Air

Learning Objectives

In this chapter, students will understand the presence and importance of air in our surroundings. They will learn about the composition of air, the atmosphere, oxygen and nitrogen, water vapour, the oxygen cycle, the presence of air in soil and water, and the various uses of air in everyday life. Students will also understand why clean air is essential for all living organisms.

Introduction to Air

Air is an invisible mixture of gases that surrounds the Earth and supports all forms of life. Although we cannot see air, we can feel its presence through moving leaves, flying kites, spinning pinwheels, and blowing winds. Every living organism depends on air for survival, making it one of the most important natural resources.

The thin blanket of air surrounding the Earth is called the atmosphere. It protects life by providing essential gases and maintaining suitable environmental conditions.

Properties and Composition of Air

Air occupies space, has mass, and exerts pressure. Simple experiments, such as inflating a balloon or immersing an empty bottle in water, show that air takes up space even though it is invisible.

Air is a mixture of several gases. Approximately 78% of air is nitrogen, 21% is oxygen, and the remaining 1% consists of carbon dioxide, water vapour, argon, dust particles, and other gases.

Each component plays an important role in maintaining life and balancing the Earth’s environment.

Oxygen, Nitrogen, and Water Vapour

Oxygen is essential for the respiration of humans, animals, and many other living organisms. It also supports burning, which is why a candle goes out when the oxygen inside a covered glass is used up.

Nitrogen is the largest component of air. Although living organisms cannot directly use atmospheric nitrogen, it is important for plant growth after being converted into usable forms by nature.

Air also contains water vapour, which forms clouds and contributes to rainfall. Water vapour condenses on cold surfaces, producing tiny water droplets.

Air in Soil, Water, and the Oxygen Cycle

Air is present not only in the atmosphere but also in the spaces between soil particles and dissolved in water. Fish and other aquatic animals obtain oxygen dissolved in water for respiration, while earthworms require air present in the soil.

Plants and animals continuously maintain the oxygen cycle. During photosynthesis, plants absorb carbon dioxide and release oxygen. Humans and animals inhale oxygen and exhale carbon dioxide during respiration. This natural cycle helps maintain the balance of gases in the atmosphere.

Uses and Importance of Air

Air is essential for breathing, burning, seed dispersal, pollination, flying birds and aircraft, generating wind energy, and moving rain-bearing clouds. It also plays an important role in regulating weather and climate.

Clean air is necessary for good health. Air pollution caused by smoke, harmful gases, and dust can lead to serious health problems. Therefore, protecting air quality is everyone’s responsibility.

Practice Questions

1. What is air? Name its major components.
2. Why is oxygen important for living organisms?
3. Explain the oxygen cycle.
4. Why do bubbles appear when dry soil is placed in water?
5. Mention any three uses of air.

Answer Key

ANSWER 1

Air is a mixture of gases surrounding the Earth. Its major components are nitrogen, oxygen, carbon dioxide, water vapour, and dust particles.

ANSWER 2

Oxygen is essential because humans, animals, and many other living organisms need it for respiration and survival.

ANSWER 3

Plants absorb carbon dioxide and release oxygen during photosynthesis, while humans and animals use oxygen for respiration and release carbon dioxide. This continuous exchange is called the oxygen cycle.

ANSWER 4

Bubbles appear because air trapped in the spaces between soil particles escapes when water fills those spaces.

ANSWER 5

Air is used for breathing, burning, flying birds and aircraft, generating wind energy, moving clouds, and dispersing seeds.