Cell Transport Mechanisms and Permeability
Name: Jeffery Cook
Lab Time/Date: 12pm 2/09/2015
Activity 1 Simulating Dialysis (Simple Diffusion)
1. Describe two variables that affect the rate of diffusion. a. Two variables that affect the rate of diffusion are size and whether or not there is an electrical or concentration gradient. 2. Why do you think the urea was not able to diffuse through the 20 MWCO membrane? How well did the results compare with your prediction? a. My prediction was incorrect. I think the urea was not able to diffuse through the 20 MWCO membrane because the molecular weight of urea is about 60. This means it is above the molecular weight cut off and cannot diffuse. 3. Describe the results of the attempts to diffuse glucose and albumin through the 200 MWCO membrane. How well did the results compare with your prediction? a. The glucose was able to diffuse because its molecular weight was less than 200, while the albumin was much larger than 200 and could not diffuse. My prediction was wrong as I originally thought that the MW of glucose was higher than 200. 4. Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea. a. The molecular weight from smallest to greatest is Sodium Chloride, Urea, Glucose, Albumin. Activity 2 Simulated Facilitated Diffusion
1. Explain one way in which facilitated diffusion is the same as simple diffusion and one way in which it differs. a. One way that facilitated diffusion and simple diffusion are the same is that the substance being moved will both move along or down with the concentration gradient. They are different in that Facilitated diffusion requires a membrane bound carrier protein while simple diffusion does not. 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 results compare with your prediction? a. The rate increased because there were more carriers to assist with diffusion, but not so many that saturation occurred maxing out the rate of diffusion. This was predicted.
3. Explain your prediction for the effect Na+Cl− might have on glucose transport. In other words, explain why you picked the choice that you did. How well did the results compare with your prediction? a. I was not sure how this would affect the rate of diffusion so I honestly made a guess. After looking at the results, I feel like this was not a correct prediction. I think that adding the sodium chloride actually slowed the rate of transport for glucose alone. Activity 3 Simulating Osmotic Pressure
1. Explain the effect that increasing the Na+Cl− concentration had on osmotic pressure and why it has this effect. How well did the results compare with your prediction? a. Increasing the Sodium Chloride concentration had an increase on osmotic pressure. This is most likely because it was moving from a higher concentration gradient to a lower concentration gradient caused by the added sodium. My prediction was incorrect.
2. Describe one way in which osmosis is similar to simple diffusion and one way in which it is different. a. Osmosis is similar to a simple diffusion in that they both move along the concentration gradient while it is different in the fact that it moves in response to a higher concentration of solutes on the other side of a membrane. 3. Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.” a. Water always moves down the concentration gradient in a direction moving from a higher concentration to a lower concentration. 4. The conditions were 9 mM albumin in the left beaker and 10 mM glucose in the right beaker with the 200 MWCO membrane in place. Explain the results. How well did the results compare with your prediction? a. The pressure in left beaker increased because the albumin had a lower concentration gradient than the glucose, causing an increase in pressure in the left beaker. My prediction was correct.
Activity 4 Simulating Filtration
1. Explain in your own words why increasing the pore size increased the filtration rate. Use an analogy to support your statement. How well did the results compare with your prediction? a. Increasing pore size will allow for more room in order to pass through. This is similar to a salt or pepper shaker. The bigger the openings in the top of the shaker are, the more salt can pass through them. My prediction was correct. 2. Which solute did not appear in the filtrate using any of the membranes? Explain why. a. Powdered Charcoal did not appear in any of the filtrate because there is not enough pressure and the pores are not large enough to allow it to pass through. Charcoal is often used as a filtration substance in itself for water filtration systems so this did not seem surprising to me. 3. Why did increasing the pressure increase the filtration rate but not the concentration of solutes? How well did the results compare with your prediction? a. Increasing the pressure increases the filtration because of the downward force but does not increase the concentration of the solutes because the size of the pores still did not change. My prediction was incorrect.
Activity 5 Simulating Active Transport
1. Describe the significance of using 9 mM sodium chloride inside the cell and 6 mM potassium chloride outside the cell, instead of other concentration ratios. a. 3Na+ ions are ejected from the cell for every 2 K+ ions entering the cell. 2. Explain why there was no sodium transport even though ATP was present. How well did the results compare with your prediction? a. There was no sodium transport even though ATP was present because there were not enough sodium potassium pumps. My prediction was not correct. 3. Explain why the addition of glucose carriers had no effect on sodium or potassium transport. How well did the results compare with your prediction? a. The addition of glucose had no effect on sodium or potassium because glucose is too large to pass through the pores. My prediction was incorrect. 4. Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment? Explain your answer. a. Glucose is being actively transported in this experiment. Glucose is too large to fit though the wholes without ATP or some other energy source.