Insane in the Membrane

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Students will be able to develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.

Big Idea

Students use soap bubbles to model the function of a cell membrane!

Introduction and Connection to the NGSS and Common Core

In this lesson, students use reading strategies to learn about the structure and function relationship in the cell membrane as they create a model of membranes using soap bubbles.

This lesson is specifically designed to address the following NGSS and Common Core Standards:

MS-LS1-2  Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.

CCSS.ELA-LITERACY.RST.6-8.7 Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).

Science and Engineering Practices:

The NGSS explains that students should be able to develop a model to describe unobservable mechanisms (SP2).  As students in this lesson use bubbles to model cell transport through a membrane, they do just that!  In order to create these models, students use reading strategies to obtain information (SP8) and generate questions (SP1) and ideas relating to the NGSS Crosscutting Concepts.

Crosscutting Concepts:

In this lesson, students connect to all of the NGSS Crosscutting Concepts as they read using a strategy I call "The Ladder of Discourse".  While they may connect to all of these concepts, specifically, students in this lab begin to tie together the idea of how the structure of the cell membrane relates to its job for the cell (Structure and Function).

Connecting to the Essential Question: What are you supposed to learn today?

5 minutes

Begin class by asking, "What are you going to learn today?".  Students should respond by referring to the Essential Question, "How do cells contribute to the function of living organisms?". This EQ can be referenced both on my front board as well as on their Cells Unit Plan.

Have students get out their Cells Unit Plan. Explain that their focus of this particular lesson is Skill 2: I can provide evidence that cells are made up of organelles that have specific jobs. As this is the students' second lesson on this learning target, have students reread the skill and self-assess where they stand in their level of mastery in this skill. Students rank themselves on a scale of 1 to 4 (4 being mastery). Remind them that it is understandable that they might be at a 1 or 2 at this point.  Learning is about growth and the path to mastery. It is not expected that the skill be mastered today.

As the unit moves forward, I have the students continually self-assess on each skill. In my class, this will be the students' second self-assessment, so they change their scores if they feel that their learning has improved. Check out a student's unit plan below to see how students update their mastery level with each lesson.

Mini Lesson: The Ladder of Discourse and the Crosscutting Concepts

25 minutes

In order to gain background about the structure and function of the cell membrane, students read the Membranes article.  I only have the students use an excerpt of this article.  It is located in the document titled Insane in the Membrane Lab Document. As students read, they climb the Ladder of Discourse and "talk to the text".

The "Ladder of Discourse" is a strategy I use in my class to help students think critically as they read.  For middle school students, informational reading can just become words on a page.  The "Ladder of Discourse" is a way to help students recognize what they should be thinking about as they read so that they can gain an understanding of the text.  The levels of the Ladder of Discourse are "Tweets" (text to self connections), "Huh?'s" (questions or concepts they do not understand), "Found It" (finding answers to questions through context clues or finding science answers), and "Discourse" (combining ideas to think beyond the text).  The resource Ladder of Discourse: Description of Rungs"provides background about the "rungs" students use when reading.  

As they read, they try to make connections to the NGSS Crosscutting Concepts.  This could be in the form of a statement, idea for an experiment, a prediction, or a question.  In order to do this, students have to slow down when they read.  Every 2 - 3 sentences they stop and think about what connections they are making to the text and they document their thinking by "talking to the text".

Notice in the picture below how the student wrote, or "talked", on her paper what she was thinking about as she read.  (I know you can't quite read everything in this picture - I just wanted to give you a visual of what "talking to the text looks like.  There are readable examples coming.  Keep reading to see them!)


Ladder of Discourse Student Examples:

Tweet: The student makes a connection between a science concept and something she connects to in her life.

Huh? and Found it!:  The student here actually has two "Huh's?" and "Found It's!" in the same paragraph.  She asks, "What's hydrophobic?" and then finds the definition in the text.  In addition, I would like to note the place that she scribbled out "Huh?" next to bilayer.  This means that she didn't understand it the first time she read it and then went back to reread and found the answer she needed.  Effective readers reread and use context clues to find the meanings of new words.

Discourse:  Each of these connect to a specific NGSS Crosscutting Concept.  I only used a few examples here; but each student connected to a different crosscutting concepts in their reading.  However, with this text, the most common connection students make is to "Structure and Function".

Scale, Proportion, and Quantity:  


 Structure and Function:



Insane in the Membrane!

40 minutes

After the students read, provide each group of 4 - 5 with a procedure.  Make enough lab stations for each group member equipped with the following materials:  

  • 4 Cups                                     
  • 4 Straw Contraptions  (Cut straws in six inch sections.  Thread a piece of yarn through them and tie a knot.)


  • Bubble Solution (10 parts water/1 part Joy/ 1 tsp of Karo)
  • Cotton thread                          
  • Scissors                                              
  • Tweezers

Explain to the students that in this lab they will be using soap solution to represent a cell membrane, a string tied in a circle to represent a hole in the membrane, and a Starburst to represent a sugar molecule that has to enter the cell to be broken down for energy.  Have them follow the procedure carefully.  

Model #1:  Cell Membrane and Transport

Watch the video below to see what it looks like as students complete the procedure:

It is a tricky process. Some bubbles will pop and the students will need to try again. However, if you feel like your bubbles are popping too frequently, add more corn syrup and mix it around in the solution. The procedure asks the students to pop the bubble area on the inside of the circle of string. This is best done with a dry finger!  If students are struggling with that process, I allow them to drop the Starburst through the circle and that will pop the bubble circle. In the video above, the students use this strategy to pop the bubble inside the circle.

Model #2:  Prokaryotic vs Eukaryotic

Once the students have modeled transport through the membrane, tell them that we are changing what the materials represent in order to create a different model. Now, the bubble represents cytoplasm, the circle string represents the nucleus, and the small pieces of string that were cut off in the first procedure represent DNA, or genetic information. Explain that they are to create a model of a prokaryotic cell and then a eukaryotic cell. I remind them to use their text as reference (they had learned about this concept in a previous lesson). The Cell Organelle Notes Page is included with this section. In addition, a requirement of this part of the procedure is that they have to show me their model and explain the reasoning for their choices before moving on.

Eukaryotic Model:

Prokaryotic Model:

FYI:  The resource titled Insane in the Membrane Lab Document includes the procedure, student lab sheet, and membrane reading all in one document.

A Look at Student Work

In the first question, the students use the text to draw a diagram of the structure of the cell membrane.  

In the second questions, the students connect the structure to the function.  They note that the proteins aid in allowing molecules to move in and out of the cell and the lipid bilayer can act as a bag that holds the cell together.

Students note many different similarities and differences.  Some of the most common similarities is that they both are flexible, allow things to go in and out, and can reseal themselves.  Some common differences students note are that they are made of different substances, are different sizes, and let different materials through them.

In the fourth question, students note that organelles have their own membranes because organelles themselves have a need for letting important molecules in and out of them.

In this questions, students recognize that the membranes in each organelle may vary depending on the function of the organelle.

Last, students explain the choices they made in their models of prokaryotic and eukaryotic cells.  They explain that in the prokaryotic cell the DNA was floating around in the cytoplasm while in the eukaryotic cell the DNA was held in the nucleus.

Closure: Exit Ticket Formative Assessment

5 minutes

Have students complete this Formative Assessment as an exit slip.  For an upcoming lesson, sort these slips in to stacks of similar learners that have common needs.  Then, you can pull these groups and conference with them.

Notice that the student drew a model with labels of the structure of the membrane and then connects to the membrane's function in the caption.  Typically, when sorting these formative assessments I meet with the following groups of learners:

1.  Students that draw a simple model of a membrane as simply a plastic bag with holes in it.

2.  Students that can identify the structure but not both of the functions.

3.  Students that can identity the functions but don't connect to the structure in the membrane that helps the membrane serve the function.

When meeting with students, have students graph their level of mastery on their "Working Towards Mastery" list.  This is a place for students to track their growth and the specific feedback they receive during the unit.  The picture below shows a student that recorded their score and feedback after meeting in a conference group with me about this exit ticket in a lesson following this one.