1. 3.4 Diffusion and Osmosis
Somewhere on pg. 30 or 31
If the cell membrane was rigid (solid or hard), as opposed to fluid (oil or liquid like), explain why the membrane would no longer be selectively permeable.

2. The phospholipids would be unable to move to allow material in or out!
3.4 Diffusion and Osmosis
If the membrane was rigid:
The phospholipids would not be able to move from side to side or slide past one another
The phospholipids would be unable to move to allow material in or out!

3. 3.4 Diffusion and Osmosis
Standard
1.a Students know cells are enclosed within a semipermeable membranes that regulate their interaction with their surroundings.

4. 3.4 Diffusion and Osmosis
KEY CONCEPT Materials move across membranes because of concentration differences.

5. 3.4 Diffusion and Osmosis
Solution: A homogenous mixture of two or more substances, which may be solids, liquids, or gases, or the combination of these.
Ex: Salt water
Solute: Substance dissolved in another substance
Ex: Salt
Solvent: Substance doing the dissolving (usually the substance present in the greatest amount)
Ex: Water

6. Which one is the Solute? Solvent? Solution?
Water Colored Water Food Coloring
Solution
Solvent
Solute
Air Nitrogen (78%) Oxygen, argon, CO2 (22%)
Solution
Solvent
Solute

7. 3.4 Diffusion and Osmosis
Passive transport- the movement of molecules across a cell membrane without energy input from the cell
There are two types of passive transport.
1. diffusion
2. osmosis

8. 3.4 Diffusion and Osmosis
Diffusion: is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.

9. 3.4 Diffusion and Osmosis
Diffusion: is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.

10. 3.4 Diffusion and Osmosis
Diffusion: is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.

11. Concentration gradient- the difference in the concentration of a substance from one location to another.
Molecules diffuse down their concentration gradient

12. Diffusion Demonstration (Mini Lab)
Materials: 2 Cups, Water, Dye, Salt,Graph
Identify the solvent, solute, and solution for each demonstration
Hypothesize what is going to happen when you drop the food coloring in the water. Salt in the water?
Did your hypothesis match the results?
Explain how these experiments demonstrated diffusion

13. 3.4 Diffusion and Osmosis
Osmosis is the diffusion of water molecules across a semipermeable membrane.
Sugar molecules
Water molecules

14. 3.4 Diffusion and Osmosis There are three types of solutions.
Same amount of solutes/water inside and outside cell
= amounts of water enter and leave the cell
Stays the same size!
More solutes outside the cell
More water inside the cell
More water exits cell
Shrinks!
Less solutes inside the cell
More water outside cell
More water enters cell
Expands!

15. Osmosis Demonstration (Mini Lab)
Materials: 3 cups (labeled), 3 grapes, water, grape juice, sugar, and a scale
Label each cup: Water, Sugar water, grape juice
Hypothesize what is going to happen when you put a grape in each solution?

16. Weigh a grape- record its weight in the “Before the grape juice” box
Place the grape in the grape juice cup
Next partner, weigh a grape, record its weight in the “Before the water” box
Place the grape in the water cup
Next partner, weigh a grape, record its weight in the “Before the Sugar Water” box
Place the grape in the sugar water
Wait 24 hrs and record the weight of the grapes

17. Grapes after 24 hrs
Dry off your first grape- be careful!
Weigh your grape and record the results
Repeat these steps for each of the remaining grapes (Don’t mix them up!)
Did your hypothesis match the results?
Explain how this experiment demonstrated osmosis

18. 3.4 Diffusion and Osmosis
Some molecules cannot easily diffuse across the cell membrane.
Facilitated diffusion is diffusion through transport proteins.