(1) Air from the environment mixes with the air remaining in the anatomic dead space in the respiratory tract; (2) oxygen diffuses out of the alveoli into the blood, and ____________ diffuses from the blood into the alveoli; and (3) more water vapor is present within the alveoli because of the higher humidity there. Consequently, the percentage of oxygen in the alveoli is lower and the percentage of carbon dioxide in the alveoli is higher than in the atmosphere.