Egg Osmosis Lab
The cell membrane is a selectively permeable membrane that regulates what materials enter and leave the cell.
When substance is able to pass through a membrane, we say that the membrane is permeable to that substance.
Membranes may be more permeable to some substances like oxygen and carbon dioxide than to others, these
membranes are said to be selectively permeable or semi-permeable. In other words, these membranes have
different permeability to different substances. Perhaps a small urea molecule will pass easily, but not a large
starch molecule. Sometimes, membranes do not permit substances to pass through at all. Then they are said to
be impermeable to that substance.
Water also is permeable to the membrane and can cross freely. Whether the net movement of water is into or
out of the cell is a function of osmosis. Osmosis is the special process of water moving across a membrane. When
materials are impermeable to the cell membrane and are not in equilibrium, there is a net movement of water
across the membrane. The rule of thumb is “Water likes to dilute”. Water, like other substances, will cross the
membrane from where the water is most concentrated to an area where it is least concentrated.
If a semi-permeable membrane separates two solutions and those solutions are different in their concentrations,
one can expect that there will be a net movement of water. The solution that has the greatest concentration of
solutes is said to be hypertonic relative to the other side. The solution that has the least concentrations of solutes
is said to be hypotonic relative to the other side. The net movement of water will be from hypotonic side of the
membrane to the hypertonic side of the membrane as “water dilutes” the side with greater amount of solutes.
In other words, whatever side of the membrane has more solutes, is hypertonic. And whatever side of the
membrane has less solutes is hypotonic.
Purpose:
The purpose of this lab is to investigate the process of osmosis through a semi-permeable membrane. It explores
the change in the mass of an egg with a change in the concentration of corn syrup through the process of osmosis.
Materials:
1 egg
Vinegar
Corn syrup
200 ml beaker
Balance
Plastic spoon
Paper towels
Lab apron
Safety:
Warning: Be sure to wash your hands after handling raw eggs. Salmonella is a bacteria commonly found in
poultry and eggs. To avoid food poisoning, one should always wash their hands after handling raw eggs.
Making the corn syrup solutions:
You will be assigned a percentage of corn syrup by your teacher. Use the chart below to guide you in making the
assigned corn syrup percentage. Select the appropriate percentage of corn syrup on the left column and
measure out the appropriate amounts of corn syrup and water into a beaker.
Percent Corn
Syrup
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Amount of Corn
Syrup
0 ml
20 ml
40 ml
60 ml
80 ml
100 ml
120 ml
140 ml
160 ml
180 ml
200 ml
Amount of
Water
200 ml
180 ml
160 ml
140 ml
120 ml
100 ml
80 ml
60 ml
40 ml
20 ml
0 ml
Mix the two thoroughly if syrup and water are both used. If you are using a high concentration of corn syrup (80%
or 90%), it is easier to mix 20ml of the corn syrup with the water thoroughly and then add the remaining syrup
slowly while mixing.
Procedures:
Day One
1. Obtain a raw egg that has already been soaked in vinegar over night. You should note that the egg
shell has been dissolved leaving behind the surrounding outer membrane.
2. Carefully rinse and dry off the egg. Place the egg on the protective tray on the scale and mass it.
3. On a piece of masking tape that will be placed on the beaker, write your name, mass of the egg and
percentage of corn syrup assigned to your group.
4. Place the tape on the beaker, the egg in the beaker and pour your assigned corn syrup solution over
the egg making sure to complete cover it.
5. Clean up your work station. Be sure to wash your hands after handling the eggs.
6. Write a Hypothesis on how the mass of the egg will change. (Question #1 on Data Worksheet)
Make sure to write it in an “If… then… because…” statement.
7. Record the mass taken as the Initial Mass on the data table under your assigned Percent syrup.
Day Two
8. After two days, observe what has happened to the egg and how it has changed. Note your
qualitative observations on Question #2 on the Data Worksheet. Remove the egg from the beaker
and carefully rinse and dry taking care not to break the membrane.
9. Place the egg on the protective tray on the scale and mass it. Record this mass as the Final Mass on
the data table under your assigned Percent syrup.
10. Answer Questions 3, 4 and 5 on the Data Worksheet.
11. Place your egg for display by period under the % solution assigned to your group.
12. Clean up your work station. Be sure to wash your hands after handling the eggs.
13. Get together with your assigned group and complete the Group Work Sheet.
Day Three
14. Determine the percent change in mass by doing the following:
%change in mass = (Final Mass – Initial Mass) X 100
Initial Mass
15. Pool your data with that of the class, and then record all class data.
16. Graph the percentage of corn syrup used versus the percent change in mass. Be sure to label the
graph and the units. Realize that when the egg gained mass, the percent change will be a positive
number and when the egg lost mass, the percent change will be a negative number.
17. Once you have placed all of the plots, draw a best fit line. The point where the best fit line crosses the
X axis is where there is no change in mass. The egg is thought to be in an isotonic solution.
Egg Osmosis Lab
Student Data Worksheet
1. Write a Hypothesis on how the mass of the egg will change.
Make sure to write it in an “If… then… because…” statement.
2. Qualitative Observations of egg after it was placed in the corn syrup solution.
3. What happened to the mass of the egg after it was left in the solution? Explain what accounts for the
change in the mass of the egg in terms of osmosis.
4. Was your Hypothesis correct or incorrect?
5. If you want to bring the resulting egg back to equilibrium, in what type of solution will you place it in?
Egg Osmosis Quantitative Data Table:
Egg
1
2
3
4
Percent
Syrup
0%
10%
20%
30%
Final
Mass
Initial
Mass
Change in
Mass
Percent
Change in
Mass
5
6
7
8
9
10
11
40%
50%
60%
70%
80%
90%
100%
Graph:
Analysis:
1. Determine the percent corn syrup that would be isotonic to the egg.
2. Do the results seen in the display agree with your calculated values for an isotonic solution? Explain.
3. What is the relationship between the percent change in mass and increasing amounts of corn syrup?
4. At 100% corn syrup solution, where there are more solutes outside the cell, the solution is
______________ (hypertonic / hypotonic) to the egg. Likewise, the egg is _______________ (hypertonic
/ hypotonic) to the corn syrup.
5. In distilled water, where there are more solutes inside the cell, the solution is ________________
(hypertonic / hypotonic) to the egg. Likewise, the egg is _______________ (hypertonic / hypotonic) to
the distilled water.
Conclusion:
6. A patient comes into the emergency room. She is unconscious and is obviously dehydrated. Explain what
sort of inter venous solution (IV) you would inject into your patient and why?
7. If carrot sticks are put into water and refrigerated, they become turgid or stiff. If red blood cells are given
the same treatment, they explode. Account for the difference in the results. (Hint: Pay attention to the
structures of the cells.)
8. Why if you were in a life boat on the ocean and thirst, it would be harmful to drink the ocean water?
9. What implications do these processes have on single celled organisms like bacteria and protist?
10. What errors might have occurred in performing this lab?