When is the rate of gaseous diffusion across a biological membrane decreased?
a. The diffusion distance is small.
b. The gas diffusion constant increases.
c. The partial pressure gradient is low.
d. The surface area is large.
ANS: C
Given that the area of and distance across the alveolar-capillary membrane are relatively constant in healthy people, diffusion in the normal lung mainly depends on gas pressure gradients.
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