hydrophilic head

hydrophobic tail

quite a bit of movement-not static

tails are unsaturated-kink at double or triple bond

bilayer is asymmetrical

• allows: oxygen, carbon dioxide, small nonpolar molecules, some water molecules
• does not allow: glucose, large polar water souluble molecules, ions (enter through proteins)

have binding sites that trigger changes in cell activity

peripheral (outside of the cell) that accelerate reactions (catalysts) 

ex: cell signalling

allow substances to pass through the lipid bilayer 

1. Active transporters (use ATP)
2. Passive Transporters (dont use energy)

1. Size- increase size, decrease in rate
2. Temp.- increase in temp, increase in rate
3. Concentration Gradient Steepness- increase in steepness, increase in rate
4. Charge- increase in charge, increase in rate
5. Pressure- increase in pressure, increase in rate
6. Diffusion Distance- increase in distance, decrease in rate

move down concentraion gradient 

no energy input needed 

Simple Diffusion

Substances move down their concentration gradient

Facilitated Diffusion

(AKA Passive Transport)

requires a channel where large, polar molecules can pass 

channel is typically a transport protein

still no energy required

Active Transport

(AKA Pumps) 

substances move against their concentration gradient

need energy or ATP

ex: Sodium-Potassium Pump: 3 NA+ moves out while 2 K+ moves into cell 

tendency for water to be pulled across a semi-permiable membraneinto a solution

high osmotic pressure stops osmosis

realative concentration of solutes in 2 fluids 

ex: extracellular fluid vs. cytoplasm

lower concentraion of solute outside of the cell than the inside of the cell (more water on outside)

cells will swell cuz water will go into them

higher concentraion of solute outside of the cell than inside the cell (less water on outside)

cell will shrink cuz water will leave the cell)