The purpose of this lesson is to introduce the concept of the structure and function of the cell membrane. Given the complexity of this concept it is highly doubtful that students will get a full understanding in one day. That is why this is a two part lesson. Other concepts that are layered in this lesson are form and function and models. Both of these will be more explicitly taught in the later lessons of the week.
Learning Goal: Understand the structure and Function of the membrane.
Essential Question: What do you think the cell membrane does?
Students come in the room, get ready (get their stuff), get set (get settled in their seats), and engage in writing the learning goal and answering the essential question on the board.
When students are done with the opening question they pick an object off the table out of several on the table and explain how this object is like a membrane. (plastic wrap)
For my hook today, I am going back to that incredible video The Inner Life of the Cell. However, I only use the section that shows the cell membrane. The purpose of the video today is to give the students a taste of how complicated the cell membrane is. After all, they are used to simply drawing a circle and calling that the cell membrane!
The section of the video I show falls between :22 Sec to :41 Sec. I want to make sure that they see there are two main parts to the membrane; the surface of fat molecules and the structural proteins. I also want them to see how it looks from the outside of the cell and then from the inside of the cell.
Getting these ideas firmly across takes multiple showings. I will often stop and talk about a section on the video.
In the following video, I explain how to use this video for the purpose of teaching the structure and function of the cell membrane.
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Today, using direct instruction, I take students through looking at and writing about a picture of the cell membrane and creating a Structure/Function Table.
The first step is to add a picture of the membrane to the student notebooks. (To make this go easier and faster, I cut out the pictures ahead of time and keep tape and a stapler on the desk in a little container. This way adding a foldable or other resource into their notebook takes very little time.) This a scientific, although simple, drawing and the intent is to create an accurate and specific representation and that's the reason I don't have students draw it. I find that it is much easier to go from a simple drawing and then transfer to a more complicated one than the other way around. Students can easily become frustrated and withdrawn if the picture seems out of their league.
Once the drawing is in the notebooks, I point out the labels to the students and have them highlight or underline them. As I point out a label, I'll orient the students within the cell. For example, "This is labeled as a fat molecule, so these (pointing) are the fat molecules within the membrane." My goal is to make sure they look closely at the picture, and relate the label to the part.
Then we start to create the structure/function table. In our notebooks we draw a four column, five row table and label it. Then we go through each part - I point back to a cell "part", we name it, and then I share my thinking. For example, "This is the cell membrane. Notice that it's a double layer (pointing as I speak), and its made of fats and proteins. It controls what goes in and out of the cells." Students record this, and draw a picture to go with it. My objective here is to create accurate notes that students can return to, as we dig into understanding of the structure - function of the cell membrane.
When we are done it will look like this.
For Guided Practice, I use questioning to make sure that students can return to the structure-function table, and use that information to describe the simulation we are about to run. I like to use Think-Pair-Share for this and call on students at the end using my "random sticks". Using this system allows all students to process together, but creates accountability. My questions are:
1) What is the purpose of the cell membrane? (Students have to connect the word function to "purpose".)
2) What two types of molecules make up the cell membrane? (Students have to do some reasoning here, to deduce this answer.)
3) What is the purpose of the fat molecules?
4) What is the purpose of the protein molecules?
Now that we have the parts of the cell membrane and a basic idea of how it works, we're going to take a look at how its structure allows it to achieve its function of controlling what goes in and out of the cell.
I run the PhET Simulation for them, naming the parts. This is demonstration only, but the students will be playing with the simulation in the next section. I want the students to attach the vocabulary we're using (fat molecule, cell membrane, etc.) to the simulation. You can find this simulation online here.
When demonstrating I want to simply show the students the fat part of the membrane and the protein part and then demonstrate adding molecules outside of the cell and inside of the cell.
At this point it is time to let students explore the simulation and see what they discover. (This is open ended, and deliberate - the purpose really is just to explore and see what happens. Allowing this time pays off later - when given the problems later they were able to solve them without the frustration of trying to figure out how to manipulate the simulations.) I walk around and help students but also push them when I hear comments that might lead somewhere interesting.
I deliberately have students sharing a computer while working with a partner , even if I have enough computers for a 1:1 environment. The research on computer use is interesting but one thing I found important in John Hattie's book Visible Learning was that students need to have a partner to work with to engage in the critical thinking. I have seen this play out in the classroom again and again. Students working together will push each other more and discover more than students working independently.
Once the initial engagement/excitement has wound down (you can tell by the level of noise in the classroom), I add some problems to the mix to see if students can make certain situations happen.
1. What types of proteins would a cell have if only blue molecules are to stay in while green molecules move in and out?
2. What types of proteins would a cell have if it is keeping blue molecules in and also preventing the number of molecules from rising above 20 while the cell is continually making these molecules?
At this point, though it might be difficult, I ask the students to close their computers and get ready for a very short quiz. I use SMART clickers* to give the quiz so I an easily have access to this information (can you believe they love it - technology!). It's short for a reason - I want a quick check to see if today's information "download' and practice is beginning to make some sense.
*You could also use an online app like Doodle poll if you do not have access to clickers or of course give a hard copy. I will use this quiz to give me data so that I know who to check in with immediately on the next day.
I am giving my students a project to complete at home during this unit. At the end of the unit we will display our projects in a cell museum. You can find the rubric and assignment here.
I like to check in with the students just briefly during class to remind them about the assignment and see where they are in it.
1) Students chose to do a model or a poster. I give students the option of a poster to support my free and reduced lunch students. They can still make a fabulous poster that looks the same or better than anybody else's with no financial outlay. Models can be made out of any material.
2) Students fill in the structure/function/picture/thinking chart. This is where students actually show understanding of the structure and function of cell organelles. Advanced students are encouraged to use metaphors as opposed to make a pure model, as this allows them to display more thinking. For example, one might say, I chose a whiffle ball for the nucleus because it has holes in it and could hold things inside.
As the cell models come in, I display them like a museum. Students are allowed to look at everyone elses and are encouraged to have discussions and give feedback using the rubric. Depending on time, students can vote on their favorites.
The closure today is an exit ticket that will go on my exit ticket board.
"How does the cell membrane control what goes in and out of the cell?"