1. Describe two variables that affect the rate of diffusion. The two variables that affect the rate of diffusion are:
• The composition of the lipid layer, this content varies from tissue to tissue. For example kidney tissues have a high cholesterol content which makes them impermeable to water. • The size of the molecule, the larger the molecule the slower the rate of diffusion.
2. Why do you think the urea was not able to diffuse through 20 MWCO? How well did the results compare with your predictions? The urea was not able to diffuse through the 20 MWCO because the membrane pores are too small and the urea molecules are large. The molecular weight of Urea is 60.07 g/mol which is too large thus the molecules were not able to pass through the pores of the 20 MWCO. The results that I obtained from the experiment agreed with these predictions because urea was no able to diffuse through the 20 MWCO.
3. Describe the results of the attempts to diffuse glucose and albumin through the 200 MWCO membranes. How well did the results compare with your predictions? Glucose was able to diffuse through the 200 MWCO membrane, however albumin was not able to diffuse through the 200 MWCO. This is due to the difference of the molecular weight between the two molecules. Glucose has a molecular weight of about 180 g/mol and albumin (a protein composed of 67 amino acids and each amino acid is 67 g/mol) has a molecular weight of (67 *135 g/mol) 9045 g/mol. By comparing these numerical values we can understand why albumin was not able to diffuse through the 200 MWCO. The results that I obtained from the experiment supported these predictions because only glucose was able to diffuse through the 200 MWCO.
4. Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea. Sodium chloride < urea < glucose < albumin.
Activity 2: Stimulated Facilitated Diffusion
1. Explain one way in which facilitated diffusion is the same as simple diffusion and one way in which it differs. One way in which simple and facilitated diffusion are the same is that they both transport molecules along or down the concentration gradient of the solute and they do not require energy from an outside source. One way in which simple and facilitated diffusion are different from each other is that facilitated diffusion requires a membrane bound carrier protein to aid in the transportation of a molecule across the membrane. However, simple diffusion occurs without the assistance of membrane proteins.
2. The larger value obtained when more glucose carriers were present corresponds to an increase in the rate of glucose transport. Explain why the rate increased. How well did the result compare with your predictions? The rate of glucose transportation increased when more glucose carriers were present, since more glucose molecules could bind to the glucose carriers present. This resulted in an increase number of glucose molecules to cross the membrane. The results from the experiment supported these predictions because as the number of glucose carriers increased the rate of glucose transportation via facilitated diffusion also increased.
3. Explain your prediction for the effect of Na+ Cl- might have on glucose transport. In other words, explain why you picked the choice you did. How well did the results compare with your predictions? I believe that Na+ Cl- will not affect the rate of glucose transport, because Na+ Cl- is transported via simple diffusion which does not require a carrier protein. Therefore Na+ Cl- is completely independent from the glucose transport, so adding Na+ Cl- has no effect on the rate of glucose transport. The results I obtained from the experiment supported these predictions because the presence of Na+ Cl- did not affect the rate of glucose transportation.
Activity 3: Stimulating Osmotic Pressure