A chicken egg is one cell – one unusually large cell! The Eggsperiment A chicken egg is one cell – one unusually large cell! Manipulating it can teach us how our much smaller cells behave and help us understand much about what goes on in our bodies. By the way, this cell, like most of yours, has a NUCLEUS which contains the cell’s DNA. http://www.enchantedlearning.com/egifs/eggcrosssection.GIF

How can we enlarge or shrink this cell? This very specialized cell is especially unusual because it has a calcium carbonate (or calcite) shell which obviously restricts its size. Just under the shell is a thin, somewhat flexible CELL MEMBRANE; every one of your cells has a similar membrane How, then, can we dissolve the shell and leave the membrane intact?

Dissolving the shell Calcium carbonate will dissolve in acid CaCO3 (calcium carbonate) + C2H4O2 (acetic acid) = CO2 (carbon dioxide) + H2O (water) + Ca(C2H3O2)2 (calcium acetate) This leaves the cell membrane in tact And now this cell is much more like the cells in your body – they have membranes, but they don’t have shells!!

And after the shell is dissolved… But why does the cell enlarge?? And how can we shrink it?

They are always moving*! The answer has to do with molecules. One thing we need to remember about molecules… They are always moving*! And if we can get molecules to move in and out of our egg cell, we can shrink and expand the egg at will! First, you can easily demonstrate that water molecules are in constant motion by adding a drop of food coloring to some water. Add a drop of food coloring to a small beaker of water and observe it. Predict how long it will take for the color to diffuse throughout the beaker so that the water is evenly colored throughout. *unless they are at “absolute zero” (minus 273 degrees Celsius).

So why do moving molecules matter? In your food coloring demonstration, you saw evidence that the water molecules were in motion. You saw the water molecules cause the food coloring molecules to diffuse until they were evenly distributed in the beaker. Find a good definition of the scientific meaning of diffusion. So which is the true statement? a. After a few minutes, the food coloring molecules diffused until they were evenly distributed in the beaker. At that point, the molecules stopped moving. b. After a few minutes, the food coloring molecules diffused until they were evenly distributed in the beaker. The molecules continued to move around, but since the water and the food color had blended thoroughly, the motion of the molecules was no longer obvious.

The answer is, of course, B. But what does this have to do with the egg?? Think back to the Scale of the Universe website which shows the relative sizes of things. http://htwins.net/scale2/?bordercolor=whiteDetailed%2520Map%2520of%2520the%2520Universe All the molecules in your egg are in constant motion…. But their ability to move in and out of the egg depends on their SIZE.

Cell membranes (made of phospholipid bilayers) are semi-permeable They have tiny holes, and they let only certain materials in and out White is Protein – BIG molecules! Yolk is FAT – BIG molecules!! …and that’s often determined by SIZE. http://htwins.net/scale2/?bordercolor=whiteDetailed%2520Map%2520of%2520the%2520Universe Acids like vinegar are mostly water - tiny molecules!

Yolk is FAT – BIG molecules!! So…. The big fat molecules and protein molecules can not diffuse out of the egg, but they would if they could. They are just too big to pass through tiny pores in the cell membrane! Since acids like vinegar are mostly water and are tiny molecules…. And since the cell membrane has some tiny holes and is semi-permeable… Yolk is FAT – BIG molecules!! White is Protein – BIG molecules! Water is able to DIFFUSE into the cell When WATER diffuses it’s also called OSMOSIS

Osmosis is the diffusion of water across a membrane Yolk is FAT – BIG molecules!! When will the egg stop expanding? When there’s an EQUILIBRIUM of water on the inside and outside of the membrane. Find a good definition of EQUILIBRIUM .

So your egg stops expanding when it reaches equilibrium When it’s as watery inside the egg as it is outside the egg, the egg will stop expanding. Water molecules are still moving across the membrane, but the concentration of water remains the same both inside and outside the egg. And after your egg has expanded, it’s a lot more watery inside the egg than it was at the start!

So how can we now shrink this “watery” egg? What environment will make water diffuse OUT of the egg? Yolk is FAT – BIG molecules!!