1. SECTION 3-4 How Things Get Into and Out of Cells

2. Permeability
The ease with which substances can cross the cell membrane
Nothing passes through an impermeable barrier
Anything can pass through a freely permeable barrier
Cell membranes are selectively permeable

3. Diffusion
Movement of a substance from an area of high concentration to low
Continues until concentration gradient is eliminated

4. Figure Diffusion
Figure 3.18

5. Figure 3.19 Diffusion across the Cell Membrane

6. Osmosis
Diffusion of water across a semipermeable membrane in response to solute differences
Osmotic pressure = force of water movement into a solution
Hydrostatic pressure opposes osmotic pressure
Water molecules undergo bulk flow

7. Figure Osmosis
Figure 3.20

8. Tonicity The effects of osmotic solutions on cells
Isotonic = no net gain or loss of water
Hypotonic = net gain of water into cell
Hemolysis
Hypertonic = net water flow out of cell
Crenation

9. Figure 3.21 Osmotic flow across a cell membrane