Membrane Magic!

4 teachers like this lesson
Print Lesson

Objective

To investigate the factors which affect membrane permeability and homeostatic actions of the cell.

Big Idea

The cell membrane's hydrophobic nature dictates the movement of materials in and out of the cell!

Introducton

Lesson Background & Justification:

     Cellular homeostasis is a process which maintains the balance of several factors that make a cell healthy and keeps the organism alive. The cell membrane, the cell's homeostatic gatekeeper is a lipid bilayer that keeps the passage of water, nutrients, bulk materials and ions in balance according to the unique demands of each specialized cell that it surrounds. No matter the cell type and function, all cellular membranes are unique composites of mostly hydrophobic materials which aid in its ability to regulate materials consistently. In this lesson, students investigate the chemical structure of the membrane and learn to describe its chemical nature as it relates to its ability to regulate chemicals such as ethanol and folic and explain the physical consequences of their movement on brain development of a fetus. 

Lesson Preparations:

 In the effort to prepare for this lesson, I make certain that I have the following items in place: 

a) A class set of Science Take Out Kit: Life Support for a Developing Baby (1 per student pair)

b) A class set of phospholipid cut outs, glue, scissors & chemical cut outs (ethanol, water & folic acid).

c) Student lab books.

d) Six Cups of Chemistry of Water Modeling Kits: Purchase or Get on Loan.

Common Core and NGSS Standards:

SP4- Analyzing and interpreting data.

SP2- Developing and Using Models.

HS-LS13: Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.

Standards Rationale:

      Modeling is the process by which scientists represent ideas about the natural world to each other, and then collaboratively make changes to these representations over time in response to new evidence and understandings. It is intimately connected to other scientific processes (asking questions, communicating information, etc.) and improves students ability to recall scientific jargon through association. In the classroom, it is important that teachers engage students in modeling practices, to set the foundation of success in a lesson or instructional unit. In this lesson modeling is used in concert with other science practices in the classroom to promote students’ reasoning and understanding of core science idea presented (mechanisms of maintaining homeostasis).

Engage

10 minutes

Section Primer: 

        Commonly referred to as alcohol or spirits, Ethanol is also called ethyl alcohol, and drinking alcohol. It's unique chemical nature and structure allows it to interact with both hydrophobic materials due to its saturated core and hydrophilic material due to its open hydroxyl group at one of its terminal ends. Consequently, ethanol can penetrate the hydrophobic membrane of cells and create complications by disrupting the cell's delicate water balance.

Section Sequence:

           In this section of the lesson, my goal is to draw students interest into the impact of consuming alcohol during pregnancy on the fetus. The idea is to empower students to inquire about why or how this actually happens to set them up for the proceeding section which explains why and how alcohol moves to the fetus. This activity proceeds as follows:

a) Ask "What do you think happens to a child who is born to a mother who drank during gestation?" Discuss. Verbally inform students that we will learn a little more about this topic and play the following video clip. Post video, ask students what they have learned regarding FAS. Discuss. Facilitate the discussion so that it explicitly defines FAS, and describes the physical and psychological impacts of the condition before its conclusion.  

       

 

 

 

Explore

25 minutes

Section Primer:

       The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply, fights against internal infection & produces hormones to support pregnancy. Said processes rely heavily upon the process of diffusion in cells which promote the movement of materials based on a concentration gradient. This assures a constant flow of materials needed for fetal growth and development.

Section Sequence:

In the section of the lesson, my goal is to provide students with an opportunity to discover how items, good and bad generally transfer from mother to embryo. I proceed as follows:

a) Slide 1: Announce to students that we will learn how ethanol contacts the fetus through exploration and explain the protocol for their lab experience as it appears on the slide. During teacher checks, check for accuracy and redirect students if needed to avoid misconceptions. 

b) Slide 2: Read and discuss each question presented on the slide. Use the timeline to both review previous content and to clarify why specific characteristics arrive in children impacted by ethanol typically starting with Neuronal Proliferation. 

c) Slide 3: Discuss students results from the activity as a class, using the image to aid in discovery descriptions. Use graphics at the bottom to edify cellular transactions between embryonic and mother's vessels. 

Standards Covered:

SP4- Analyzing and interpreting data.

SP2- Developing and Using Models.

HS-LS13: Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.

 

Explain

30 minutes

Section Sequence:

     In this section of the lesson, my goal is to help students truly understand the concept that structure dictates function. In this case, we examine how the chemically, mostly hydrophobic cell membrane permits limited movement of ethanol across the membrane and therefore utilizes other, more chemically conducive structures embedded within to expedite the diffusion of ethanol into the cell. I proceed as follows:

a) Slide 4: State: "We are now going to use manipulatives to try to explain how and why the ethanol freely moves from the cells of the mother's vessels through the placenta and into the fetus's vessels. Provide student groups of 4 with 1 large post note sheet (to create their models on), a *water cup model kit, and phospholipid  cut out structures. Read and explain specifics of the Cell Membrane Construction Challenge as it appears on the screen. Before students attempt the challenge, be certain to explain or iterate the chemical nature of phospholipids (hydrophilic heads and hydrophobic tails) using the illustrations on the slide.

b) Slide 5: State: "There is more to this complex structure. Based on the image, what do we need to add to our current models?" Provide students with color construction paper to cut, and add proteins.

c) Slide 6: Repeat step b  with cholesterol and glycogen cut-outs. 

d) Slide 7: Read question on slide, discus and direct students to model and verbally describe the movement of ethanol on their desks to and with one another.

* Note: If water kit is unattainable, use paper models attached as a resource.

Standards Covered:

SP2- Developing and Using Models.

 

 

Extend

10 minutes

Section Primer: 

        In early developmental stages, Folic Acid or vitamin B, a water soluble supplement helps the embryo to make healthy new cells (particularly spine and brain in embryos). Low levels of this vitamin can lead to spinal malformations as well other physical and mental complications within a child. In the lesson Fetal Brain Development Explained, students explored this this concept, but have yet to learn the mechanism by which folic acid enters the system to preform its task. This lesson's extension activity aids in accomplishing this. 

 Section Sequence:

      I proceed with this section as follows:

a) Slide 8: Ask if anyone recalls the name of a chemical that enters the placenta during gestation that can help the embryo with healthy brain development. (Students should recall this information from Unit 2, Lesson #3) Probe students until folic acid is brought about. Present the following video Folic Acid Revisited and pursue the remaining discussion questions presented on the slide. 

b) Slide 9: Ask the question presented and encourage students to form a hypothesis regarding FA's movement across the membrane as compared to the ethanol on the screen (Folic Acid is circled in red). Explain the chemistry (hydrophilic) of folate while providing students with the respective cut outs. Challenge students to figure out how it gets into the cell (consider size and chemistry). Explain cell mediated endocytosis (using glycoprotein receptors as an entry point) and get students to model it using their pieces. Finally, have them explain folic acid movement to one another using the manipulatives.

Standards Covered

SP2- Developing and Using Models.

HS-LS13: Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.

 

Evaluate

15 minutes

Section Sequence:

         In this section, my goal is to assess students comprehension of the structure and function of the plasma/cell membrane. I proceed as follows:

Slide 9: Provide each student with a Plasma Membrane Practice strip to glue inside of their lab books. Explain the directions as they appear on the screen. Check students work as they progress.

Standards Covered:

SP2- Developing and Using Models.

HS-LS13: Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.