1. Cell transport
Section 7.3

2. Objective
Know processes involved in active transport Know processes involved in Passive transport

3. What is passive transport?
Diffusion!
Solute particles will move from a high concentration to a low concentration
Like adding sugar to tea or coffee
Diffusion is the driving force for many things crossing cell membrane
Even at equilibrium particles are still moving across
Same number in both directions
Depends on random particle motion
When no energy is used to move across cell membrane this is passive transport

4. Diffusion explained

5. Facilitated diffusion
Only small uncharged molecules can pass through the lipid bilayers
Ions such as Cl-, or molecules such as glucose still pass through quickly, how?
Proteins act as conduits/ channels allowing diffusion to occur
Facilitated diffusion
There are hundred of different types that allow particular substances to move
Although fast and specific it is still diffusion – it uses no energy

6. Osmosis – facilitated diffusion
Water requires facilitated diffusion – why?
Water can not cross the oily layer inside cell membrane
Instead Aquaporins allow transport of water
Water channel protein
Osmosis – diffusion of water through selectively permeable membrane
Water molecules move from high to low concentration

7. Isotonic vs Hypertonic vs hypotonic

8. Osmotic pressure Osmotic pressure can cause cells to shrink or expand
Cells are always hypertonic in fresh water
Very rare that cells are in contact with fresh water
Cell walls can also help prevent cells from expanding/shrinking too much

9. Active transport
The movement of materials against a concentration gradient
It requires energy
Carried out by transport proteins or pumps
Common for Ca, Na, K
Allows particular substances to concentrate
Alternative – endocytosis or exocytosis
Bulk transport

11. Bulk transport Endocytosis Exocytosis
Stuff enters the cell through in folding of cell membrane
Phagocytosis – example
White blood cells eat damaged cells
Exocytosis
Membrane of vacuole fuses with cell membrane
Contents are expelled