Modeling the cell membrane

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Objective

Students will model the cell membrane using bubble solution and perform a close read in order to better understand the fluid mosaic properties of the cell membrane.

Big Idea

Having fun with bubbles can help us model the characteristics of the cell membrane.

Warm-Up

5 minutes

Warm-Up: What does it mean to be selective?  How does the term relate to the cell membrane?

This warm-up question serves to assess how well students understand the main function of the cell membrane as taught in lesson, The Cell Membrane.  Engage students in a discussion around the term, selective.  Ask students to name synonyms for the term, selective.  Listen to students’ ideas for words that have the same meaning as selective.  Be sure to correct any misuse of words students wrongly think are synonyms for selective.  This helps to eliminate misconceptions.  

Content Review

20 minutes

Check the homework from the previous lesson, Cell Transport, part 1. Allow 2-3 students to share their one best question and answer with the class.  The homework sample shows that this is an effective way for students to build their ability to predict the types of questions that they will need to be able to answer on an assessment. Point out questions that use inquiry questions like “how” or “why” and remind students that these type of questions push students’ critical thinking beyond level one questions using words like “what”.

Display a cartoon image and ask students to take 2 minutes to think about why some of the fish in the picture are sad and others are happy.  Encourage them to refer to their notes as needed to assist them in understanding the picture.  After the 2 minutes period, instruct students to “pair” for 2 minutes with a seatmate to explain why two of the fish are sad and one is happy. This type of visual activity is an effective way to build conceptual understanding.

After the 2 minute period, instruct the pair of students to “share” their collective opinion with another small group of two students.  This activity, “Think, Pair, Share” allows students to think, discuss and likely defend their explanations with their peers.  After the period of sharing ends, ask one student from each “share group” to tell with the class what they learned or taught through their peer conversations.

Guided Practice

10 minutes

Prior to the class, identify and prepare the materials needed for the lab:

  1. Collect trays, straws and twine. 
  2. Bubble makers. Note: I strongly suggest making the bubble makers in advance of class because students sometimes spend too much time trying to make the bubble makers at the expense of the actual lab procedure and analysis. he good news is that once they are made, they can be reused year after year. Just wash them after use to remove the soap residue and air dry before storing. 
  3. Prepare a bubble solution using Joy soap, glycerin and corn syrup in a large flask.  Note: I find the bubble solution I make to perform better than the bubble solutions one can buy in a dollar store.

Display the Bubble Lab on an LCD projector to address the different learner types.  Model safe lab practice by wearing goggles while summarizing the lab procedures.  Emphasize the importance of safety and remind students, “No goggles, no lab”.

Part 1:  Display and distribute copies of the Bubble Activity procedures. Summarize the procedures and inform students that the bubble makers have been made for them.  Distribute copies of the Bubble Activity questions and read each question aloud to the class.

Part 2: Display and distribute copies of the Close Read , which is Part 2 of the assignment. I usually place part 1 and part 2 copies back to back in a plastic page protector, which allows me to use the same pages throughout the day.  Preview the close read activity and ensure that students are aware of how to locate the articles. Review the RACE writing strategy with students. Remind them to cite facts to support their position when responding to the writing prompt.  

Independent Practice

20 minutes

 Make sure that students are aware that there are two parts of the lab: 

  • Part 1 consists of a hands-on activity using the bubble solution and completion of a set of analysis questions
  • Part 2 consists of performing a close read of several articles about the effects of ingesting too much water before responding to a writing prompt:

Instruct students to work in groups of two to complete Part 1 of the lab, with each students writing his/her responses to the lab question on their own papers. The Part 1 student work sample indicate that students will be able to apply what they've learned and observed from the lab to be able to demonstrate understanding of the concepts.

As students work, walk around to observe and listen as they complete the lab. Expect to see students fully engaged as they create a fluid mosaic, attempt to create a make a nucleus in the bubbles and create a pore.

Inform students that Part 2 of the assignment is an Part 2 student work individual task that is completed independently using computers. The constructed writing response is:

You are babysitting your infant brother and all he does is cry unless he is drinking formula milk from a bottle. You begin to realize that you must watch your brother for two more hours before your father comes home and you are going to run out of formula soon. You call your best friend who is an experienced babysitter and she suggests that you water down the formula milk to stretch it out. You try it and it seems to work and satisfy your baby brother.  However, you get a call back from your friend who advises against watering down the formula milk because she worries about water intoxication.

In Part 2 of the assignment students must first conduct research and then decide what to do based on what was read about water intoxication. Students must explain how cell transport concepts support their decision to dilute the milk or not. In order to have a well written essay, students ]must cite evidence for their argument. Remind students to use the content specific vocabulary in your response, as well. The two student work samples reflect actual responses to the prompt.

Display a timer and require groups to submit part 1 of the lab within a timed period, before distributing the readings that are used for Part 2 of the lab. Give periodic time checks as students work to help them remain on task. 

The Part 2 student work sample demonstrates that students are able to synthesize what they learn from the reading to craft a thoughtful response to the question.

Close

5 minutes

Distribute post-it notes and give students one minute to write one “sticky thought” that they learned from the lab assignment that will remain with them after this class. Ask for a few students to share their sticky thoughts before class ends so that you will be able to affirm accurate thinking or correct misconceptions before class ends.

Instruct students to stick their notes on the chart paper as they are dismissed from the class.