Biology Action Model— Diffusion, Facilitated Diffusion and
Active Transport
Teacher Guide
Topic
Semi-permeability and transport across cell membrane: Diffusion, Facilitated Diffusion, and Active
Transport
Objectives/Goals
•
•
Students will explain and demonstrate how a concentration gradient affects diffusion across cell
membrane
Students will describe and demonstrate how basic organic and inorganic compounds move across
membranes
• Passively by diffusion and facilitated diffusion
• Actively through active transport using ATP
California State Standards
California State Standard 1a. Students know cells are enclosed within semi-permeable membranes that
regulate their interaction with their surroundings.
Vocabulary
concentration
concentration gradient
semipermeable
diffusion
osmosis
passive diffusion
facilitated diffusion
homeostasis
lipid bilayer
Pre-requisite Knowledge
Students need to have knowledge of basic organic and inorganic compounds. Students need to have
knowledge of basic structure and function of the cell membrane.
Time
It is recommended that all model pieces be prepared at home to save time. The pre-activity questions
can also be done at home to save time. When this is done, the guided practice and assessment can
happen in one 55 minute class period.
a. For All Activities
b. Per Activity
• Background Reading and Questions
• Vocabulary Practice
• Creating the Model
• Guided Practice with Model
• Model Assessment
(teacher)
c. Optional Extension Activities
• Storyboard:
Two 55 minute class periods
20 minutes
10 minutes
25 minutes
30 minutes
25 minutes
30 minutes
Materials (per Group of 4 Students)
• 2 copies of Action Model Templates of molecules on colored paper
(Teacher Guide pp. 20-22)
• Scissors—one pair per student
• Suggested models for cell membrane=yarn, clay, or simple drawing that represents
cell membrane in guided practice and situations.
• One copy each of the Student Directions
Optional: Print molecules on white paper or have students color using colored pencils/ crayon as prelab.
Directions about the Model
This model will allow students to demonstrate an understanding of diffusion, osmosis, facilitated
diffusion, and active transport.
Suggested model construction and set-up: Students can construct their own cell membrane from yarn,
clay, or even drawing on paper to model each situation set in the biology action model. Students should
cut out model pieces and complete any coloring the day before or at home. If the resources are
available it may be more efficient to create one class set. Have one class of students color molecules or
print molecules on colored paper then laminate them for continued practice.
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Instructions: Model to the class before having students model independently or in pairs, especially for
beginning students. It is important to guide students through the movement of molecules through the
model of the cell membrane.
Passive Diffusion
In the osmosis model, students should move water molecules across the cell membrane until the
molecules reach equilibrium. Provide a variety of examples and using the “Questions for model” to
check for understanding (see Rubric p.2).
Emphasize that molecules are moving not just across the cell membrane but also in and out of the cell.
After modeling as a class, have students model passive diffusion in pairs or independently. Use the
provided Rubric to assess whether students are ready for the cell situations A and B.
Facilitated Diffusion and Active Transport
Show students examples of protein channels using the handout provided. Emphasize protein channels
require ATP molecules to move ions like sodium and calcium molecules in and out of the cell. Note:
The model shows one molecule of ATP on a protein channel being used to move three sodium
molecules. Explain to students this is an example of how a sodium pump may move molecules, but
number of ATP molecules needed to move a molecule varies. Depending on skill level you may also
explain protein channels change shape during active transport.
As an extension create other scenarios for students to demonstrate using the model.
Rubric for Assessment: Use the rubric below after guided and independent practice
Encourage students to use vocabulary terms in their explanations.
Scoring Guide for Student Groups
On the following page are questions which can be used during the modeling processes to assess
whether the students are able to demonstrate mastery on each part of the Action Model. Keep in mind
that these are only suggested guiding questions and may be modified to suit the level of your students
and your curriculum. You will need to make one scoring guide per group.
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Scoring Guide
Students _____________________________________________________________
Model Activity
Identifying the
Pieces
Passive Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Example Questions
Evaluation
Ask students to:
a) identify all major pieces of the model.
1 2 3 4 5
Ask students to:
a) demonstrate in which direction
molecules move passively across a
membrane.
b) explain why molecules move in
this direction
Ask students to:
a) demonstrate in which direction
water molecules move across a
membrane.
b) explain why water molecules
move in this direction.
Ask students to:
a) explain what a membrane
channel protein is.
b) demonstrate how glucose
molecules move across the
membrane.
1 2 3 4 5
1 2 3 4 5
Ask students to:
a) explain the difference between
diffusion and active transport.
b) demonstrate active transport
Situation A: The cell How will oxygen molecules move and
is deficient in water
why?
and oxygen and high
in glucose.
Situation B: A cell is
deficient in oxygen
and high in sodium.
1 2 3 4 5
How will sodium molecules move and
why?
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1 2 3 4 5
1 2 3 4 5
Rubric Performance
Description
1
Poor
Unable to communicate or move model pieces
2
Unsatisfactory
Somewhat able to communicate and model,
some confusion with vocabulary and/or
molecule movement; constant reference to
student directions/vocabulary.
3
Satisfactory
Able to communicate using basic vocabulary
and models basic movement; some references
to student directions/vocabulary.
4
Good
Clearly communicates using vocabulary and
effectively models movement of molecules; has
good grasp of concept. Rare reference to
student directions/vocabulary.
5
Excellent
Clearly communicates using vocabulary and
effectively models movement of molecules.
Clearly grasps concept without reference to
student directions/vocabulary.
Pre-, Guided Practice, and Post-Modeling Assessments/Keys
Student Pre-lab Questions—Answers
1. Why could you compare the cell membrane to gates of a stadium?
The cell membrane controls which molecules enter and leave the cell.
2. How does the cell membrane allow only some molecules to pass through?
The physical and chemical structure of the cell membrane allows some molecules to pass more
easily than others.
3. How is homeostasis similar to equilibrium? How are they different?
Homeostasis the maintenance of chemicals at a certain concentration. At equilibrium, chemical
concentrations are the same inside and outside the cell.
4. Describe and give an example of passive diffusion.
Passive diffusion occurs when a molecule moves from an area of higher concentration to an area of
lower concentration, such as oxygen moving across a cell membrane.
5. How does water cross the cell membrane?
Water moves by passive diffusion across a cell membrane—osmosis.
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6. Why do some molecules like sodium and potassium require energy to cross the cell membrane?
They have to be moved against a concentration gradient, which requires energy.
7. Discuss two reasons why semipermeability is important to a cell.
It helps keep unwanted molecules out, and allows the cell to take in nutrients.
Guided Practice with Answers
Guided Practice: (Teacher) Although students have copies of both the pictures and teacher prompts, be
sure to check for understanding individually or in small groups. Be sure students set up models as
shown below before movement.
Prompt students to draw a cell membrane or construct one from yarn. (See suggested materials in
Directions)
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Passive Diffusion: (Before)
Passive Diffusion: (After)
O2
Inside cell
O2
Outside Cell
Yarn= semipermeable
membrane
Directions for Passive Diffusion
Model
1. Set up your model by showing
oxygen molecules as shown above
on either side of the cell membrane.
2. Show how molecules move by
passive diffusion using your model
pieces.
3. Move oxygen molecules until they
reach equilibrium.
Recall, in equilibrium number of
molecules inside the cell should be
the same as molecules outside the
cell.
Inside cell
Outside cell
Questions for your model: Answer
the questions below and be prepared
to use your model to answer these
questions for your teacher.
1. Explain what causes oxygen
molecules to move across the
membrane. Oxygen molecules
move from an area of high to low
concentration.
2. What is passive diffusion? When
molecules move from an area of high
to low concentration.
3. What are some molecules that can
move by passive diffusion? Oxygen,
water, carbon dioxide
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Osmosis: (Before)
Osmosis: (After)
Na+
H2O
Yarn=Semipermeable
Membrane
Inside Cell
Na+
H2O
Inside cell
Outside cell
Outside Cell
Directions to model Osmosis
1. Create a cell membrane from yarn=
semipermeable membrane which
allows water to pass, but not
sodium.
Questions for your model: Answer
the questions below and be prepared
to use your model to answer these
questions for your teacher.
1. In the beginning, there is more
2. Set up your model with sodium and
Sodium inside the cell. There is
water molecules as shown above on
more water outside the cell.
either side of the cell membrane.
2. Explain why water molecules move
3. Demonstrate osmosis by moving the
across the membrane. They move
water molecules in your model.
from an area of higher
concentration to an area of lower
4. Practice moving water molecules
concentration of water.
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across the cell membrane until they
reach equilibrium.
3. After the diffusion of water, how
much water is inside the cell
compared to outside the cell? Why?
How much sodium? Why? The
amount of water is equal. It moves
until the concentrations are equal in
side and outside. The sodium does
not move; the membrane stops it.
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Facilitated Diffusion: Before
Facilitated Diffusion: After
Glucose
Glucose
Inside cell
Channel Protein
Channel Protein
Outside Cell
Inside Cell
Directions to Model Facilitated
Diffusion
1. Set-up your model as shown above.
Place a channel protein in the
membrane and glucose molecules
outside the membrane.
Recall channel proteins are embedded
within the membrane
2. Using your model demonstrate
facilitated diffusion by moving the
glucose molecules through the protein
channel.
3 Practice moving glucose molecules
across the cell membrane to show
facilitated diffusion.
Outside Cell
Questions for your model: Answer
the questions below and be prepared
to use your model to answer these
questions for your teacher.
1. Why do glucose molecules require a
channel protein? They are too large
to fit through the membrane.
2. How is the transport of glucose the
same as passive diffusion? How is it
different? Same =Glucose moves
from high to low concentration.
Different= It requires a membrane
channel protein.
3. Why is the diffusion of glucose
“facilitated”? It requires a membrane
channel protein.
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Active Transport: (Before)
ATP
Channel
Protein
Na+
Active Transport: (After)
H2O
ATP Channel
Protein
Inside cell
Na+
H2O
Outside cell
Inside cell
dgdDirections to model Active Transport
1. Set-up your model by showing sodium,
water molecules, and ATP as shown
above on either side of the cell
membrane.
2. Demonstrate active transport by moving
the sodium molecules across the
membrane in your model.
Recall, in active transport molecules require
energy in the form of ATP to cross the
channel.
Outside cell
Questions for your model: Answer the
questions below and be prepared to use
your model to answer these questions for
your teacher.
1. Describe and explain how sodium
molecules move across the membrane.
Active Transport
2. What is necessary for a molecule to
move with active transport? ATP
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4. Place an ATP molecule on the channel
protein to model energy in this process.
5. You can move three sodium molecules
through the channel protein with one
ATP.
Note: The energy provided by ATP, not
concentration gradients, moves
molecules in active transport. Molecules
do not need to reach equilibrium.
3. Why do molecules like sodium enter
the cell by active transport and not
passive diffusion?
They must move against the
concentration gradient.
4. Give an example of a cell that uses
active transport to move molecules
across its membrane.
A neuron
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Cell A: Students should set up the cell as shown. (Low in oxygen and water and low in
glucose) Be sure to direct them how to make the cell membrane.
Students should use the concepts from practice to describe and model how molecules
move by active transport, osmosis, and/ or passive diffusion.
A cell with a high concentration of glucose outside may use facilitated transport to move glucose
into the cell through the large protein channel.
Although water appears in equilibrium it will continue to pass in and out of the cell equally by
passive diffusion. Oxygen molecules will diffuse passively into the cell.
Note: There is no ATP in this model.
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Cell B: Low in oxygen and water and high in sodium. Be sure to direct them how to make
the cell membrane. Students should use the concepts from practice to describe and model
how molecules move by active transport, osmosis, and/ or passive diffusion.Water
molecules will move into the cell by osmosis because there is a high concentration outside the cell
membrane. Oxygen molecules will move inside the cell by passive diffusion because there is a
higher concentration outside the cell. Sodium molecules will be pumped out of the cell against the
concentration using ATP to access the protein pump.
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Cell C: (Practice and review). Allow students time to practice modeling and explaining
examples of diffusion, osmosis, and active transport using all model cut-outs. Encourage
them to create their own scenarios. Students should be assessed individually or in pairs
using the rubric provided to show understanding of semi-permeability in membranes.
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Post Lab Assessment
1. Which of the following processes requires no energy but needs a channel protein?
a. passive diffusion
b. osmosis
c. facilitated diffusion
d. active transport
2. Which of the following processes requires energy to cross the cell membrane?
a. osmosis
b. passive transport
c. facilitated diffusion
d. active transport
3. One way osmosis is similar to diffusion is:
a. both require energy
b. molecules move against a concentration gradient
c. molecules move from a high concentration to low concentration
d. both require water
4. The cell membrane of the red blood cell will allow water, oxygen, carbon dioxide, and glucose
to pass through. Because other substances are blocked from entering, this membrane is called
a. permeable
b. perforated
c. open
d. semi-permeable
5. A nerve cell uses _______________ transport to pump ______ molecules across in a nerve
cell in a nerve impulse.
a. active, sodium
b. facilitated, calcium
c. passive, oxygen
d. osmosis, water
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6. Glucose crosses the cell membrane by
a. osmosis
b. facilitated diffusion
c. photosynthesis
d. diffusion
7. The cell membrane could best be compared to
a. a gate
b. a wall
c. the brain
d. a red blood cell
Post Lab Assessment Key:
1. c
2. d
3. c
4. d
5. a
6. b
7. a
Extensions: Storyboarding
Have students use the 6 cells on the following page to storyboard the events in passive diffusion,
osmosis, facilitated diffusion, and active transport.
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1.
2.
Caption:____________________________ Caption:__________________________
Description:__________________________Description: ______________________
4.
3.
Caption:_____________________________ Caption:________________________
Description:__________________________ Description: ____________________
5.
6.
Caption:_____________________________ Caption:_______________________
Description:__________________________ Description: ___________________
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Model Pieces
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
H2 O
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Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Glucose
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Glucose
Glucose
Glucose
Glucose
Glucose
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ATP
ATP
Channel Proteins
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