Which of the following statements is true regarding gas exchange within the lungs?

• A. Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.
• B. Gas exchange in the lungs occurs by active transport.
• C. Both oxygen and carbon dioxide diffuse from the blood into the alveoli.
• D. Carbon dioxide diffuses from the alveoli into the blood, while oxygen diffuses from the blood into the alveoli.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the process of gas exchange in the lungs. Gas exchange occurs in the alveoli, which are tiny air sacs in the lungs surrounded by capillaries. This process is driven by diffusion, a passive transport mechanism where molecules move from areas of higher concentration to areas of lower concentration.
2. Step 2: Recall the concentration gradients of oxygen and carbon dioxide. Oxygen is more concentrated in the alveoli compared to the blood in the surrounding capillaries, while carbon dioxide is more concentrated in the blood compared to the alveoli.
3. Step 3: Apply the principle of diffusion to gas exchange. Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration), and carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration).
4. Step 4: Eliminate incorrect statements. Gas exchange does not occur by active transport, as it relies on passive diffusion. Both oxygen and carbon dioxide do not diffuse from the blood into the alveoli, and carbon dioxide does not diffuse from the alveoli into the blood.
5. Step 5: Identify the correct statement. Based on the principles of diffusion and the concentration gradients, the correct statement is: 'Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.'