What is the second step in the process of oxygenation?

• A. Diffuse oxygen into blood to be carried to all cells of the body.
• B. Transport air through the respiratory tract to alveoli.
• C. Obtain oxygen from the air.
• D. Oxygen exchange in tissues.

Answer: (B)

The second step in bringing oxygen into your body is transporting air through the respiratory tract to the alveoli. After you obtain oxygen from the air by inhaling, the next move is to get that air down the conducting airways—nostrils or mouth, pharynx, larynx, trachea, bronchi, and bronchioles—so it reaches the tiny air sacs called alveoli. This ventilation step is essential because it delivers fresh air to the gas-exchange surfaces, where oxygen can then diffuse into the blood in the next step. So the sequence is inhalation (obtain oxygen), ventilation (move air to alveoli), diffusion into blood, then transport of oxygen in the bloodstream to tissues, and finally diffusion from blood into tissues.