Bio Lab
josef1
Lab6-OsmosisDiffusion-Fall20201.docx
![]()
Diffusion and Osmosis –
Osmosis Jones Badge
(Adapted from Biology Laboratory Manual 10th Edition, by Darrell Vodopich and Randy Moore)
All molecules display random thermal motion or kinetic energy: this is why a dissolved molecule tends to move around in a solution. Kinetic energy cause molecules to diffuse outward from high concentration to lower concentrations. The process of molecules moving from an area of higher concentration to an area of lower concentration is called diffusion. This random movement is constant, but the net movement of molecules from areas of high concentration to areas of low concentration continues until the distribution of molecules is even throughout the solution. This point is called equilibrium. At equilibrium, the random motion continues, but there is no net change in the concentration of solute through the solution. In some cases, the areas with differing concentrations are separated by a membrane that will only let water and not solutes pass through it. In this case, the movement of water down its concentration gradient is called osmosis.
Heat cause an increase in the random motion of molecules that can passively move in biological systems. This motion was originally described by Robert Browning and so it is called Brownian motion (or movement). Although we cannot directly see molecules move, we can see small particles move after they collide with moving molecules. In this lab exercise, we are going to observe diffusion and what causes diffusion rates to change, diffusion through a semi-permeable membrane, and osmosis.
Procedure 1: **ONLINE SIMULATION**
Login to the Hayden-McNeil Lab Simulation (https://courses.hayden-mcneil.com/local/ecologin/). Click on the blue notebook next to the “Expanded Osmosis and Diffusion” module. Read through the introduction information and click the forward arrow at the bottom of the page. Click on the green button to launch the simulation. Complete the following exercises in this module.
Part 1: Membrane Size Selectivity
1. Take a diffusion bag and a 250 mL beaker from the Containers shelf and place them onto the workbench.
2. Fill the bag with 45 mL of water and 5 mL of Lugol's iodine solution from the Materials shelf.
3. Fill the beaker with 150 mL of water and 50 mL of 2% starch solution. Record the color of the liquid in the beaker and of the liquid in the diffusion bag to reference later.
4. Move the diffusion bag into the beaker.
5. Watch the beaker and bag for signs of color change. After 30 seconds, move the diffusion bag out of the beaker and onto the workbench. Answer questions below.
6. Empty the beaker and diffusion bag into the waste bin, then place the empty containers in the sink.
Questions:
1) Initially, Lugol's iodine was placed inside the diffusion bag, and starch was placed outside the bag. Which of these materials was able to pass through the diffusion membrane? How do you know?
2) Which material did NOT diffuse across the membrane? Why not?
Part 2: Dependence on the Rate of Diffusion on the Concentration Gradient
7. Take four diffusion bags from the Containers shelf and place them onto the workbench. Double-click the diffusion bags and change the labels to 1, 2, 3, and 4.
8. Make up the following four solutions in the four dialysis bags with items from the Materials shelf.
|
Dialysis Bag |
10% Acetic Acid (mL) |
Water (mL) |
Final Concentration of Acetic Acid (%) |
|
1 |
50 |
0 |
|
|
2 |
25 |
25 |
|
|
3 |
12.5 |
37.5 |
|
|
4 |
5 |
45 |
|
9. Calculate the final concentration of acetic acid (%) in the diffusion bags. Record these values to reference later.
a. The first diffusion bag has 10% acetic acid.
b. The second bag contains a total of 50% (50 mL of 100 mL total) of 10% acetic acid. Therefore, the second bag contains a final concentration of 5% acetic acid (50% multiplied by 10%).
10. Take four 250 mL beakers from the Containers shelf and place them onto the workbench. Double-click the beakers to label them 1 – 4. Fill each beaker with 200 mL water.
11. Take four pH meters from the Instruments shelf and place one into each beaker. Record the pH of each beaker under the “pH at 0 minutes” row in the table below.
|
|
Diffusion Bag |
|||
|
|
1 |
2 |
3 |
4 |
|
Acetic Acid Concentration |
|
|
|
|
|
pH at 0 min |
|
|
|
|
|
pH at 1 min |
|
|
|
|
12. Take diffusion bag 1 and place it into beaker 1. Start a timer or note the time on the lab clock. This reaction should run for 1 minute.
13. After 1 minute, remove the diffusion bag from the beaker and record the pH of the liquid in the beaker in table above.
14. Repeat steps 6 – 7 for the remaining diffusion bag and beaker pairs.
15. Clear the workbench by dragging instruments back to the Instruments shelf and by emptying containers in the waste bin and then placing the empty containers in the sink. Answer the question on the next page.
Question:
Explain how the rate of diffusion changes according to the concentration gradient.
Part 3: Evidence for Osmosis
1. Take a 250 mL beaker from the Containers shelf and place it onto the workbench.
2. Add 200 mL of 35% egg albumin solution from the Materials shelf to the beaker. Record the contents of this beaker below.
Observations:
3. Take a balance from the Instruments shelf and place it onto the workbench. Place the beaker on the balance. Click the Zero button to set the starting mass to zero. Move the beaker from the balance to the workbench.
4. Take a diffusion bag from the Containers shelf and place it onto the workbench.
5. Add 50 mL of water from the Materials shelf to the diffusion bag. Record the contents of the diffusion bag below.
Observations:
6. Move the diffusion bag into the beaker containing the egg albumin solution. Start a timer or note the time on the lab clock and wait 1 minute.
7. While you are waiting for the 1 minute to elapse, take two test tubes from the Containers shelf and place them onto the workbench.
8. Add 5 mL of biuret solution from the Materials shelf to each test tube. Record the color of the liquid below.
Observations:
9. When the 1 minute has elapsed, move the diffusion bag out of the beaker and onto the workbench.
10. Place the beaker on the balance and record its mass. Write down whether the beaker has gained or lost mass, no matter how slight.
Observations:
11. Perform a biuret test for the presence of protein in both the beaker and diffusion bag. This test will determine if the dissolved albumin moved out of the beaker and into the diffusion bag or whether only water moved out of the diffusion bag and into the beaker.
a. Take two droppers from the Containers shelf and place them onto the workbench.
b. Place one dropper into the solution in the beaker. You should observe the dropper filling with liquid.
c. Place this dropper onto the first test tube containing biuret solution. Select the Pour All option. Record any color changes in the test tube. If there is protein present in the solution from the dropper, the biuret solution will turn purple. Record your observations below.
Observations:
d. Place the second dropper into the diffusion bag. You should observe this dropper filling with liquid.
e. Place the dropper in the second test tube filled with biuret solution. Dispense the entire contents of the dropper. Look for any color changes in the test tube. Record your observations.
Observations:
12. Clear the workbench by dragging instruments back to the Instruments shelf and by emptying containers in the waste bin and then placing the empty containers in the sink. Answer question below.
Questions:
1) What was the amount of mass change for the solution in the beaker at the end of the experiment? Report 0 for no change, and use + or – signs to indicate a mass gain or mass loss respectively.
2) Explain what caused an imbalance in osmotic pressure on either side of the diffusion bag membrane.
Part 4: Concentration Gradients and Osmosis
1. Take four diffusion bags from the Containers shelf and place them onto the workbench.
2. Double-click the diffusion bags to label them 1, 2, 3, and 4. Fill the diffusion bags according to the chart below with items from the Materials shelf.
|
Diffusion Bag |
20% Fructooligosaccharides Solution (mL) |
Water (mL) |
Final % of Fructooligosaccharides |
|
1 |
50 |
0 |
|
|
2 |
37.5 |
12.5 |
|
|
3 |
25 |
25 |
|
|
4 |
12.5 |
37.5 |
|
3. Calculate the final percent (%) fructooligosaccharides in each diffusion bag. Record these calculations in the table.
a. The first diffusion bag has 20% fructooligosaccharides.
b. The second bag contains a total of 75% (75 mL of 100 mL total) of 20% fructooligosaccharides. Therefore, the second bag contains a final concentration of 15% fructooligosaccharides (75% multiplied by 20%).
4. Take four 250 mL beakers from the Containers shelf and place them onto the workbench.
5. Fill each of the four beakers with 100 mL 20% fructooligosaccharides solution and 100 mL of water from the Materials shelf. Record the final concentration of fructooligosaccharides in each of these beakers. _____________________.
6. Take a balance from the Instruments shelf and place it onto the workbench.
7. Weigh each of the full beakers and record these initial masses in the table below.
8. Place one diffusion bag next to each beaker. You will run four osmosis trials of 1 minute each by doing the following:
a. Place one diffusion bag into its corresponding beaker.
b. Immediately start a timer or note the time on the lab clock.
c. When the minute has elapsed, remove the diffusion bag from the beaker and place the beaker on the balance. Record the new mass of the beaker in the table below. Record whether it increased in mass, decreased in mass, or did not change in mass in the table below..
d. Repeat steps a – c for each diffusion bag and beaker combination.
|
|
Diffusion Bag |
|||
|
|
1 |
2 |
3 |
4 |
|
Beaker Initial Weight |
|
|
|
|
|
Beaker Final Weight |
|
|
|
|
|
Change in Beaker Mass |
|
|
|
|
9. Double-check that you have recorded all of the necessary information. Clear the bench of all materials, containers, and instruments. Answer the questions below.
Questions:
1) For each of the four bag/beaker systems explain which substance moved in order to cause change in mass and what caused the substance to move.
2) Suppose you are given a diffusion bag that is permeable to both water and a protein. You fill the diffusion bag such that it contains 99% water and 1% protein. You place the diffusion bag into a beaker filled with 98% water and 2% protein. Predict what will happen next.
3) Define Osmosis.
4) Suppose you are given a container that has a membrane permeable only to metabolic wastes. The container is filled with 5M metabolic waste in an aqueous solution. You wish to reduce the amount of waste dissolved in the container. You see a 5L beaker of pure water sitting across the room on a shelf. What is your plan?
Part 5: Osmosis in Living Cells
1. Take two empty slides from the Containers shelf and place them on one side of the workbench.
2. Add Elodea from the Materials shelf to each slide. One Elodea leaf and a drop of aquarium water will automatically load onto the slide for you.
3. Take a microscope from the Instruments shelf and place it onto the workbench.
4. Examine one slide with the microscope. Increase the magnification, if necessary. Identify the cell walls, cell membrane, cytoplasm, and chloroplasts. How close is the cell membrane and cytoplasm to the cell wall? Take a screenshot of your image and upload below.
5. Move the slide from the microscope back to the workbench.
6. Take a test tube and a dropper from the Containers shelf and place them on the workbench.
7. Add 10 mL of hypertonic solution from the Materials shelf to the test tube.
8. Use the dropper to transfer one drop of the hypertonic solution to the slide.
9. Return the slide to the microscope. Record any changes you observe. Are your observations what you expected? Record your answer and an explanation for your answer to reference later. Save a screenshot of the Elodea in the hypertonic solution in order to upload below.
10. Remove the slide with hypertonic solution from the microscope and empty its contents into the waste container. Note: Elodea is an invasive species in many areas and thus should not be released directly to the environment. Place the empty slide in the sink.
11. Empty the dropper and test tube in the waste bin, then place them in the sink.
12. Take a test tube and a dropper from the Containers shelf and place them on the workbench.
13. Add 10 mL of the hypotonic solution from the Materials shelf to the test tube. Use the dropper to transfer one drop of the hypotonic solution to the second slide.
14. Examine the slide with the microscope. Record your observations. Again, be sure to observe the cell membrane, cell wall, cytoplasm, and chloroplasts. Save a screenshot of the Elodea in the hypotonic solution in order to upload below.
15. Clear the bench of all materials, containers, and instruments, then return to your course page to complete any assignment for this lab.
Questions:
1) Upload your Elodea picture from step 4 here.
2) Upload your Elodea picture from step 9 here.
3) Upload your Elodea picture from step 14 here.
4) How did the Elodea cells change when aquarium water was replaced with hypertonic solution? What caused those changes?
4
