1. AIM: How does diffusion and the cell membrane help maintain homeostasis?

2. The amount of a substance
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

3. It’s all about concentration

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

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

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

7. YES 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:
There must be a concentration
gradient
2) There must be no barrier blocking
the movement of particles.

10. What is a concentration gradient?
The difference in concentration
between an area of high concentration and an area of
lower concentration.
Does this picture illustrate a concentration gradient?

11. Identify which pictures illustrates a concentration gradient:

12. What do we mean by a barrier?
Anything serving to stop the passage of objects.
Ex. the CELL MEMBRANE

13. YES NO Will diffusion take place? Will diffusion take place now?
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 able to pass?
SIZE

17. 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
Blank = homeostasis

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

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