Homeostasis and Transport

1. Homeostasis and Transport Part I: Passive Transport

2. Diffusion • Diffusion is the movement of molecules from a higher concentration to a lower concentration. • The difference in concentration of two solutions is called the concentration gradient • Diffusion is driven by kinetic energy • Demonstration: food coloring in water • http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html

3. Molecules that dissolve in lipids can cross the lipid bilayer through diffusion. Example: O2 and CO2. Diffusion across membranes

4. Osmosis • Think back to solutions: solutes and solvents • Osmosis is the process by which water molecules diffuse across a cell membrane from an area of lower solute concentration to an area of higher solute concentration. • Direction of movement depends on relative concentrations of solutions. • http://www.colorado.edu/epob/academics/web_resources/osmosis/

5. Direction of movement into cells • Hypotonic to the cytosol • solution outside the cell is less concentrated than inside the cell • water moves into the cell • Hypertonic to the cytosol • solution outside the cell is more concentrated than inside the cell • water moves out of the cell • Isotonic • concentrations are equal • http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

6. Predicting water movement • http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s3/cem3s3_3.htm

7. Active Transport • Endocytosis • Active Transport Movie 1 • Active Transport Movie 2