CT-STEM

Phospholipids Between Us: (Part 2) Transport Through Cell Membranes

Phospholipids Between Us: (Part 2) Transport Through Cell Membranes

Subject: Biology
Time: 2-3 class periods
Level: All high school levels of biology

Overview

The activity focuses on student understanding of the biology concept of passive diffusion. Each activity is divided into three main CT activities: 1) recording observations and gathering data and 2) analyzing data and 3) testing different simulation scenarios to understand a problem.

Lesson Plan developed by Kai Orton, PhD and Apurva Naik, PhD (Northwestern University) and based on the PhET Interactive Simulation: Membrane Channels (http://phet.colorado.edu/en/simulation/membrane-channels)


Learner Objectives:

1.     Students will understand how the cell membrane regulates what comes in and out of the cell.

2.     Students will understand the process of passive diffusion and facilitated transport and how/when molecules and particles will move through a membrane and when they will not.

3.     Students will be able to predict rates of diffusion and ion transport based on the number of protein channels present.

4.     Students will understand the differences between passive and selective diffusion and facilitated transport through a cell membrane.

 

Materials and Tools

Computer Systems Requirements:

Windows

Macintosh

Microsoft Windows 
XP/Vista/7 
Sun Java 1.5.0_15 or later

OS 10.5 or later 
Sun Java 1.5.0_19 or later

 

1.Students will use a PhET Interactive Simulation: Membrane Channels (http://phet.colorado.edu/en/simulation/membrane-channels)

2.In the simulation, students will drag the channels onto the membrane and then investigate what happens to molecules/particles.

3.The concentrations graphs are meant to give students qualitative, relative information to help them understand diffusion.

 

Preparation

Begin the lesson by reviewing the differences between the cell wall and cell membrane, which can easily be confused by students. This is also an important topic because these two structures are very important to diffusion and osmosis.  Ask questions such as, “What is the difference between the cell wall and cell membrane?”

Explain how the cell wall is the outside lining of the cell that helps support cell structure and holds the cell together.  For plant cells the cell membrane lies within the cell wall, while it is the outer structure for animal cells. 

The cell membrane has the quality of being semi-permeable so it can allow various substances to go in and out of the cell.  A great example of a very simple cell everyone is familiar with is an egg, one of the largest cells. The shell is the cell wall and the thin lining we sometimes peel off the shell is the cell membrane. The white of the egg (clear runny part) is the cytoplasm and the yolk or yellow part is the nucleus. Plants have both a cell wall and a cell membrane. Animal cells usually do not have a cell wall.  Bird eggs are an exception.

After they have a firm understanding of this topic you can move on to the concept of diffusion and equilibrium. Next, discuss the topic of osmosis and how these two topics relate to one another.

There are data tables and graph paper attached as documents to this lesson

 

Setting up the simulation:

Open the “Membrane Channels” interactive simulation on the computer:

  1. Type http://phet.colorado.edu/en/simulations into the Internet browser.

  2. Click “Run Now” (bright green icon)

Background

  1. Students should understand concepts of the cell and organelle function

  2. Student should have a clear understanding of the differences between a cell wall and cell membrane

  3. Students should be familiar with concepts like concentration, equilibrium and diffusion.

  4. Students should have already studied concepts in osmosis like tonicity and osmotic pressure.

Compatible With


mac

windows

laptops

chrome books

phones

tablets

What's Next?

Standards

Next Generation Science Standards
  • Life Science
    • [HS-LS1] From Molecules to Organisms: Structures and Processes

Computational Thinking in STEM
  • Modeling and Simulation Practices
    • Using Computational Models to Find and Test Solutions
    • Using Computational Models to Understand a Concept
  • Computational Problem Solving Practices
    • Assessing Different Approaches/Solutions to a Problem
  • Data Practices
    • Analyzing Data
    • Collecting Data
    • Creating Data
    • Visualizing Data
  • Systems Thinking Practices
    • Understanding the Relationships within a System

Comments, Feedback, and Quesitons

Phospholipids Between Us: (Part 2) Transport Through Cell Membranes

Teacher Notes

1.     A computer lab with at least one computer per two students is recommended, but groups may be formed for classrooms with less computer resources

2.     Keep in mind that a strong student may dominate the group work.

3.     Students should work in small groups (even when they have their own computer) to compare their observations

4.     In a real cell, leakage channels are always open, whereas gated channels only open in response to some stimulus. Some gated channels respond to the presence of a certain molecule (ligand gated), some respond to a change in membrane potential brought about by changes in ion concentrations (voltage gated), some respond to changes to tension in the cell membrane (mechanically gated), and some respond to light (light gated).

5.     In real cells, channels do not actively move things through them; they only allow things to diffuse through them. This is true in the simulation too, though in some cases it may appear that an ion is being pulled across a channel. Teachers should make sure that students understand that the motion through the channels is passive – a result of diffusion and that membrane channels do not ‘pump’ anything across the membrane.

6.     In real cells, channels do not actively move things through them; they only allow things to diffuse through them. This is true in the simulation too, though in some cases it may appear that an ion is being pulled across a channel. Teachers should make sure that students understand that the motion through the channels is passive – a result of diffusion and that membrane channels do not ‘pump’ anything across the membrane.

7.     In the virtual lab activities, students are asked to input a certain number of green circles or blue diamonds. A few molecules more or less won’t affect the equilibrium conditions.

8.     In the virtual lab activities, students are asked to state when they observe equilibrium. A few molecules more or less on either side of the membrane will not matter for equilibrium conditions, but these fluctuations may appear significant to the students when they graph. You can ask the students to take an average of the values after equilibrium is reached to make a smoother curve.

9.     Equilibrium point is reached when there are approximately equal numbers of blue diamonds on each side of the membrane or when both the blue bars in the concentration plot appear to be of the same size.

10.  A timer is required for most of the activities. If the students don’t have hand stop watches, they may make use of cellphones with timers or also use a window with timer. The PhET simulation window doesn’t have to take up the whole screen.

11.  Within the simulation environment the placement of the channels (into the membrane) may affect the rate at which equilibrium is reached, although there isn’t be a big difference in the students’ general observations

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