SJK Revised 3/23/2016
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Hocus Pocus Egg Osmosis:
How Solute Concentration Effects Osmosis
Introduction
For a cell is to perform its functions properly, it must maintain homeostasis within
an ever-changing environment. This steady state is maintained by the regulation
of movement of materials into and out of the cell. To maintain control of what
crosses in and out of a cell, a semipermeable membrane differentiates between
different substances, slowing down the movement of some while allowing others
to pass through.
The extracellular and intracellular environments of cells consist of an aqueous (water) solution of
dissolved inorganic and organic molecules. Movement of these molecules, both in the solution
and through the cell membrane, involves a passive physical process called diffusion – the
spontaneous movement of molecules from a region of higher concentration to a region of lower
concentration.
A special kind of diffusion is the process of osmosis which is the diffusion of water through a
semipermeable membrane from a region of higher concentration to a region of lower
concentration. Osmosis is usually defined in terms of the effects that solutes have on the activity
of water. For example, the addition of a solute to water alters the concentration of the solution.
Remember, a solution = solvent (water) + solute (dissolved substance) and the solvent + solute
concentrations must ALWAYS add up to 100%. So, if we change the solute concentration, we
change the solvent concentration in the solution (i.e. if the solute goes up, the solvent goes down
and vice-versa as solute goes down, solvent goes up in concentration).
We use the terms hypotonic, hypertonic and isotonic in referring to the relative concentrations
of solute particles of different solutions. Note, the terms refer to the solutions and their pull
on the water molecules in comparison to the concentration inside the cell. Below are the
definitions of the three terms according to Curtis, 1983.
Solute
particles
in solution
Solute
particles
in solution
Hypotonic
(Gk. hypo, under + tonos, tension): The solution that contains the lower
concentration of solute particles; water moves across a semi-permeable
membrane into a cell’s solution. The outside solution has less pull on the
water and it enters the cell. [Everything is less: the solute concentration
and the pull on the water]
Hypertonic
(Gk. hyper, above + tonos, tension): The solution that contains the higher
concentration of solute particles; water moves across a semi-permeable
membrane out of the cell. [Everything is more: the solute concentration
and the pull on the water]
SJK Revised 3/23/2016
Isotonic
Solute
particle in
water
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(Gk. isos, equal + tonos, tension): Having the same concentration of
solutes as another solution. If two isotonic solutions are separated by a
semi-permeable membrane, there will be no net flow of water across the
membrane it is in dynamic equilibrium.
The process of osmosis can be observed in a single cell such as a red blood cell or in a collection of cells
as in multicellular organisms or their structures. The following video link is a good resource for
understanding osmosis and the tonicity of different solutions:
http://youtu.be/7-QJ-UUX0iY
A decalcified chicken egg [shell removed by soaking in diluted acetic acid (vinegar)] is surrounded by an
external membrane. In this experiment, the membrane of the decalcified chicken egg will represent the
cell membrane and demonstrate how osmosis is altered by solutions of different solute concentration.
The changes will be measured by changes in mass of the decalcified egg after soaking in solution.
Measured changes in the mass of the decalcified egg means that water has either entered (gain in mass) or
left (loss in mass) the egg through the membrane.
Learning Target: Observing Osmosis
I Can… Utilize laboratory and critical thinking skills to determine what happens to the volume
of water in a decalcified egg placed in different solutions due to the process of osmosis and infer
the tonicity of the various solutions.
I know I am successful when I can…
*Calculate the percent change in mass of three decalcified eggs placing one each in solutions
of distilled water, 50% strength maple syrup, and 100% maple syrup.
*Infer the correct tonicity of each of the solutions.
Scientific Method:
1. What question is this experiment attempting to answer?
___________________________________________________________________________
___________________________________________________________________________
2. Predict what change will occur to the mass and appearance of each egg placed in the different
solutions:
a. Egg #1 in Distilled Water: _________________________________________________
b. Egg #2 in 50% Syrup Solution: _____________________________________________
c. Egg # 3 in 100% Syrup Solution: ____________________________________________
3. Define relevant vocabulary terms:
a. Diffusion- _______________________________________________________________
b. Osmosis - _______________________________________________________________
c. Isotonic solution-_________________________________________________________
d. Hypertonic Solution-_______________________________________________________
e. Hypotonic solution-_______________________________________________________
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Experimental Design:
Materials:




Decalcified eggs (3)
100% Syrup solution
50% Syrup solution
Distilled water




Procedure:
Electronic balance
Weighing containers (3)
Timer
Paper towels



400 ml beakers (3)
Markers
Plastic spoons (3)
Figure 1
1. Label each weighing container:
a. One as Distilled Water
b. One as 50% Syrup
c. One as 100% Syrup
2. Label each beaker:
a. One as Distilled Water
b. One as 50% Syrup
c. One as 100% Syrup
3. Place 200 ml of Distilled water into beaker labeled “Distilled water”.
4. Place 200 ml of the 50% syrup solution into the beaker labeled “50% syrup”.
5. Place 200 ml of the 100% syrup solution into the beaker labeled “100% syrup”.
Figure 2
6. Turn on electronic and zero it out with a distilled water weighing container on
the scale. Figure 2
7. Take one decalcified egg and gently pat any excess liquid off with paper towel
and place in weighing container on the scale. Figure 3
8. Record the initial mass of the egg in Table 1.
Figure 3
9. Gently, place egg #1 into the beaker marked “Distilled Water” and note the
time in Table 1.
10. Repeat steps 6 – 9 for egg #2 (50% solution) and egg #3 (100% solution).
11. At ten minute intervals from initial time noted,
a. Use a spoon to gently remove egg #1 from distilled water and place on paper towel and
gently pat off excess liquid.
b. Zero distilled water weighing container on scale (see step 6).
c. Place egg in container and record mass in Table 1 (see step 7).
d. Replace egg #1 back into distilled water solution and note time.
12. Repeat step 11 for egg #2 (50% syrup) and for egg #3 (100% syrup).
13. Repeat step 11 for all eggs at indicated ten minute intervals recording the mass of each egg at
each interval in Table 1.
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Data:
Table 1: Mass in Grams of Decalcified Eggs Immersed in Solution
0 Mins
Initial Mass
(g)
10 mins
Mass
(g)
20 mins
Mass
(g)
30 mins
Mass
(g)
40 mins
Mass
(g)
Distilled Water
(egg #1)
Start
Time:________
50% Syrup
(egg #2)
Start
Time: _______
100% Syrup
(egg #3)
Start
Time: _______
Calculate the percentage of change in mass for each egg/solution for each ten-minute
interval using the following formula:
(Mass after immersion – Initial mass) X 100
Initial mass
Table 2: Percent Change in Mass of Decalcified Eggs Immersed in Solution
0 Mins
Δ Mass
(%)
Distilled Water
(egg #1)
0%
50% Syrup
(egg #2)
0%
100% Syrup
(egg #3)
0%
Example of previous lab results:
10 mins
Δ Mass
(%)
20 mins
Δ Mass
(%)
30 mins
Δ Mass
(%)
40 mins
Δ Mass
(%)
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Create a graph that indicates the percent change in mass of each egg over time. Be sure to
include a title, labeled axes with unit, and key.
Scientific Method:
4. Identify the independent variable in this experiment:
___________________________________________________________________________
5. Identify the dependent variable in this experiment:
___________________________________________________________________________
6. Identify three controlled variables (constants) in this experiment:
_______________________
_______________________
_____________________
7. Did this experiment have a control?
a. If yes, identify what the control was. _________________________________________
b. If no, explain why a control was not possible.
________________________________________________________________________
________________________________________________________________________
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Analysis:
8. Describe what happened to the mass and the physical appearance of egg #1 when it was
placed in a Distilled Water solution: [QUOTE data in your description]
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
9. Describe what happened to the mass and the physical appearance of egg #2 when it was
placed in a 50% Syrup solution: [QUOTE data in your description]
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
10. Describe what happened to the mass and the physical appearance of egg #3 when it was
placed in a 100% Syrup solution: [QUOTE data in your description]
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
Conclusion:
11. Based on the data collected in the experiment, your observations of physical change of the
eggs, and your understanding of osmosis across a semipermeable membrane, identify the
tonicity of each solution as Isotonic, Hypotonic, or Hypertonic.
a. Distilled Water: _________________________________
b. 50% Syrup solution: _____________________________
c. 100% Syrup solution: ____________________________
12. How did the solute concentration in the solution effect the direction and rate of osmosis?
[Refer to and use your data in your conclusion for this question]
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
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Validity of Experimental Design:
Explain if the data collected in this experiment was valid; describe factors that made the data
reliable and factors that may have caused errors. Suggest potential ways to improve the
experiment or a new experiment to perform based on information gained from this experiment.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Extend & Apply:
Human erythrocytes (red blood cells) are necessary for survival since they transport the oxygen
and carbon dioxide throughout our body to and from cells. Our blood consists of anywhere from
35 to 50% erythrocytes and is the contributing factor to our blood being red in color. Besides a
small percentage of the blood being leukocytes (white blood cells) and thrombocytes (platelets)
the rest of the blood consists of liquid called plasma that is mostly water with dissolved gases,
organic and inorganic materials.
The cell membrane of the erythrocyte is permeable to water just as the egg membrane was and
osmosis occurs. When someone gets an I.V. in the emergency room, the Dr. orders “Normal
Saline” which has a NaCl concentration of 0.9%. This acts as an isotonic solution around the
erythrocytes in the blood.
a. What is the concentration of water and of NaCl in erythrocytes?
Water - _________________
NaCl - ______________________
b. What would happen to the erythrocytes if a solution containing a NaCl concentration
greater than 0.9% was used?
___________________________________________________________________________
___________________________________________________________________________
c. What would happen to the erythrocytes if distilled water was used in the I.V.?
___________________________________________________________________________