1. The Plasma Membrane
Section 7.2 p

2. Maintaining a Balance
All living cells must maintain a balance regardless of internal + external conditions
Survival depends on the cell’s ability to maintain proper conditions within itself

3. Why cells must control materials
Cells need nutrients to function
Glucose
Amino acids
Lipids
Must enter through the plasma membrane
The flexible boundary between the cell + its environment

4. Why cells must control materials
Substances such as wastes + products must leave through the plasma membrane
Substances enter + leave to maintain homeostasis
Selectively permeable
Ability to allow some molecule to pass through while keeping others out
Examples
Water vs. Na+ ions

5. Selectively Permeable

6. Structure of the Plasma Membrane
Recall – LIPIDS (Fatty Acids + glycerol)
Phospholipid
Two fatty acids, glycerol, + a phosphate group
Plasma membrane is composed of a phospholipid bilayer

7. The Phospholipid bilayer
Fatty acids “tails” are hydrophobic
Don’t want to interact with water
Phosphate group “head” is hydrophilic
Wants to interact with water
Creates a barrier that regulates the ease in which substances cross the plasma membrane

8. Fluid Mosaic Model
The proteins embedded in the bilayer create the “mosaic”
The phospholipids move within the membrane (like a fluid)

9. Other components of the P.M.
Cholesterol
Helps to stabilize the phospholipids by preventing their FA’s from sticking together

10. Other components of the P.M.
Proteins
Transport
Move substances through PM
Markers
Identify chemical signals + each other
Inner surface
Gives cell’s structure flexibility

11. A video clip….
Plasma Membrane