Diffusion Time & Distance:
Cellular vs. Desktop Diffusion

A realistic virtual laboratory contains a beaker of water containing diffusing glucose molecules is compared side-by-side with glucose molecules across gut cells. The realistic random movements of glucose molecules show that diffusion is very efficient over short distances (crossing a cell in milliseconds), but very inefficient over long distances (spreading throughout a beaker in hundreds of hours). This indicates why large multicellular organisms need a circulatory system to move molecules quickly over long distances, while relying mostly on diffusion at small cellular scales.

This movie is part of the Molecular Transport in Cells module.