Passive VS Active Transport
Hydrophilic Head
• Loves water
Phospholipid
Hydrophobic
Tails
• Hates water
• Also known as the ”fluid mosaic model”
• Named after the embedded proteins and cholesterol into
the bilayer, giving the look of a mosaic.
Extracellular Fluid
Selectively
Permeable –
only allowing
certain
substances
into/out of the
cell
Phospholipid
Intracellular Fluid
• Passive transport processes DO NOT require any
energy expenditure from the cell
• Particles move by using energy they already have
• Types of Passive Transport
•
•
•
•
Diffusion
Osmosis
Filtration (and dialysis)
Facilitated Diffusion
• Diffusion is the movement of particles from an area of
high concentration to low concentration
Particles will move down a concentration gradient until
EQUILIBRIUM is achieved (# of molecules balanced on
both sides) …
• Osmosis deals with the diffusion of water
through a selectively permeable membrane
• Starches, sugar, and salts SUCK water in their
direction
Eventually
the cell
will
explode
*Homeostasis*
INSIDE
BALANCED
IN
Cells shrivel
up and die
OUTSIDE
OUT
• Movement of water and other permeable solutes
through a membrane by the force of hydrostatic
pressure
• Hydrostatic pressure is the force, or weight, of a fluid
pushing against a surface
• Molecules move through a membrane from an area of
high hydrostatic pressure to an area of low
hydrostatic pressure
• A type of filtration which moves small particles
through a membrane but not larger ones
-Dialysis is a process
for removing waste
and excess water
from the blood
Glucose and
water are small
enough to pass
through
membrane
pores
-This is used
primarily as an
artificial
replacement for lost
kidney function in
people with kidney
failure.
Proteins are too
large to move
out of the pores
Over time …
• Facilitated diffusion is the movement of particles
through a membrane by means of carrier
molecules
• Carrier proteins attract a solute to a binding site and
changes shape to move the solute from an area of high
to low concentration (down a concentration
gradient).
Specific only for one chemical or substrate;
protein changes shape to bind to substrate
and transport it through
Mostly ions passing through; no
shape change happens
• A carrier-mediated process in which cellular
energy is used to move molecules from an area of
low concentration to an area of high
concentration, or, against a concentration
gradient.
• Requires ATP
• Types:
• Ion/Protein Pumps
• Endocytosis
• Phagocytosis
• Pinocytosis
• Exocytosis
• This pump allows cells to move certain ions across the
membrane requiring cellular energy (ATP)
• This requires the use of intramembrane proteins to move the
ions across
Example: Calcium Pumps
• In membranes of muscle cells to
force out calcium ions for proper
functioning
Inside Cell
Example: Sodium-Potassium Pumps
• In membranes of all cells, actively
transporting sodium and
potassium ions in opposite
directions. It transports sodium
ions out of the cell and potassium
ions into the cell.
• Cell membrane “traps” some extracellular
material and brings it into the cell
• Phagocytosis: “cell eating” – ingestion and digestion
of particles by a cell.
• Microorganisms or large particles are engulfed by the cell
membrane and pinched off to form a vesicle
• Pinocytosis: “cell drinking” – ingestion of fluids and
particles dissolved into it.
• Fluid is engulfed by cell membrane and pinched off to form
a vesicle
• Movement of large particles (like proteins) out
of the cell without actually passing through the
cell membrane
• Particles are enclosed in a vesicle, the vesicle is then
pulled to the cell membrane, the vesicle fuses to the
cell membrane and releases its contents.