Osmosis and Diffusion.
In this Experiment you will measure diffusion of small molecules through dialysis tubing, an example of a selective permeable membrane.
MATERIALS & METHODS:
1. Obtain a 30-cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end ofthe bag, rub the end between your fingers until the edges separate.
2. Test the 15% glucose/1% starch solution in the bag. Tie off the other end of the bag, leaving sufficient space for the expansion of the contents in the bag. Record the color of the solution in Table 1.1
3. Place 15 mL of the 15% glucose/1% stanch solution in the bag. Tie off the other end of the bag, leaving sufficientspace for the expansion of the contents in the bag. Record the color of the solution in Table 1.1
4. Fill a 250-mL beaker or cup two-thirds full with distilled water. Add approximately 4 mL of Lugol’s solution to the distilled water and record the color of the solution in the Table 1.1. Test this solution for glucose and record the results in Table 1.1
5. Immerse the bag in the beaker ofsolution.
6. Allow your setup to stand for approximately 30 minutes or until you see a distinct color change in the bag or in the beaker. Record the final color of the solution in the bag, and of the solution in the beaker, in table 1.1.
7. Test the liquid in the beaker and in the bag for the presence of glucose. Record the results in the Table 1.1.
| Initialcontents | Solution ColorInitial Final | Presence of GlucoseInitial Final |
Bag | 15% glucose &1% starch | Clear Black | ++++ +++ |
Beaker | H20 & IKI | Yellow Amber | _______ +++ |
To understand more thisexperiment, it’s necessary to define same concepts that will make easier to understand everything in this discussion. First like the title say this is an experiment that is working with diffusion, and that means, “The spread of particles through random motion from regions of higher concentration to regions of lower concentration.” In this experiment we used dialysis bags that represent a membrane ofour body, and dialysis is “the movement of a solute through a selective permeable membrane.”
With this definition of diffusion, is time to apply this in the experiment and see what particles are leaving and what particles are entering to the bag. The small solutes molecules and water molecules can move freely through a selective permeable membrane, but larger molecules will pass through moreslowly, or perhaps not at all.
The initial solution in the bag have a clear color while the solution in the beaker is yellow, after all the processes, the solution in the bag have a black color and the solution in the beaker is amber, or a more clearly yellow. With this we can see that the water is going to inside of the bag making the solution inside of the bag take a black color while the solutionin the in the beaker is more clear. In the other side the presence of glucose in the bag is high, and the water don’t have any presence of glucose, in the final stage the presence of glucose in the bag is less and the presence of glucose in the beaker is increase, showing that the glucose is leaving the bag in direction of the water.
For substance more simples its more easy topass through a membrane, while the more complex substance take a while or sometimes they can’t pass this membrane.
In this experiment you will use dialysis tubing to investigate the relationship between solute concentration and the movement of water through a selective permeable membrane by the process of osmosis.
MATERIALS & METHODS:
1. Obtain six 30-cm strips...