Diffusion Flashcards
What is diffusion?
The net movement of particles or ions from a region where they are more highly concentrated to one where their concentration is lower
What is Fick’s Law?
(surface area x difference in concentration) / length of diffusion pathway = proportional to diffusion
Which factors affect the rate of diffusion?
- Concentration gradient
- Surface area over which gradient takes place
- Thickness of exchange surface
Effect of concentration gradient?
Steeper = faster
Effect of surface area?
Larger = faster
Effect of thickness of pathway?
Thinner = faster
Which factors also affect the rate of diffusion in cells?
- The nature of the plasma membrane (composition and number of pores)
- The size and nature of the diffusing molecule
How does the size and nature of the diffusing molecule affect the rate of diffusion in cells?
Smaller molecules = faster than larger
Fat soluble molecules = faster than water soluble molecules
Polar = faster than non-polar
Where does facilitated diffusion occur?
At specific points at the plasma membrane where there are special protein molecules
Details of facilitated diffusion
- Passive process
- Relies on molecules’ kinetic energy
- Occurs down concentration gradient
- Occurs across protein channels
- Water-soluble molecules like glucose and amino acids pass through
- Channels are selective
- Control over entry and exit of substances
Alternative form of facilitated diffusion
- Involves carrier proteins that span plasma membrane
- Specific molecules bind with the (carrier) protein
- Causes it change shape, releasing molecule to inside of membrane
- No external energy
Example of diffusion?
Starch, digested by amylase into maltose, maltase in glucose, absorbed across small intestine into epithelial cells that line it. This occurs partly by absorption
