1. Transport through cell membranes

2. Transport through cell membranes
The cell membrane is made of a phospholipid bilayer which allows certain molecules in and out of the cell
We will discuss 2 basic mechanisms of transport:
DIFFUSION
OSMOSIS

3. Diffusion of liquids

4. Diffusion is the net movement of molecules from a region of their high concentration to a region of their lower concentration. The molecules move down a concentration gradient. Molecules continue until they reach equilibrium.

5. AS Biology, Cell membranes and Transport
DIFFUSION
Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural kinetic energy.
AS Biology, Cell membranes and Transport

6. 5 Factors that affect diffusion
Temperature- Higher temperature  diffuse faster
Surface area- greater surface area diffuse faster
Concentration gradient- Higher gradient  diffuse faster
Size of particles- Smaller particles diffuse faster
Diffusion Medium- Solid  slowest
Liquid  faster
Gas  fastest

7. Diffusion through a membrane
Cell membrane
Outside cell
Inside cell
AS Biology, Cell membranes and Transport

8. Diffusion through a membrane
Cell membrane
diffusion
Outside cell
Inside cell
AS Biology, Cell membranes and Transport

9. Diffusion through a membrane
Cell membrane
Outside cell
Inside cell
EQUILIBRIUM
AS Biology, Cell membranes and Transport

10. Osmosis
‘The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane.

11. AS Biology, Cell membranes and Transport
Osmosis
CONCENTRATED SOLUTION
DILUTE SOLUTION
Cell membrane partially permeable.
Sugar molecule
VERY Low conc. of water molecules. High water potential.
VERY High conc. of water molecules. High water potential.
Outside cell
Inside cell
AS Biology, Cell membranes and Transport

12. AS Biology, Cell membranes and Transport
Osmosis
Cell membrane partially permeable.
Low conc. of water molecules. High water potential.
OSMOSIS
High conc. of water molecules. High water potential.
Outside cell
Inside cell
AS Biology, Cell membranes and Transport

13. AS Biology, Cell membranes and Transport
Osmosis
Cell membrane partially permeable.
OSMOSIS
Outside cell
Inside cell
EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water
AS Biology, Cell membranes and Transport