Cell Transport Mechanisms and Permeability
Name ____________________________________________________________ Lab Time/Date ______________________________
Activity 1 Simulating Dialysis (Simple Diffusion)
1. Describe two variables that affect the rate of diffusion. * The size of the pores of the membrane
* The size of the molecule diffusing through the membrane
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? * Because the pores of the membrane were not large enough * I predicted this correctly.
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? I predicted that only glucose would diffuse through it and was right. Albumin is too heavy to diffuse through that membrane. 4. Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea. NaCl, 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. -Similar – They pass through the membrane without the use of ATP, they’re both forms of passive transport. -Different – The solutes in facilitated diffusion pass through a carrier protein while the solutes pass through the membrane in simple diffusion. 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? Since there were more carrier proteins, more glucose could diffuse into the cell at one time which made the process go along much quicker. I predicted this correctly. 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? I said that
the rate of diffusion would decrease, which was wrong, because I figured that having the NaCl would equalize the concentration gradient and make the concentration gradient and make it a slower process. The rate actually remained unaffected because NaCl is not required for glucose in the simulation.
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? I predicted correctly in saying that the NaCl concentration would increase the pressure because they are directly related, meaning if one increased, that means the other one must have increased as well. 2. Describe one way in which osmosis is similar to simple diffusion and one way in which it is different. -Similar – Solutes can still pass through the membrane in both simple diffusion and osmosis. -Different – In diffusion, the particles go from high concentration regions to low concentration regions, while in osmosis it crosses from a region of low solute concentration to high solute concentration. 3.Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.” Water follows the solutes (milliosmoles) into higher concentrated areas of solutes, meaning it was going against the concentration gradient and “chasing the milliosmoles.” 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? Keeping in mind the past activities, I predicted correctly before doing this activity. The glucose diffused through to the left beaker forming equilibrium, which created osmotic pressure on the left side. The albumin cannot fit through that membrane so it didn’t reach equilibrium.
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. Because the sodium-potassium pump needs a 3:2 ratio to function, meaning once the concentration of the KCl runs out then the NaCl cannot
function either. 2. Explain why there was no sodium transport even though ATP was present. How well did the results compare with your prediction? I predicted wrong with this activity because I said that the Na+ would be maximally transported. I know now that although in the presence of ATP, the pump still cannot function without any K. 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? I also predicted incorrectly on this one because I did not realize that the glucose carriers don’t need ATP to function so they were still at the mercy of how much potassium there was in the sodium-potassium pump. I thought that there would be easier access into the cell for the Na and K cells. 4.Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment? Explain your answer. Facilitated diffusion because it is moving with the concentration gradient and the glucose carriers don’t require ATP to transport the glucose.
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