1. Movement through the Membrane
Chapter 7-3

2. Cell Membrane
Regulates what enters and leaves the cell (kind of like a security guard)
Made of a lipid bilayer
2 layers of lipids
Provides a tough, flexible barrier between the cell and its surroundings
Proteins and carbohydrates can also be found in the cell membrane.

3. Cell Membrane
One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other.
The cell membrane is selectively permeable (it doesn’t let just everything through; it is selective).

4. Equilibrium
Equilibrium—same concentration (amount per area) on both sides; equal
Molecules are constantly moving across the membrane.
In equilibrium, the molecules are moving at the same rate.

5. Isotonic Solution same strength same concentration as cell
water molecules move in and out at same rate

6. Hypertonic Solution above strength higher concentration than cell
water moves out of the cell

7. Hypotonic Solution below strength lower concentration than cell
water moves into the cell

8. 4 Types of Movement through the Membrane
Diffusion
Osmosis
Passive Transport (also called facilitated diffusion)
Active Transport

9. Diffusion
Diffusion is the movement of molecules from an area of high concentration (crowded) to an area of low concentration (uncrowded) until equilibrium is reached
Diffusion does NOT require the cell to use energy.

10. Diffusion

11. Osmosis Osmosis is the diffusion of water.
Water moves from high concentration to low concentration.
It does NOT require energy.

12. Osmotic Pressure Fresh water is ALWAYS hypotonic to a cell.
Water will move into a cell in fresh water, causing it to swell and possibly causing it to burst.
The cell wall prevents the cell from expanding too much.

13. Passive Transport
Some molecules cannot cross the lipid bilayer of the cell membrane.
Proteins in the cell membrane act as a channel (path). The proteins passively allow the molecules through the membrane.
High to low concentration
Does NOT require energy

14. Active Transport LOW (uncrowded) to HIGH (crowded) concentration!!!!
Proteins act as pumps and actively force molecules through the membrane
Active transport REQUIRES energy!!!