Cell Membrane Physiology
Cell Membrane


Gatekeeper
“Selectively Permeable” – only some
things can get in or out
Passive Transport

NO ENERGY REQUIRED !!!!

Diffusion
 Movement from HIGH concentration to
LOW concentration until equilibrium is
reached
 Must be SMALL enough to fit through
pores (holes)
 Must DISSOLVE in FAT
 Examples – oxygen, Carbon dioxide
III. Passive Transport
A. Diffusion
Facilitated Diffusion



Molecules are too big or don’t dissolve
in fat
Molecules use a PROTEIN channel in
the membrane
Still moves HIGH to LOW concentration
B. Facilitated Diffusion
OSMOSIS

Facilitated Diffusion of WATER ONLY!
Active Transport

ENERGY REQUIRED !!!

Solute-pumping
 BIG THINGS or movement from
LOW to HIGH concentration
 ATP is used to activate a protein in
the membrane
 NO PUMP: NO TRANSPORT
(very specific)
IV. Active Transport
A. Solute-pumping
BULK TRANSPORT

Exocytosis
 “Exiting the cell”
 Golgi packages the stuff into a sac
made of phospholipids
 Sac fuses with the membrane and
spills contents out
BULK TRANSPORT

ENDOCYTOSIS
 “Into the cell”
 Pushes the membrane in, pinches
into a sac, lysosome opens the sac
B. Bulk Transport