Dialysis Membrane


This is a picture of a demonstration conducted in lab. The test tube is filled with a starch solution and sealed with dialysis tubing. The beaker contains iodine. The test tube is inverted into the iodine solution.


It can be clearly seen from this demonstration that ioding freely passes through the dialysis membrane, but starch does not.


What phsical factor prevents the starch from passing freely through the membrane?