1. Taking a look at the plasma membrane
Cell Transport
Taking a look at the plasma membrane

2. The Cell Membrane His friends call him the plasma membrane
He is thin and flexible
He has two main functions:
Protection – protects the cell from the outside environment
Regulation – controls what can enter and exit the cell
He is selective: allows some things to pass through more easily than others
He is selectively permeable: permeate is a fancy way to say “pass through.”

3. What is the Fluid-Mosaic Model?
What’s a mosaic?
What does it mean to be fluid?
The cell membrane is NOT a rigid structure with immovable components!
The cell membrane is fluid-like and flexible
Within the membrane, molecules can move around

4. What Is the Cell Membrane Made of?

5. The (Phospho-)Lipid Bilayer
LIPIDS: Phospholipids make up the majority of the cell membrane
Hydrophilic heads (polar) are made of phosphates (Phospho)
Hydrophobic tails (nonpolar) made out of fatty acids (Lipid)
To protect the hydroPHOBIC
tails from water, they form a
bilayer which keeps the tails
inside and the water- loving
heads outside.

6. STEROLS
Cell membranes of eukaryotes contain sterols between the tails of phospholipids
CHOLESTEROL – major membrane sterol in animals
Make the membrane more firm
Prevent the membrane from freezing at low temperatures

8. PROTEINS
Protein molecules - bring materials into cell and receive signals from outside cell
Integral proteins – embedded within the bilayer
receptor proteins – detect signals and transmit them inside cell
transport proteins –passage ways that allow certain substances to pass
cell markers – carbohydrates attached to help cells identify or recognize other cells
Peripheral proteins – lie only on one side of membrane (enzymes)
YouTube:
Membrane

9. Draw the Cell Membrane!

10. Your turn!
Use your notes and what you’ve learned so far to complete the matching exercise in your notes
Protein (only) = B
Carbohydrate (only) = D
Lipid Bilayer = A
Phosphate Head = F
Fatty Acid Tail = G
Involved in Cell Recognition = D
Carbohydrate attached to a lipid = E
Helps move large material across the membrane = B
Carbohydrate attached to a protein = C
Outside cell = H

11. Solutions SALT WATER Molecules dissolved in a liquid = SOLUTES
Liquid/fluid dissolving them = SOLVENT
This makes a SOLUTION
In a salt solution, ______________ is the solute and _____________ is the solvent
In a sugar solution, sugar is the solute and water
is the solvent.
Dots = solute
Space = solvent
SALT
WATER

12. Concentration and Equilibrium
Solutions will spread out their dissolved molecules until they are equal throughout.
EQUILIBRIUM = molecules are spread equally
CONCENTRATION = # of molecules in an area per unit volume.
CONCETRATION GRADIENT = the difference in the concentration of molecules across a distance
High concentration: more solutes
per unit volume
Low concentration: less solutes 

13. What happens with a barrier? (like a cell membrane)
If solutions on either side of the barrier have the same concentration, they are at equilibrium.
At equilibrium, both the solvent and solute move back and forth across the barrier: there is always movement.

14. Transport of Materials Across the Cell Barrier
Materials move across the plasma
membrane in two ways:
Passive Transport
– movement across the membrane
without using energy
Active Transport
– movement across membrane
that requires energy

15. Types of Passive Transport: 1. Diffusion - simulation
Solutes move across a membrane from areas of high concentration (crowded) to low concentration
Diffusion = random particle movements, so does not use energy.
Imagine warm air coming through an open window…

16. Moving down the gradient requires no energy

17. Because cell membranes are selectively permeable….
….concentration gradients can build up across a cell (like a dam in a lake)
Potential Energy

18. What affects the rate of diffusion?
Concentration of the solution
Temperature of the solution
Pressure also speeds up particle motion

19. Types of Passive Transport: 2. Osmosis
the process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration
Water molecules (fast and small) pass through the cell’s selectively permeable membrane
Solute molecules are too large to pass -- only the water diffuses until equilibrium is reached.

21. Three conditions that control the direction of osmosis- In each of the following conditions we are comparing the solute concentration outside the cell to inside the cell.

22. HYPOTONICITY
the concentration of solute molecules outside the cell is lower than the concentration in the cytosol.
This will cause water to flow into the cell until equilibrium is reached.

23. HYPERTONICITY
the concentration of solute molecules outside the cell is higher than the concentration in the cytosol.
This will cause water to flow out of the cell until equilibrium
is reached.

24. ISOTONICITY
the concentration of solutes outside the and inside the cell are equal so water will flow in and out of the cell at equal rates.

25. How cells deal with osmosis:
Many cells, especially unicellular fresh water organisms, must deal with living in extreme hypotonic environments.
-water continually rushes into the cell forcing it to constantly rid itself of excess water. (Paramecium are unicellular freshwater organisms with this problem.)
contractile vacuoles -organelles that remove excess water by collecting it and then contracting, pumping the water out of the cell. This action requires energy.
Multi-cellular organisms respond to hypotonic environments by pumping solutes out. This helps control the flow of water into the cell.

26. Plants in a hypotonic environment can stand upright.
water fills the cell pressing the membrane up against the cell wall which is strong enough to resist breaking.
The pressure water molecules exert against the cell wall is called turgor pressure.
In hypertonic environments water leaves the cell through osmosis, the cell membrane then shrinks away from the cell wall causing the plant to wilt. This process is called plasmolysis.

28. Animal cells like red blood cells have no cell walls to stop them from expanding and when in a hypotonic environment will swell until they burst. The bursting of cells is called cytolysis.
VIDEO

29. Types of Passive Transport: 3. Facilitated Diffusion
Large molecules or those with a charge (not soluble in lipids) need the help of a protein to pass across a cell membrane
Proteins form a channel
and molecules move through the “doorway.”
From high to low concentration.
Each channel is specific to a particular type of molecule
Doesn’t require energy => passive transport

31. Each carrier protein is specific for a certain molecule
As soon as the molecule binds to its carrier protein, the carrier protein changes shape
The change in shape shields the molecule from the hydrophobic interior of the lipid bi-layer
The molecule can then be delivered either into or out of the cell
Example- glucose is too large to diffuse across the membrane but essential for the cell
VIDEO -

32. Diffusion Through Ion Channels-
allow for the passage of ions through the cell membrane
Each ion channel is specific for one kind of ion
Some ion channels are always open
Some ion channels have gates that open and close as needed
They open and close in response to 3 different stimuli
Stretching of the cell membrane
Electrical signals
Chemicals in their environment

33. Active Transport
Movement AGAINST the concentration gradient requires energy (because it moves solutes from low to high concentration—where it’s already crowded)
Difference in solution concentrations = concentration gradient
Three types of active transport…

34. Pump – a protein PUSHES molecules across the membrane
Active Transport 1. Pump
Pump – a protein PUSHES molecules across the membrane
Ex: the Sodium and Potassium (Na/K) Pump.
YouTube:
Na/K Pump

35. Active Transport 2. Endocytosis
Endocytosis (endo=in): a pocket (vacuole) forms around a large molecule outside the cell and buds inward to release the material inside the cell.

37. Active Transport 3. Exocytosis
Exocytosis (exo=out): a vacuole inside the cell fuses with the cell membrane and forces the material outside the cell.

38. Animation