2. AIM: How does the process of diffusion and the structure of the cell membrane help the cell maintain homeostasis? DN: Can all substances move through the cell membrane? What determines what substances are able to move through the cell membrane? Give an example of a substance that can move through the cell membrane and an example of a substance that cannot move through the cell membrane. HW: Page 198-199 #15,16,26,27

3. What is diffusion? The movement of particles from an area of high concentration to an area of low concentration.

4. What do we mean when we say concentration? The amount of a particular substance

5. The reason diffusion occurs is because molecules are always… MOVING

6. What is the end result of diffusion? The number of particles are now evenly distributed This is called: Dynamic Equilibrium

7. Dynamic Equilibrium At this point, the number of particles have spread themselves out equally throughout the beaker. Are the particles still moving after dynamic equilibrium has been reached? YES

8. An illustration of diffusion:

9. Two Conditions for Diffusion: 1) concentration gradient 2) no barrier blocking the movement of particles.

10. What is a concentration gradient? The difference in concentration between a region of high concentration and a region of lower concentration.

11. What do we mean by a barrier? Will diffusion take place? YES Will diffusion take place now? NO The particles must be free to move down their concentration gradient in order for diffusion to occur.

12. Does diffusion take place across the cell membrane? Yes, the cell is: Selectively Permeable

13. Cell Membranes are: Selectively Permeable A selectively permeable membrane allows some substances to cross the membrane more easily than others and blocks the passage of other substances altogether.

14. Cell Membranes help organisms maintain By controlling what substances may enter or leave cells. To stay alive, a cell must exchange materials such as food, water, and wastes with its environment. HOMEOSTASIS

16. What is the main job of the cell membrane? Cell membranes helps organisms maintain _____________ by controlling what substances may enter or leave cells To stay alive, a cell must exchange materials such as food, water, & wastes with its environment HOMEOSTASIS & TRANSPORT