Summary:
A series of four experiments related to diffusion, or the process through which a substance goes from a high concentration to a low concentration. The experiments enable students to learn more about the properties of diffusion, osmosis, water potential, and plasmolysis pertaining to the study of science.
The Many Processes of Diffusion
Diffusion is the process by which a substance moves from an area of high concentration to an area of low concentration. In the first lab experiment, the students in my group measured the diffusion of 15% glucose and 1% starch out of a 30-cm dialysis bag into a 250mL beaker of distilled water and IKI solution. My group allowed the setup to sit for thirty minutes and found the following conclusions:
As the chart shows, there were no major changes in the colors of the bag or the beaker. However, there was change in the chemicals of the bag and the beaker. The glucose left the bag and entered the substances of the beaker. The iodine solution was expected to enter the bag, but could not because its presence was not strong enough. My group found that the glucose left the bag, because the small size of its molecules, by testing the beaker with glucose testing strips. Throughout the experiment, my lab group used safety goggles and aprons.
The second experiment involved the process of osmosis. It is a type of diffusion through which water exits from an area of higher water potential to an area of lower water potential through a permeable membrane. My group used safety goggles and aprons while in the lab because of the many chemicals involved. My experimental group used two 30-cm strips of presoaked dialysis tubing of 15-25mL distilled water and 1.0M of sucrose. Then the initial masses of the bags were measured in grams with the distilled water weighing 14.17 grams and the 1.0M of sucrose weighing 16.50 grams. Next, the bags were put in two 250mL beakers, which were filled two-thirds full of distilled water. After letting them sit in the beakers for thirty minutes, the group then weighed the dialysis bags for their final masses. The final results are shown in the charts and graph below.
We concluded that water moved out of the dialysis bag into the beaker due to osmosis. On the other hand, the dialysis bag of 1.0M sucrose gained mass because some of the distilled water seeped in. All of this was a result of diffusion or the moving of a substance to an area of higher concentration to an area of lower concentration.
The third experiment involved water potential. Goggles and aprons were used in this experiment also. First, a potato was sliced with a cork borer into eight cylinders. Then the potato cylinders were kept in two 250mL beakers over night. One beaker was filled with distilled water while the other was filled with 1.0M of sucrose. The next day, the students in my lab removed the cores, blotted them, and determined their total mass. The information gathered was graphed and put in tables as so below.
The students in my lab also calculated the water potential from the experimental data. The equation is fÉ= -iCRT where I is ionization constant for the sucrose (molar concentration of sucrose is 0.4), C is molar concentration, R is pressure constant of 0.0831 liter bars/mole K, and T is temperature K of 295. The equation was calculated with the information obtained by the experiment. The water potential of the potato cells resulted from: fÉ= -(1)(0.4 mole/liter)(0.0831 liter bar/mole K)(295 K). In our lab it was found that the water potential equaled fÉ= 9.8058. The greatest water potential was outside the bag, allowing water to enter the potatoes. What would happen to a red blood cell placed in distilled water was also considered. My lab partners came up with the conclusion that the distilled water would have a higher concentration of water molecules and higher water potential. This is because the red blood cells would swell up due to lower water potential. From this, it was seen that the red blood cell now had more potential in order for the distilled water to move in.
The final experiment involved onion cell plasmolysis. Plasmolysis is the shrinking of the cytoplasm of a plant cell in response to diffusion of water out of a cell and into hypertonic solution surrounding the cell. In this lab, the students looked at an already prepared small piece of the epidermis of an onion under a 100X microscope. The appearance was observed and sketched. The cell looked lie scales with purple spots.
Then, two or three drops of 15% NaCl was added to the end of the cover slip. This allowed the nucleus and organelles to be seen more clearly although the cells sill appeared to resemble scales. The NaCl allowed the process of plasmolysis to take place, pulling out the water in the cells so the organelles could be seen.
Throughout the experiments, the students gained much information about diffusion, osmosis, water potential, and plasmolysis. However, there were some flaws in the labs. In the diffusion lab, the dialysis tube was supposed to turn blue due to the IKI solution entering the bag, mixing with some of he glucose and starch that hadn¡¦t diffused out. Instead, the bag became cloudier but stayed just about the same opaque color. The beaker solution also had little change because it lost most of its yellow tint but yellow tint was still seen. The second lab proved to work out in the favor of the students. However, when put with the whole class, the calculations seemed to differ extremely with negative and positive numbers. This left the students of my group kind of worried and confused. This also happened in the third experiment involving the potato cylinders. The fourth lab proved to be successful with everything going as planned. These labs were great aspects to help us learn more about the properties of diffusion, osmosis, water potential, and plasmolysis pertaining to the study of science.
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