[Triggered high schooler]

My biology class recently did an experiment in which we mixed 4ml of glucose and 4ml of starch in a bag made of dialysis tubing (a synthetic selectively permeable membrane), and submerged it in a beaker containing an iodine solution (200ml of distilled water mixed with 0.8ml of iodine), to see what size of molecules and ions that can pass through a selectively permeable membrane.  Through lab execution and research, I found that the glucose molecules pass through the membrane into the beaker solution, and the iodine particles also passes through the membrane, to the bag solution.  On the experiment sheet it says that the concentration of the bag solution is larger than the concentration of the beaker solution.  This was where the confusion started.  I began wondering why the iodine passed through the membrane, going from an area of lower concentration to higher concentration.  How could the iodine ions diffuse through the membrane if this were the case? I tried researching online but no sources i visited mentioned the issue of particles from a lower concentration moving to an area of higher concentration.  I found, however, that there is something called active transport, but that could not have occurred in this particular experiment as that process requires energy (from what I read), and dialysis tubing is non-living.  Moments later I thought of a possible explanation, being that the water molecules in the iodine solution diffused through the membrane as there was no water located in the bag.  This therefore caused the concentration of the beaker solution to further increase (as the glucose molecules entering the beaker solution already was increasing its concentration), so the iodine particles perhaps had to move through the membrane into the bag solution to balance out this large gain in concentration in the beaker solution.  However, I am very unsure of this explanation.  Can someone please explain why the iodine particles moved from an area of lower concentration to higher concentration if there is no evidence of active transport?  I have an analysis due soon and I'm not very sure how to provide reasoning for the iodine particles "diffusing" to the bag solution.  Thank you in advance.    (Note that I am positive that the iodine ions were supposed to move through the membrane).

[thetada]

On the experiment sheet it says that the concentration of the bag solution is larger than the concentration of the beaker solution.

Surely this was in reference to the glucose molecules rather than the iodine molecules? From what you've said, at the start, concentration of glucose was higher inside the bag, whereas concentration of iodine was higher outside the bag. Because the bag contained a solution of glucose and starch, and you added the bag to a solution of iodine, right? In which case I can't see a problem.

[Triggered high schooler]

I'm not sure I understand what you are saying.  However, what I stated in the question wasn't what the sheet exactly said.  The sheet read, "the concentration of solutes is higher in the starch and glucose solution in the bag than in the iodine solution in the beaker."

Unless I'm reading it incorrectly, I'm pretty sure it is saying that the area of higher concentration is the bag solution?

[thetada]

I'm reading it as the concentration of glucose and starch in the bag, is greater than the concentration of iodine outside the bag. But at first, the concentration of iodine in the bag is zero, just as the concentration of glucose and starch outside the bag is zero. If you concentrate on the iodine only, there is none inside the bag, but some outside the bag, so the concentration of iodine is higher outside the bag than inside.

[Triggered high schooler]

So what you are saying is during diffusion its not the concentration of a specific area that matters, rather, the concentration of specific molecules are ions that matter?

If that is the case then that solves this whole issue, like you have stated above.  Thank you so much!  And if I understand correctly, you have taught me something very important  about the process of diffusion!

[thetada]

Glad to have helped!