Osmosis Through a Cell membrane of an Egg

Joe Lockwood

Introduction:

When a cell membrane is said to be selectively permeable, it means that the cell membrane controls what substances pass in and out through the membrane.  This characteristic of cell membranes plays a great role in passive transport.  Passive transport is the movement of substances across the cell membrane without any input of energy by the cell.  The energy for passive transport comes entirely from kinetic energy that the molecules have. The simplest type of passive transport is diffusion, which is the movement of molecules from an area of high concentration to an area of lower concentration.  Diffusion moves down the concentration gradient, which is the difference in the concentration of molecules across a space.  Osmosis is a type of diffusion in which water molecules move down the concentration gradient. 

When the concentration of solute molecules outside the cell is lower than the concentration of solute in the cytosol , the solution outside is hypotonic to the cytosol.  If the concentration of solute molecules is higher outside of the cell, the solution outside is said to be hypertonic.  The solution outside is isotonic if the concentration is equal on both sides of the cell membrane. 

The egg shell is made of calcium carbonate and vinegar contains acetic acid.  These two can react to produce calcium acetate and carbonic acid which then decompose into water and carbon dioxide as shown in the two chemical equations:

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 Hypothesis:

The eggs will increase in mass in all three solutions, showing that diffusion and osmosis occur when the concentration of two solutions is different, so that equilibrium can be established. 

Materials:

To conduct this experiment, these materials will be needed:  1-2 fresh hen eggs in their shells, masking tape and marker, distilled water, clear sugar syrup, vinegar, clear jar with lid, tongs, electronic balance, paper towels, paper, and a pencil.

 Methods:

On Day 1, the first step should be to label the jar with your lab group and the word “vinegar”.  Next, the group will mass the egg with the electronic balance and record the results in the data table.  After this, the group will carefully place the raw egg into the jar and cover the egg with vinegar.  Finally, the group is to loosely recap the jar and allow the jar to sit for 24 to 48 hours until the outer calcium shell is removed. 

On Day 2, the day should begin with the group opening the jar and pouring off the vinegar.  Next, they will use tongs to carefully remove the egg to a paper towel and pat it dry.  When this is done, the group should mass the egg on an electric balance and record the size, mass, and appearance of the egg.  After this, they will clean and re-label the jar with their lab group and the word “distilled water”.  They will carefully place the egg into the jar and cover the egg with distilled water.  Finally, they will loosely re-cap the jar and allow it to sit for 24 hours. 

On Day 3, the first step is to open the jar and clean out the distilled water.  Then tongs should be used to carefully remove the egg to a paper towel and pat it dry. The size is to be recorded and so should the appearance of the egg on the table.  Next, the group will mass the egg on an electric balance and record the results.  After this, the jar should be cleaned and re-labeled with the name of the group and the word “syrup”.  Finally, the group should place the egg into the jar cover it with clear syrup, loosely re-cap the jar and allow it to sit for 24 hours. 

On Day 4, the day should begin by the group opening the jar and pouring off the syrup.  Next, the group will use tongs to very carefully remove the egg, rinse off the excess syrup under slow running water, and pat the egg dry on a paper towel.  After this, the size and appearance of the egg should be recorded in the data table.  Then, the mass of the egg should be taken on an electronic balance and recorded.  Finally, the work area should be cleaned and all the lab equipment should be put away.

 Results:         


Questions:

1. Vinegar is made of acetic acid and water.  Explain how it was able to remove the calcium shell.  The reaction of the acetic acid and calcium carbonate of the egg shell produces calcium acetate and carbonic acid, which then decomposes into water and carbon dioxide.

 

2.(a) What happened to the size of the egg after remaining in vinegar? The egg got bigger.

(b) Was there more or less liquid left in the jar?  There was less liquid left in the jar.

(c) Did water move into or out of the egg? Why?  Water moved into the egg because there was a lower concentration of solute molecules in the vinegar than there was inside the egg.

 

3.(a) What happened to the size of the egg after remaining in distilled water? The egg got a little bit bigger, but not by very much.

(b) Was there more or less liquid left in the jar?  There was a little bit less liquid left in the jar, but the change was very small.

(c) Did water move into or out of the egg? Why?  A small amount of water moved into the egg because the distilled water had a slightly lower concentration of solute molecules than inside the egg.

 

4. (a) What happened to the size of the egg after remaining in syrup? The egg became smaller.

(b) Was there more or less liquid left in the jar?  There was more liquid left in the jar.
(c) Did water move into or out of the egg? Why?  Water moved out of the cell because the syrup molecules were hypotonic to the solute molecules inside the egg.

 

5.  Was the egg larger after remaining in water or vinegar? Why?  The egg was larger after remaining in water because the water has the lower concentration of solute molecules than the vinegar so more water would diffuse to an area of higher concentration of solute particles.

 

6.  Why are fresh vegetables sprinkled with water at markets?  They do this so that water will diffuse into the vegetables and keep them plump and allow them to keep their look of freshness.

 

7.  Roads are sometimes salted to melt ice.  What does this salting do to the plants along roadside and why?  This salting dehydrates the plants because the higher salt concentration causes the water to diffuse out of the plant to even up the concentration.

  

Error Analysis:

A few errors may have happened over the course of this experiment. The washing of the egg could have affected the mass.  Also, the jars might not have been thoroughly cleaned out before putting in the next substance.  This could have affected the rate of diffusion because it would have changed the concentration of the solute particles.  These errors and a few others may have occurred. 

 Discussion and Conclusion:

The hypothesis was not correct.  While two of the solutions caused the eggs to increase in mass, syrup caused the egg to lose mass.  This shows that the syrup was hypertonic to the solution inside of the egg, causing water to diffuse out of the egg to try and establish equilibrium. The egg’s mass increased in the distilled water and vinegar because they were hypotonic to the solution in the egg, causing water to diffuse into the cell.  The shell on the egg dissolved because    the egg shell is made of calcium carbonate and vinegar contains acetic acid.  These two can react to produce calcium acetate and carbonic acid which then decompose into water and carbon dioxide.


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