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Diffusion in time and space (SA)

Page history last edited by Joe Redish 7 years, 2 months ago



A. A common small-molecular weight (and therefore fast diffusing -- for an organic molecule) ingredient in perfumes is vanillin, the primary component of vanilla bean extract (molecular weight = 152). The D for vanillin in air is 0.114 cm2/s. If I open a bottle of vanilla on the other side of the room 3 meters away, and the air is still so there is no convection, about how long would I have to wait before I could expect to smell the vanilla?

B. The diffusion constant for glucose in water is 0.70 x 10-5 cm2/s. About how much time would it take to get significant diffusion across the following structures? Assume that glucose diffuses through cells and membranes as fast as it does through water.

  1. Across a cell membrane 8 nm thick?
  2. From the center of a eukaryotic cell 6μm in radius to the cell membrane?
  3. Across the wall of the human heart 2.5 cm in thickness?
  4. From the cells in the center of the cactus to the photosynthetic cells on the surface of a barrel cactus if the cactus has a radius of 12 cm?



Problem by Todd Cooke, adapted by Joe Redish




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