what is dialysis tubing? how can it be used to demonstrate osmosis?
Dialysis tubing is actually a semi-permeable membrane when used in water. Experiments illustrating osmosis and pressure gradients across a membrane use dialysis tubing. This tubing usually comes in rolls and when wet, will open up into a cylindrical tube that can be tied off at the ends. The tubing can also be fitted over a thistle tube for such experiments. Dialysis tubing is literally a semi-permeable sheet of plastic. [Like a cell membrane, it can allow certain things in, but not everything.] In a dialysis tubing experiment, one fills the inside of the sheet with a concentrated liquid of some sort and then seals off the open ends of the tube. Then, one places the tube and liquid into another type of liquid and after awhile, the liquid from the outside moves inside the tube. What I did for my first dialysis tubing experiment was filling the inside of the tube with a concentrated starch solution and placed the tubing into a beaker of Lugol's solution diluted with distilled water. After a 1/2 hr, some of the Lugol's and distilled water will have entered the dialysis tubing. One can see that osmosis has happened because the Lugol's in the tube would have turned blue when in contact with the starch. Osmosis caused the diluted/unconcentrated solution of Lugol's and dH2O to go through the semi permeable membrane and into the concentrated solution of starch. Like a cell's membrane, if the outside of the cell is more concentrated, the cell would lose water because the the water will leave the cell and go for the concentrated outside environment. If the inside of the cell was more concentrated than the outside, the outside water will go into the cell through the semipermeable membrane.
