Final answer:
The process of breathing in and out is called respiration, encompassing both the active phase of drawing air in, called inspiration, and the passive phase of letting air out, known as expiration.
Step-by-step explanation:
The process of breathing in and out is called respiration, which includes both inspiration and expiration.
Breathing, or ventilation, is essential for respiration. It involves two principal steps: inspiration, where air enters the lungs, and expiration, where air exits the lungs. During inspiration, muscle contraction, including the diaphragm and external intercostal muscles, increases the thoracic cavity volume, causing air to fill the lungs due to the generated pressure gradient. Expiration, on the other hand, typically occurs passively due to the elastic recoil of the lungs when the diaphragm relaxes. The entire cycle of inspiration and expiration ensures that oxygen is brought into the body and carbon dioxide is expelled, which is vital for cellular respiration and energy production.