Diffusion of a gas through a alveoli capillary membrane:

Question

a) is inversely related to the diffusion constant of the gas

b) requires active transport

c) is inversely related to the surface area for diffusion

d) is directly related to the thickness of the membrane

e) is directly related to the difference in partial pressure of the gas on each side of the membrane

Answer 1

Based on the wording of the question and answers, it seems like it will be important for you to understand why the choices are right or wrong.

a) diffusion constant is an inherent property of every substance and describes how readily the substance diffuses. Higher values indicate greater propensity to diffuse so the relationship would be direct and not inverse.

b) diffusion by nature is a passive process - no energy input is required and it "just happens" when there's a difference in concentrations or partial pressures (depending on the substance) across a membrane or barrier. Be sure you understand why this answer is wrong

c) greater surface area for diffusion allows for more diffusion so the relationship here would be direct and not inverse

d) a thicker membrane would inhibit diffusion (make it harder for diffusion to occur) so the relationship would be inverse and not direct

e) a difference in partial pressures (not concentration) drives diffusion of O2 and CO2 in the body. A greater difference will result in more rapid diffusion ( a greater tendency to equalize the difference). This is the correct answer.

Because it's multiple choice, you could of course get the answer as long as you can identify the right answer, but I expect other questions will expect you to apply all of the concepts discussed in this question.