Question about diffusion

[Harrow]

Question about diffusion

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Post by Harrow » Sat Oct 15, 2011 7:42 pm

I have a question about diffusion of cells. Why would you expect more of a smaller cell to be diffused in the same period of time than a large cell. Is it just because the smaller ones move faster? And also why would you expect a cell with the same volume as a cubic one, but with a different surface area, to be more diffused than the cubic one?

[Harrow]

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Post by Harrow » Sat Oct 15, 2011 7:43 pm

As you may have noticed I'm somewhat of an amateur at biology.

[Harrow]

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Post by Harrow » Sat Oct 15, 2011 7:45 pm

In the example with the same volume but different surface area we used a 8x2x1/2 and a 2x2x2.

[JackBean]

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Post by JackBean » Sun Oct 16, 2011 8:37 am

you mean how quickly some substance will diffuse inside the cell?

It's not about being faster, but being smaller (-> shorter distance). Regarding different shapes, imagine, what's the longest distance from surface to reach each spot inside.

[aptitude]

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Post by aptitude » Sun Oct 16, 2011 5:52 pm

The shape of the cell determines the surface area. The greater the surface area, the more area is available for diffusion. The equation for this is called Fick's Law of Diffusion:

J = PA (C2-C1)

Where J is the flux due to diffusion, P is a constant, C2-C1 is the concentration difference and A is the area. So the greater the area, the greater the flux due to diffusion, and the more diffusion will occur.

Therefore, in two cells with the same volume, one cubic and one shaped irregularly, the irregularly shaped cell has a higher diffusion flux because it has a greater surface area.

Hope that helps.

[JackBean]

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Post by JackBean » Thu Oct 20, 2011 1:59 pm

aptitude: but that is only about diffusion through membrane (or something like that), but the question is probably how long will it take to diffuse into whole cell (volume)