Wednesday, May 8, 2013

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. 

7 comments:

  1. Very cool activity! My 8th graders loved it! Took a little bit to get them to curl in the water. Some curled as we pulled them apart, but curled even more after we added them to the water.

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    1. I love that you did it right away!!

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  2. I love this activity.... especially because they are so plentiful and free!! Thanks!

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    1. My 4 year old has been making them every day, and talks about how he can keep doing it every day because "there are lots more dandelions"!

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  3. My students are still investigating ... during their study hall time, they tested the dandelions in hot water, salt water, and soda to see what happened. Very cool that they came up with these ideas on their own! : )

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    1. Love it when that happens!

      Gotta admit, I'm a bit curious how it works (or doesn't work) in salt water...

      Thanks for taking the time to let me know how things are going!

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  4. The salt water made them straighten out. They had predicted that the stems would curl, but the opposite way as with plain water.

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