Introduction to membrane
transport
The cell membrane is SEMIPERMEABLE: some substances can
move across the cell membrane while
others can’t.
• Concentration gradient: a difference in
concentration between one side of the
membrane and the other
• Processes that allow substances to move
across the membrane without energy are
PASSIVE TRANSPORT. They use the
concentration gradient
• Includes diffusion, osmosis and facilitated
diffusion
Active transport
• Movement of molecules against a
concentration gradient
• Requires energy (in the form of ATP)
• Includes active transport, and membraneassisted transport (endocytosis and
exocytosis)