Osmosis

 

 

Introduction

Students will observe osmosis on a model of a cell.

 

KEY POINTS OF THE ACTIVITY:

  • We will use an egg to model a cell.  Now, we know that an egg and a cell are not quite the same, but we will use an egg because it will make it easier for us to understand what we ar interested in.

  • We will have to removethe shell of the egg with Vinegar (Acetic Acid).  We know that egg shells are made of an alkiline solid, and that it will dissolve if exposed to an acidic liquid.  We will use vinegar (Acetic Acid) because it is readily available, and it is inexpensive.

  • We will see the affects of a Hypertonic solution and a Hypotonic solution on the egg (how these afffect the content of the egg membrane). 

  • We will define Hypertonic, Hypotonic and Isotomic solutions.

  • We will Draw and Label what we see in each step of the activity to illustrate what we are learning.

  • We will describe what happens to the egg.

     

Materials:

  • One or two uncooked eggs

  • 2 cups of Vinegar

  • One plastic or Glass Cup that can hold the eggs and vinegar

  • Corn Syrup or Maple Syrup

  • Water

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stage 1 Procedure:

  • Place the egg in a cup.

  • Add cool water.

  • Allow egg to stay in water for 24 hours.

  • Observe and draw what you see.  Measure the egg if you can. 

  • Describe how the egg has changed.

Initial Procedure:

  • Gently place the egg(s) in your cup. Be sure that the egg is not cracked

  • Add 2 cups of vinegar

  • Allow the egg to sit in the vinegar for at least one day, up to two days, or until the shell is soft and dissolved.

  • Gently rinse and wash the egg to remove any remnants of egg shell.  The egg shell should rub off easily under running water.  Be gentle - you don't want the shell to cut the membrane.

  • Observe and draw what you see.  Measure the egg if you can. 

Stage 2 Procedure:

  • Gently dry egg.

  • Add enough corn syrup or maple syrup to cover the egg.  You will probably have to put something on the egg to keep it submerged.

  • Allow egg to stay in syrup for 24 hours.

  • Observe and draw what you see.  Measure the egg if you can. 

  • Describe how the egg has changed.

The egg will be rubbery when the shell has been removed.  This is because the shell keeps it firm, but the membrane contains the contents.

Observations and Conclusions:

Write a description of what happened to the egg.  Why did the egg get  bigger when it was in the water?  Why did the egg shrink when it was in the syrup?  WHich direction did the water move in each stage of the activity (into or out of the egg, through  the membrane)?  Whu could the water move through the egg membrane?  What is the definition of Hypertonic, Hypotonic and Isotonic solutions?  Which liquid was Hypertonic - the water or the syrup?  How do you know?  E-mail a picture of your egg to your teacher, and hand in this information to recieve credit.

Illustrations of Hypertonic, Isotonic and Hypotonic solutions, and the effect on the cell. 

 

We observed these same results happen to the egg in our activity.

Red Blood Cell (animal cell)

Leaf Cell (plant cell)