Diffusion Coefficient Example

A typical small molecule is glucose. Glucose in watery hemolymph might diffuse ten to the minus five seconds centimeters squared per second. Consequently, the time glucose needs to diffuse one micron is ten to the minus three seconds, to diffuse ten microns is a tenth of a second, and to diffuse one millimeter is ten to the third seconds or fifteen minutes. Diffusion is rapid at intracellu-lar scales, so cells need not add energy to this metabolically free transport mechanism, but diffusion alone is inadequate over distances greater than one millimeter. So remember; if you are larger, you need a heart.

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