1. The cells environment 1. All cells live in a fluid environment.
Fluid = moist or water filled.
2. Cells must obtain nutrients from the outside and release substances into their moist environment.

3. Plasma Membrane Plasma membrane- the outer boundary of a cell.
Gatekeeper - the plasma membrane prevents certain materials from entering the cell and allows certain materials to pass into the cell.

4. Selectively permeable membrane
Selectively permeable membrane- membrane allows certain structures to pass into and out of the cell while keeping others inside or outside of the cell.
Ex. Tea bag.
SPM- maintains the organization of the cell.

5. Lipid Bilayer Lipid Bilayer- makes up the plasma membrane.
Made up of two layers of phospholipids.
Phospholipid - composed of a phosphate head and a fatty acid tail

6. Phospholipid bilayer
Hydrophilic head - the phosphorous head is attracted to water.
Hydrophobic tails - the fatty acid tails are “afraid” of water.
Results in a two layered (bilayer) membrane

7. Membrane Proteins Proteins are scattered about the plasma membrane.
Proteins serve as a door in which large molecules can pass through the membrane.
Cholesterol - (lipid) provides rigidity to the cells membrane.

8. Fluid Mosaic Model
Fluid mosaic model - model for the structure of a plasma membrane in which the membrane is a phospholipid bilayer with proteins embedded within it.
Ex. Tile floor
fig page 95

9. Membrane function Membranes are selectively permeable.
Random movement - “In nature, there is a tendency toward randomness. Energy is required for nonrandomness.”
Diffusion - random movements of ions and other particles.

10. Diffusion
1. Results in movement of particles from a region of greater concentration to a region of lesser concentration.
Dynamic equilibrium - condition in which there is a continuous movement of molecules but no overall change.

11. Osmosis
Osmosis - the diffusion of water into and out of cells across a selectively permeable membrane.
Osmotic balance - occurs when the movement of water into and out of the cell is equal.
Blood cells
plant cells

12. Types of Solutions
Isotonic Solution – equal concentration of solution and the cell. (Osmotic balance)
Hypotonic Solution – Greater water concentration outside the cell than inside the cell (The cell bursts)
Hypertonic Solution – Greater water concentration inside the cell than outside the cell (The cell shrinks)

13. Passive transport
Passive transport - the cell plays no active role and does no work in moving the particles. Requires no Energy
1. Water
2. Lipids
3. Substance soluble in lipids
4. very small particles

14. Types of passive transport
1. Osmosis
2. Diffusion
3. Facilitated Diffusion

15. Facilitated Diffusion
Many particles needed by cells must have some help getting across the cell membrane.
Facilitated diffusion - the use of transport proteins to aid the passage of materials across the plasma membrane

16. Transport proteins
1. Channel proteins - simplest type. These are simply called pores. These serve as channels that allow ions to pass through.
Depend on size and charge.
Even if an ion is small enough to pass through the pore, it may be prevented by its charge.

17. Transport proteins (continued)
Carrier proteins or GATE Proteins- more complex, works like a gate.
1. A particle on one side of a membrane attaches to a protein
2. The protein changes shape
3. Allows the desired particle to pass into or out of the cell.
4. When the signal molecule is released, the gate closes

18. Active Transport
Active transport - the moving of particles from a region of lesser concentration to a region of greater concentration.
Requires Energy
Pumps - transport proteins used to move a particle through a plasma membrane.
Requires chemical energy to alter the shape of the protein.

19. Active Transport (continued)
Examples of Active Transport
1. Marine Fish - actively pump out salt even though the concentration of salt is more outside their body.

20. Other methods of entering and exiting the cell.
1. Endocytosis - the process by which the mambrane engulfs and takes in a substance.
Phagocytosis - solid particles are ingested
Pinocytosis - liquid particles are ingested.
2. Exocytosis - cell products or wastes are released to the surroundings
see figs 4-17, 18, 19