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Osmosis: Experiment with Diffusion across a semi-permeable membrane
In this part of the activity, you are going to build a model yourself. First you will become familiar with authoring a model by actually adding pieces, and then you will do some experimentation with it.
How to use this Model
1. Remember, inserting molecules is simple. You just need to click the button on the tool bar that corresponds to the type of molecule you would like to add, then click somewhere in the box. You need not click the button again if you want to add more molecules of the same type. In this model the pink molecules represent syrup, the green molecules represent water.
2. You may need to add energy to some of the molecules so that all are moving. To do this click the"heat" button (it looks like this: ) and then click on different molecules.
3. You can change the temperature by moving the slider to the right of the model. Moving the slider up heats up the model.
4. You can reset the model by clicking the reset button below the model (it looks like this: ).
Experiment 1
Your Challenge: Create multiple scenarios that show how concentration affects the rate of movement across the membrane.
What to do:
1. Set up a model that that explains how the concentration of water affects the rate of movement across the membrane.
2. BEFORE you run the model, save the initial state by right-clicking (Ctrl-clicking on the Mac) on a place of the model where there is no atom or barrier, selecting "Save Model As", and then giving it a file name to save. If you need to go back to your initial setup, just right-click (Ctrl-click on the Mac), select "Open Model" from the pop-up menu, and then select the file you have saved. The setup will be restored.
3. Create an Osmosis Experiment Report (a new window will open up) by clicking on the Create Osmosis Experiment Report button.
4. This report will include a snapshot of the intial state of your model. Type your name at the top of the report, AND describe your model below the report.
5. Run your experiments. Take snapshots of initial and final states (by clicking the button above) as a record by which to illustrate what you have learned. To import new snapshots into your diffusion activity report you need to:
Click the "Take a Snapshot" button.
THEN- Go to the "Osmosis Experiment report" and and click the snapshot icon on your menu bar.
Your snapshot manager will appear.
Select the image you want. Click the "insert" button. The snapshot will now be added to your report.
Below the snapshot describe your model and the important features of it. (You can type as if you were in any word processer.)
Experiment 2
Your Challenge: Find a way to take items of the same size and allow some of them to cross the membrane while stopping others.
1. Use the model above to accomplish your challenge. Note that there are more buttons on the model toolbar - some of which may come in handy.
2. You should click the #2 element button and add about 10 #2 elements on the left side of the 'membrane'.
3. Click the 'mark' button and mark any three of the elements you just placed.
4. Your goal is to setup the model so that your 'marked' elements do not cross the 'membrane' but the other elements of the same size are able to cross. Your 'marked' elements
must otherwise be moving around freely on the left side (you can not 'freeze' them in place or wall them off in a corner.)
5. Once you think you have it setup correctly, be sure to save your initial state (as you did above) so you do not have to completely start over if it does not work as expected.
You are now finished this activity and will be returned to Page 7 of the SAM activity.
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