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Lesson 6 Membrane Transport

  Virtual Lab


Osmosis, Diffusion, and Paramecium Homeostasis © Explore learning


Background Information:
These labs will allow you to observe how osmosis and diffusion work. You will complete a lab on osmosis, a lab on diffusion, and then a lab on a paramecium (a small single-celled organism) to see these two processes in action. They will also let you observe what happens in a hypertonic and a hypotonic solution.

Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.

  1. Open the Osmosis Gizmo by clicking on the play button in this section. Print students can access the Gizmo in the Online Resources for Print Students section of their online course.
  2. The pink square represents a cell, the green dots represent water molecules, and the blue dots represent a large molecule such as starch or sugar.
  3. Check that the simulation has loaded with the default settings of five large molecules outside the cell and an initial cell volume of 30%. Take note of the initial concentrations inside and outside of the cell and the initial number of solute and solvent particles inside and outside of the cell. These are found on the right-hand side of the simulation. (You can take a screenshot of this information using the camera icon if you wish.)
  4. Click the play button located at the bottom of the screen to run the simulation. Watch what happens to the size of the cell as the simulation plays out. What is happening to the concentration inside and outside of the cell?
  5. After 20 seconds, take note of the final concentrations inside and outside of the cell, what happened to the size of the cell, and the number of solute and solvent particles inside and outside of the cell. (You can take a screenshot of this information using the camera icon if you wish.)
  6. Click on the reset button found next to the pause/play button.
  7. Change the solute outside to 10 molecules and the initial cell volume to 60%. Record or screenshot the initial information.
  8. Click on the play button to run the simulation. Watch what happens to the size of the cell as the simulation plays out. What is happening to the concentration inside and outside of the cell?
  9. After 67 seconds, click the pause button and record or screenshot the final information.
  10. Repeat steps 6 to 9, changing the initial cell volume to 20% and leaving the solute outside at 10 molecules. You only need to run this simulation for 30 seconds.
  11. Please return to the top of this activity and click on analysis to complete the analysis questions.


©Explore Learning
A6.18 Default Settings



©Explore Learning
A6.18 Camera icon
  1. What did you observe happening to the concentrations of each run of the simulation?

    Since the concentrations evened out at the end of each run, the cells were in isotonic solutions.


  2. Complete the following chart:
Run #
What happened to size of cell?
Why did the cell change that way?
Was the outside solution hypotonic or hypertonic to the inside of the cell?
1
2
3

Run #
What happened to size of cell?
Why did the cell change that way? Was the outside solution hypotonic or hypertonic to the inside of the cell?
1 It got bigger.
The concentration outside the cell was lower than inside, so the cell took in water to try to dilute the inside of the cell. Hypotonic
2
It got smaller.
The concentration inside the cell was lower than the outside, so water left the cell to try to dilute the concentration outside. Hypertonic
3
It got bigger.
The concentration outside the cell was lower than inside, so the cell took in water to try to dilute the inside of the cell.
Hypotonic
  1. At the end of each run of the simulation, were the cells in a hypertonic, hypotonic, or isotonic solution?

    Since the concentrations evened out at the end of each run, the cells were in isotonic solutions.




  1. Open the Diffusion Gizmo by clicking on the play button in this section. Print students can access the Gizmo in the Online Resources for Print Students section of their online course.
  2. Make sure the simulation opens with the default settings shown in image A6.19. The clear space in this simulation represents water, and the purple dots represent small particles.
  3. Click the play button in the bottom right half of the simulation. What happens to the number of particles in region B?
  4. Run the simulation for 60 seconds. What has happened to the number of particles in regions A and B?
  5. Click the reset button next to the pause/play button.
  6. Increase the number of y in B to 50 and decrease the wall height to 25%. You will now see purple and green particles.
  7. Click on the play button to run the simulation. What happens to the number of particles in regions A and B?
  8. Run the simulation for 120 seconds. What has happened to the number of particles in regions A and B? What has happened to the number of x and y particles in each region?
  9. Please return to the top of this activity and click on analysis to complete the analysis questions.




©Explore Learning
A6.19 Default settings in Diffusion lab
  1. In the first run of the simulation, what happens to the number of particles on each side of the wall? Why does this happen?

    The number of particles on each side of the wall even out as the simulation runs. This happens because the particles are trying to reach equilibrium. Once equilibrium is reached, there will be no net movement of particles.


  2. In the second run of the simulation, what happens to the number of particles on each side of the wall? What happens to the number of purple and green particles on each side of the wall? Why does this happen?

    The total number of particles on each side of the wall stays the same as both sides started at 50. The total number is in equilibrium, so it does not change. The number of purple and green particles changes to try to reach equilibrium. The purple particles move into region B, and the green particles move into region A. They will keep moving until equilibrium is reached. 


  3. Try changing the number of x and y particles in the simulation. If the particles are not even on both sides, what happens to the total number of particles as the simulation runs?

    Since the total number of particles are not in equilibrium, this number will change until they are in equilibrium.


  1. Open the Paramecium Homeostasis Gizmo by clicking on the play button in this section. Print students can access the Gizmo in the Online Resources for Print Students section of their online course.
  2. Check that the simulation has opened with a water solute concentration of 1% and paramecium controlled.
  3. Click on the play button located in the bottom left side of the simulation. What is happening to the contractile vacuole (the pink sphere)? Why do you think this is happening?
  4. Pause the simulation and change the water solute concentration to 2%. Click on the play button and observe what happens to the contractile vacuole.
  5. Pause the simulation again and change the water solute concentration to 0%. Click on the play button and observe what happens to the contractile vacuole.
  6. Pause the simulation and change the water solute concentration back to 1%. Change the simulation from “Paramecium controlled” to “User controlled.” You are now in charge of when the contractile vacuole does its job.
  7. Click the play button and observe what happens to the contractile vacuole and size of paramecium. Do not click on the contract button. What eventually happens to the paramecium?
  8. Reset the simulation, making sure the simulation is still user controlled. Click on the play button and try to click on the contract button at the right time to keep the paramecium healthy. If you would like a challenge, change the water solute concentration to 0%.
  9. Pause the simulation and change the water solute concentration to 2%.
  10. Click the play button and observe what happens to the size of the cell. (This is a small difference, so you really have to watch to see it!)
  11. Please return to the top of this activity and click on analysis to complete the analysis questions.

  1. What do you think the job of the contractile vacuole is based on your observations?

    The job of the contractile vacuole is to remove the excess water that is entering the Paramecium. This helps to keep the Paramecium from exploding. 


  2. Complete the following chart:
    Water Solute Concentration
    		Is water moving into or out of the cell?
    		How do you know?
    		Is the Paramecium in a hypertonic, hypotonic, or isotonic solution?
    1%
    2%
    0%

    Water Solute Concentration Is water moving into or out of the cell? How do you know? Is the Paramecium in a hypertonic, hypotonic, or isotonic solution?
    1% Moving into the cell
    • The contractile vacuole is working to push water out.
    • The paramecium gets bigger.
    		Hypotonic
    2% Moving out of the cell
    • The contractile vacuole doesn’t appear to be doing anything.
    • The paramecium is getting smaller.
    		Hypertonic
    0% Moving into the cell
    • The contractile vacuole is working very quickly to push water out.
    • The paramecium gets bigger until it explodes if the contractile vacuole does not do anything.
    		Hypotonic