How Your Body Turns Air Into Energy

Breathing is the physical process of taking in oxygen-rich air and giving out carbon dioxide, while respiration is the chemical process by which cells use oxygen to release energy from food. In breathing, air enters and leaves the lungs, but in respiration, oxygen is used by cells to break down glucose and produce energy, carbon dioxide, and water. There are two types of respiration: aerobic (with oxygen) and anaerobic (without oxygen). Aerobic respiration is more common in humans and releases more energy. Its word equation is:

Glucose + Oxygen → Carbon dioxide + Water + Energy (stored as ATP)

For example, when you run, your muscles use more oxygen to release energy quickly, so your breathing rate increases to supply more oxygen for aerobic respiration. A common misconception is thinking breathing and respiration are the same; however, breathing is just the first step that brings oxygen into the body, while respiration happens inside cells.

Air enters the body through the nostrils, passes through the nasal cavity, pharynx, larynx (with vocal cords), trachea, bronchi, bronchioles, and finally reaches the alveoli in the lungs, which are covered by the pleura.
- Nostrils: Let air enter and filter large dust particles.
- Nasal cavity: Warms, moistens, and further filters air.
- Pharynx: Common passage for air and food.
- Larynx: Contains vocal cords; produces sound and prevents food from entering the windpipe.
- Trachea: Windpipe; carries air to the lungs and traps dust with its lining.
- Bronchi: Two branches from the trachea that lead to each lung.
- Bronchioles: Smaller branches inside the lungs.
- Alveoli: Tiny air sacs for gas exchange.
- Lungs: Main organs where oxygen is absorbed and carbon dioxide is released.
- Pleura: Thin membrane covering the lungs, protecting them and reducing friction.
For example, when you smell agarbatti, the air carrying the scent passes through all these organs before you sense it. Students often forget the order of organs, especially the difference between bronchi and bronchioles.

Breathing involves two main steps: inspiration (inhaling) and expiration (exhaling), controlled by the diaphragm and intercostal muscles. During inspiration, the diaphragm contracts and moves downward, while the intercostal muscles between the ribs contract to lift the rib cage up and out. This increases the size of the chest cavity and lowers the air pressure inside, so air rushes into the lungs. During expiration, the diaphragm relaxes and moves upward, and the rib cage moves down and in as the intercostal muscles relax. This reduces the chest cavity size, increasing the air pressure and pushing air out of the lungs. The normal breathing rate of a person at rest is about 16-18 times per minute.
For example, when you yawn deeply, you can feel your chest expanding as your diaphragm contracts. Some students think only the lungs do the work, but the diaphragm and rib muscles are essential for moving air in and out.

Inhaled air has more oxygen and less carbon dioxide, while exhaled air has less oxygen and more carbon dioxide. The lime-water test shows this: blowing exhaled air through lime-water turns it milky, proving it contains more carbon dioxide. Gas exchange happens in the alveoli, where oxygen from the air passes through the thin walls into the blood, and carbon dioxide from the blood passes into the alveoli to be breathed out. Haemoglobin in red blood cells carries oxygen to body tissues, where it is exchanged for carbon dioxide. Two common respiratory disorders are asthma and bronchitis. To keep the respiratory system healthy, avoid smoking and breathe clean air.
For example, after running, you breathe faster to remove more carbon dioxide and take in more oxygen. Some students believe exhaled air has no oxygen, but it still contains some, just less than inhaled air.