The small capillaries in the lungs are in close contact with the alveoli. A red blood cell takes up oxygen during the 0.5 s that it squeezes through a capillary at the surface of an alveolus. What is the diffusion time for oxygen across the 1-μm -thick membrane separating air from blood? Assume that the diffusion coefficient for oxygen in tissue is 2×10−11m2/s.