration? Ans. Oxygen in the air is essential for living beings during the process of respiration.
- How will you prove that air supports burning? Ans. Refer Activity 1 above.
- How will you show that air is dissolved in water? Ans. Refer Activity 2 above.
- Why does a lump of cotton wool shrink in water? Ans There is air in the pores of the lump of cotton wool. When wool is dipped in water, the air in it escapes out and thus the wool shrinks.
- The layer of air around Earth is known as atmosphere.
- The component of air used by green plants to make their food is carbon dioxide.
- List five activities that are possible due to the presence of air. Ans Five activities that are possible due to the presence of air are:
- Respiration in living things.
- Photosynthesis in green plants.
- Rotating of windmills to produce electricity.
- Burning of fuel and other things.
- Dispersal of seeds and pollen.
- How do plants and animals help each other in the exchange of gases in the atmosphere? Ans. Plants and animals take in oxygen from the atmosphere and give out carbon dioxide during respiration process. Green plants take in carbon dioxide from the atmosphere for making their own food through a process called photosynthesis and give out oxygen. Thus, green plants help animals by giving them oxygen while animals help green plants by giving them carbon dioxide.