Gotcha

This year due to the number of classes in our school there had to be some shifting of subjects teachers would be required to teach. For me, this meant that I would be teaching Grade 8 science. This is a subject that I have never taught at the intermediate level and I would be lying if I said that I wasn't a little nervous about the idea. The grade 8 science curriculum is more complex and in depth than the science curriculum I had taught for other elementary grades. I knew that I was going to have to first learn these concepts before I would be able to teach them. So, I did what teachers do best. I dove into the grade 8 textbook and scoured the internet in an effort to learn all about Cells, Fluids, Hydraulics and more. I knew that I wanted the students to learn science in a hands on way. This meant that I would have to find some fun experiments to do in class. I don’t have a science lab but I knew that I could come up with some things that could be easily done in my classroom. Our first unit of the year was to be all about cells. Students would be learning about different types of cells, cell theory, parts of cells and how they function as well as osmosis and diffusion in relation to cells.

Osmosis:

Osmosis is a type of diffusion that, in biology, is usually related to cells. Diffusion is when molecules or atoms move from an area of high concentration to an area of low concentration. Osmosis is when a substance crosses a semipermeable membrane in order to balance the concentrations of another substance. In biology, this is usually when a solvent such as water flows into or out of a cell depending on the concentration of a solute such as salt. Osmosis happens spontaneously and without any energy on the part of the cell.
Source

In my search I found the experiment that my students have had the most fun with this year. Maybe it was the name of the experiment “Naked Eggs” that they got a kick out of. We had finished learning all about parts of a cell and the students had a good understanding of things like the nucleus, mitochondria and vacuoles just to name a few. The next step was to learn about how cells get nutrients to function properly and survive. Like all living things cells, which are the building blocks on which living things are created, need to be nourished in order to survive and function properly. Cells accomplish this through the process of osmosis where the cell allows needed materials through its membrane and removes waste as well.

The Naked Eggs

I found this experiment while researching about cells as I prepared to teach a brand new science unit to my grade 8 class. The experiment is designed to demonstrate the way in which a cell membrane will allow materials to flow in and out of the cell through osmosis. This transference happens from areas of high concentration to areas of low concentration. The results of the experiment a a great representation of these properties as well as it is a really cool visual on many levels. An egg is a perfect representation of what a cell looks like as it is essentially a cell itself but we can see it with the naked eye. Although there has been much scientific debate an egg is widely considered to be the largest cell. The first part of this experiment is the creation of our “naked eggs”. In order to accomplish this you need a cup of vinegar and an egg. By submerging the egg in vinegar you will create a chemical reaction that causes the shell to disintegrate leaving only the membrane of the egg and the contents. This happens because the acid in the vinegar reacts with the Calcium Carbonate in the shell. The vinegar breaks it down and causes it to dissolve. It usually takes between 24 and 48 hours for this effect to take place. The length of time can differ based on the thickness of the shell or acidic level of the vinegar.

Once the eggs have been “undressed” so to say you should have a squishy but intact egg. This part is really cool as you can see the yolk or nucleus of the egg. Now we are able to do some preliminary observations and record some predictions for the next part of the experiment. All hypothesis, observations, results and conclusions were recorded using our “lab” sheets. The next stage of the experiment was the osmosis side of things. Each group needed 2 eggs for this part of the experiment. Each egg was going to be weighed and measured to have a benchmark to work with through the rest of the experiment.

Eggs were placed in two different solutions. One solution was just plain old water. The second solution was corn syrup. The eggs were submerged in each solution and left to sit for 24 hours. We used food colouring in the water solution to help make any changes more noticable. The results were incredibly cool to watch.

The egg in the water only solution started to grow. The water that was in higher concentration outside the egg started to move through the eggs membrane and fill the inside of the egg with water until there was a balance between the concentration inside and outside. Basically, until the egg could no longer fit any more water.

The egg that was in the corn syrup had the complete opposite effect. The corn syrup is highly concentrated with sugar and other materials but the eggs actually has a higher concentration of water. The result is that the corn syrup essentially sucks the moisture/water out of the egg and the egg shrivels up. This was fascinating for the students to watch. At all phases of this process the egg membrane was fully intact. Again, all results were observed and recorded. The eggs were weighed and measured to see the differences. We actually took it one step further and put the shriveled egg back into a water solution to see if it would again grow back to its original shape and it did.

It was fun to see how engaged and astonished the students were throughout this experiment. Many groups even named their eggs. This truly helped to make the connection between the theoretical work we did in class and how the concepts work in reality. I even feel like I learned a lot more about the way cell membranes work through this process. It was so much fun in my class that I decided to do the experiment at home with my own children just for fun and they loved it as well. So next time you are wondering about cells and osmosis just remember “Naked Eggs”

Unfortunately, my iphone completely died shortly after this experiment and I lost all of the pictures I took in my class during the project so I had to use images found online to show what we did.
Images: 1, 2, 3, 4, 5, 6

Fun video demonstrating the whole process

Source

Printable Instructions and Lab Worksheets

Making Naked Eggs https://www.michigan.gov/documents/explorelabscience/Making_Naked_Eggs_606498_7.pdf

Experimenting With Naked Eggs
http://www.michigan.gov/documents/explorelabscience/Experimenting_with_Naked_Eggs_606503_7.pdf

Lab https://pa01000192.schoolwires.net/cms/lib7/PA01000192/Centricity/Domain/48/The%20Naked%20Egg%20Lab.pdf