The ____ are the tiny air sacs in the lungs that provide a very large surface area for gas exchange. The ____ cells produce mucus in which pathogens and particles can become trapped. The trachea divides into two ____ which carry air to and from the lungs. The ____ contract to increase the volume of the thorax. This causes a decrease in the air pressure. The function of ____ in the trachea is to prevent it from collapsing inwards causing a blockage to the air flow. An increased carbon dioxide concentration in the blood is detected by the ____ causing an increase in the rate of breathing. Oxygen moves from the space in an alveolus to the blood by the process of ____. The ____ is a sheet of muscles that contracts and relaxes to change the volume of the thorax. ____ can be used to test for the presence of carbon dioxide in exhaled air. The decrease in concentration of oxygen in exhaled air compared with inhaled air is due to ____.

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