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A Memorable Membrane

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Author: Jane Healey

Grade Leve: 6th; Type: Biology

Objective:

The goal of this project is to reveal that membranes can be semi-permeable—allow for the inward and outward flow of materials. Eggs offer students a tangible example of membranes. They also help students understand the interactions of chemicals such as the calcium carbonate of the shell and vinegar.

Research Questions:

  • How does a membrane function? 
  • What is semi-permeable?

Membranes are enclosures that protect the cell within. Semi-permeable membranes allow substances like nutrients to pass through and waste to pass out. Once the vinegar dissolves the calcium carbonate of the eggshell, the thin membrane around the egg white allows the vinegar to pass through into the interior. The egg pulls the vinegar in through osmosis, enlarging and becoming rubbery. 

When the rubbery egg is submerged in the second jar, the corn syrup pulls the moisture through the membrane, carrying small molecules with it and leaving behind the larger ones. The rubbery egg shrivels with the loss of mass. The combination of reactions demonstrates the semi-permeable characteristic of the egg membrane.

Materials:

  • A medium sized jar with lid
  • A shallow bowl
  • White vinegar
  • Corn Syrup
  • Raw egg
  • Tongs
  • Paper towels
  • Logbook

Experimental Procedure:

  1. Use the tongs to gently place the egg in the jar. If the egg cracks, remove it and start again.
  2. Cover the egg with white vinegar and observe for approx. 20 minutes as tiny bubbles rise—carbon dioxide released as from the dissolving calcium carbonate of the shell.
  3. Leave the egg in the jar for 5 days, observing changes each day.
  4. After 5 days, carefully pour out the vinegar and use the tongs to gently remove the egg to paper towels to dry.
  5. Observe the egg closely and record the details.
  6. After recording the observation, carefully lower the rubberized egg into the clean jar.
  7. Pour corn syrup over the egg to cover it.
  8. Put the lid on the jar and place it where it will not be disturbed.
  9. Leave the egg in the jar and observe the changes daily.
  10. After 5 days, carefully pour out the corn syrup and use the tongs to gently remove the egg to paper towels.
  11. Note changes in appearance from the original egg and the rubbery version.

This experiment can be visually chronicled through photographs accompanied by logbook excerpts as captions. The logbook can follow a simple design, and the entries should be descriptive and detailed.

 
Day

Condition—Rubberizing

 
1

The egg rests on the bottom of the jar. The shell is white, hard and bumpy. Tiny bubbles float from the surface of the shell to the top of the vinegar. The rate is constant, and the bubbles come from everywhere.

 
2

The bubbles have stopped. The shell seems to be losing color as if it is disappearing. It looks thin in places like large holes.

 
3
Etc.
 
4
Etc.
 
5
Etc.
 
 
 
Day

Condition—Shrinking

 
1
Etc.

 

Terms: Membrane; Osmosis; Semi-permeable

References:

 

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