Dandelion Curls

It's spring in the northeast and that means (at least in my yard): Dandelions!

Did you know you can use dandelion stems to teach a simple (and pretty fun) lesson in osmosis as well as introducing the terms hydrophilic and hydrophobic?

Separate the stem from the flower and pull the stem into long strings.

Drop the strings into a tub of water and watch the stems curl up into all kinds of fun shapes! 

 If you drop the stem pieces one at a time, you can actually watch the curling process take place within just a minute or two.  Or you can dump a whole bunch in and have fun sorting through the results!

 What's happening?

The inside of the stem is hydrophilic, which is sometimes referred to as water-loving.  It's the part of the plant that absorbs the water.  And when it's placed into a tub of water, there's a whole lot of water to absorb!  The water moves into the cells through the process of osmosis. 

The outside of the stem is hydrophobic - it repels water.

The cells that make up the inside of the stem absorb so much water that they swell up.  The cells on the outside of the stem stay the same size.  The increasing size of the cells on the one side of the stem forces the stem into curls of various shapes.  

There's definitely something fun about sitting outside on a warm day and watching the curls form!  And if you can't be outside, grab some dandelions on your way to school and bring a bit of the outdoors in for your students.   

PS The idea of one side expanding more than the other side is similar to the way a bimetallic strip in a thermostat works.  The expansion is caused by temperature instead of water movement and it isn't as drastic as this, but it's conceptually similar. 

Osmosis: Should I Salt My French Fries Before or After Cooking?

Cut a potato into 4 sticks, about 1/2 cm thick (5 mm or about 1/4 inch).  You could try other shapes as well.

Fill two beakers or small bowls with water.

Dissolve salt in one of the beakers of water, about 1 tablespoon per cup of water.

Place 2 potato slicks in each beaker and allow to sit for about an hour (you can leave it overnight if need be).

After the time has elapsed, pick up the potato slices and observe.

You should find that the potato slices that were in water are limp and bend easily, which the ones in pure water are still rigid and crisp. 

Through osmosis, water moved out of the potato and into the salt water. 

Gummy Bear Lab

This is one of my all-time favorites!

I use this lab at the beginning of the school year, when we're reviewing measurement.  However, it is equallly apprpopriate for the study of osmosis.  (As fate would have it, I first did this lab with my 7th graders who go on to study life science, including osmosis.  When we got to osmosis, they made the connection back to our measurement study.  It was great, and I've never considered doing it any other way, or with any of my other classes).

The procedure is simple enough....

Each student gets a gummy bear*.  The gummy bear gets measured thoroughly: length, width, height and mass.  Volume and subsequently density can be determined.

The gummy bear then spends a night in a cup of water.

When the students return the next day, the bears get measured once more (after students get over the shock of seeing their newly enlarged gummy bear).

Conclusions are drawn.

In my experience, this lab leads to all kinds of questions for further experimentation... What if I place my gummy bear in Coke/tea/milk/etc?  What if I leave my gummy bear in the water for 2 days?  What if I allow my newly enlarged gummy bear to sit out for a day?  What if I use a gummy worm instead of a gummy bear?  If you have the time and resources, it's a great opportunity for students to design their own experimental process and carry it out. 


*I tried to use a gummy worm one time, when I had some at home.  It didn't work, it completely fell apart.  Fortunately, it was just me playing around at home.  For that reason, always do a test run on the gummy bears you plan to use with your students.  You really want a gummy product that's going to hold up, at least for the initial experiment.

Osmosis: Egg-speriment

A classic demonstration of osmosis using a large cell: an egg.

Place an egg in a beaker filled with vinegar for a day or two (over a weekend works well). The vinegar will remove the shell of the egg, leaving the cell membrane. Additionally the process of osmosis will begin with the water found in the vinegar.


Place the egg in a variety of other substances, for one night each.


Vinegar – water flows into the egg, increasing its size.
Water – water flows into the egg, increasing its size (but not as dramatic after a day in the vinegar)
Colored Water – water and dye particles flow into the egg, increasing its size and changing its color
Corn syrup – water flows out of the egg, decreasing its size


You can make the experiment as complex or simple as you wish. You can present this activity as a demonstration, or have students complete it as a lab experiment. Have students measure and record the egg’s dimensions by wrapping a string around the egg’s circumference. Students could also keep track of the volume of liquid that is placed in the beaker and how much remains the following day. After students have recorded data, they can graph it.

Make sure you have antibacterial cleaning supplies ready and available if you take on this lab, especially if you have students working with the eggs – some will break!

Diffusion: Food Dye in Water

A very simple way to illustrate diffusion. Place a clear container filled with water on a table in the front of the room. Add a drop of two of food dye to the water. Point out to the students how dark and concentrated the dye is initially. The dye will spread out until it has reached an equal concentration throughout the entire container.

Diffusion: Perfume in the Room

Place an open container of perfume (or other scented substance, such as vanilla) in a corner of the room. Have students raise their hand when they first smell the scent. Or, they could quietly note the time at which they first notice it and you can analyze the data later. You should find that students nearest the container are the first time notice it and it spreads outward from there.

To keep the results as honest as possible, don’t tell students where you’ve placed the container or what scent you’ve used.