Diffusion and Osmosis

Name: _______________________________

Date: ________________________________

BIOL 1014 Lab 7 Osmosis                                                   

Skill: Diffusion and Osmosis

Introduction

It will take you a minimum of five days to complete this lab. Follow all steps accurately and record your data. 

Problem

How do the shells and inner membranes of eggs act like cell membranes?

To solve this problem, we need to get at the actual membrane of an egg, which is found beneath the shell.  In order to do that, you will be placing an un-cracked egg in vinegar to remove its shell and to leave the semi-permeable membrane exposed. You will then place the egg in light corn syrup (a hypertonic solution) and then in water (a hypotonic solution).  It is a really good idea to do 2 eggs just in case one breaks.

 Some Terminology

 “hyper” means above strength (lots of a solute—less solvent (in this case the solvent is water))

“hypo” means below strength (not a lot of solute— more solvent (water))

The concentrated sugar (syrup) solution is hypertonic compared to the egg cells contents.

The water is hypotonic compared to the egg cells contents.

Isotonic means the two solutions are equal in concentration strength.

Hypothesis

Make a tentative explanation of what will happen to the egg after 24 hours in each solution. (Must answer below)

After 24 hours in each solution, what will happen to the egg and its circumference?

 Vinegar                       __________________________________________________________

Corn Syrup Solution   __________________________________________________________

Pure Water                  __________________________________________________________

MATERIALS NEEDED:

One or two eggs in un-cracked shells                                     A wide mouthed jar or cup

2-3 cups of vinegar                                                                 A spoon

10-16oz. Light Corn Syrup                                                     Aluminum foil

10-16oz. of water                                                                    A string (shoe string will work)

A ruler

PROCEDURE

1. Fill a large mouthed cup with 5% white vinegar. Using a spoon, gently lower the egg into the vinegar. Make sure that the egg is completely covered by the vinegar. Cover the jar with the aluminum foil and leave for 24 hours.  (If you are doing 2 eggs to have a spare, just do them both at the same time in the vinegar.)

2. After 24 hours, rotate the egg so there is not a section that has not been immersed in vinegar. Recover the jar and leave for another 24 hours.

3. Carefully remove the egg from the vinegar. Gently run the egg under warm water in the sink and very carefully rub it to remove any bits of remaining shell. If the egg breaks at any point during the lab, you must begin again, so be careful.

4. Using the string, measure the egg carefully around the shorter axis (equator). Wrap the string around the egg and mark where the ends meet. Then move the string to the ruler and measure the circumference in centimeters to the nearest tenth. Record your data on the data table. Also observe the egg and note its appearance and texture on your data table.

5. Rinse out the jar and fill it ¾ of the way to the top with the corn syrup. (A saturated sugar solution can be used: dissolve as much sugar as possible into 1 cup of water until no more sugar can be stirred into the water.) Gently place the egg in the corn syrup with the spoon. It will probably float. Don’t worry. Recover the jar with the foil and leave for 24 hours.

6. After 24 hours, take the egg out of the corn syrup carefully. Observe it and measure its circumference again using the same procedure as in step 4. Record all data and observations in your data table.

7. Rinse out the jar and fill it ¾ of the way to the top with water. Gently place the egg in the water. It will probably sink. Recover the jar with the foil and leave for 24 hours

8. After 24 hours, take the egg out of the water carefully. Observe it and measure its circumference again using the same procedure as in step 4. Record all data and observations in your data table.

ANALYSIS QUESTIONS:

1. What effect did vinegar have on the egg?

2. What happened to the materials that made up the shell?

3. Did the egg increase or decrease its circumference after being in the corn syrup?  Explain why.

4. Is the corn syrup hypertonic or hypotonic to the egg?

5. How did the egg appear after you removed it from the water?  Why?

6. Is the water hypertonic or hypotonic to the egg?

7. What would likely eventually happen to the egg if it was left in the pure water?

8. What might happen if you put food coloring in the water in step #7 of the procedure?

9. Define osmosis? 

10. How are a cell membrane and the outer layer of an egg without its outer shell similar?

Bonus:

Submit digital pictures of the results of your lab.  I will probably share the best of these photos with the class and credit you if one of yours is chosen.  You may either paste in pictures or place them separately into the folder for this assignment.