1. Cell Membrane and Transport

2. Cell Membrane AKA plasma membrane **All cells have a cell membrane
Made up of a lipid bilayer (phospholipids)
Controls what enters and leaves the cell to maintain internal balance called homeostasis

3. Cell Membrane
Selectively permeable - Some molecules can pass through the cell membrane but some cannot
In: Glucose, water, oxygen
Out: Waste and carbon dioxide
* Small molecules can pass through the membrane easily (contains pores)

4. Cell Membrane Structure
Lipid Bilayer - two layers of phospholipids make a flexible barrier.
Phospholipids are composed of a:
Phosphate head (polar - water loving)
Fatty acid tail (nonpolar - water fearing)

5. Cell Membrane Structure
Proteins are embedded in the membrane
Called a fluid mosaic because it is composed of many different organic macromolecules that can move
Cell Membrane
Fluid Mosaic Model

6. Cell Membrane Structure
Lipids act as a barrier between the inside and the outside of the cell
Carbohydrates act as receptors to decide if some materials can pass through the membrane or not.
Proteins act as pumps or channels for larger molecules

7. Cell Transport Two categories of cell transport:
Passive Transport (High → Low) *cell does NOT use energy to move molecules
Diffusion Facilitated Diffusion
Osmosis
Active Transport (Low → High) *cell DOES use energy to move molecules
Protein pumps
Endocytosis and exocytosis

9. Cell Transport Particles move in response to a concentration gradient
*Difference between concentration (number of molecules) in a space
[Solutes = substance being dissolved (ex: sugar); Solvent = Dissolver (ex: water)]
Equilibrium - When particles are evenly distributed over a given space
High Low Equal Low High

10. Equilibrium
All molecules move so they can reach equilibrium (equal on both sides or balance).
Once it is reached there is equal movement in both directions.
Molecules never stop moving!

11. Concentration Gradient
Concentration gradient is created when there is a difference in the amount of molecules on each side of the cell membrane (not at equilibrium)
It causes particles move!

12. Passive Transport - Diffusion
Diffusion - the random movement of any molecule across the cell membrane
High to low concentration gradient
Does NOT require energy Example: Food coloring in water

13. Passive Transport - Diffusion
Diffusion continues until all molecules are evenly spread out → equilibrium!
**Molecules will still move around but stay spread out

14. Passive Transport - Diffusion
Practice!! Which way would the molecules move across the membrane?

15. Passive Transport - Diffusion
Practice!! Which way would the molecules move across the membrane?

16. Passive Transport- Diffusion
Let’s try some more diffusion practice problems using percentages:
Inside a cell is 40 percent salt and outside the cell is 60 percent salt.
Inside a cell is 50 percent salt and outside the cell is 50 percent salt.
Inside a cell is 75 percent water and outside the cell is 55 percent salt.

17. Passive Transport - Osmosis
2. Osmosis - the diffusion of WATER molecules across the cell membrane
High to low concentration gradient
Does NOT require energy
Ex: Fingers wrinkle in bath tub
*SALT (Solute) SUCKS WATER!!!

18. Passive Transport - Osmosis
More solute outside of the cell Outside=inside More solute inside the cell
Water leaves cell Equilibrium Water enters the cell
Cell shrinks Cell expands ***can burst!

19. Passive Transport - Osmosis
Practice! Which way would the water molecules move?
= water molecule = salt molecule

20. Passive Transport - Osmosis
Osmosis Video
Virtual Lab??

21. Osmotic Pressure Turgor Pressure - The pressure of water pushing
the inside of the cell membrane against the cell
wall of a plant cell.
**Organisms have mechanisms for dealing with osmotic pressures.
Ex: Bacteria and plants have a cell wall that prevent them from over expanding.
Ex: Kidneys help remove excess water from the blood
Ex: Saltwater fish pump salt out of their specialized gills so they do not dehydrate
Video

22. Passive Transport- Facilitated Diffusion
Facilitated Diffusion is the movement of LARGE molecules across the cell membrane through a protein
High to low concentration
Goes with the gradient
Does NOT require energy

23. Active Transport
Active Transport - the movement of molecules against a concentration gradient
Requires energy (ATP) since molecules are moving from a low concentration to a high concentration. Uses a protein pump. Purposefully moves the molecule.
High
Cell Membrane
Low Watch video clip

24. Types of Active Transport
Sodium Potassium Pumps (Active Transport using proteins)
1. Protein Pumps - transport proteins that require energy to do work
Example: Sodium / Potassium Pumps are important in nerve responses.
Protein changes shape to move molecules: this requires energy!

25. Types of Active Transport
2. Endocytosis: taking bulky material into a cell
Uses energy
Cell membrane in-folds around food particle
“cell eating”
forms food vacuole & digests food
This is how white blood cells eat bacteria!

26. Types of Active Transport
3. Exocytosis: Forces material out of cell in bulk
membrane surrounding the material fuses with cell membrane
Cell changes shape – requires energy
EX: Hormones or wastes released from cell
Endocytosis & Exocytosis animations