1. After 30 minutes of placing dialysis tube in the water, note the color change in the beaker of the dialysis tube.
After putting the dialysis tube that had the orange dye in the beaker filled with water, the water changed color to light orange. Initially, we thought there was an error and that the dye might have leaked and therefore decided to repeat the experiment and observe if the same results would be achieved. Therefore, we placed the dye again this time ensuring there was no leaking or spilling of it in the water. This time around, it took about 15 minutes for the water to change color. The green color on the other experiment took time to turn color. There were no observable changes in the experiment that contained the green dye even after placing the dye with the color in water for 30 minutes. However, after 24 hours there were changes that were noted. There was diffusion of the dye from areas of low concentration, to areas of high concentration.

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2. Observe the changes that happened on the other day. Write down your observations.
The following day, there were notable changes in the beaker that contained the green dye. Its green color had some slight fading from the initial dark green color to light green color. The leaked dye affected the water and hence its light color. This change was not noticeable in the initial 24 hours. On the other hand, the beaker that had the orange color and was filled with the dialysis tube had a rapid response to the color change. The initial changes showed a light orange-yellow color and gradually turned into opaque orange the following day. This color change was more evident compared to the other experiment of the green color.

3. Explain what you have observed and determine how this experiment on dialysis models permeability across the plasma membrane.
Dialysis tubing can be defined as a permeable membrane that allows only certain molecules to go through it. The dialysis tubes contain microscopic pores that allow particles to pass through it based on the particle size. Therefore the molecules in this experiment were smaller than the pores and were able to pass through whereas the lager moles could not pass and were trapped on the other side of the membrane.

4. Why did we use dye in this experiment?
The main reason why the dye was the best option to use in this experiment was that it created an easier platform for easy separation of the two types of substances which had different molecular weight. This has an effect on which of the two substances will pass through the membrane as in the case of the dialysis tube. In the orange dye experiment, its low molecular weight contributed to its passing easily through the dialysis tubes and hence the color change in water. The green dye experiment can be categorized in a state of large molecular weight sample and this explains why it took much time to change the water color as well as pass through the tube.
5. Look up another experiment modeling dialysis using substances other than dyes. Explain it briefly.
In this experiment, the molecules that were used were glucose, starch, and iodine. The objectives of that experiment were to test the permeability of these three substances using dialysis tubes. Glucose and starch were put in the bag and the dialysis tube clipped on one end and the other end used to insert the components. The clipping was done to avoid leaking of the solution into the water. Water containing iodine was added gradually until there was a visibly yellow amber color. The amount added was about 400ml. The bag containing these components was then placed in water and stirred using a magnetic strip and left to stand for about 30 minutes. After 30 minutes, there was notable color change to blue-black. This created the impression that iodine was able to pass through the membrane into the bag. The solution in the beaker changed color into pale yellow amber leading to a conclusion that starch did not pass through the membrane into the beaker. To confirm the presence of glucose in the solution a benedict test was carried out including a controlled rest by use of tap water. The solution in the beaker changed color into a light brown after adding Benedict’s solution, and it suspended in the water for 10 minutes. The solution in the beaker also changes color to brown whereas the tap water remains bluecolour. In summary, this experiment showed that dialysis tubing is normally selective when it comes to the permeability of molecules through its membrane. This is evident from how it permeated glucose and iodine and not starch.


Dye Before 24 hours After 24 hours
Orange Watercolor changed  to a light orange-yellow color Colour of water noticeably changed into a more clear, opaque orange
Green Watercolor remained clear  Watercolor changed into light green



In summary, it is evident that dialysis tubing does not permit all sorts of particles to pass through its membrane pores. This can be explained by the fact that it only allows particular substances to pass depending on their particles sizes.  The reason as to why the orange dye was able to pass through the membranes of the dialysis tubes was because the particle sizes were small hence lower molecular weight.  On the other hand, the green dye could not pass through due to its large particles size hance high molecular weight. Further investigation into such an occurrence can be carried out using the different substance that has different molecular weights.