What is the active part of breathing called?

The active part of breathing is known as inhalation. During inhalation, the diaphragm contracts, and the intercostal muscles expand the ribcage, creating a negative pressure in the thoracic cavity that allows air to flow into the lungs. This process involves the active movement of the respiratory muscles to draw air in, making it essential for the intake of oxygen necessary for cellular functions.

The other options, while related to the respiratory process, are not specifically defining the active part of breathing. Expiration refers to the process of breathing out, where the diaphragm and intercostal muscles relax. Ventilation encompasses both inhalation and expiration as the overall process of moving air in and out of the lungs. Respiration broadly includes both the mechanical process of breathing and the biochemical processes occurring at the cellular level for gas exchange.