3.2 Diffusion Flashcards
Give three facts about the movement of particles
- All particles are constantly in motion due to their kinetic energy
- The motion is random with no set pattern
- Particles are constantly bouncing off one another and other objects e.g the sides of a container
Diffusion is an example of which type of transport?
Passive transport (energy comes from the natural inbuilt motion of particles)
Define diffusion
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower.
What is the situation called where the number of particles on each side remains the same but individual particles are continuously changing position?
Dynamic equilibrium.
What are the three factors which effect the rate of diffusion?
Concentration gradient
Area over which diffusion takes place
Thickness of exchange surface
What is the formula for rate of diffusion?
(Surface area x difference in concentration)/length of diffusion path
Why is the rate of diffusion formula not wholly applicable to cells?
It is also effected by the composition of the plasma membrane and the number if pores it has
It is affected by the size and nature of the diffusing molecule:
Small molecules diffuse faster than large ones
Fat soluble diffuse faster than water-soluble ones
Polar molecules diffuse faster than non-polar ones
What type of diffusion is facilitated diffusion?
Passive diffusion
Where in the plasma-membrane does (protein CHANNEL) facilitated diffusion occur?
In protein molecules - they form water filled channels across the membrane which allow water soluble ions to pass through (which would otherwise diffuse only very slowly through the phospholipid bilayer of the plasma membrane.)
What word describes the protein channels in the plasma membrane?
Specific. They only open in the presence of a specific ion. Otherwise they remain closed.
What is an alternative form of facilitated diffusion to facilitated diffusion by protein channels in the plasma membrane?
Facilitated diffusion by carrier proteins
What do carrier proteins in the cell-surface membrane do?
Carrier proteins bind to molecules specific to them. This causes them to change shape in such a way that the molecule is released on the other side of the membrane. This is passive.
In starch digestion where does diffusion take place?
Glucose is absorbed from the exchange surface of the small intestine into the epithelial cells that line it. This absorption occurs partly by diffusion.
