Modeling Diffusion, Facilitated Diffusion, and Active Transport

Students will be able to explain the role of cell membranes as a highly selective barrier by modeling the process of diffusion, osmosis, facilitated diffusion, and active transport and collaborative discussion. Learning Objective

1.Why might you compare the cell membrane to the gates of a stadium? 2.How does the cell membrane allow only some molecules to pass through? 3.What does it mean to stay that a cell is in equilibrium? 4.Describe and give an example of passive diffusion? 5.How does water cross the cell membrane? 6.Why do some molecules like sodium and potassium require energy to cross the cell membrane? 7.Discuss 2 reasons why semipermeability is important to a cell. Pre-assessment

Modeling Passive diffusion Create a cell membrane from yarn (or other provided material) to create a semipermeable boundary Set up your model by showing oxygen molecules as shown on either side of the membrane Move molecules until they reach equilibrium (in equilibrium the number of molecules inside the cell should be the same as molecules outside the cell) Let’s get started!

 Molecules are moving not just across the membrane but also in and out of the cell  Molecules move from an area of high concentration to low concentration  No assistance is needed (no protein carrier or ATP) because the molecules are small enough and are nonpolar (non charged) Passive Diffusion

Set up your model cell with sodium and water molecules as shown on either side of the membrane Demonstrate osmosis by moving the water molecules in your model until they reach equilibrium Modeling Osmosis

Diffusion (movement of molecules from high concentration to low concentration) of water Water (polar molecule) moves through the phospholipid bilayer because of its small size without assistance Osmosis

Osmosis is a red blood cell

Set up your model with the addition of a channel protein in the membrane and glucose molecules as shown (channel proteins are embedded within the membrane) Move glucose molecules through protein channel until they reach equilibrium Modeling Facilitated Diffusion

A form of passive transport (no energy required) that allows molecules that are too large to pass through the membrane to pass through with the help (facilitation) of a channel protein. Movement is still from an area of high concentration to low concentration Glucose is an example of a molecule that uses facilitated diffusion Facilitated Diffusion

Set up your model by showing sodium, water, and ATP as shown on either side of the membrane Move the sodium molecules across the membrane using the channel protein (in active transport, molecules require energy in the form of ATP to cross the channel) Note: 1 ATP can move 3 sodium molecules! Modeling Active Transport

The use of ATP to move molecules through a channel protein to cross a membrane Movement of molecules is from an area of low concentration to an area of high concentration Ions (charged particles) like sodium and potassium use active transport to move in or out of a cell Active Transport

Passive Transport vs Active Transport