1
E x e r c i s e
Cell Transport Mechanisms
and Permeability
Advance Preparation/Comments
1. A “#” symbol after “rate” data indicates that equilibrium was not reached for that solute.
Answers to Questions/Experimental Data
Pre-lab Quiz in the Lab Manual
1. active transport
2. a. diffusion
3. d. It can only occur in certain animals.
4. plasma membrane
5. molecular weight
Activity 1: Simulating Dialysis (Simple Diffusion) (pp. PEx-4–PEx-6)
Predict Question 1: The correct prediction is “no.” Urea is too large to diffuse through this membrane.
Predict Question 2: The correct prediction is that glucose will be able to diffuse through the membrane.
Albumin, however, is too large and will not diffuse.
Chart 1: Dialysis Rates (average diffusion rate in mM/sec)
Membrane MWCO
Solute
20
Na1Cl2
0.0000
50
0.0150
0.0300
100
200
0.0150
Urea
0.0000
0.0094
Albumin
0.0000
Glucose
0.0040
Activity Questions:
1. No, none of the solutes tested passed through the 20 MWCO membrane. They were all too large.
2. Yes, Na1 Cl2 diffused through the 50 MWCO membrane.
3. Increasing the size of the solute slowed down the rate of diffusion.
4. Increasing the solute concentration increased the rate of diffusion.
Activity 2: Simulated Facilitated Diffusion (pp. PEx-6–PEx-8)
Predict Question 1: Increasing the number of protein carriers will increase the glucose transport rate.
Predict Question 2: Adding Na1Cl2 will have no effect on the glucose transport rate because the carrier is only
transporting glucose through the membrane.
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Chart 2: Facilitated Diffusion Results (glucose transport rate, mM/sec)
Number of glucose carrier proteins
Glucose concentration
500
700
100
2 mM
0.0008
0.0010
8 mM
0.0023
0.0031
0.0017#
10 mM
2 mM w/2.00 mM
Na1Cl2
0.0010
Activity Questions:
1. They are moving with their concentration gradient.
2. The rate of facilitated diffusion increased when the number of carriers was increased.
3. Equilibrium was not reached with 100 membrane carriers and 10 mM glucose because the carriers became
saturated and unable to move the glucose across the membrane fast enough.
4. The membrane imbedded carrier in this simulation is only transporting glucose. It is not depending upon
the cotransport of Na1Cl2, so the addition of Na1Cl2 had no effect.
Activity 3: Simulating Osmotic Pressure (pp. PEx-8-PEx-10)
Predict Question 1: Increasing the Na1Cl2 concentration will increase the osmotic pressure.
Predict Question 2: There will only be pressure above the left beaker because the albumin is too large to
­diffuse. The glucose will diffuse freely, generating no osmotic pressure.
Chart 3: Osmosis Results
Solute
Membrane
(MWCO)
Pressure on left
(mm Hg)
Diffusion rate
(mM/sec)
Na1Cl2
20
170
0.0000
Na1Cl2
20
340
0.0000
Na1Cl2
50
0
0.0167
Glucose
100
136
0.0000
Glucose
100
0
0.0000
Glucose
200
0
0.0036
Albumin w/glucose
200
153
0.0044
Activity Questions:
1. The 20 MWCO membrane generated the most pressure. Na1Cl2 diffuses through the other membranes.
2. The osmostic pressure increases proportionally with increasing solute concentration.
3. No, if solutes diffuse, no osmotic pressure is generated.
4. The albumin can’t diffuse, so osmotic pressure is generated on the left. The glucose is small enough
to diffuse.
Activity 4: Simulating Filtration (pp. PEx-11–PEx-13)
Predict Question 1: The filtration rate should increase when the pore rate is increased.
Predict Question 2: Increasing the pressure above the beaker should increase the rate of filtration.
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Chart 4: Filtration Results
20
50
200
200
Solute
Filtration rate (ml/sec)
1.00
2.50
10.00
20.00
Na1Cl2
Urea
Glucose
Powdered
charcoal
Membrane (MWCO)
Filter concentration (mg/ml)
0.00
4.81
4.81
4.81
Membrane residue
present
present
present
present
Filter concentration (mg/ml)
0.00
0.00
4.74
4.74
Membrane residue
present
present
present
present
Filter concentration (mg/ml)
0.00
0.00
4.34
4.34
Membrane residue
present
present
present
present
Filter concentration (mg/ml)
0.00
0.00
0.00
0.00
Membrane residue
present
present
present
present
Activity Questions:
1. The solutes filtered were too large to pass through the 20 MWCO filter.
2. The two variables that affected the rate of filtration were the size of the pores in the membrane and the
pressure applied to the filter.
3. The best way to increase the filtration rate in living membranes would be to increase the pressure applied.
The powdered charcoal had the largest molecular weight because it was not able to pass through the
­filtration membrane.
Activity 5: Simulating Active Transport (pp. PEx-13–PEx-14)
Predict Question 1: No, sodium will not be transported because it must be cotransported with potassium. The
sodium/potassium pump requires sodium and potassium on opposite sides of the membrane.
Predict Question 2: The addition of glucose carriers should not have an effect on the transport of sodium or
potassium because the glucose carriers work independently of the sodium/potassium pump.
Activity Questions:
1. Some of the ions were transported, but there wasn’t enough ATP to transport all of the ions. If no ATP
were present, there wouldn’t have been any movement of ions.
2. Sodium must be transported with potassium, so even though ATP was present, no sodium was transported.
3. When more pumps were added, the rate of transport of sodium and potassium increased proportionally.
4. Glucose is transported by its own carriers and is not dependent upon sodium or potassium. Nor is sodium
or potassium dependent upon glucose, as evidenced from previous experimental runs.
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Lab Time/Date _________________________
E x e r c i s e
1
A c t i v i t y
1 S h ee t
Cell Transport Mechanisms
and Permeability
Simulating Dialysis (Simple Diffusion)
1. Describe two variables that affect the rate of diffusion. Increasing the size of the solute decreases the rate of diffusion. Increasing the concentration of a solute increases the rate of diffusion.
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? Urea was not able to diffuse because it was too large to fit through the pores. This matched the prediction made. Student predictions vary.
Re v i e w
Name _________________________________
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? Glucose was able to diffuse through the 200 MWCO; the albumin, however, was too large.
Student predictions vary.
4. Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea. The following are put in order from smallest to largest: sodium chloride, urea, glucose, and albumin.
A c t i v i t y
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. Similarities
include: solutes move with their concentration gradient; the processes are both passive. A difference is that facilitated diffusion requires a carrier.
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? With more carriers present, more glucose is able to be moved across the membrane. The correct prediction is that the rate increases.
3. Explain your prediction for the effect Na1Cl− might have on glucose transport. In other words, explain why you picked
the
1 2
choice that you did. How well did the results compare with your prediction? Na Cl should have no effect because it is not
required for the transport of the glucose. The carrier is only moving glucose.
A c t i v i t y
3 Simulating Osmotic Pressure
1. Explain the effect that increasing the Na1Cl− concentration had on osmotic pressure and why it has this effect. How well did
1 2
the results compare with your prediction? Increasing the Na Cl concentration increased the osmotic pressure, because these variables are directly proportional to each other.
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2. Describe one way in which osmosis is similar to simple diffusion and one way in which it is different. Osmosis is similar because it is a passive process. It is different because it is the movement of water, rather than solutes.
3. Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.” The net movement of water is with its concentration gradient. This means that it moves toward the higher concentration of solutes.
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? The osmotic pressure was generated by the albumin, which was too large to diffuse. The glucose diffused through the membrane.
A c t i v i t y
4 Simulating Filtration
1. Explain in your own words why increasing the pore size increased the filtration rate. Use an analogy to support your state
ment. How well did the results compare with your prediction? Increasing the pore size should proportionally increase the filtration rate.
2. Which solute did not appear in the filtrate using any of the membranes? Explain why. The powdered charcoal did not appear in the filtrate because it was too large to go through.
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? At the lower pressure, all of the solutes were filtering through, so increasing the pressure just caused
them to filter through faster.
A c t i v i t y
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. The concentration of the ions is significant because sodium and potassium are transported at a ratio of three to two, respectively, by the pump.
2. Explain why there was no sodium transport even though ATP was present. How well did the results compare with your
prediction? Sodium and potassium are required to move these ions using the pump. If one is absent movement will not occur.
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? Glucose is not tied in any way to the movement of sodium or potassium in this simulation. It is moving through its own carrier.
4. Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment? Explain your
answer. Glucose is moving with its concentration gradient through a carrier. This is facilitated diffusion.
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Review Sheet 1
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