Cellular Processes

Introduction to Diffusion

Discover the wild and wacky world of things that move around randomly. We’ll discuss gradients and diffusion, define flux and flow, and draw several graphs. A whole lot of graphs, in fact.

Time to Diffuse

Who is Adolf Fick? Why do rhinoceroses have lungs but amoebas don’t? How many angels can dance on the head of a pin? Well, we can’t help you with the last question, but once you learn about Fick and his creatively named Second Law, you’ll be on your way to understanding rhinos and amoebas.

Bonus questions: how do fish survive in the winter? How do you smell perfume from across a room? How long will it take a macrophage to search and destroy a virus in your lungs?

Diffusion through a Membrane

What could be more fun than stuff that moves around randomly? How about stuff that moves randomly between two compartments separated by a semi-permeable boundary?

I know this sounds like a description of the US House of Representatives, but it’s not… Build your own equation for diffusion in a two-compartment model, then try it out on some real problems. Note: this model comes in two flavours, discrete and continuous. Pick one or both, and don’t miss the afterword using fantasy geography to show the difference.


This short but sweet module puts the oz in osmolarity — or in an unnamed but popular soda that comes in a red can.

Use osmolarity to figure out where the water is headed and what, if anything, is going on when the water reaches equilibrium. All this and you get to answer the burning question, why don’t sharks get thirsty???

The Nernst Potential

New and Improved! You have to read this one to believe it. Starts with potassium, sodium, and chloride, and ends by explaining Life As We Know It.

Well, almost. Along the way, you’ll learn the Goldman and Nernst equations, and see how back of the envelope calculations explain how our brains work. We’ll also explore how ions get to where they’re going — through pumps, channels and gates. Don’t miss our most mind-blowing module yet!