Day 1: Passive Transport: Diffusion, Osmosis, Facilitated Diffusion
Note: Dialysis tubing can be used to demonstrate diffusion instead of the plastic sandwich bags, following the procedure shown below:
1. Obtain a piece of dialysis tubing. Tie a knot at one end then fill it 1/4 with water.
2. Make sure the tube does not leak. Empty the water out of the tubing.
3. Add 3 teaspoons of corn starch to the tubing.
4. Squeeze the air out of the tubing. Tie a knot on the open end.
5. Rinse off the tubing under running water.
6. Fill a 250-mLbeaker 3/4 full with water. Add 10 to 15 drops of iodine and stir.
7. Place a paper clip around each knot in the tube. Hang the tube in the beaker of water.
This lab will help students understand about how diffusion works with a selectively permeable (or “semipermeable”) cell membrane. You may choose to have small groups of students do the lab, or you can set it up as a demonstration.
Give students the Diffusion Lab worksheet (S-B-7-3_Diffusion Lab and KEY.doc). Read the introduction with students and define selectively permeable membrane. Follow the procedure to set up the lab activity, and have students answer the questions on the worksheet while they are waiting for about fifteen minutes. Then, have them observe the changes and answer the post-lab questions.
Students may think that the iodine “ate through” the bag. Explain that the bag has tiny pores in it like a window screen and that iodine is a small molecule that can pass through the openings.
Show students the Plasma Membrane Diagram (S-B-7-3_Plasma Membrane Diagram.doc). Explain that the plasma membrane is selectively permeable to allow only certain materials to pass in and out. Describe the parts of the plasma membrane and explain the functions of proteins as channels and pumps for transporting materials and carbohydrates as chemical identification tags for other cells. Explain that scientists today use the fluid mosaic model, a widely accepted model of the plasma membrane in which proteins are embedded in lipids.
Instruction continues by handing out Comparing Types of Transport across the Plasma Membrane (S-B-7-3_Comparing Types of Transport and KEY.doc). Tell students to fill in the chart as you go through the PowerPoint on passive transport.
Show students the Passive Transport PowerPoint (S-B-7-3_Passive Transport PPT.pptx). Make sure that they understand that passive transport does not require energy because it is the movement of materials in the direction of the concentration gradient.
If time permits, show students an osmosis animation at www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf. Before you press the “Add Salt” button, have students predict what will happen to the movement of water molecules.
Day 2: Active Transport: Pumps, Endocytosis, Exocytosis
Warm-up the lesson for today: “What is the role of ATP in photosynthesis and cell respiration?” (ATP stores energy in its chemical bonds. Photosynthesis produces ATP, and cell respiration uses the energy stored in ATP to break down glucose to release energy.)
Use a projector to show students the interactive ATP and Energy Storage animation at http://biologyinmotion.com/atp/index.html. Read through the short tutorial about the role of ATP and then have students explain what is happening at each stage of the animation.
Show students the Endocytosis and Exocytosis diagram (S-B-7-3_Endocytosis and Exocytosis.doc).
Have students take out Comparing Types of Transport across the Plasma Membrane (S-B-7-3_Comparing Types of Transport and KEY.doc). Tell students to continue filling in the chart as you go through the PowerPoint on active transport.
Show students the Active Transport PowerPoint (S-B-7-3_Active Transport PPT.pptx). Make sure that they understand that active transport requires energy from the cell because it is the movement of materials against the direction of the concentration gradient.
Review the role of ATP (and ADP) in active transport.
Define homeostasis as the process by which organisms maintain a stable internal environment. Have students write a sentence that explains the relationship between active transport and homeostasis. (Example: Cells take in or remove materials through active transport to keep a balance inside the cell.)
- Students who might need an opportunity for additional learning can create a concept map that organizes the ways cells move materials in and out (active and passive transport mechanisms).
- Students who might need an opportunity for additional learning can draw diagrams that symbolize each of the different types of passive and active transport.
- Students who might need an opportunity for additional learning can view the animations for active and passive transport on the Web sites provided in the Related Resources section.
- Students who might need an opportunity for additional learning can write a one-sentence summary for each type of active and passive transport.
- Students who may be going beyond the standards can design and carry out an experiment to demonstrate how osmosis affects plant cells (e.g., placing plant cells on a wet mount slide in hypertonic and hypotonic solutions and observing the results).