1. Diffusion
Diffusion – net movement of particles from an area of higher concentration to an area of lower concentration
Caused by random movement
Is a slow process because it relies on the random molecular motion of atoms

2. Rate of Diffusion Three key factors affect the rate of diffusion:
1. Concentration. The most important factor. The more the concentrated the substances, the faster diffusion occurs.
2. Temperature. Increased temperature can speed diffusion because of more rapid molecular movement
3. Pressure. Increased pressure will accelerate molecular movement and speed up diffusion.

3. The Result of Diffusion
Eventually, the two different concentrations (the concentration gradient) will be distributed evenly.
This is called dynamic equilibrium.
Diffusion is one of the methods that cells move substances in and out of the cell

4. Osmosis
Osmosis – the diffusion of water across a selectively permeable membrane
Regulating water is a very important factor in maintaining homeostasis in the cell.

5. What controls Osmosis?
If two solutions are separated by a selectively permeable membrane…
Water will flow to the side of the membrane where the water concentration is lower
However, the substances in the water are prevented from moving and keep their original concentrations.
Therefore, osmosis is controlled by a concentration gradient, that is an unequal distribution of particles across a membrane.
Movement from a low solute concentration (high water potential) to a solution with high solute concentration (low water potential)

6. Your Turn! Which way will the water go?
On your sheet, record what will happen to the red blood cells in each of these three cases:
Red Blood Cells (5% salt) in
40% Salt Solution
5% Salt Solution
Pure Water (0% salt solution)

7. Check your work!

8. How Osmosis affects cells: Isotonic Solution
All cells are subject to osmosis since they are surrounded by water.
In an Isotonic Solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.
There is equal flow and water goes in both directions.
Therefore, cells retain their original shape since the water concentrations are equal.

9. How Osmosis affects cells: Hypotonic Solution
In an Hypotonic Solution, the concentration of dissolved substances in the solution is lower than the concentration of dissolved substances inside the cell.
Therefore, there is more water outside the cell than inside & water flows in!
Animal cells may burst
Plant cells become more rigid…
how does this explain the misting machines in the produce section of grocery stores?

10. How Osmosis affects cells: Hypertonic Solution
In an Hypertonic Solution, the concentration of dissolved substances in the solution is higher than as the concentration of dissolved substances inside the cell.
Therefore, there is less water outside the cell than inside & water flows out!
Animal cells shrink
Plant cells become less firm called plasymolysis…
How does this explain why plants will wilt without water?

11. Passive Transport
Passive Transport When the cell uses NO ENERGY to move particles across the membrane via DIFFUSION
Includes Water, Lipids, and Lipid-Soluble proteins
Why? The membrane is attracted to them.

12. Facilitated Diffusion
Type of Passive Transport with the aid of Transport Proteins is called Facilitated Diffusion
Includes Sugars and Amino Acids
Fast and specific, but does not use energy!
Driven by a concentration gradient

13. Active Transport
Active Transport is the movement of materials through a membrane against a concentration gradient.
Often called “pumps” such as Calcium, Potassium and Sodium
Requires ENERGY from the cell
Which organelle supplies this energy?
MITOCHONDRIA

14. How Active Transport Works
Each Transport Protein (also called a Carrier Protein) binds to its unique ion
Energy is supplied to change the shape of the protein to allow the ion to pass
Types of Active Transport:
Endocytosis = cell surrounds and takes in material from the environment (via vacuoles)
Phagocytosis = means “cell eating” The Cytoplasm surrounds a particle and packages into a vacuole.
Exocytosis = expulsion or secretion of materials from the cell
Used to expel wastes or indigestible materials, release hormones