movement across p.m

facilliated diffusion:

• diffusion through a trans-membrane protien molecule.

channel protiens:

• allows charged substabces to diffuse across the membranes.
• cells can change their permeability to certain ions.
• ions go through.

carier protiens:

• have a binding site for a specific solute to costantly flip between two states.
• site is alternatly open to opposite sides.
• substabce binds on the side at a high conc then will be released where it is at low conc.
• can co transport if it has twi binding sites (sodium/glucose co transport).