Diffusion Limits

It might take up to a minute for diffusing oxygen to penetrate to the center of a single amoeba floating in a bath, if we calculate that the average time for diffusion equals the diffusion distance (centimeters) squared divided by a diffusion constant that is about ~ 10-5 for most small molecules in water. If our amoeba's cell membrane is one hundred Angstroms thick, then diffusion time might be 0.0000001 seconds, but for diffusion to supply a spherical animal ten centimeters in diameter, time to diffuse might take one hundred and twenty days (Ref: Diffusion Rates). But now what happens when body size and or activity increase?

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