Diffusion, Osmosis and Tonicity:
How Osmotic Pressure Impacts Biological Cells

Illustration Showing the Diffusion of Molecules

What Is Diffusion?
Diffusion is the passive transport of molecules from an area of higher concentration to an area of lower concentration; and, surprisingly, you are very familiar with this process, whether you realize it or not.

Article Summary: Looking for a simple explanation of the potentially confusing terms 'diffusion', 'osmosis' and 'tonicity'? Here you go.

Diffusion, Osmosis & Tonicity
Animated graphic of osmosis
Virtual Cell Biology

You have free access to a large collection of materials used in a college-level introductory Cell Biology Course. The Virtual Cell Biology Classroom provides a wide range of free educational resources including Power Point Lectures, Study Guides, Review Questions and Practice Test Questions.
Endomembrane System of a Eukaryotic Cell, Mariana Ruiz
Page last updated: 8/2015
Instructor's Corner
When you put on perfume or aftershave, you can't just do it once and stay smelling sweet for the rest of your life (much to the relief of perfumers). 
Continued ... 
What Is Osmosis?
Go to PAGE 2 >

See Page 2 for information on Osmosis!
Illustration Depicting Diffusion
Another unpleasant example of diffusion is the very recognizable smell of skunk stink. If you are driving down the road towards a dead (or detonated) skunk, the unpleasant smell gets stronger and stronger as your car approaches the skunk, and weaker as you move away. 
This is because the stinky molecules are more concentrated closer to their skunky source. 

from the free STEM 
education site 
Science Prof Online
This article has 
3 pages: 
1  . 2 .  3
Video from Crash Course Chemistry
"Passing Gases: 
Effusion, Diffusion and the Velocity of a Gas"

The molecules of scent slowly diffuse from the area where you applied them, until so many have departed that you can no longer detect your signature scent.

Fart Sign
That's why farts aren't forever. When you let one fly, the fart molecules eventually spread out so much that the scent of your "bottom burp" is no longer detectable. Fanning the air behind your bum helps this happen faster.