Download Sodium-Potassium pumps

Transport across the cell
membrane
Active Transport – requires energy in the
form of ATP (Na+K+ pump, endocytosis &
exocytosis)
Passive Transport – no energy required
(diffusion, osmosis, facilitated diffusion)

Active transport is responsible for cells
containing relatively high concentrations
of potassium ions but low concentrations
of sodium ions.

The mechanism responsible for this is the
sodium-potassium pump which moves
these two ions in opposite directions
across the plasma membrane.
Concentrations of Na+ and K+ ions on the
two sides of the membrane are
interdependent = same carrier protein
transports both ions.
The carrier is an ATP-ase and it pumps 3 sodium
ions out of the cell for every 2 potassium ions
pumped in.
Function of the pump
The Na+/K+-pump helps maintain
resting potential that assist s
transport & regulates cell volume
 low concentration of sodium ions
within cell
 high levels of potassium ions within
the cell

Facilitated Diffusion
Cells need to bring in substances
(glucose, amino acids) by facilitated
diffusion
 Carrier proteins combine with and
transport substances across the cell
membrane
 Possible because active transport
maintains a concentration gradient

Osmosis

Movement of sodium from one side
of a cell membrane to the other side
creates an osmotic gradient that
drives the absorption of water.

Water diffuses back into the cell
carrying needed substances
Endocytosis & Exocytosis
Larger substances are moved into &
out of the cell by vesicle formation
 Requires ATP
