Time required for diffusion across different distances

Range Table - link
Organism Generic
Reference Ocqueteau C et al., Three-dimensional morphometry of mammalian cells. I. Diameters. Arch Biol Med Exp (Santiago). 1989 Jul22(2):89-95 p.94 right column top paragraphPubMed ID2694968
Primary Source Berne, R.M. & Levy, M.M. (1983) Physiology. St. Louis, Mosby
Comments P.94 left column bottom paragraph: "The constancy of cell dimensions can be related with the exchange processes between the cell protoplasm and the surrounding medium. The exchange of matter between the interior of each cell and its environment is governed primarily by Ficks's law of diffusion (Florey, 1966). dm/dt = -SK(dc/dx) (equation 4) whereby the transport of matter (m) depends upon the cell surface area (S), the diffusion constant of a specific substance across membranes and protoplasm (K) and the concentration gradient (dc/dx) among the distance (x) that the substance (m) has to be transported. Assuming that three of these parameters are kept constant (S, K, c) then the transport of matter is inversely proportional to the distance (x) between the cell surface (plasma membrane) and the center of each cell (nucleus). In order to illustrate the paramount importance of this distance (x), with regard to the time (t) required for the diffusion process (assuming that K ~ 10^-5 cm^2/sec) let [investigators] examine the following numerical data (primary source): see Table - link . From these data [they] may conclude, that the diffusion time in the millisecond range is only possible in the microscopic realm (µm). When the diffusion distance (x) is within the millimeter, or centimeter range, the diffusion time (t) increases very markedly. In consequence, all cell diameters must be restricted to the micrometer scale (µm)."
Entered by Uri M
ID 115474