Science: VLab: Membranes, 3
To open this resource in SAS® Curriculum Pathways® :
1. Go to http://www.sascurriculumpathways.com/login
2. Enter the student user name: rdhsstudent1
3. In the Quick Launch box, enter: 3
-----------------------------------------------------------------------------------------------------------You will use the BioScope to see how a cell responds to changing water activity and how the
membrane controls this response. But first, you must identify and describe all of the components
involved.
Holding Tank
A. Use the selections available in the Cell Control panel to switch between the Plant and
Animal cell and to turn the membrane On and Off. Examine both cells, with and without a
membrane; then answer these questions.
1.
2.
3.
4.
Describe the motion of the molecules through the tank.
How does the plant cell differ from the animal cell?
Do the sucrose molecules enter either of the cells?
Do the sucrose molecules enter the cells when the membrane has been
turned Off?
5. Does the cell wall of the plant cell act as a barrier to the movement of
sucrose?
6. From your observations, what is a function of the cell membrane?
B. Focus on the arrows to the right of the cell.
7. What do the arrows indicate?
C. Click the Equilibrate button at the bottom of the screen to observe the cell's response as
it seeks equilibrium with its environment. Answer the following.
8. Is there any change in the appearance of the arrows?
9. Are there any changes in the direction or amount of water movement as
listed above the Holding Tank?
10. Is the cell at equilibrium (balanced) with the tank? Explain.
Conditions Panel
D. The Conditions panel shows various solutes. You will use the sliders to adjust the amount
of each solute. You will observe the effects of changing solute levels on water activity.
Note that the conditions in the Holding Tank respond immediately when you move a
slider; however, the cell does not respond until you click on the Equilibrate button.
11. Compare the image of sucrose located next to the name above the control
slider with the image of the molecules moving through the tank. Are the
images the same? If not, describe how they differ.
12. Set the solute concentration for sucrose (or [sucrose]) to 0.00 M and
adjust [glucose] to .30 M. Compare the images of glucose on the slider
and in the tank. Are the images the same? If not, describe how they
differ.
13. Repeat the procedure for NaCl. Are the images the same? If not, describe
how they differ.
14. Repeat the procedure for CaCl2. Are the images the same? If not, describe
how they differ.
E. Sometimes substances break apart (dissociate) into two or more particles when they
dissolve. Re-examine the behavior of each solute using the simulation.
Part 2: Factors Affecting Water Activity
Cells respond to changing water activity in their environment by gaining or losing water. By
moving the sliders to change conditions, you will alter the water activity in the Holding Tank. You
will measure these changes using the response of the Animal cell.
Solutes
15. Describe the response of the cell to the change in conditions of glucose.
16. What happens to the cell when water moves out of it?
17. What happens to the cell when water moves into it?
18. Does the cell respond to changing concentrations of glucose, NaCl, and
CaCl2 in the same way it responds to changing concentrations of sucrose?
Describe any differences you see.
Temperature and Pressure
J.
Reset the simulation. Make sure that the Animal cell is still selected. Use the sliders at
the bottom of the Conditions panel to investigate the effects of temperature on water
movement. Adjust the temperature to a value greater than 25 °C. Click Equilibrate.
K. Reset and repeat the process for a second temperature above 25 °C and for two
temperatures below 25 °C.
L. After you Reset the simulation, adjust the pressure to a value greater than 0. Click
Equilibrate.
19. Describe the response of the cell to changes in water activity caused by
changes in temperature and pressure.
Part 3: The Roles of the Membrane and Cell Wall
You have explored conditions that affect water activity. Now you can look at how the membrane
influences the cell's response to water activity. You have already seen how the cell responds with
its membrane intact, so most of your work is done. Now see what happens when you eliminate
the membrane. Also, see if a plant cell's response to changes in water activity is affected by its
cell wall.