ACTIVITY ONE- Cell Transport Mechanisms and Permeability: Simulating Dialysis (Simple Diffusion)
1. Describe two variables that affect the rate of diffusion.
Molecular weight affects the rate of diffusion because the bigger the size of the molecule the longer it will take to diffuse. Membrane size is another variable that affects the rate of diffusion because if the membrane’s pores are small it will take molecules longer to diffuse though it than if the pores were larger. Also, membrane thickness is a variable because the thinner the membrane the quicker the 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?
Our prediction was that urea was not going to be able to diffuse through the 20 Molecular Weight Cut Off (MWCO) membrane because urea is too big of a molecule to diffuse through the 20 MWCO membrane’s pores aren’t large enough for the urea to pass through. Our prediction was correct, the Urea was unable to diffuse though such a small membrane.
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?
We predicted that glucose and albumin would both diffuse very slowly through the 200 MWCO because they are large molecules. The results were; the glucose diffused through the 200 MWCO membrane at a rate of 0.0040 per minute. The albumin was not able to diffuse through the 200 MWCO because it is too large of a molecule to fit through the membrane pore.
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4. 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- Cell Transport Mechanisms and Permeability: Simulated Facilitated Diffusion
1. Explain one way in which facilitated diffusion is the same as simple diffusion and one way in which it is different from simple diffusion.
Facilitated diffusion is the same as simple diffusion in that they are both passive and go down (or with) the concentration gradient. It is different from simple diffusion in that facilitated diffusion uses a carrier protein to transport it across the membrane.
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?
The rate of glucose that was transported increased because when the concentration of glucose got higher, so the rate of diffusion went up. When there is a higher concentration gradient the rate of diffusion increases, so the more glucose carriers made it easier for the glucose to diffuse more quickly though the membrane. We predicted that the rate of diffusion would be slower due to more molecules, but the result was the opposite, and at the time we didn’t know about Fick’s Law of diffusion.
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?
We predicted that the glucose transport rate would increase. We predicted this because we thought that with the help of Na+Cl- it would help the glucose molecules diffuse through the membrane more quickly than without it. Our results matched our prediction. The Na+Cl- facilitated the glucose though the membrane more quickly.
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ACTIVITY 3- Cell Transport Mechanisms and Permeability: 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?
By increasing the Na+Cl- concentration we changed the concentration gradient in the water, which raised the osmotic pressure. Our results coincided with our prediction because we thought that by adding more Na+Cl- would increase the osmotic pressure and increase the rate of diffusion.
2. Describe one way in which osmosis is similar to simple diffusion and one way in which it is different.
Osmosis is similar to simple diffusion in that it is a passive diffusion and moves down the concentration gradient. It is different because Osmosis takes place when there is a difference in concentration gradient across a selectively permeable membrane.
3. Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.”
“Water chases milliosmoles” is referring to the diffusion of water or osmosis. Water moves though most membranes easily and moves when there is a change in water concentration between two sides of membrane; meaning that water is chasing the concentration gradient.
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 results were that the albumin was not able to pass through the membrane because it is too big of a molecule, and glucose passed though the membrane at a rate of 0.0044 per minute. The osmotic pressure for both was 153 L. Even with a high osmotic pressure albumin was still unable to pass though the 200MWCO membrane. We predicted that with a higher osmotic pressure both would diffuse though the membrane, but glucose was the one molecule that was able to diffuse through the membrane.
ACTIVITY 4- Cell Transport Mechanisms and Permeability: 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?
By increasing the pore size in the membrane the filtration rate increased because more molecules were able to diffuse though the larger pres faster than smaller pores. Our prediction was that the rate of filtration would increase because the pores were larger, allowing more molecules to pass the pores. In the kidneys, the membrane pores are larger which allows glucose and urea to pass though the pores.
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2. Which solute did not appear in the filtrate using any of the membranes? Explain why.
Powdered charcoal did not appear in any of the filtrates though the membranes because it is too large of a molecule to pass though the pores of the membrane, even though the membrane pores are large; they weren’t large enough.
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?
The increase of pressure made the filtration happen more quickly but did not change the concentration of the solutes because the pressure affects the rate at which it diffuses through the filter, not the amount
that passes though the membrane. We predicted that the rate would increase.
ACTIVITY 5- Cell Transport Mechanisms and Permeability: 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 significance of using those concentrations rather than other ratios is because for every 3 Na+ ions that leave the cell, 2 K+ ions enter the cell. Also, we were able to see the rate of diffusion
2. Explain why there was no sodium transport even though ATP was present. How well did the results compare with your prediction?
There is more Na+ outside the cell than inside the cell so Na+ tends to stay inside the cell unless it needs to be actively transported out.
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 carries had no effect on Na+ or K+ because glucose is transported independently.
4. Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment? Explain your answer.
Glucose is being actively transported in this experiment because the ATP that was there was used to transport it.
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