The cells in our body perform functions like growth, excretion, reproduction, etc. A cell needs energy to perform these functions. The food we take in is converted into glucose by the digestive system.
The cells of living organisms require a constant supply of oxygen to release energy. This is done by a process called breathing. Breathing involves two steps - one inhalation and one exhalation. The breath rate of human beings is 15 -- 18 breaths a minute.
Air passes through the tiny hair in the nasal cavity, and then through the pharynx, larynx and windpipe before reaching the lungs. The hairs in the nasal cavity prevent the entry of dust particles and pollen. The mucous lining is present from the nasal cavity to the lungs.
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