1. Diffusion and Osmosis Passive Movement into and out of cells H2O Solutes Cell Membrane Membranes 1

2. Molecules can move long distances 2 3. Solutes Solutes Cell Membrane Molecules diffuse in and out of cells. 3 4. Diffusion is spontaneous and passive DIFFUSION H2O Energy is always required for movement in and out Active transport uses energy from the cell in the form of ATP and facilitating proteins. Passive transport does not require energy from the cell. It is powered by spontaneous molecular movement. 4 5. Why do molecules move at all? Where do they get their energy? DIFFUSION H2O Heat causes random movement of molecules. H2O 5 6. Brownian Movement the movement of small particles in response to collision with water molecules. Can we see molecules move? Molecular Movement H2O The answer is no. H2O 6 7. Defining Diffusion Working Definition 1 Diffusion is the net movement of molecules from an area of high concentration, pressure, and/or temperature to an area of low concentration, pressure, and/or temperature. H2OH2O 7 8. Defining Diffusion Temperature + Concentration + Pressure = Free Energy All three factors combine as the Free Energy of molecules. Molecules diffuse from high free energy to low free energy. H2OH2O 8 9. Defining Diffusion Working Definition 2 Diffusion is the net movement of molecules from an area of high free energy to an area of low free energy. H2O Final Definition of Diffusion Diffusion is the net movement of molecules from an area of high concentration to an area of low concentration. H2O 9 10. Defining Diffusion Final Definition of Diffusion The NET movement of molecules from an area of high concentration to an area of low concentration. H2OH2O 10 11. Left Right High Concentration Low Concentration DIFFUSION Concentration Gradient 11 12. High Concentration Low Concentration DIFFUSION Net Movement 12 13. Left Right Equilibrium Concentrations Diffusion Stops at Equilibrium 13 14. Concentration Gradient Concentration Gradient 14 15. Concentration Gradient Concentration Gradient Diffusion Diffusion 15 16. Equilibrium of and Diffusion Stops at Equilibrium 16 17. H2O Solutes Cell Membrane Diffusion is driven by heat. Diffusion is the net movement of molecules from an area of high free energy to an area of low free energy. Free energy gradients in biological systems are usually determined by concentration differences. When diffusion of molecules eliminates the concentration gradient, then equilibrium is achieved diffusion stops. In Summary: 17 18. 18 Photo Credits Slide 2: Masterfile RF Line Art Credits Slide 1, 2-10, 17: Peter Raven, Biology, 9e 2011 reproduced with permission of McGraw-Hill Education; Sylvia Mader, Biology 10e 2010 reproduced with permission of McGraw-Hill Education