Wednsday, 10/6/10

Period 4 had a substitute today, and all we basically did was start our Diffusion Lab in class. Diffusion is the slow transfer of substances through a filtering barrier, molecule by molecule, from an area of higher concentration to another area of lower concentration. Here is a brief overview of what was done (Remember that all of this is on UP p.33-34):

1. A tied-off cellophane dialysis tube is filled with a starch solution and then a glucose solution to represent a membrane full of fluid.


2. The filled tube of starch and glucose is submerged into a glass of water and iodine, where it will sit for about 15 min. (During this time, we took the Organelle Quiz.)


3. Upon returning, the solutions in the tube and the glass should show some results. If the iodine water in the glass has turned blue, that means there is starch in the water. Then, a piece of Tes-Tape is dipped into the iodine water, and if the tip turns green or yellow, then there is glucose in the water. Meanwhile, if the tube full of starch and glucose solution has turned purple, then there is iodine inside the tube.



4. For our group's lab test, the membrane tube turned purple, the iodine water solution stayed orange and didn't change color, but the piece of Tes-Tape turned blue instead of green or yellow.
   

Overall, it can be concluded that the glucose passed through the tube and went into the water surrounding it, the iodine in the water passed through the tube and went inside, the starch never went anywhere and stayed in the tube, and the water passed throughout freely. This is explained by the fact that the cellophane tube is full of holes that can allow individual molecules to pass through one by one through each tiny hole. This is what allowed the small iodine and glucose molecules to pass slowly through the barrier of the tube, but starch is made up of larger molecules made from glucose, which is why starch was unable to transfer through the tube at all.


As for our own experiment, however, the tape turning blue rather than green or yellow was probably a small fault in our preparation.

BTW, who's the next scriber? :P