# The concentration of a substance affecting the rate of absorption? help mee pleeeaseWatch

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#1
There is a graph which shows how the concentration of a substance affects the rate of absorption into a cell.

There are two lines on the graph:

A) substance a enters the cell by simple diffusion

B) substance b enters the cell by facilitated diffusion (the line is a curve)

Use Fick's law to explain the shape of the curve

Fick's law:

Rate of diffusion is proportional to . . .

Surface Area * difference in concentration / thickness of exchange surface

Would really appreciate the help!
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5 years ago
#2
(Original post by Maya331)
There is a graph which shows how the concentration of a substance affects the rate of absorption into a cell.

There are two lines on the graph:

A) substance a enters the cell by simple diffusion

B) substance b enters the cell by facilitated diffusion (the line is a curve)

Use Fick's law to explain the shape of the curve

Fick's law:

Rate of diffusion is proportional to . . .

Surface Area * difference in concentration / thickness of exchange surface

Would really appreciate the help!
In facilitated diffusion, the factor causing a curve instead of a straight line (as in diffusion) is the presence of a carrier protein. There is a limited number of carrier proteins and if all of them are engaged in diffusion, the process is said to be "saturation" and further diffusion diminishes. Simple diffusion has no such limiting factor and continues indefinitely, giving us a straight line on the graph.

Now, the carrier protein has a specific affinity for the particle to be transported. The Fick's law, as you mention, does not take in account this factor. It also does not acknowledge the presence of a carrier protein. It is applicable to simple diffusion, which does not have a carrier mechanism.
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