Soapy, Fun, Hands-on Learning with the Cell Membrane Bubble Lab

This Friday I covered Subtopic 1.3 Membrane Structure with my G11 IB DP Biology students and we has a blast using bubbles to demonstrate the various properties of membranes. Bubbles, like membranes use phospholipids in their structure, the main difference being the hydrophobic tails face out towards the air while the hydrophilic heads face in towards the thin layer of water. I recommend taking a minute to explain why we use bubbles as models for membranes before conducting this lab with your students.

I have been tweaking this lab, specifically the student tasks and the bubble mixture for a few years and this year it seems to have worked really well...so I thought I'd share! I cannot take credit for this lab idea, I have googled various versions of it over the years, but this is my version...hopefully it's useful. This can of course be used to teach about cell membrane structure, specifically the properties of phospholipid bilayers or just to make really big and sturdy bubbles...the choice is yours. ;)

Depending on how much prep time you have &/or how much class time you want to take for this activity you can have your students make their own bubble solution & frame or you can do it for them. I usually make the bubble solution ahead of time to avoid extra mess, but have the students make their own frames. I also recommend groups of 3 students, it is tricky to make the bubbles and demonstrate the concepts with only two partners, but more than four students doesn't keep everyone engaged.

The bubble solution recipe:

• 900 ml of tap water

• 100 ml of dish soap

• 25 ml of glycerol

• mix together in a 1000 ml beaker

• I have found that this makes enough for 3 groups of students and I recommend group sizes of 3 or 4 maximum

Other materials:

• a large flat rectangular bin or cafeteria tray with a lip

• four plastic straws (can be cut to 5.5 inches or 14 cm long) & 30 inches or 75 cm of string to make your bubble frame

• a stirring rod or other stick-like object to poke through the bubble

• a small loop of string or thread, about 3 inches or 8 cm long

• scissors

Allow for your students to take some time to play with the bubbles and get the sillies out, they will also need quite a bit of practice making bubbles and keeping them intact before they can demonstrate any of the concepts listed below. I try to let students discover these properties on their own rather than telling them how to do it, but helpful hints can of course be provided along the way. Depending on your school's cell phone policy &/or your own comfort level you can encourage students to take short video clips of their bubbles being used to demonstrate concepts 1-5. This is particularly helpful if you have a really big class to work with.

The membrane structure concepts students can demonstrate with their bubbles:

1. Cell membranes are not static, they bend and flex in order to adapt to changing conditions

2. Attraction between phospholipids allows cell membranes to repair small breaks in the bilayer

3. Eukaryotic cells have membranes within membranes

4. Some specialized membrane proteins embed within the lipid bilayer, giving the membrane unique properties. Channel proteins are one example. Use the loop of thread to model a channel protein.

5. Membranes allow cells to divide and form two new cells. Use thread to help complete the division.

I highly recommend you try this lab our yourself first and encourage your students to both have fun and be prepared to try many, many times before they successfully demonstrate these concepts with their bubbles. It's a good time for everyone!

Thanks for reading teachers, travelers & curious souls of all kinds.

The Roaming Scientist