The spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient is known as osmosis. Osmosis allows cells to regulate the amount of water within their membrane in order to keep from shrinking or swelling (Glencoe/McGraw-Hill, 2006, p. 83). Both diffusion and osmosis play a substantial role in maintain the homeostasis of a cell, which is the tendency of an organism or a cell to regulate its internal conditions, so as to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes (Marze, 1985). .
The movement of particles within the processes of diffusion and osmosis both occur across a selectively permeable membrane, which is defined as a membrane that allows certain molecules or ions to pass through it by means of active or passive transport (Glencoe/McGraw-Hill, 2006, p. 80). This experiment explores the properties and qualities of this type of membrane. Two dialysis tubes are filled, respectively, with starch and glucose. The starch is placed into a beaker containing iodine, while the glucose is placed into a beaker containing water. The hypothesis for the starch is that the iodine will diffuse into the dialysis tube, changing the colour of the starch to a dark blue due to the chemical reaction. The hypothesis for the glucose is that neither the glucose or the water will be affected by the other and no form of diffusion will occur. By evaluating these hypotheses, a better understanding of the properties of a selectively semi-permeable membrane will be achieved.
Method.
Materials Required .
1 pair of safety goggles.
1 lab apron.
2 250-mL beakers.
2 15-cm pieces of dialysis tubing.
2-4 10-cm pieces of string.
distilled water.
15 mL glucose solution.
15 mL soluble starch solution .
Lugol's iodine solution in dropping bottle .
