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 diffusion facilitated diffusion concentration gradient osmosis homeostasis semipermeable passive diffusion 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.

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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 Two 55 minute class periods b. Per Activity • Background Reading and Questions 20 minutes

• Vocabulary Practice 10 minutes • Creating the Model 25 minutes • Guided Practice with Model 30 minutes • Model Assessment (teacher) 25 minutes c. Optional Extension Activities

• Storyboard: 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 pre-lab. 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 Example Questions Evaluation Identifying the Pieces

Ask students to: a) identify all major pieces of the model.

1 2 3 4 5

Passive Diffusion

Ask students to: a) demonstrate in which direction molecules move passively across a membrane. b) explain why molecules move in this direction

1 2 3 4 5

Osmosis

Ask students to: a) demonstrate in which direction water molecules move across a membrane. b) explain why water molecules move in this direction.

1 2 3 4 5

Facilitated Diffusion

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

Active Transport

Ask students to: a) explain the difference between diffusion and active transport. b) demonstrate active transport

Situation A: The cell is deficient in water and oxygen and high in glucose.

How will oxygen molecules move and why?

1 2 3 4 5

Situation B: A cell is deficient in oxygen and high in sodium.

How will sodium molecules move and why?

1 2 3 4 5

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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) O2

Passive Diffusion: (After) O2

Inside cell Outside Cell

Inside cell Outside cell

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.

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

Yarn= semipermeable membrane

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Osmosis: (Before)

Na+ H2O

Osmosis: (After)

Na+ H2O

Inside Cell Outside Cell

Inside cell Outside cell

Directions to model Osmosis 1. Create a cell membrane from yarn=

semipermeable membrane which allows water to pass, but not sodium.

2. Set up your model with sodium and

water molecules as shown above on either side of the cell membrane.

3. Demonstrate osmosis by moving the

water molecules in your model. 4. Practice moving water molecules

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

Sodium inside the cell. There is more water outside the cell.

2. Explain why water molecules move

across the membrane. They move from an area of higher concentration to an area of lower concentration of water.

Yarn=Semipermeable Membrane

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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

Inside cell Outside Cell

Inside Cell Outside 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.

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.

Glucose

Channel Protein

Channel Protein

Glucose

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Active Transport: (Before)

ATP Channel Na+ H2O Protein

Active Transport: (After)

ATP Channel Na+ H2O Protein

Inside cell Outside cell

Inside cell Outside 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.

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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2.

Caption:____________________________ Caption:__________________________ Description:__________________________Description: ______________________ Caption:_____________________________ Caption:________________________ Description:__________________________ Description: ____________________ Caption:_____________________________ Caption:_______________________ Description:__________________________ Description: ___________________

1.

3.

5. 6.

4.

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Oxygen

Model Pieces

Oxygen

Oxygen Oxygen

Oxygen

Oxygen

Oxygen

Oxygen

H2O

H2O

H2O

H2O H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O H2O

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Na+

Na+

Na+ Na+ Na+ Na+ Na+

Na+

Na+ Na+

Na+ Na+ Na+ Na+ Na+

Na+ Na+ Na+ Na+

Na+

Glucose

Glucose

Glucose Glucose

Glucose

Glucose

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Channel Proteins

ATP ATP