Cell Transport Mechanisms and Permeability

Simple Diffusion
1. The following refer to Activity 1: Simulating Dialysis (Simple Diffusion). Which solute(s) were able to pass through the 20 MWCO membrane? None of them did

According to your results, which solute had the highest molecular weight? Albumin
Which solute displayed the highest rate of diffusion through the 200 MWCO membrane? Na+CI
Using the data from Chart 1, explain the relationship between the rate of diffusion and the size of the solute. The higher rates of diffusion occurred with a smaller weight of solute.

Facilitated Diffusion
2. The following refer to Activity 2: Simulating Facilitated Diffusion. Did any of the substances travel against their concentration gradient? Explain why or why not. No, because the solutes can only move down the concentration gradient in a facilitated diffusion, not against the concentration gradient.

Using your results from Chart 2, what was the fastest rate of facilitated diffusion recorded? 0.0039
Describe the conditions that were used to achieve this rate. Glucose concentration was 8mm, glucose carriers were 900
Name two ways to increase the rate of glucose transport.
A higher number of glucose carriers , or a higher amount of glucose in a solution.

Did NaCl affect glucose transport?
Did NaCl require a transport protein for diffusion? Why or why not? NaCI is small enough to diffuse down its concentration gradient, enabling it to not need a transport protein.

Osmotic Pressure
3. The following refer to Activity 3: Simulating Osmotic Pressure. For NaCl, which MWCO membrane(s) provided for the net movement of water without movement of NaCl? 20 MWCO
Explain how you determined this. (Hint: Correlate your results to the data in Chart 3.) The build up of osmotic pressure occurring from the non diffusible NaCI in the solution causes the water to diffuse down it’s concentration gradient.

For glucose, which MWCO membrane(s) provided for the net movement of glucose without net movement of water?

Explain how you determined this.

Is osmotic pressure generated if solutes diffuse freely?
Explain how the solute concentration affects osmotic pressure.

4. The following refer to Activity 4: Simulating Filtration. Using your results in Chart 4, which MWCO membrane had the greatest filtration rate? Explain the relationship between pore size and filtration rate.

Which solute did not appear in the filtrate using any of the membranes? What is your prediction of the molecular weight of glucose compared to the other solutes in the solution? What happened when you increased the driving pressure?

Explain why fluid flows from the capillaries of the kidneys into the kidney tubules.

How do you think a decrease in blood pressure would affect filtration in the kidneys?

5. The following refer to Activity 5: Simulating Active Transport. With 1 mM ATP added to the cell interior (left beaker) and the extracellular space (right beaker), was all of the Na+ moved into the extracellular space? Why or why not?

Describe the effect of decreasing the number of sodium-potassium pumps. Describe how you were able to show that the movement of sodium was due to active transport.

What do you think?

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