Osmosis and diffusion question?

Question

In Biology class, we are doing a lab on osmosis and diffusion that involves a dialysis membrane. I understand most of it (hypotonic, hypertonic, isotonic, etc) but there's one question that I don't quite get. It says: What are the kinds of molecules that are available for diffusion through the dialysis membrane?

I'm guessing it would be the glucose/starch mixture, but is there anything else?

Answer 1

ANYTHING THAT IS SMALL AND SOLUBLE  CAN DIFFUSE  THROUGH TTHE MEMBRANE ! AND  STARCH IS TO BIG TO DIFFUSE!  

Answer 2

Any small molecules are able to diffuse through dialysis membrane (I guess it is common cellulose membrane. And glucose molecules too. Regular pore size for such membranes is 12-14 kiloDaltons. It mean, through such membrane can penetrate even small proteins.

Answer 3

Hi =]

I have done the same prac ...

Dialysis is the movement of molecules by diffusion from high  concentration to low concentration through a semi-permeable membrane. Only those molecules that are small enough to fit through the membrane pores are able move through the

membrane and reach equilibrium with the entire volume of solution in the system. So large molecules cannot be diffused through.

What kind of things are you testing on though? Because starch is too large to diffuse through the membrane, smaller molecules like water (H2O), oxygen (O2), and carbon dioxide (CO2).

Answer 4

Dialysis tubing has big pore size. Normally most salts, small molecules and water can pass through the membrane, while starch and proteins can not.

Answer 5

You observed, prior to the lab, that iodine is a chemical indicator showing the presence of starch as the starch turns a blue black color when it combines with iodine.

In the lab you're doing, you put a starch solution in the dialysis tubing and tied off the ends.  You then put the tubing into an iodine solution.  

You observed that the starch solution inside of the tubing turned blue black which means the iodine molecules were small enough to pass through the dialysis tubing.

However, you also observed that none of the iodine solution turned blue black which means that none of the starch passed through the membrane.  That means that the starch molecules were too large to pass through.  

Answer 6

diffusion relates to smaller particles getting through such as salts, ions, minerals, sometimes small waste particles, but usually glucose and starch are too big and require enzymes for them to be broken down into smaller particles, making it easier to diffuse accross the membrane or requires active transport, where energy is involved and carrier proteins to carry it accross...

osmosis as you know is just water (sometimes salt and ions)