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| Respiratory system | The series of tubes and organs involved in breathing. The function of breathing is to bring oxygen into the body and remove carbon dioxide. The human respiratory system includes the trachea, lungs, and other body parts |
| Respiration | Breathing-inhaling and exhaling air |
| Cellular respiration | A process that takes place inside body cells. This process uses oxygen and glucose and releases energy, which the cells need to perform their jobs. Carbon dioxide and water are also produced |
| Excretion | The process of removing excess water, salts, and the waste products of cells from the body. Excretion occurs through the lungs and skin, and in urine produced by the kidneys |
| Breathing rate | The number of times you breathe in a minute |
| Lung | A pair of spongy organs that receive air during inhalation. The lungs are made up of clusters of tiny air sacs, called alveoli, surrounded by blood vessels |
| Alveolus (plural: alveoli) | Tiny air sacs, found in the lungs, where the exchange of gases takes place. |
| Chest cavity | A sealed compartment in the body that holds the lungs and heart. The walls of the chest cavity are formed by the diaphragm and the bones and muscles of the rib cage. The chest cavity is also called the thoracic cavity |
| Rib cage | The rib bones and the muscle that connects them |
| Diaphragm | A large, dome-shaped sheet of muscle that forms the bottom of the chest cavity. Movement in this muscle helps in breathing |
| Nasal cavity | The space within the nostrils and behind the ears. Air travels through your nasal cavity when you breathe through your nose |
| Trachea | The tube that carries air from the throat to the lungs. Rings of cartilage prevent the trachea from collapsing. The opening of the trachea is covered by the epiglottis when you swallow. |
| Cilia | Tiny hair-like projections of cells. Cilia are able to move back and forth. In the air passages, cilia move mucus and any trapped matter away from the lungs. |
| Bronchus (plural: bronchi) | The two branches of the trachea. Each bronchus carries air into one lung |
| Vital capacity | The maximum amount of air that a person can in and out of his or her lungs in one breath |
| Residual air | The amount of air that stays inside the lungs even after as much air as possible has been exhaled |
| Second-hand smoke | Unfiltered smoke from the burning end of a cigarette, cigar, or pipe, along with the exhaled smoke that enters the environment when a person smokes |
| Tar | Tars are made up of several substances that condense out of smoke as it cools. For example, tars from cigarette smoke contain substances that cause cancer and substances that paralyse the cilia of cells |
