Fick's Law of Diffusion

by Greg Crowther

This is a short song about the Fick equation for calculating diffusion rates. It was written for Biology 220 at the University of Washington. Ideally, "diffusion barrier" is pronounced so that it rhymes with "surface area." Also, the words "multiplied together" can be sung in harmony to reinforce the idea that factors are being multiplied.

When equations are expressed concisely, as in a jingle, the meaning of the abbreviations may be forgotten. “Fick’s Law of Diffusion” addresses this issue by presenting the abbreviations in the first half of the jingle, then spelling out the full terms (in the same order) in the second half. Thus, “delta P” corresponds to “pressure difference,” “A” corresponds to “surface area,” and “D” corresponds to “diffusion barrier.”

Fick says how quick
A molecule will diffuse.
Delta P times A times k
Over D is the law to use.

Fick says how quick
A molecule will diffuse.
Delta P times A times k
Over D is the law to use.

(Fick) Pressure difference,
(Fick) Surface area,
(Fick) And the constant k
Are multiplied together.
(Fick) They're divided by
(Fick) Diffusion barrier
(Fick) To determine the exact rate of diffusion.

• MP3 (demo)

• music video

• sheet music (with melody play-back)

Songs like this one can be used during class meetings and/or in homework assignments. Either way, the song will be most impactful if students DO something with it, as opposed to just listening.

An initial, simple follow-up activity could be to answer the study questions below. A more extensive interaction with the song might entail (A) learning to sing it, using an audio file and/or sheet music as a guide, and/or (B) illustrating it with pictures, bodily poses, and/or bodily movements. The latter activity could begin with students identifying the most important or most challenging content of the song, and deciding how to illustrate that particular content.

(1) Which term of the equation reflects a concentration gradient, which is necessary for diffusion?

(2) What does the “constant” k depend on?

(3) In what units may D and A be expressed?

(4) According to the Fick equation, if D increases, what happens to diffusion rate?

(5) Do mammalian lungs generally have a high A, a high D, both a high A and a high D, or neither a high A nor a high D?

(6) Your classmate tells you that the Fick equation governs blood flow because blood flows down a pressure gradient, represented by delta P, which is part of the Fick equation. Is this correct?

(7) Considering the specific content covered by this song, is there anything important that is missing, unclear, or misleading? If so, what?