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?

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

Problem by Todd Cooke, adapted by Joe Redish