Ion flux?

[lumpyduster]

What exactly is ion flux? Is there a "per unit time" in the definition anywhere? Just wondering because a TPR Science Workbook question asked what would increase net ion flux across a membrane for a certain ion and "increasing leak channels" was one of the correct answers. I thought more leak channels = ions will move across membrane faster, but I didn't think it would change how many ions would move across the membrane until equilibrium was reached. Only thing that makes sense is if flux has to do with rate as well.

Thanks!

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[lumpyduster]

And actually, re-reading the answer they gave has made me think of another question.

So the actual question was:

The concentration of K on one side of a membrane populated by potassium leak channels is 1 mM and 10 mM on the other side. Which of the following will increase net potassium flux across the membrane?

I. Increasing the K+ concentration on one side of the membrane from 10 mM to 11 mM
II. Increasing the concentration of K+ on both sides of the membrane by 10 mM
III. Increasing the density of potassium leak channels in the membrane.

Correct answer: I and III only.

So I understand why (I) is correct. You would change the equilibrium slightly and then ions will move across the membrane to obtain a 1:10 ratio (I am assuming it starts at equilibrium)

But they say (II) isn't correct because you add the same amount of ion to both sides? I disagree- the ratio would change from 1:10 to 11:20 and they're clearly not the same; why wouldn't you get any net flux?

And my confusion with III is already explained in my first post and I probably missed it because I didn't understand the definition of flux.

Thanks again!

 

[lumpyduster]

Bump.

 

[Cawolf]

Flux is the rate of diffusion across a membrane.

Fick's Law of Diffusion would be what I would look up to learn about this.

The approximate equation is J = PA (C1 - C2)
J is flux or the rate of diffusion, P is the permeability, A is the surface area of diffusion, and (C1-C2) is the concentration gradient.

So we can see that the permeability here won't change. For choice III in your question, increases the number of channels increases the surface area of diffusion - increasing flux.

Concentration gradient is the difference between the sides so dC initially is 9 mM and if we made them 11 mM and 20 mM it is still 9 mM - leaving flux constant.