PADI Divemaster Certification 2025 – 400 Free Practice Questions to Pass the Exam

Dead air space refers to the portion of the respiratory system where air is present but does not participate in the process of gas exchange. This occurs in areas such as the trachea and bronchi, where the airways do not have the alveoli necessary for exchanging oxygen and carbon dioxide with the blood. Understanding the concept of dead air space is important for divers, as it highlights the volume of air that may not contribute to effective ventilation during diving.

In contrast, the other choices refer to different respiratory processes. Gas that participates in gas exchange refers to the air found in the alveoli, where oxygen is absorbed and carbon dioxide is expelled. The gas remaining in the lungs after exhalation describes the residual volume, which is the amount of air that cannot be exhaled and is still present in the lungs to keep the alveoli open. Lastly, gas that is actively used during breathing would refer to the fresh air being inhaled and exchanged within the lungs. Thus, dead air space specifically denotes the air that is not actively involved in gas exchange, making it a distinct and important concept in respiration.