1. Figure 8.1 Artificial membranes (cross sections)

2. Figure 8.4 The fluidity of membranes

3. Figure 8.5 Evidence for the drifting of membrane proteins

4. Figure 8.6 The detailed structure of an animal cell’s plasma membrane, in cross section

5. Figure 8.7 The structure of a transmembrane protein

6. Figure 8.9 Some functions of membrane proteins

7. Movement of substances through the membrane
May be
passive – requires no energy expenditure by cell.
Diffusion
Osmosis
Facilitated diffusion
Active – does require energy expenditure

8. Passive transport Depends on concentration gradients.
Materials move from area of high concentration to low concentration
If occurs across a membrane, the membrane must be permeable to the substance.
Size is a major factor
Electrical charges
Polar vs non-polar

9. Diffusion
Movement of particles (solute) from high to low concentration will continue until there is an even distribution of particles.
This is called equilibrium.
Particles move across the membrane randomly at equilibrium.

10. Diffusion of two solutes
If there are 2 or more kinds of solute, each moves independently of the other; 2 different concentration gradients exist.
Membranes may be permeable to some substances and not others – selective permeability.

11. Figure 8.10 The diffusion of solutes across membranes

12. Osmosis Diffusion of water (solvent) is called osmosis.
Water molecules will move from regions of lesser solute concentration to regions of greater solute concentration.
Movement of water stops when equilibrium is reached.

13. Osmotic equilibrium
In osmosis, water accumulating on one side of a membrane exerts pressure on the membrane.
If this pressure is great enough, it may stop entry of water molecules from the other side, even though a concentration gradient still exists.
This is important for plant cells!

14. Figure Osmosis

15. Tonicity When comparing the concentrations of 2 solutions:
Isotonic – same concentration of solute
Hypertonic – higher concentration of solute
Hypotonic – lower concentration of solute

16. Figure 8.12 The water balance of living cells

17. Movement through the membrane - passive
In diffusion and osmosis, very small molecules may pass directly between the phospholipids as long as they are not charged.
Ions can NOT pass through
Some water can pass
O2 and CO2 can pass
Small lipids can pass

18. Facilitated Diffusion
Charged particles and some molecules can move passively through protein channels.
The channels facilitate passage through the membrane.
The proteins may undergo a shape change as the particles pass, but no energy is expended.

19. Figure 8.14 Two models for facilitated diffusion

20. Figure 8.15 The sodium-potassium pump: a specific case of active transport

21. Figure 8.16 Review: passive and active transport compared

22. Figure 8.17 An electrogenic pump

23. Figure Cotransport

24. Figure 8.19 The three types of endocytosis in animal cells