Table of Contents

• Prequiz...
• Fick's Laws, Part II
• 1: Fick's Second Law ...
• 2: ... is about "time to diffuse"
• 3: A Very Useful Formula
• 4: Time-to-diffuse increases dramatically
• 5: General Functions and Diffusion
• Biological Applications
• 6: Biological Applications
• 7: Why do rhinos have lungs and amoebas don't?
• 8: Diffusion is efficient in small organisms, but not big ones
• 9: Why we have lungs
• 10: How many macrophages does it take to kill a virus?
• 11: You need a lot of macrophages - or one smart one!
• Review
• 12: Summary

A Very Useful Formula

 

On the last page, every time we multiplied distance by 10, the time to diffuse increased 100-fold!

10 times as far --> 100 times as much time

What’s going on here? If time to diffuse were directly proportional to distance, then 10 times the distance would require 10 times as long -- not 100. This over-inflation is like if you went to McDonald’s to buy 10 hamburgers and they charged you 100 times (not 10 times) the price of a single hamburger. Not fair? Well, that means time to diffuse is not directly proportional to distance.