In the lungs, dissolved carbon dioxide leaves the capillaries in either of two ways: • by diffusion across the endothelial cells of the capillaries • by leaking through pores in the endothelial cells of the capillaries. What is the minimum number of times that a carbon dioxide molecule, after being carried to the lungs in a red blood cell, has to cross a cell surface membrane in order to reach an air space in an alveolus?
- A2
- B3
- C4
- D5