1. Cell Membranes and Transport
Animation of cell membrane

2. plasma membrane
Fig. 5-23a, p.88

4. Cell Membrane Structure
Phospholipid Bilayer
Phosphate head towards the water (hydrophilic)
Lipid tails towards each other (hydrophobic)

5. Fluid Mosaic Model of the Cell Membrane
Fluid (dynamic)
Phospholipids are not rigid
Proteins also move around within the membrane
Mosiac
A network of many proteins/cholesterol
Some proteins go through the membrane
Others stay on one side of the membrane

6. Function of the Cell Membrane
Protects the cells from the surroundings
and
Selectively allows substances to pass through the membrane (what kind of substances?)
Proteins: Enzyme activity, cell recognition, cell signaling, cell transport

7. glucose and other large, polar, water-soluble molecules; ions (e.g.,
oxygen, carbon
dioxide, and other
small, nonpolar
molecules; some
water molecules
glucose and other large,
polar, water-soluble
molecules; ions (e.g.,
H+, Na+, K+, Ca++,
Cl–); water molecules
Fig. 5-15, p.82

8. Passive Transport
Flow of solutes through the interior of passive transport proteins down their concentration gradients
Passive transport proteins allow solutes to move both ways
Does not require any energy input

10. Passive Transport Diffusion
Small molecules move from a region of high concentration to a region of low concentration till they are equally dispersed (equilibrium is reached)
Ex. Oxygen, carbon-dioxide
Fig. 5-16, p.82

11. Osmosis
Diffusion of water molecules across a selectively permeable membrane
Direction of net flow is determined by water concentration gradient
Side with the most solute molecules has the lowest water concentration

12. Tonicity and water transport
compartment 1
compartment 2
HYPOTONIC
SOLUTION
HYPERTONIC
SOLUTION
membrane permeable to
water but not to solutes
fluid volume increases
In compartment 2

13. Tonicity Solvent – the medium for mixing i.e. water
Solute- what is mixing i.e. salts, gases
Tonicity - Refers to relative solute concentration of two fluids
Hypertonic - having more solutes than solvent
Isotonic - having same amount solutes and solvent
Hypotonic - having fewer solutes than solvent

14. Tonicity and Osmosis 2%
sucrose
water
10% sucrose
2% sucrose

15. Facilitated Diffusion
glucose transporter
solute (glucose)
high
low
Facilitated Diffusion
Stepped Art
Fig. 5-18b, p.84

16. Active transport

17. Active transport Opposite to passive transport
Against the concentration gradient
Needs energy (ATP)
Uses membrane proteins
Example: Sodium and potassium pumps in nerve cells

18. Bulk Transport Endocytosis (vesicles in) Exocytosis (vesicles out)
Fig. 5-17b, p.83

19. parasite
macrophage
Fig. 5-25a, p.89

20. edible
bacterium
amoeba
phagocytic
vesicle
Stepped Art
Fig. 5-25, p.89

21. Cell transport review Go to: