MCAT Biology Question 85: Answer and Explanation

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Question: 85

10. Some forms of pneumonia cause an excess of fluids such as mucus or pus to build up within an entire lobe of the lung. How will this affect the diffusion of gases within the affected area?

  • A. Carbon dioxide can diffuse out, but oxygen will not be able to enter the blood.
  • B. Oxygen can diffuse into the blood, but carbon dioxide cannot diffuse out.
  • C. No change in diffusion will occur.
  • D. No diffusion will occur in the affected area.

Correct Answer: D

Explanation:

If an area of the lung becomes filled with mucus and inflammatory cells, the area will not be able to participate in gas exchange. Because no air will enter or leave the area, the concentration gradient will no longer exist, and neither oxygen nor carbon dioxide will be able to diffuse across the alveolar wall.

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