Learning Objectives
- Understand that air is present everywhere around us
- Learn about the composition of air
- Know the importance of air for living organisms
- Understand how air supports burning and life
Key Concepts
Air Is Everywhere
Air is present all around us, even though we cannot see it. We can feel air when wind blows. Air fills up space — when we pour water into a bottle, bubbles come out because air is being pushed out. Air is present in soil (earthworms breathe through it), in water (fish use dissolved air), and in every empty-looking space around us.
Composition of Air
Air is a mixture of many gases. The main components are:
- Nitrogen: About 78% of air. It does not support burning or breathing directly.
- Oxygen: About 21% of air. It is essential for breathing and supports burning.
- Carbon Dioxide: A very small amount (about 0.04%). Used by plants for photosynthesis.
- Water Vapour: Present in varying amounts. It determines humidity.
- Other gases: Argon, neon, helium, etc. in very small amounts.
- Dust and smoke: Tiny particles floating in air.
Oxygen and Breathing
All living organisms need oxygen for respiration (breathing). Humans and animals breathe in oxygen and breathe out carbon dioxide. Plants also breathe, but during the day they take in more carbon dioxide for photosynthesis than they release. Animals living in water use the oxygen dissolved in water.
Oxygen and Burning
Oxygen is needed for burning (combustion). Without oxygen, things cannot burn. If we cover a burning candle with a glass jar, it goes out after some time because the oxygen inside the jar is used up. This shows that air contains a limited amount of oxygen.
Carbon Dioxide
Carbon dioxide is used by plants to make food through photosynthesis. It is also released when things burn and when animals breathe out. Too much carbon dioxide in the air can be harmful. Planting more trees helps balance the gases in the air.
Air Pollution
When harmful gases, smoke, and dust are added to the air, it becomes polluted. Sources of air pollution include vehicle exhaust, factory smoke, burning garbage, and dust from construction. Air pollution is harmful to health and the environment. We can reduce it by planting trees, using clean energy, and reducing the burning of fossil fuels.
Summary
Air is a mixture of gases found everywhere around us. It mainly contains nitrogen (78%) and oxygen (21%), along with small amounts of carbon dioxide, water vapour, and other gases. Oxygen is essential for breathing and burning. Carbon dioxide is used by plants for photosynthesis. We must keep the air clean by reducing pollution and planting trees.
Important Terms
- Atmosphere: The blanket of air surrounding the Earth
- Nitrogen: The most abundant gas in air (78%)
- Oxygen: The gas essential for breathing and burning (21%)
- Carbon Dioxide: The gas used by plants for photosynthesis
- Water Vapour: Water in gas form present in air; causes humidity
- Combustion: The process of burning, which requires oxygen
- Air Pollution: Contamination of air with harmful substances
Quick Revision
- Air is a mixture of gases: 78% nitrogen, 21% oxygen, and other gases
- Oxygen supports breathing and burning
- Carbon dioxide is used by plants for photosynthesis
- Air contains water vapour (varies by humidity), dust, and smoke
- A candle goes out in a closed jar because oxygen is used up
- Dissolved oxygen in water is used by aquatic animals
- Air pollution is caused by smoke, vehicle exhaust, and factory emissions
- Trees help purify air by absorbing CO₂ and releasing O₂