The process of diffusion
DIFFUSION : The net movement of particles from an area of high concentration to an area of low concentration.
NET MOVEMENT : This is only to an area of low concentration.
-Net movement continues until particles are evenly spread through liquid/gas.
CONCENTRATION GRADIENT : Path from area of high conc. to an area of low conc.
-Particles diffuse down a concentration gradient.
-Diffusion is a passive process (REQUIRES NO ENERGY)
SIMPLE DIFFUSION : When particles diffuse directly through a cell membrane.
Factors affecting rate of diffusion
The rate of diffusion depends on the following:
CONCENTRATION GRADIENT : The higher this is, the faster the rate of diffusion (however an equilibrium is eventually reached)
THICKNESS OF EXCHANGE SURFACE : The thinner this is, the shorter the pathway is for diffusion therefore the rate is increased.
SURFACE AREA : The larger the surface area, the faster the rate of diffusion.
-Larger molecules (amino acids, glucose ect) and charged particles would diffuse super slowly through a phospholipid bilayer, so therefore to speed up the process, they diffuse through carrier proteins or channel proteins in the membrane.
-Particles are still moved down a concentration gradient.
-Its a passive process.
Facilitated Diffusion - Carrier Proteins
1) a LARGE MOLECULE ATTATCHES to a CARRIER PROTEIN in the membrane at a BINDING SITE.
2) The PROTEIN CHANGES SHAPE.
3) This RELEASES THE MOLECULE on the OPPOSITE SIDE of the membrane.
Facilitated Diffusion - Channel Proteins
-Form pores in the membrane for charged particles to diffuse through (down their conc. gradient).
-Different channel proteins facilitate the diffusion of different charged particles.
Factors affecting rate of facilitated diffusion
The rate of facilitated diffusion depends on:
CONCENTRATION GRADIENT : The higher the conc. gradient, the faster the rate of diffusion (However at some point, an equilibrium will be reached)
NUMBER OF CHANNEL/CARRIER PROTEIN : Once you use up all of the proteins, the rate will never be increased, even if you increase the concentration gradient.
Calculating the rate of diffusion.
(Refer to diagram page 103)
Straight line graph : Finding the gradient.
Curved Graph : Drawing a tangent and finding the gradient of the tangent.
(UNIT : MS-1)
Gradient = (Change in Y) + (Change in X)