Simple diffusion (diffusion)

Facilitated diffusion (channels)

ATP-driven
pumps         

Coupled transport   

Types of molecules transported:

—

—

—

—

Size
(small/large)

Polarity
(polar/nonpolar)

Charge
(neutral/charged)

Requires a channel or transporter protein?
(No/Yes; if yes, which?)

Requires an additional energy source?
(No/Yes; if yes, what?)

Do any molecules travel against their concentration
gradient? (No/Yes)