Anatomy & Physiology 168
March 14, 2014
Diffusion across a Selectively Permeable membrane
Diffusion is movement of molecules from one area of concentration to another. This process is vital for the life functions of cells. Cells have selectively permeable membranes that allow only certain solutions to pass through them.
Osmosis is a special kind of diffusion that allows water to go through semi-permeable membranes of high water potential to a region of lower water potential. Water potential measures the tendency of water to leave one place and into another.
Diffusion and osmosis is responsible for the movement of molecules in and out of cells.
Diffusion and osmosis can be shown using dialysis tubing which is a membrane that is made of regenerated cellulose fibers into a flat tube. When solutions that contain dissolved substances, are separated by a membrane like the dialysis tubing, some may readily pass through it and others may not due to the size of the molecules.
Diffusion and osmosis will occur once dynamic equilibrium is reached. If a substance contains molecules small enough to pass through a selectively permeable membrane then they will readily pass through it without the solution or substance, which is inside the membrane, getting out. \
Disposable transfer pipettes
Strips of dialysis tubing soaked in water
First you will have your dialysis tubing soaked in water ready for the experiment. Once the dialysis tubing in being soaked, wash your hands to get rid of any oils or dirt that may be on them. Remove the tubing from the water and tie off one end. Open the other end using two fingers in a rubbing motion so that the tubing will separate and open. Use a disposable pipette to fill the tubing with starch solution. Once the tubing is filled leave a bit of space so that expansion may occur and tie off the