1. Cell Membrane

2. Phospholipid bi-layer
Cell Membranes
Phospholipid
bi-layer
The main portion of the cell membrane is constructed of a phospholipid bi-layer. There are two layers that are mirror images of each other.

3. Phospholipids Each phospholipid is made of two parts:
The head is a PHOSPHATE molecule (PO4)
The Phosphate is polar which makes it HYDROPHILLIC (attracted to water).
The tails are made of FATTY ACIDS.
The Fatty Acid tails are non-polar which make it HYDROPHOBIC (repelled by water)

4. Cell Membranes - Proteins
Receptor proteins: enables cell to sense surroundings by binding to substances.
Transport proteins: moves substances through the bi-layer that cannot do so themselves.

5. Cell Membranes - Carbs
Surface markers: chains of carbohydrates that identify what type of cell it is.

6. Homeostasis
The Cell Membrane plays an important role in homeostasis by managing the amount of water is in the cell.

7. Selectively Permeable
The Cell Membrane SELECTIVELY PERMEABLE. This means that only some items are able to pass through the membrane.

8. SELECTIVELY PERMEABLE (Semi-permeable)

9. Passive Transport
Passive transport is when a cell transports things across the membrane without energy.
Things always move from high concentration to low concentration when no energy is used.

10. Diffusion Across a Space
Type of passive transport
Molecules move automatically down the concentration gradient from an area of higher concentration (more particles) to an area of lower concentration (less particles).
Examples: Blue dye in a beaker demo
someone making popcorn or grilling (smell)
strong perfume
bad smell in room

11. Concentration Gradient
A difference in the
concentration of a
substance
across a
distance

12. Diffusion Through a Cell Membrane
The particles move until they are evenly distributed, which is called “equilibrium”
semipermeable

13. Osmosis
The diffusion of water molecules across a selectively permeable membrane is known as osmosis

14. Diffusion of H2O Across A Membrane
High H2O potential Low solute concentration
Low H2O potential High solute concentration

15. Osmosis
If a cell has more particles (like sugar) inside the cell than outside, this means that there is a higher concentration of water outside than inside
Remember that osmosis is the movement of WATER across a membrane
Also remember that in diffusion, particles move from areas of HIGHER CONCENTRATION TO LOWER CONCENTRATION

16. Osmosis
Therefore the water is going to move INSIDE the cell until equilibrium is reached
This cell is said to be in a hypotonic solution. Hypotonic solution has less particles outside than inside the cell.
As water moves in, the cell will get bigger.

17. Cell in Hypotonic Solution
10% NaCL 90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?

18. Osmosis
If the concentration of particles is higher outside of a cell than inside, then the concentration of water is higher inside and the water will move out of the cell until equilibrium is reached.
This cell is said to be in a hypertonic solution where there is more particles outside of the cell.
As water moves out of the cell, the cell will shrink.

19. Cell in Hypertonic Solution
15% NaCL 85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?

20. Osmosis
If the concentration of particles outside the cell are the same as inside of the cell, water will not move in or out.
A cell in this case is said to be in an isotonic solution where the concentration of particles is the same on both sides of the cell membrane.

21. Cell in Isotonic Solution
10% NaCL 90% H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10% NaCL
90% H2O
What is the direction of water movement?
equilibrium
The cell is at _______________.

22. Osmosis Type of Solution Particle concentration in solution
in cytoplasm
Where is there more water?
Which way will water move?
Hypotonic
Hypertonic
Isotonic

23. Simple & Facilitated Diffusion
Passive Transport
Simple & Facilitated Diffusion
Doesn’t require energy
Moves high to low concentration
Example: Simple-O2. H2O, CO2 Facilitated- amino acids, glucose

24. Active Transport Requires energy or ATP
Moves materials from LOW to HIGH concentration
AGAINST concentration gradient

25. Exocytosis- moving things out.
Moving the “Big Stuff”
Exocytosis- moving things out.
Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
This is how many hormones are secreted and how nerve cells communicate with one another.

26. Exocytosis
Exocytic vesicle immediately after fusion with plasma membrane.

27. Moving the “Big Stuff”
Large molecules move materials into the cell by one of three forms of endocytosis.

28. Moving Ions through pumps
The Sodium/Potassium Pump