Exercise 1: Cell Transport Mechanisms and Permeability Worksheet
ACTIVITY 1: Simulating Dialysis (Simple Diffusion) Answers
1. The molecular weight of urea is approximately 60. Which of the membranes can it pass through?
a. 50 MWCO membrane
b. 100 MWCO membrane
c. 200 MWCO membrane
d. Both the 100 and 200 MWCO membranes d. Both the 100 and 200 MWCO membranes
2. True or False: A solution containing glucose will diffuse faster through a 200 MWCO membrane if it is heated. True
3. The molecular weight of carbon C is 12; the molecular weight of hydrogen (H) is 1; the molecular weight of oxygen (O) is 16. The chemical formula of glucose is: C6H12O6 . Using some simple multiplication and addition, determine the molecular weight of one molecule of glucose. (6x12)+(12x1)+(6x16)= 72+12+96= 180g/mol
4. Describe two variables that affect the rate of diffusion. The temperature of the solutions and the difference in concentration of the ion or molecule between the sides of the membrane
5. Why do you think that the urea was not able to diffuse through the 20 MWCO membrane? Since the chemical formula for urea is (NH2)2CO and its molecular weight is about 60. It will not diffuse through the 20 MWCO membrane because it does not ionize.
6. Describe the results of the attempts to diffuse glucose and albumin through the 200 MWCO membrane. Glucose will diffuse through the 200 MWCO membrane because its MW is 180. The MW of the protein albumin is much greater than 200 so it will not diffuse through the 200 MWCO membrane.
7. Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea. Sodium chloride, urea, glucose, and albumin
ACTIVITY 2: Simulated Facilitated Diffusion
8. True or False: The facilitated diffusion of glucose requires energy from ATP. False
9. Which of the following might cause the facilitated diffusion of glucose from one solution to another to occur faster?
a. Add Na+Cl- to the beaker on the left.
b. Add K+Cl- to the beaker on the left.
c. Add ATP to the beaker on the left.
d. None of these would cause it to happen faster. d. None of these would cause it to happen faster
10. True or False: If there are a sufficient large number of transport proteins present, glucose can be transported from a solution of lower concentration to a solution of higher concentration (i.e. up its concentration gradient.) False
11. Explain one way in which facilitated diffusion is the same as simple diffusion; one way in which it is different. They are the same as they are both passive processes and the solute can only diffuse down its concentration gradient. It is different as facilitated diffusion requires the presence of a membrane-bound carrier protein in order to occur. Furthermore, simple diffusion does not.
12. 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. With fewer carriers present they can become saturated and this will slow or stop the transport of glucose.
13. You were asked to predict what effect you thought that adding Na+ Cl- would have on the glucose transport rate. Why did you pick the choice you did? How well did the results compare with your prediction? The transport of Na+ Cl- is simple diffusion and does not require carrier proteins. Therefore it is completely independent from the glucose transport. As a result, adding Na+CI- has no effect on the glucose transport rate.
ACTIVITY 3: Simulating Osmotic Pressure
14. True or False: Osmosis is considered a type of passive transport, i.e. it does not need energy from ATP. True
15. If a cell is placed in a ________ solution of water, there will be no net movement of water in or out of the cell.
a. hypotonic
b. isotonic
c. hypertonic b. isotonic
16. If you “cut” the concentration of a non-diffusible solute that is on one side of a membrane in half, the osmotic pressure will
a. double.
b. not change.
c. be half of what it was before. c. Be half of what it was before
17. Explain the effect that increasing the Na+Cl- concentration had on osmotic pressure and why it has this effect. The Na+CI- will diffuse through the 50 MWCO membrane but will not diffuse through the 20 MWCO membrane. So, adding more Na+CI- with the 20 MWCO membrane increased the osmotic pressure. Adding it to the 50 MWCO membrane did not result in any pressure whatsoever because it diffused through this membrane.
18. Describe one way in which osmosis is similar to simple diffusion; describe one way in which it is different. One way they are the same is that they are both passive processes and the ions or molecules can only pass down their concentration gradients. As far as being different, osmosis is a special form of diffusion, is the diffusion of the solvent through a selectively permeable membrane.
19. Solutes are sometimes measured in milliosmoles. Explain this statement: “Water chases milliosmoles.” Osmosis is the diffusion of the solvent such as water. The water in this simulation diffuses to the side of the membrane that has the highest concentration of the solutes.
20. The conditions were 9mM albumin in the left beaker and 10mM glucose in the right beaker with the 200 MWCO membrane in place. Explain the results. The glucose diffuses from the right beaker to the left beaker until equilibrium is accomplished. The albumin cannot diffuse through the membrane. An osmotic pressure of 153mmHg results.
ACTIVITY 4: Simulating Filtration
21. The filtration rate of Na+Cl- in the simulation was dependent on
a. the pore size of the membrane.
b. the hydrostatic pressure applied to the top beaker.
c. the concentration of the solutes in the lower beaker.
d. both the pore size and the hydrostatic pressure applied. d. Both the pore size and the hydrostatic pressure applied
22. True or False: The simulation would not function if the top beaker were open to the atmosphere instead of having pressure applied to the top beaker. False
23. Explain in your own words why increasing the pore size increased the filtration rate. Use an analogy to support your statement. Tea can pass quicker through a plastic filter with a bigger pore size as opposed to a paper filter such as the ones used in coffee makers.
24. Which solute did not appear in the filtrate using any of the membranes? Activated charcoal
25. Why did increasing the filtration pressure increase the filtration rate but not the concentration of solutes? Increasing the filtration pressure increased the filtration rate. Nonetheless, it did not increase the amount of solute that passed through the filter. Therefore, the concentration was the same.
ACTIVITY 5: Simulating Active Transport
26. In this simulation, each of the following was (were) required In order for active transport to occur:
a. sodium ions (Na+)
b. potassium ions (K+)
c. energy from ATP
d. All of the above were required. d. All of the above were required
27. True or False: The amount of ATP that you dispensed did not affect the rate that the solutes passed from one beaker to the other. False
28. Which of the following processes require ATP?
a. Simple diffusion
b. Facilitated diffusion
c. Filtration
d. Osmosis
e. Active transport e. active transport
29. Describe the significance of using 9mM sodium chloride inside the cell and 6mM potassium chloride outside the cell. The 3 Na+ ions are transported out of the cell and 2 K+ ions are transported into the cell. This ratio of 3:2 is the same as the ratio of 9mM:6mM
30. Explain why there was no sodium transport even though ATP was present. In order for the Na+/K+ pump to function, both these ions and ATP must be present. In this simulation, no K+ was present.
31. Explain why the addition of glucose carriers either had no effect or did have an effect on sodium or potassium transport. The addition did not have an effect on the sodium or potassium transport due to solute pumps.
32. Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment. Why? Glucose is being transported down its concentration gradient by facilitated diffusion. The glucose is not actively transported since they are lipid insoluble and too large to pass through the membrane pores.
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