Diffusion

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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.

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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.

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Facilitated 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.

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Facilitated Diffusion - Carrier Proteins

PROCESS:

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.

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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.

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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.

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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)

 

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