Air is all around us. We cannot see it, but we can feel it when the wind blows. We breathe air every moment, but we rarely think about it. Air is essential for all living organisms. Without air, there would be no life on Earth. In this chapter, we learn about air, its components, and its importance.
Air is a mixture of many gases. The main components of air are nitrogen, oxygen, carbon dioxide, water vapour, and some other gases. Oxygen supports burning and is needed for respiration. Nitrogen is present in the largest amount. Carbon dioxide is used by plants to make food.
We also learn how to prove that air occupies space, has weight, and is present everywhere, even in soil and water. We study the atmosphere, the composition of air, and the importance of air for all living things. Air is truly a precious resource.
Air is present everywhere around us. It is present in the atmosphere, in the soil, and even dissolved in water. We can prove that air is present everywhere with simple experiments:
These experiments show that air is everywhere, it occupies space, and it has weight.
The blanket of air that surrounds the Earth is called the atmosphere. The atmosphere extends many kilometres above the surface of the Earth. It is held around the Earth by the force of gravity.
The atmosphere has many functions: - It provides the air that living organisms need to breathe. - It protects us from the harmful rays of the Sun. - It keeps the Earth warm by trapping some of the Sun's heat. - The weather and wind are caused by the movement of air in the atmosphere. - The atmosphere contains water vapour, which forms clouds and brings rain.
The atmosphere is divided into different layers. The layer closest to the Earth is called the troposphere, where we live and where weather changes happen.
Air is a mixture of several gases and other substances. The main components of air are: - Nitrogen: About 78% of air is nitrogen. It is present in the largest amount. Nitrogen is a very inactive gas and does not support burning. - Oxygen: About 21% of air is oxygen. Oxygen is essential for respiration and burning. - Carbon dioxide: A small amount of carbon dioxide is present in air. Plants use it to make food. - Water vapour: Air contains water vapour, which forms clouds and rain. - Other gases: Small amounts of argon, helium, neon, and other gases are also present. - Dust particles: Air also contains tiny dust particles and smoke.
The amount of water vapour in air varies from place to place and time to time. Air over the sea has more water vapour than air over the desert.
Oxygen is the most important gas for life processes. It has two main functions: - Supports respiration: All living organisms need oxygen to breathe and get energy from food. When we breathe in, we take in oxygen, and when we breathe out, we release carbon dioxide. - Supports burning: Oxygen supports burning. A substance burns only when oxygen is present. When we cover a burning candle with a glass jar, the candle goes out after some time because the oxygen inside the jar is used up.
We can prove that oxygen supports burning with a simple activity. When a burning candle is covered with an inverted glass, the flame flickers and goes out because the oxygen gets used up.
Nitrogen: Nitrogen is present in the largest amount in air (about 78%). It is a very inactive gas. It does not support burning, and we cannot breathe nitrogen alone. Nitrogen is important for the growth of plants. Some plants get nitrogen from the soil with the help of bacteria. Although we breathe in nitrogen with air, our body does not use it, and we breathe it out.
Carbon dioxide: Carbon dioxide is present in a small amount in air. Plants use carbon dioxide and sunlight to make food through photosynthesis. In this process, plants give out oxygen. During respiration, animals and humans give out carbon dioxide. The balance of carbon dioxide and oxygen in air is maintained by plants and animals.
There is a beautiful balance between plants and animals in nature: - Plants take in carbon dioxide and give out oxygen during photosynthesis. - Animals take in oxygen and give out carbon dioxide during respiration. - Plants use the carbon dioxide given out by animals, and animals use the oxygen given out by plants.
This exchange of gases maintains the balance of oxygen and carbon dioxide in the air. This is why trees and forests are so important. Cutting down trees reduces the oxygen in the air and increases carbon dioxide, which is harmful for all living things.
Air is useful to us in many ways: - We breathe air to get oxygen. - Oxygen is used for burning fuels like wood, coal, and petrol. - Air helps in the drying of clothes, food grains, and other things. - Wind energy is used to generate electricity and to run windmills. - Air helps birds and aeroplanes to fly. - The movement of air, called wind, helps in the dispersal of seeds and pollen. - Air-filled tyres make vehicles comfortable to ride.
Air is essential for life and for many human activities. Without air, plants and animals cannot survive.
Air in motion is called wind. Wind can be gentle or very strong. Wind is caused by the unequal heating of the Earth's surface by the Sun. Warm air rises, and cooler air moves in to take its place, creating wind.
Wind has many uses: - Wind blows away the lighter chaff in winnowing. - Sailboats use wind to move across water. - Windmills use the energy of wind to grind grain or pump water. - Modern wind turbines use wind energy to generate electricity. - Wind helps disperse pollen and seeds of plants.
Strong winds can also cause damage during storms and cyclones. Air and wind are powerful forces of nature.
Air pollution is a serious problem. Smoke from factories and vehicles, and burning of fuels, add harmful gases and dust to the air. Polluted air can cause many diseases and harm plants and animals.
We can help keep the air clean by: - Planting more trees. - Using public transport or bicycles instead of private cars. - Not burning garbage and leaves. - Reducing the use of vehicles and fuels. - Following rules to control pollution from factories.
Clean air is essential for good health and for the survival of all living things. We must protect the air around us.
| Gas | Percentage in Air | Role |
|---|---|---|
| Nitrogen | About 78% | Largest component, inactive gas |
| Oxygen | About 21% | Supports burning and respiration |
| Carbon dioxide | Small amount | Used by plants to make food |
| Water vapour | Variable | Forms clouds and rain |
| Activity | Proves That |
|---|---|
| Empty glass in water | Air occupies space |
| Bubbles from soil in water | Air is present in soil |
| Inflated balloon heavier | Air has weight |
| Heating water, bubbles appear | Air is dissolved in water |
In this chapter, we discovered the invisible world of air around us. We learned that air is present everywhere, even in soil and water, and that it occupies space and has weight. The blanket of air around the Earth, called the atmosphere, protects life and shapes our weather. Air is a mixture of gases, with nitrogen in the largest amount, oxygen supporting life and burning, and carbon dioxide used by plants. We understood the beautiful balance in which plants give out oxygen and animals give out carbon dioxide. We also learned about wind, the uses of air, and the importance of keeping the air clean. Air is the invisible gift of nature that sustains every breath of life.