Homeostasis and Transport Part I Passive Transport Diffusion

Homeostasis and Transport Part I: Passive Transport

Diffusion n 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 n http: //www. biosci. ohiou. edu/introbioslab/Bios 170/diffusion/Diffusion. html n n n

Diffusion across membranes n Molecules that dissolve in lipids can cross the lipid bilayer through diffusion. Example: O 2 and CO 2.

Osmosis n n 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/

Direction of movement into cells n Hypotonic to the cytosol – solution outside the cell is less concentrated than inside the cell – water moves into the cell n Hypertonic to the cytosol – solution outside the cell is more concentrated than inside the cell – water moves out of the cell n Isotonic – concentrations are equal n http: //www. tvdsb. on. ca/westmin/science/sbi 3 a 1/Cells/Osmosis. htm

Predicting water movement n http: //www. mhhe. com/biosci/esp/2001_gbio/folder_structure/ce/m 3/s 3/cem 3 s 3_3. htm

Active Transport n n n Endocytosis Active Transport Movie 1 Active Transport Movie 2