Osmosis Through the Cell Membrane of an Egg
by Brett Helms

Introduction:
An egg can be used to show the process of osmosis through the egg’s cell membrane. Osmosis is the process in which water diffuses across a cell membrane from an area of high concentration to an area of low concentration. Osmosis occurs when the cell needs to release water to the exterior of the cell membrane or it can occur when water needs to diffuse into the cell. Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration. Diffusion and osmosis are both types of passive transport. A passive transport is the movement of molecules across a cell membrane without the cell having to exert any energy. Water will move into the cell when the solution is hypotonic to the cytosol. A hypotonic solution is defined as a solution whose solute concentration is lower than that inside a cell. The cell membrane is the thin outer layer of a cell. It allows certain substances to diffuse across, into and out of the cell. When a solution is hypertonic the solute concentration is higher than that inside a cell. This would result in molecule movement into a cell. When a solution is isotonic, the solute concentration equals that inside a cell. This would result into no movement of molecules across the cell membrane. Molecules that are very small but not soluble in lipids may diffuse across the membrane by moving through the pores of the cell membrane.

Hypothesis:
The water and the vinegar will diffuse through the cell membrane more easily then the syrup.

Materials:
The materials used included paper, pencil, 200ml beakers, vinegar, distilled water, syrup, 2 eggs, tray, plastic wrap, colored marker, tape, and a digital balance.

Methods:
The two eggs were weighed on a digital balance and their initial masses were recorded. The eggs were then placed in a beaker of vinegar to dissolve the calcium shell and leave the cell membrane exposed. The eggs were weighed after they were removed from the vinegar and their masses were recorded. The two eggs were then placed in a beaker of syrup.  The eggs were once again weighed on the digital balance and their masses recorded. The eggs were then placed a beaker of distilled water. After the eggs were removed and their weights and appearance recorded.

Results:

Results of Osmosis
Table for Egg 1

Solutions

Egg Mass Before in Grams

Observations Before Placed in Solution

Egg Mass After in Grams

Observations After removed from Solution

Vinegar

56.9g

Hard exterior

84.3g

Egg lost shell

Syrup

84.3g

Shell had a firm jelly-like membrane

48.4g

Outside not firm anymore, very shriveled

Water

48.5g

The jelly-like membrane was soft and not firm at all

77.9g

Egg firmed up and looked like the shell just came off

Results of Osmosis
Table for Egg 2

Solutions

Egg Mass Before in Grams

Observations Before placed in solution

Egg Mass After in Grams

Observations After removed from solution

Vinegar

60.5g

Hard exterior

87.65g

Egg Lost Shell

Syrup

87.65g

Shell had a firm jelly-like membrane

54.4g

Outside not firm anymore

Water

54.4g

The jelly-like membrane was soft and not firm at all

79.3g

Egg firmed up and looked like the shell just came off

1. When the egg was placed in the water, in which direction did the water molecules move? The water molecules moved into the egg.

2. On what evidence do you base this? The egg mass increased.

3. How do you explain the volume of liquid remaining when the egg was removed from the syrup? It was less because some had moved into the egg.

4. When the egg was placed in the water after being removed from the syrup, in which direction did the water move? The water moved into the egg.

Error Analysis:
This experiment is based upon changes in egg mass in various solutions. The balance used was not checked for accuracy with two standard masses. The changes in masses may or may not be correct.

Discussion and conclusion:
There were significant increases in egg mass when the eggs were submerged in vinegar and water. However there was a significant decreased in egg mass when the eggs were submerged in syrup causing the egg to appear shriveled. The reason for the increasing and decreasing is called diffusion, which is the movement of molecules from an area of high concentration to an area of lower concentration. That is why when the egg was submerged in syrup much of the water in the egg diffused out because of the higher amount of water in the egg compared to the smaller amount in the syrup. That is also why when the egg was placed in vinegar and in distilled water its mass increased meaning that more water molecules moved into the eggs because the solution outside the egg was lower in water than that inside the egg. These results support the hypothesis that water diffuses from an area of high to an area of low concentration across a cell membrane. This experiment demonstrated the process of osmosis through the egg cell membrane.

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