1. The Plasma/Cell Membrane

2. Objective
Recognize the importance of semi-permeable membranes in regulating diffusion and maintaining homeostasis.

3. The Cell Membrane
The “cell membrane” is also known as “the plasma membrane.”
To survive, ALL living things must maintain a balance regardless of internal and external conditions.

4. The plasma membrane is the boundary between the cell and its environment.
It allows a steady supply of glucose, amino acids, and lipids to enter the cell no matter what the external (outside) conditions are.
Remove excess amounts of nutrients when levels are too high.
Allow wastes and other products to leave the cell

5. Homeostasis
The plasma membrane helps maintain homeostasis, which is the process of maintaining the cells internal (inside) environment

6. Selective Permeability
The cell membrane is selectively permeable.
Is a process used to maintain homeostasis in which the plasma membrane allows some molecules in the cell while keeping others out.

7. “Selective” “Permeable”
Selective – able to regulate which particles enter and leave (it’s choosey)
Permeable – allows particles to pass through
*another way to say selectively permeable is “semi-permeable”

8. Why is the orange membrane considered semi-permeable?
What particles can’t get through the pores (holes) in the membrane?

9. Structure of the Membrane
The plasma membrane is composed of TWO layers of phospholipids back to back

10. The phospholipid bilayer is made up of:
A Hydrophilic head that is attracted to water
A Hydrophobic tail that is NOT attracted to water (scared of water).

11. The cell’s environment is mostly water
The cell’s environment is mostly water. It is the most abundant material inside a cell as well.

12. “Fluid” Mosaic Model
The plasma membrane is described as being a flexible boundary of a cell. The phospholipids move within the membrane.

13. Other Components: Cholesterol
Cholesterol plays an important role of preventing the fatty acid chains of the phospholipids from sticking together.

14. Other Components: Transport Proteins
Allow substances or water materials to move across through plasma membrane.

15. Other Components: Receptor Proteins
The surface of the membrane bind to chemical messengers to allow certain substances to pass through the plasma membrane.

16. Passive Transport versus Active Transport
NO energy required
Energy REQUIRED