Table of Contents

• Prequiz...
• Just Plain Movement
• 1: Measuring Movement
• 2: Directed vs. Undirected Movement
• 3: Measuring Movement Using Flux
• Introducing Gradients
• 4: What is a gradient?
• 5: Watching diffusion happen (applet)
• 6: Visualizing the Gradient
• Fick's Laws, Part I
• 7: Fick's First Law
• 8: The gradient in Fick's First Law
• 9: A familiar equation for Fick's first law
• 10: The diffusion coefficient is the slope
• 11: What are the units for D?
• 12: How does flux depend on distance?
• 13: A fragrant example
• 14: General Transport Equations and Fick's First Law
• Fick's Laws, Part II
• 15: Fick's Second Law ...
• 16: ... is about "time to diffuse"
• 17: A Very Useful Formula
• 18: Time-to-diffuse "explodes"
• 19: General Functions and Diffusion
• Biological Applications
• 20: Biological Applications
• 21: Why do rhinos have lungs and amoebas don't?
• 22: Diffusion is efficient in small organisms, but not big ones
• 23: Diffusion within lungs
• 24: How many macrophages does it take to kill a virus?
• 25: You need a lot of macrophages - or one smart one!
• Review
• 26: Final Review

Final Review

• Flux density is the movement of particles per time (through a given area).
• In diffusion, individual particles are moving at random, and net movement is a result of more particles moving from high to low concentrations than are moving from low to high, thus, (Fick’s First Law)
  
  
• Fick’s First Law is phenomenological, i.e., it cannot be derived from first principles, but it shares the same form as several other transport equations.
• D (the diffusion coefficient) has units of cm²/sec, and is NOT equal to the speed at which an individual particle moves.
• In diffusion, the time to diffuse across a distance is given by
  ,
  so that time to diffuse increases with the square of distance (consequence of Fick’s Second Law).
• Diffusion is efficient only at very short distances. If organisms need to transport materials over longer distances, they need mechanisms such as lungs and circulatory systems.
• Diffusion (and all the math that goes along with it) can be used as an analogy to understand the movements of cells and more complex organisms.

 

 

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