What is the role of the rebreather bag on an oxygen mask in a continuous-flow system?

The rebreather bag on an oxygen mask in a continuous-flow system plays a key role in conserving oxygen. In a continuous-flow system, oxygen is delivered at a steady rate, but when the user inhales, some of the oxygen within the bag is used and not all is expelled fully with each exhale. The rebreather bag captures some of the exhaled gas, allowing the user to re-inhale a portion of the oxygen-rich gas that contains a higher concentration of oxygen than atmospheric air. This mechanism ensures that less oxygen is wasted, effectively maximizing the efficiency of oxygen supply during use.

Other options do not correctly represent the function of the rebreather bag. For example, while filtering environmental air and enhancing oxygen purity are important in various oxygen systems, these functions do not pertain specifically to the rebreather bag. Additionally, the rebreather bag does not serve to increase the flow rate of oxygen, as its primary function is related to oxygen conservation rather than altering flow characteristics in the system.