1. Materials move across membranes because of concentration differences.
3.4 Diffusion and Osmosis
Materials move across membranes because of concentration differences.
High
Concentration
Low
Concentration

2. Molecules can move across the cell membrane through passive transport.
3.4 Diffusion and Osmosis
Molecules can move across the cell membrane through passive transport.
Passive transport does not require energy input from a cell.
There are two types of passive transport:
diffusion
osmosis

3. Diffusion
Diffusion- movement of molecules from a region of higher concentration to a region of lower concentration

4. Molecules diffuse down a concentration gradient
3.4 Diffusion and Osmosis
Concentration gradient is the difference in the concentration of a substance from one location to another
Molecules diffuse down a concentration gradient

5. 3.4 Diffusion and Osmosis
Osmosis is the diffusion of water molecules across a semipermeable membrane.

6. Osmosis There are three types of solutions. tonic = pressure
1) isotonic
2) hypertonic
3) hypotonic

7. 3.4 Diffusion and Osmosis
Some molecules can only diffuse through transport proteins and cannot easily diffuse across the cell membrane.
Facilitated diffusion is diffusion through transport proteins.

8. Facilitated Diffusion