1. Plasma Membrane

2. I. Maintaining Balance How do cells maintain balance?
Cells need to maintain a balance by controlling material that move in and out of the cell –> HOMEOSTASIS.

3. I. Maintaining balance
Small molecules like water, oxygen, and carbon dioxide can move in and out of the cell freely.
Large molecules like proteins and carbohydrates cannot.
Eliminating wastes.

4. I. Maintaining balance

5. Structure of the Plasma (cell) membrane
All cells are surrounded by a plasma membrane
Functions like a GATE, controlling what ENTERS and LEAVES the cell.
The cell membrane is semipermeable or selectively permeable.

6. Structure of the Plasma (cell) membrane
A semipermeable membrane only allows certain molecules to pass through.
Some substances easily cross the membrane, while others cannot cross at all.

7. Structure of the Plasma (cell) membrane
Made of a thin layer of lipids and proteins
Made mostly of phospholipid molecules (phosphate + lipid).
Phospholipids are a kind of lipid that consists of 2 FATTY ACIDS (tails), and PHOSPHATE GROUP (heads).

8. Structure of the Plasma (cell) membrane
Cell membranes consist of TWO phospholipid layers called a LIPID BILAYER.

9. Structure of the Plasma (cell) membrane

10. Structure of the Plasma (cell) membrane
Water molecules surround both sides of the cell membrane.
Polar phosphate heads sticking TOWARD the water (hydrophilic)
Nonpolar lipid tails pointing AWAY from the water (hydrophobic)

11. Structure of the Plasma (cell) membrane
The cell membrane is constantly being formed and broken down in living cells.

12. III. Lipid bilayer
Moving with and among the phospholipids are cholesterol, proteins, and carbohydrates.
Cholesterol:
Nonpolar, found among the phospholipids to help prevent the fatty acid tails from sticking together
Helps with structure and homeostasis.

13. III. Lipid bilayer

14. III. Lipid bilayer Proteins:
Found on the surface of the plasma membrane = transmit signals to the inside of the cell.
Embedded in the plasma membrane = structure and support of cells shape, and move large substance in and out of the cell.

15. III. Lipid bilayer

16. III. Lipid bilayer Carbohydrates:
Attached to proteins, helps cells identify chemical signals.
Ex.: help disease fighting cells recognize and attack a potentially harmful cell.

17. Identify the following parts of the plasma membrane