Diffusion of Different Macromolecules Across Semipermeable MembraneTsion YohannesBiology 2107K LabOrezime UyehFebruary 13, 2019Abstract The central purpose of this experiment was to see if the surrounding temperature of a cell can affect the rate at which diffusion or osmosis occur across the cell’s semipermeable membrane and if so does the size of the macromolecule affect the rate of the diffusion. This experiment was performed by having dialysis bags to represent the semipermeable membrane filled with different macromolecules. Then placed one of each macromolecule (protein and starch) into either an ice bath, room temperature, or heated. The dialysis bags were then weighed, and small samples of the water were taken and tested with the appropriate indicator for the macromolecule.The results showed that the weights of the dialysis bags fluctuated and that all the samples taken came out to be negative. The overall conclusion is that hypothesis cannot be completely rejected due to only having limited time in the lab.IntroductionThe movement of a substance from high concentration to low concertation is referred to as diffusion. (1) If this substance happens to be water, then this movement would be referred to as osmosis. (1) During osmosis, the water will travel to the more concentrated area to make both sides be the same concentration in attempt to reach equilibrium. (1) A semipermeable membrane is one that allows some substances to easily pass through while other larger substances require energy. (1) Since the energy of water is directly affected by its heat therefore the movement would either be accelerated or decelerated depending if it is being cooled or heated. (3) Starches’ diameters have a range of 3.1- 100 µm (2), while proteins’ diameter ranges from 3–500 µm (4).With this information, this gained curiosity towards in a cell how will the temperature alter osmosis or diffusion of a macromolecule and if so does the size of the macromolecule have any effect. This then posed the question of how does temperature affect the rate of osmosis and diffusion of macromolecules? To test this question, dialysis bags were used to represent thesemipermeable cell membrane and place two different macromolecules and measured the weight of the dialysis bags then placed into a beaker of water that was either at room temperature, in an ice bath or heated. Indicators were used to determine if the macromolecules were present in the water.If there are differing temperatures at which the macromolecules are placed in, then the rate of diffusion would be affected. The prediction is that the due to the possibility of the proteinshaving a larger diameter than the starches then it should have a more difficult time passing through the semipermeable membrane.MethodThe dialysis bags were cut into 3-4 inches. Three 2 mL of each macromolecules (protein and starch) were in placed into the 6 bags. Bags were weighed and were placed into either beakers of water that were in an ice bath, room temperature, or heated. Every 10 minutes until 30 minutes bags were dried and weighted. Sample of the water was tested with appropriate indicator (biuret test for protein and iodine test for starch). The water was tested every 10 minutes to see if any macromolecules would appear present over the three 10-minute interval. In this experiment, the room temperature water is the control group. The independent variables were the temperature at which the waters and the dependent variables are what the weight of the bags after each 10 minutes and the color the water changed with the indicator.ResultsAs shown in figure 1, the weight of the protein dialysis bag in the ice bath steadily increased till it reached 20 minutes where it decreased back to the weight it was around 10 minutes. The weight of the protein in room temperature (RT) spiked at 10 minutes then decreased at 20 minutes and then went slightly back at 30 mins. The weight of the protein in the heated water hada similar trend as the protein that was in the ice water. All three temperatures all came to have very close and similar ending weights.As shown int Figure 2, the weight of the starch in the heated water and ice bath both had very similar trends. They both gradually increased till it got to 20 minutes then both weights slightly decreased at 30 minutes. The starch at room temperature dramatically increased at 10 minutes but then followed a similar trend from 20 to 30 minutes. The ending weighs, like the proteins, arestill relatively close to one another.As shown in Table 1, Table 2, and Table 3, none of the water samples taken showed any of the macromolecules present.Table 1 10 minutes Protein StarchIce negative negativeRT negative negativeHeat negative negativeTable 2 20 minutesProtein StarchIce negative negativeRT negative negativeHeat negative negativeTable 3 30 minutesProtein StarchIce negative negativeRT negative negativeHeat negative negativeDiscussionThe hypothesis that if there are differing temperatures at which the macromolecules are placed in, then the rate of diffusion would be affected, and due to the possibility of the proteins having alarger diameter than the starches then it should have a more difficult time passing through the semipermeable membrane was refuted. Due to none of the samples not show any of the macromolecules were not showing that they were present regardless of the temperature or size ofthe macromolecule, that shows none were passing through the dialysis bags. On both graphs, dialysis bags that were in heated water had very similar trends to one another and were both relatively had a smaller range in weight than the other two temperatures. This was because osmosis would be happening faster, so the water molecules would be passing in and out the dialysis bags more quickly and freely. On both graphs, dialysis bags that were in an ice bath also had very similar trends. This was because the kinetic energy in the water was slowed down due to the water being cold so the movement of water across the dialysis bag was slowed down. Since the exact identity of the protein or starch was not known, there was not an exact number ora smaller range of the size of the diameter of the macromolecule. There was a large range of possible diameters for both starches and proteins, so knowing the exact type of protein and starchwould be extremely useful in this experiment. The set back with this experiment is that there wasa limited time frame, so