Why Oxygen and Nitrogen Matter So Much in the Air We Breathe

Oxygen is essential for breathing, burning (combustion), and rusting, while nitrogen helps control oxygen's reactivity and is needed by plants and animals for making proteins. In ICSE Class 6 Chemistry, you will learn how these gases keep life going and how other air components like carbon dioxide and noble gases have special uses. This article covers the roles of oxygen and nitrogen, how rusting happens and can be prevented, the balance between photosynthesis and respiration, and the causes and control of air pollution.

Oxygen is vital for three main processes: respiration, combustion, and rusting. In respiration, living things use oxygen to release energy from food. Combustion is the burning of substances like wood, LPG, or petrol, which also requires oxygen to produce heat and light. Rusting is a slow reaction where iron reacts with oxygen and water to form a brownish substance called rust. For iron to rust, two conditions are necessary: the presence of both air (oxygen) and water. To prevent rusting, we can (1) coat iron objects with paint or oil to keep air and water away, or (2) use a method called galvanization, where iron is coated with a layer of zinc. For example, bicycles left outside in the rain often develop rust because both air and water are present. Many students think rusting happens only with water, but oxygen is equally necessary.

Nitrogen makes up most of the air and plays two important roles: it reduces the strong effects of oxygen and provides essential nitrogen for making proteins in plants and animals. If air had only oxygen, fires would burn out of control and living things could be harmed. Nitrogen keeps these reactions in check. Plants absorb nitrogen (mainly from the soil, after it is fixed by bacteria or lightning) to make proteins, which are needed for growth and repair. Besides nitrogen, air also contains carbon dioxide (used by plants for photosynthesis), water vapour (which causes humidity and rain), and noble gases like argon (used in bulbs to prevent the filament from burning). For example, the nitrogen in the air helps keep a candle burning steadily instead of flaring up. Some students mistakenly believe plants can use nitrogen directly from the air, but most plants need it in a combined form from the soil.

Photosynthesis and respiration are opposite processes that keep the amounts of oxygen and carbon dioxide in air balanced. During photosynthesis, green plants use sunlight to turn carbon dioxide and water into food (glucose) and release oxygen. The word equation for photosynthesis is:

Carbon dioxide + Water $\stackrel{sunlight}{\to }$ Glucose + Oxygen

Respiration is when living things use oxygen to break down food and release energy, producing carbon dioxide and water as waste. Because plants take in carbon dioxide and give out oxygen, while animals do the opposite, the levels of both gases stay fairly constant. For example, during the day, plants in a garden produce oxygen, while people and animals breathe it in and release carbon dioxide. Many students think only animals respire, but plants also respire all the time, even as they photosynthesize.

Air pollution is caused by harmful substances entering the air, making it unsafe for living things. Major causes include smoke from factories and vehicles, burning of fuels, and the release of harmful gases. These pollutants can cause acid rain (when gases like sulphur dioxide mix with rainwater), which damages plants, buildings, and aquatic life. Another harmful effect is the depletion of the ozone layer, which protects us from harmful ultraviolet rays. To control air pollution, practical steps include using cleaner fuels, planting more trees, using public transport, and reducing the burning of waste. For example, cities with many vehicles often have smog, making it hard to breathe. Some students think air pollution only affects cities, but it can harm villages and forests too, especially when wind carries pollutants over long distances.