Emergent processes, such as diffusion, are considered more difficult to understand than direct processes. In physiology, most processes are presented as direct processes, so emergent processes, when encountered, are even more difficult to understand. It has been suggested that, when studying diffusion, misconceptions about random processes are the principal cause of this difficulty. While general diffusion, membrane diffusion, and diffusion rate expressed by Fick's law are covered in numerous physiology textbooks, parameters that result from the kinetic theory of gasses are mentioned only partially and briefly in some of them. Communication with students, however, has revealed that their understanding of these parameters is often thwarted by an erroneous and, indeed, frequently nonexistent conceptual framework for the behavior of matter at a molecular level. To help students form a useful picture of diffusion and to correct misconceptions about molecular level processes, velocity, the rate of collisions, and the number of interacting molecules are presented to them in the form of analogies. This article discusses the benefits of using analogies to familiarize students with principal parameters before lectures on the movement of molecules across cell membranes. The use of analogies helps students see why diffusion is very rapid at short distances and why it is the principle transport mechanism within the cell. It also helps them to understand why, at longer distances, diffusion becomes extremely slow and inefficient and is substituted by the principal long-distance transport mechanism: circulation.