2. Diffusion and Osmosis

3. Diffusion Particles in a liquid or gas spread out… … from regions of high concentration… … to regions of low concentration… …until the particles are evenly spread out. Dissolving KMnO 4 crystal

4. The difference between the regions of high concentration and low concentration is called the concentration gradient The steeper the concentration gradient, the faster diffusion takes place High concentration gradient Fast rate of diffusion Low concentration gradient Slow rate of diffusion

5. Diffusion occurs because the particles in gases and liquids are moving.

6. Dissolving substances in water The molecules in liquid water are constantly moving When water molecules bump into particles of a soluble substance, they stick to them Free moving water molecules Sugar molecules in sugar lump

7. When the water molecules move away… … they carry particles of the solute with them

8. Adding a solute to water reduces the amount of free water molecules Free water molecules Solute molecule

9. Partially-Permeable Membranes A partially-permeable membrane will allow certain molecules to pass through it, but not others. Generally, small particles can pass through… Partially permeable membrane …but large particles cannot

10. Partially-permeable membrane More free water molecules on this side of membrane Water-solute particle is too large to pass through membrane Free water molecules diffuse in this direction

11. Osmosis Osmosis is the diffusion of free water molecules… … from a region of high concentration of free water molecules… … to a region of low concentration of free water molecules… …across a partially-permeable membrane… …until they are evenly spread out.