Transcript Diffusion, Osmosis and the Cell Membrane

Diffusion, Osmosis and the Cell Membrane
An introduction to the function of the cell membrane
and mechanisms of passive transport
by
Bob Birch, Fontbonne Academy, Milton, MA.
Ybelise Escoto, Chelsea High School, Chelsea, MA.
Bryan Henry, Chelsea High School, Chelsea, MA.
Introduction
Using both wet labs and simulations this
unit will introduce students to the:
• role of the cell membrane as the primary mediator of
transport of material into and out of the cell
• mechanisms of diffusion and osmosis
• the relationships of temperature and molecular mass to
rates of diffusion
• role of phospholipids in the structure and function of the
cell membrane
Goals
• Master the use of the virtual molecular program.
• Describe the components and their arrangement of the cell
membrane.
• Define diffusion, osmosis, selectively permeable
membrane, and equilibrium.
• Predict the effects of temperature and mass on diffusion
rates.
• Distinguish between diffusion and osmosis.
• Explain the role of the cell membrane in passive and active
transport.
• Analyze the effects of concentration on osmosis.
• Demonstrate the formation of micelles and lipid bilayers.
Audience and Adjustments
• This unit has been designed primarily for
standard level Biology students
• With additional material the unit can be
adapted for more advanced students
• With some modification the unit can be
adapted for younger students or situations
with limited computer resources
Placement in the Curriculum
• This unit is designed to be used to supplement classroom
and lab units at the point when cell structure and function
are being introduced to students.
• Specifically this unit will be used when the role of the cell
membrane in the transport of material into and out of the
cell (passive and active transport) are discussed.
• This unit is aligned with the Massachusetts Department of
Education frameworks for Biology (section 2.5)
Time and Instructional Activities
• This unit includes four lecture type lessons and
three lab units.
• Two of the labs are combinations of wet labs and
simulations.
• The third lab is a simulation lab only.
Lessons 1 and 2: Simple Diffusion
• Students begin to explore the role of the cell membrane as
the primary mediator of movement of material into and out
of the cell.
• Students compare the properties of passive and active
transport including the role of concentration gradients and
energy requirements.
• The wet lab introduces students to the relationship between
rates of diffusion and temperature.
• Simulab 1 reinforces the wet lab and challenges students to
design an experiment to test the relationship between
molecular mass and rates of diffusion.
Sample Data from SimuLab 1: Diffusion
Temperature vs. Diffusion Time
Diffusion Time
• Temperature vs Diffusion
time.
• As temperature increases
the rate of diffusion
increases.
120
100
80
60
40
20
0
y = -20.284x + 117
0
2
4
Temperature
6
Sample Data from SimuLab 1 Diffusion
Mass vs. Diffusion Time
80
Diffusion Time
• Diffusion time vs Particle
mass.
• As mass increases the
diffusion time decreases.
• Advanced student can use
this to explore the
relationship among mass,
velocity, and kinetic
energy.
70
60
50
40
y = 2.3647x + 45.537
30
20
0
5
10
Mass of Particle
15
SimuLab 1: Diffusion, Sample Data
Lessons 3 and 4: Osmosis
• Students study the properties of osmosis as a
special form of diffusion involving water moving
across a selectively permeable membrane.
• Students conduct the traditional thistle tube
osmosis wet lab predicting the direction of
movement of sugar, water, and starch, and relate
their observations to osmosis.
• The wet lab is followed by SimuLab 2 in which
student can explore the relationship between
cellular protein concentration and the influx of
water into the cell and the relationship between
osmosis and cell size.
SimuLab 2: Osmosis, sample data
40.0
35.0
Average Cell Radius
• Varying concentrations of
“proteins” in the cell from 0 to
150 molecules
• As concentration increases the
maximum radius of the cell
increases as osmosis brings
water into the cell.
30.0
0
25
50
100
150
25.0
20.0
15.0
10.0
5.0
0.0
0
500
1000
1500
Time
2000
2500
• Initial concentration of
protein in cell vs the
maximum radius of the
cell.
• As protein concentration
increases the maximum
size the cell reaches
increases.
maximum cell radius
SimuLab 2: Osmosis, Sample data
40.0
35.0
30.0
25.0
20.0
15.0
2
y = -0.0009x + 0.2319x + 20.022
R2 = 0.9865
10.0
5.0
0.0
0
20
40
60
80
100
protein concentration
120
140
160
Lesson 6 and 7: Membrane Structure
• Students begin to study the molecular structure of
the cell membrane and relate this structure to the
mechanisms of passive and active transport.
• SimuLab 3 provides students with a simple
visualization of the formation of lipid bilayers.