The pathway of the oxygen in the breathing system starts from the Nose which is the prefered entrance of air aside from the mouth and also its the exit way of the air that we breathe out,Next, to the Nasal Passages,it filters,warms and moistens the air we breathe and it goes down to the Trachea that serves as the passageway of the air that will go to the Bronchi.Bronchi are two branching tubes that lets the air passes that will go to the Bronchioles, and the Bronchioles ensure that the air we breathe are transported to each Alveoli.In the Alveoli, the gas exchange(Oxygen and Carbon Dioxide) happens.