1. Membranes and Passive TransportCh

2. Review Cell membranes are made up of some type of lipid
What is unique about the interaction of lipids and water?
Lipids are hydrophobic, or water resistant, to water!
Why do molecules like these work well for a cell’s boundary?
Cell cytoplasm is mostly water and cell exterior is mostly water --> water resistant molecule makes a good boundary layer

3. Objectives Structure of cell membranes
Function of proteins in cell membranes
Relate diffusion to equilibrium
Describe passive transport
Relate osmosis to solute concentration

4. Phospholipid Molecule
Structured like a fat molecule, but only 2 tails
Hydrophilic Head
Hydrophobic Tail

5. Phospholipid Bilayer Phospholipid Bilayer: Online Activity 6.3
Selectively permeable membrane
surrounds cell
Controls what goes in and out!
Online Activity 6.3
Contains proteins
What do these proteins do?

6. Function of Proteins in bilayer
Cell communication
Assist with passage of materials
Classroom analogy
Light, heat, electricity, internet, etc.

7. Regulating Traffic
Materials such as water, nutrients, dissolved gasses, ions and wastes must CONSTANTLY move in two-way traffic across membrane
Cell membranes function like “gatekeepers”
Some molecules pass, others do not!
How do they do this?

8. Ways to get materials across membrane
Diffusion:
Movement of particles from HIGHER--> LOWER concentration
The goal is to achieve an equilibrium
Equilibrium:
in balance
Perfume?

9. Ways to get materials across membrane
Passive Transport:
Diffusion across a membrane
no energy
Some molecules too big to get through membrane alone (sugars). Need help!
What can help them?

10. Ways to get materials across membrane
Facilitated Diffusion:
use of transport proteins
No energy
Facilitated Diffusion animation

11. Are all substances able to pass through membrane?
No!
Diffusion occurs through a selectively permeable membrane
Selectively permeable membrane:
Allows “select” substances through
Similar to a window screen: air but no mosquitoes

12. Water can pass, but sucrose too big

13. Three Ways to Get Materials Across Membrane

14. How does water get through?
Osmosis:
Diffusion of H2O
Hypertonic Solution:
Net water flow OUT of cell
Hypotonic Solution:
Net water flow INTO cell
Isotonic Solution:
Equal water flow
Osmosis Animation
Sore throat, thirsty after salty snacks