Membrane Permeability

?Results The objectives of this experiment were to investigate diffusion of molecules across a membrane and the factors that affect the rate of diffusion. The hemolysis time of sheep erythrocytes was measured for each of eight different nonelectrolyte solutions by eleven groups in BI 108 Section D2. These eight nonelectrolytes were urea, thiourea, methanol, ethanol, propanol, ethylene glycol, diethylene glycol, and triethylene glycol, and the mean hemolysis times can be seen below in Figure 1. The mean hemolysis time for urea was 11. 90 seconds (±2. 65 sec, n = 11).

Thiourea took an average of 92. 72 seconds (±12. 41 sec, n = 11) to hemolyze 75% of erythrocytes, while methanol took 9. 19 seconds (± 1. 66 sec, n = 11). The black line was seen through the ethanol solution after an average of 10. 19 seconds (± 2. 09 sec, n = 11) and through propanol after 11. 27 seconds (± 2. 38 sec, n = 11). Average hemolysis time of erythrocytes in ethylene glycol was 33. 99 seconds (± 4. 52 sec, n = 11), while it was 70. 36 seconds in diethylene glycol (±8. 75 sec, n = 11) and 177. 56 seconds in triethylene glycol (± 24. 44 sec, n = 11).

GraphPad online software was used to conduct statistical analysis of the data. After a paired, two-tailed t-test was conducted, the difference between hemolysis time of ethanol and methanol was found to be not statistically significant (P = 0. 0666, t = 2. 0577, df = 10). Similarly, a paired, two-tailed t-test conducted on the hemolysis times of ethanol and propanol also found no statistically significant difference (P = 0. 0888, t = 1. 8851, df = 10). However, the difference between hemolysis times for methanol and propanol was found to be statistically significant (P < 0. 05, t = 2. 0577, df = 10).

A paired, two-tailed t-test used to compare the hemolysis time of urea and ethylene glycol found that the difference between these hemolysis times was also statistically significant (P < 0. 001, t = 20. 9104, df = 10). Figure 1. Mean hemolysis time of sheep blood erythrocytes in each nonelectrolyte solution. These bars show the calculated average (over 11 measurements) of how long (in seconds) it took to see the black line. Discussion The purpose of this lab was to study membrane permeability characteristics by investigating hemolysis of sheep erythrocytes. The mean hemolysis times of sheep erythrocytes in 0.

3 M urea, thiourea, methanol, ethanol, propanol, ethylene glycol, diethylene glycol, and triethylene glycol were calculated, and paired, two-tailed t-tests were conducted to determine statistical significance. It was found that the difference in hemolysis time between methanol and ethanol was not statistically significant (P = 0. 0666, t = 2. 0577, df = 10); the same result was found between the results of ethanol and propanol (P = 0. 0888, t = 1. 8851, df = 10). The difference between hemolysis time for methanol and propanol, however, was found to be statistically significant (P < 0.

05, t = 2. 0577, df = 10), as was the difference between urea and ethylene glycol hemolysis time (P < 0. 001, t = 20. 9104, df = 10). The results were expected to show statistically insignificant differences between ethanol, methanol, and propanol. On the other hand, urea was expected to diffuse significantly faster than ethylene glycol (Hunter 1976). The hypothesis regarding hemolysis time was that the lipid/water partition coefficient would be directly correlated with speed of hemolysis, while molar volume would be indirectly correlated (Gardner and Godrick 2011).

Therefore, increased molar volume would increase the hemolysis time and increased lipid/water partition coefficient would decrease the hemolysis time. The results showed that, for the three alcohols, the increase in molecular weight from methanol to propanol (which would increase hemolysis time) was mostly counterbalanced by the increase in lipid/water partition coefficient, which decreases hemolysis time. This explains why the differences between methanol and ethanol and ethanol and propanol were not statistically significant.

The statistically significant difference between methanol and propanol showed that although propanol had a higher lipid/water coefficient, the difference in molar volume had more of an effect on the difference between hemolysis times of the two solutions. Propanol’s molar volume was larger enough that it outweighed the effects of a higher lipid/water coefficient.

The hemolysis times for urea and ethylene glycol were significantly different because these two nonelectrolytes must pass through carrier proteins in order to enter the cell (Lodish et al 2000). Since they do not interact directly with the lipid membrane, the lipid/water partition coefficient had no effect on diffusion speed and hemolysis time. The only thing that mattered was molar size, and the smaller molecule (urea) did in fact diffuse faster than ethylene glycol and therefore had a faster hemolysis time. This experiment could be improved through the reduction of human error, for example by using a spectrophotometer.

A spectrophotometer could measure the amount of light transferred through the test tube of blood and nonelectrolyte solution; the time until reaching a certain critical stage of absorbance would be measured to determine hemolysis time. Using the human eye to judge when the black line behind the test tube is visible is not very reliable. Thus the use of a spectrophotometer would decrease human error and would increase the accuracy of determined hemolysis time. These results could be applied to real-world situations in several ways.

Firstly, it is possible to use sheep erythrocytes as models for human erythrocyte behavior because permeability similarity increases for more closely related species (Hunter 1976). Using an even more closely related species’ erythrocytes in diffusion experiments would provide an even better model for human cell behavior. Additionally, finding out more about diffusion mechanisms may allow scientists to synthesize compounds that have specific desired diffusion characteristics. This will allow better targeting of drugs, which would have a great impact on medicine for a variety of disorders. Works Cited 1.

BI 108 Section D2. 2011. Principles of Biology II. Biology Department, Boston University, Boston, MA. 2. Gardner KE and Godrick EC (eds). 2011. Principles of Biology II. Hayden-McNeil, LLC, Plymouth Michigan. Module # 3, pp 41-64. 3. GraphPad. 2009. t test calculator. Website: http://www. graphpad. com/quickcalcs/ttest. cfm. Accessed Feb 14, 2011. 4. Hunter, F. R. “Permeability of Trout Erythrocytes to Nonelectrolyes. ” Biological Bulletin 151. 2 (1976): 322-30. Print. 5. Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. 2000. Molecular Cell Biology, 4th edition. W. H. Freeman, New York.