1. Membrane Function
Learning Target: I can explain how cell membranes interact with their environment

2. Entry Task:
Predict what will happen when the mint plant is moved from regular water to salt water.
Draw a picture to explain your thinking.

3. Mint plants after 2 hours in salt water

4. Mint plants transferred back into freshwater (4 hours later)

5. When you think osmosis, think:
Water Follows Salt!

6. Osmosis Salt concentration of solution lower than inside the cell
Water enters the cell causing it to lyse (burst)
Salt concentration of solution the same as inside the cell
The amount of water in the cell stays the same
Salt concentration of solution higher than inside the cell
Water leaves the cell causing it to shrivel

8. These are red onion cells
These are red onion cells. The purple stuff is the cytoplasm inside the cell.

9. After adding salt, look what happens
After adding salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell?

10. What do you think is causing that to happen?
After adding EVEN MORE salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell?
In osmosis: water follows salt!
- Wherever there is more salt, water will go because it loves salt!
What do you think is causing that to happen?

11. Definitions
Hypotonic solution: lower concentration of solutes outside the cell than inside the cell
Isotonic solution: same concentration of solutes outside the cell and inside the cell
Hypertonic solution: higher concentration of solutes outside the cell than inside the cell

12. More Definitions
Solute: the minor component in a solution, dissolved in the solvent
Solvent: the liquid in which a solute is dissolved to form a solution
Question: In a salt water solution, is the salt the solute or solvent? What about the water? How do you know?

13. Direction of water molecule movement

14. Movement of Matter Across the Cell Membrane
The cell membrane is made of a phospholipid bilayer, with many protein channels allowing certain molecules to pass through.

15. Movement of Non-Polar Molecules Across the Cell Membrane
Some small molecules like carbon dioxide and oxygen are able to move through the phospholipid bilayer without going through a protein channel.

16. Movement of Polar Molecules Across the Cell Membrane
Water molecules are polar. That means they have a positive (+) side and a negative (-) side. Because they are polar, they cross the cell membrane by moving through a protein channel called aquaporin.

17. Aquaporins transport water molecules across the cell membrane by facilitated diffusion

18. Can Vinegar Get Inside Cells?
Vinegar is 5% acetic acid and 95% water
Like water, acetic acid is a polar molecule:
Do we have any evidence of acetic acid entering egg cells?
If so, how would it get there?