Cell Membrane Bubble Lab

Cell Membrane Bubble Lab

 

The purpose of this slide deck is to guide students in the process of constructing the proper apparatus necessary for performing a cell membrane simulation using soap bubbles.

A Clever Idea for Teaching about Cell Membranes

The amount of time I spend searching for classroom resources is substantial. I’ve been doing it a long time.  So, when I come across good ideas I’ve never seen before, I get a little excited.  These intermittent jackpots keep me going.  In psychology this is known as a “variable ratio schedule” of reinforcement. It’s the same reason people buy so many lottery tickets.  The other day I was meandering the web looking for new ways to teach about membranes, the cellular variety.  In my opinion, cell membranes can often be over looked.  Open a student textbook and find a diagram of a cell.  The membrane is often drawn as a simple line, unassuming and uneventful.  In reality, the cell membrane is abuzz with a flurry of activity.  It’s the interface between the internal and external cellular environments.  Membrane interactions determine the cell’s destiny. Like many things “cellular,” membranes are hard to see; they’re tiny.  In my search I was hoping to find something tangible for my students to experience that might reveal the dynamic and adaptive nature of cell membranes.  To my pleasure, I came across something that does an excellent job modeling membranes, soap bubbles.

 The Beauty of Bubbles

I like to rate instructional activities on three attributes: simplicity of design, instructional value, and engagement potential.  The cell membrane bubble lab scores well across the board.  First, blowing bubbles is pretty easy – ask any preschooler.  Second, a bubble acts a lot like a cell membrane – you just have to know what to look for. Third, bubbles are fun – just ask my 2 yr old if he likes his “bubbly” bath.  The beauty of the cell membrane soap bubble lab is that no matter your age, you’re going to learn something.

Cell Membrane Soap Bubble Lab from Clear Biology on Vimeo.

 

A Bubble is a lot like a Cell Membrane

I’m not sure who first came up with the idea of using bubbles as a stand in for membranes, but they work great! A major component of cell membranes is phospholipids.  Phospholipids have a love-hate relationship with water.  One end, the “head,” is attracted to water and the other end, the “tail,” is repelled by water.  Place phospholipids in water, and they quickly form a double layer with the heads Labeled Phospholipid Diagramfacing out.  A soap molecule has the same split personality.  The “head” of a soap molecule is charged (ionic) and attracts to water, which exhibits positive and negative regions of charge (polar).  The hydrocarbon tail of the soap molecule is not charged and is repelled by water’s polar personality.  This explains why we use soap to clean.  The hydrocarbon tail of soap mixes with and dissolves in other hydrocarbons, like oils and fats, while the head region grabs a hold of passing water molecules and follows them down the drain.  The surface of a bubble has three layers.  The middle layer is a thin film of water.  On both sides of this film is a layer of soap molecules with hydrophilic heads facing water and hydrophobic tails pointing out.  The diagram below provides a nice illustration of this comparison.

 

Lipid Vesicle vs Soap Bubble

Diagram comparing the structure of a bubble with that of a cell membrane.

 

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Jeremy Conn

Science Teacher and Founder of Clear Biology at Clear Biology
I hold a Master of Arts in Teaching degree and have been teaching science in public schools since 2004. I have a love for biology and instructional design. My mission is to share with other educators the best of what I know about teaching.

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12 Comments

  1. Love! I found this lab on Access Excellence years ago, but I Google it every year to see if it pops up in some other iteration. Lo and behold! This year I’ve decided to kick off 9th grade biology with the origin of life and since the first part of our definition of life has to do with having a body or container for metabolism, I figured we go right ahead and make bubbles. Watching your video is so cool for lesson planning. Seeing the kids make bubbles (ahead of my own students making bubbles) got my brain swirling with ideas for bubble prep and follow-up. Will share if I can remember to come back here. Thanks!

    Reply
    • Now I think I want to go make bubbles. Thanks for sharing your enthusiasm! I like your plan of having the students focus on the idea of a container or compartment. You can really build upon this model. After all, eukaryotic cells are kind of like containers within containers within a container. If you use a cafeteria tray to do this lab, you can have the students make a bubble by blowing into a straw at about a 70 degree angle while touching the bottom of the tray. Once the bubble begins to grow, pull the straw back a bit, but keep adding air. Drop the straw back down to the bottom of the tray to make another bubble within the first bubble. Voila! Compartmentalization.

      Reply
  2. What is the solution made out of? How much soap detergent to how much water? Is there something else in the solution?

    Reply
    • For the solution, I used 900ml water, 100ml of dish soap, and 25ml of corn syrup. The corn syrup helps to delay how quickly the water in the bubbles evaporates. I’ve found several recipes that call for glycerol instead of corn syrup. I’ve never had glycerol on hand, so I always used corn syrup. If you have glycerol, maybe give it a try and see if your bubbles last longer.

      Reply
  3. I can’t wait to do this! What a cool lab! One year a student accused me of sitting around at home “inventing stuff” for them to do. I often began the school year with a soap bubble diameter lab to review the scientific method. Students designed their experiments then blew the bubbles using straws on to their lab table tops. They had so much fun. Other teachers in my building started doing it, so I moved away from playing with soap bubbles. Not any more! Thanks for sharing this great idea.

    Reply
    • Thanks! My students really enjoyed this lab as well. It’s hard to deny, bubbles are fun. They may be simple, but you can teach some rather complex topics with the humble bubble.

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  4. Was it just an explore activity? Did you have them record anything? Form?

    Reply
    • I had them move through several activities and each activity illustrated a particular cell process or characteristic (e.g. membrane-bound organelles, protein channels, binary fission). I did have them recored their observations as they went. I had intended to type out a more formal version of the lab, but never have. I really need to find the time to finish it.

      Reply
  5. This is such an “oldie but goodie” lab activity. We’ve used it for years with science students of all ability levels. It can be used for a “nature of science” lab activity at the beginning of the year. Students are asked to make a prediction about which of 3 dish detergents make the biggest bubbles. It also reinforces science practices and good lab technique, like the importance of controlling variables. Students make a prediction or hypothesis, collect data (bubble diameter), create data tables, make graphs, and interpret the data. Then they justify their claim (prediction or hypothesis) with evidence. :-) Thank you for sharing this Jeremy.

    Reply
    • Thanks Cheryl, these are great ideas. It seems the lowly bubble can be quite useful as a teaching tool.

      Reply
  6. Thanks so much for the great info! I made a very simple worksheet that I went through with my students right after the lab. Let me know if you would like the worksheet.

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