2. How does the process of diffusion and the structure of the cell membrane help the cell maintain homeostasis?

3. What is diffusion? The net movement of particles from where they are more concentrated to where they are less concentrated. What do we mean by concentration? The amount of a substance

4. It’s all about concentration

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

6. Why are particles always moving? ENERGY Particles are in constant motion because they have energy

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

8. 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 Dynamic Equilibrium

9. An illustration of diffusion:

10. Two Conditions for Diffusion: 1)There must be a concentration gradient 2) There must be no barrier blocking the movement of particles.

11. What is a concentration gradient? The difference in concentration between a region of high concentration and a region of lower concentration. Does this picture illustrate a concentration gradient?

12. Identify which pictures illustrates a concentration gradient.

13. 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.

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

15. 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.

16. Why do some things get through the cell membrane? Small molecules are more likely to get through the cell membrane compared to big molecules

17. Helping Cells Survive Cell membranes must help organism maintain HOMEOSTASIS by controlling what substances enter or leave the cells. To stay alive, a cell must exchange materials such as food, water, and waste with its environment.

18. 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

19. Which structure may function in the recognition of chemical signals?(1) A (3) C (2) B (4) D The diagram to the right represents a portion of a cell membrane.

20. State one possible reason why molecule A could diffuse across the membrane of the cell but molecule B could not. Two molecules, A and B, and their distribution inside and outside of a cell are represented in the diagram to the right.