Name______Hour______
DIFFUSION & OSMOSIS LAB
Background: Notes on Passive transport from class. Text 208-211.
Purpose: How are the biological processes of diffusion and osmosis similar, and how are they different?
Procedure Part 1: Starchy Cell
1. Obtain one plastic bag, a piece of string, and a plastic cup.
2. Place 50 ml of 20% starch solution into the bag, and squeeze all excess air out.
3. Tie the bag shut with the string to create your “Starchy Cell”.
4. Rinse off your cell with tap water and place it into the plastic cup.
5. Add tap water to your cup until it completely covers your “cell”.
6. Add iodine solution to the cup of water until the water turns yellowish-orange.
7. Label your cup with your names and hour and place it where indicated by your teacher until tomorrow.
8. Draw, label and color a diagram of your setup in the space provided below.
DAY 1 SETUP AFTER 24 HOURS
9. AFTER 24 HOURS, pick up the starchy cell and observe changes. Draw, label and color another diagram above showing the change after 24 hours.
10. Place your “cell” bag into the trash. Remove the label from the cup and rinse out the cup. Return the cup to your teacher.
QUESTIONS PART 1: (answer in complete sentences)
1. What color was the inside of the cell and the outside water on Day 1?
2. What color was the inside of the cell and the outside water after 24 hours?
3. What happened to cause this color change?
4. How did the iodine come into contact with the starch?
5. Why didn’t the water outside the cell turn blue-black?
6. What process is being demonstrated with this “cell”?
Procedure Part 2: Purple Onion
1. Pick up a small piece of purple onion and carefully peel off a small piece of its outer epidermis. Make sure this piece has some purple pigment.
2. Place your onion on a clean slide.
3. Add 4 drops of “Normal Saline” solution to it and cover with a cover slip.
4. Observe with a microscope under low power. Locate some purple onion cells, and work your way up to high power.
5. Draw a detailed single cell in the space provided below.
6. Use colored pencils to show the location and intensity of the color in your drawing.
7. Remove the slide from the microscope. Gently take off the cover slip. DO NOT REMOVE THE ONION!
8. Blot away the saline solution on the onion using a paper towel.
9. Add 4 drops of “5% salt solution” to the onion and replace the cover slip.
10. Observe with a microscope under low power. Locate some purple onion cells, and work your way up to high power.
11. Observe the changes in the onion cells. Draw a second, detailed cell in the space provided below. Use color pencils to show the difference in the location and intensity of color.
12. Remove the slide from the microscope. Gently take off the cover slip. DO NOT REMOVE THE ONION!
13. Blot away the 5% salt solution on the onion using a paper towel.
14. Add 4 drops of “distilled water” to your onion and replace the cover slip.
15. Observe with a microscope under low power. Locate some purple onion cells, and work your way up to high power.
16. Observe the changes in the onion cells. Draw a third, detailed cell in the space provided below. Use color pencils to show the difference in the location and intensity of color.
17. Throw the onion away. Clean and dry your slide and coverslip. Check out with your teacher. ______(teacher initials)
QUESTIONS PART 2: (answer in complete sentences)
1. How much of the cell contained purple color when you observed it in normal saline?
2. What happened to the location and intensity of the color when it was put in a 5% salt solution?
3. What happened to cause the change described in question #2?
4. What happened to the location and intensity of the color when it was placed in distilled water?
5. What happened to cause the change described in question #4?
6. Go back to your drawings and label them HYPERTONIC, ISOTONIC, or HYPOTONIC.
Procedure Part 3: Egg Demo
One or more chicken eggs have been de-shelled and placed in bowls in the front of the room.
They are labeled “A” and “B”. One of them is soaking in distilled water, and the other in a concentrated sugar solution. The eggs were identical before soaking in the two different solutions.
1. Observe both eggs.
2. Make a detailed drawing of each, and write a description of the eggs noting the differences.
EGG A EGG B
Description- Description-
QUESTIONS PART 3: (answer in complete sentences)
1. Why does egg A appear this way? (what is happening to cause it)
2. Why does egg B appear this way?
3. Which egg is in distilled water?
4. What process is being demonstrated with the eggs?
Procedure Part 4: Celery Demo
Pieces from the same stalk of celery have been soaking overnight. One has been soaking in 5% salt solution, and the other in distilled water.
1. Observe each. You may touch them to note their differences. DO NOT TASTE!
2. Make a detailed drawing of each, and write a description of the celery noting the differences.
CELERY A CELERY B
Description- Description-
QUESTIONS PART 4: (answer in complete sentences)
1. Why does celery A appear this way? (what is happening to cause it)
2. Why does celery B appear this way?
3. Which one is more “crisp and fresh”?
4. What process is being demonstrated with the celery?
Analysis Questions:
1. How does osmosis differ from diffusion?
2. In both osmosis and diffusion, which way do molecules move (think of concentration)?
CONCLUSION: Use the RERUN format to write a conclusion. Attach a separate sheet of paper if necessary.