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Using Bubbles to Explore Membranes

Sandra Wardell



Type of Activity:

This is a hands-on activity that simulates cell membrane structure and function. This inquiry type lab can be done as a group or cooperative learning experience.

Target Audience:

This lab can be used in any life science or biology classroom. If working with middle school students, the details of the membrane structure need not be explored in as much depth. Because of its hands-on nature, it is suitable for students with special needs. It can be used in advanced biology classes as an introduction to phospholipid bilayers and detailed work relating to cell membrane structure.

What questions does this activity help students answer?

  • What is the structure of the cell membrane and what unique properties does it have?
  • How do these properties relate to how it works?
  • What ordinary substances can be used to model the structure and functioning of the cell membrane?


Background Information

Notes for teacher:
This activity can either introduce or culminate a unit on cell transport and cell membrane structure.

Required of students:
Students will need to bring pencils, notebook and text (if applicable) to class.

Preparation time needed:
1 hour. All materials can be prepared several days before the activity is done.

Class time needed:
Previous class discussions on cell membrane structure (this can vary), 50 minutes for the activity, 20 minutes for follow-up discussion and questions.


Activity

Summary/Abstract:

Cell biology is an integral part of most high school Biology 1 courses. Students are asked to learn about cell structures and how they function in a variety of ways, ranging from memorization, to microscope work, to actual lab experiences. The importance of the cell membrane is usually stressed, but is hard to visualize for most tenth grade biology students. This activity provides a macroscopic model that mimics the cells' phospholipid bilayers using soap bubbles in an innovative, motivational and inexpensive way. Students can explore for themselves how a cell membrane might work and how its structure is related to function.

Materials needed: (For a class of 30 students)

  • Overhead projector
  • Three dozen all wooden clothes pins with round heads
  • Thirty pennies
  • Ball of cotton string
  • Spool of cotton thread
  • 15 pair of scissors
  • Fifteen cafeteria trays (one for every two students)
  • Thirty straws
  • A ten inch piece of aluminum wire per group
  • Pencils
  • Old newspapers
  • Bubble solution made from 10 parts water mixed with 1 part liquid Joy and about one tablespoon of Karo syrup per gallon of solution. The bubble mixture can be made ahead of time and stored in plastic gallon milk containers. One to two gallons per class is adequate.

Procedure:

  • Discuss the structure of cell membranes and phospholipid bilayers. Introduce the idea of the hydrophobic tail and hyrophilic head arrangement using a double layer of wooden clothes pins with round heads on an overhead to show the arrangement of head and tail portions of the membrane. Have several clothes pins with one leg cut off to use as a model of the single tail soap bilayer. Have students compare and contrast the differences. Insert coins or other objects (like pencils, Legos) between pins to simulate transmembrane proteins in the membrane model.

  • Spread newspapers on top of the tables and floor around where the students are working.

  • Have students work in groups of two or three. Each group will need two straws, cotton string, cotton thread, scissors, pencil or pen, cafeteria tray, aluminum wire 6-8 inches in length, bubble solution to a depth of 1-2 cm. Have students cut the straws to lengths of 15-20 cm (they should be a little shorter than the length of the tray). Put the cotton string through the straws to make a rectangle about 3/4 of the tray size and knot the ends. Cut a piece of cotton 6-7 cm. in length and knot. Have the students form a circle at the end of the aluminum wire approximately 2-3 cm. in diameter.

  • Ask students to form a film of bubble solution on their straw device and show the flexible nature of membranes by bending and folding the film. Then ask students to show the self-sealing nature of membranes and how tears might be repaired. Have the students form an opening in the membrane by floating a circle of thread on the film, popping the inside of it and then gently removing it. The membrane should self-seal. This can also be used as a metaphor for membrane pores.

  • The concept of lateral movement (lateral diffusion) of transmembrane protein complexes can be shown by having students insert a pencil or other object through the membrane and move it around. It should not break the bubble solution.

  • Have the students form prokaryotic cells using their straw device. Don't give hints--have them problem solve with each other. This is messy, but motivational.

  • Lastly, have the students and their partners "evolve" a eukaryotic cell using the aluminum "magic" wand and their straw device. They must float a bubble within a bubble. Again, let them problem solve on their own. At this point, they become active participants in the theory of organelle formation and endosymbionts. Bubbles and ideas will float freely in the classroom.


Method of Evaluation:

  • Have students show you their prokaryotic and eukaryotic cells.
  • After the lab, have students compare and contrast soap bubbles and cell membranes in regard to structure and function. This may be done in chart or paragraph form.

Extension/Reinforcement:

  • This is an activity that can easily be shared at home. Have students show this to their parents/guardians.
  • Have students build their own models of cell membranes using wooden clothes pins and oval objects. These can be glued down to a piece of cardboard.
  • Have students research other phospholipid bilayers and their use or function.
  • Have students read about endosymbionts and current research surrounding the evolution of eukaryotic cells.

(This activity was modified from the Microcosmos Curriculum Guide to Exploring Microbial Space, published by Boston University, 1992)


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