Cellular Transport
• Cell membrane is
selectively permeable
• Factors that affect
permeability:
– Size
– Polarity
– Presence or Absence or
Protein Channels or
Receptors
Diffusion
• Movement of substances
from high concentration to
low concentration
• Movement “down a
concentration gradient”
• Due in part to random,
rapid motion of molecules.
•
•
•
•
•
Net Movement
Equilibrium State
Simple Diffusion.
Roles in the Body
Factors that Affect Rate:
– permeability of membrane
– Size of gradient
– temperature
Osmosis
• Diffusion of water through
a selectively permeable
membrane.
• Movement of water
– from “less salty” to “more
salty” side of membrane
– from low solute
concentration to high solute
concentration.
– from high water
concentration to low water
concentration.
•
•
•
•
Hypertonic
Hypotonic
Isotonic
In everyday life:
– Preservation of food
– Eating of salty or sugary
foods
– Salt on a slug
– contractile vacuoles
– turgur pressure in plants
OSMOSIS DEMONSTRATION
(DIALYSIS BAGS)
OSMOSIS EXPERIMENTAL
RESULTS
OSMOSIS IN PLANT CELLS
HYPOTONIC SOLUTION=
NORMAL TURGOR
PRESSURE
HYPERTONIC
SOLUTION=
PLASMOLYSIS
OSMOSIS IN PLANT CELLS
(Elodea)
Plasmolyzed cells
Osmosis and Animal Cells
NO CHANGE
CRENATION
WILL LYSE
OSMOSIS AND ANIMAL
CELLS
WILL LYSE
CRENATE
NO CHANGE
Facilitated Diffusion
• Movement from high
concentration to low
concentration through
carrier proteins.
• Used to move ionic or
large substances into
or out of cells
• Passive process
• Carrier proteins are
specific (will only
move one substance)
• Important for moving
sugars and amino
acids into cells
Active Transport
• Movement of substances
against a concentration
gradient.
– From low concentration to
high concentration.
• requires energy
• pumping a substance
• ATP must be hydrolyzed
to fuel this process
• Sodium-Potassium Pump
• Pumps sodium out of cells
and potassium into cells.
• Important for the
functioning of nerves and
muscles.
• Pump is a membrane
protein and an enzyme-ATPase.
Sodium-Potassium Pump
3 Na+ pumped in for every 2 K+ pumped
out; creates a membrane potential
Moving the “Big Stuff”
Exocytosis
- moving
things
out.
Molecules are moved out of the cell by vesicles that fuse
with the plasma membrane.
This is how many hormones are secreted and how nerve
cells communicate with one another.
Pinocytosis
• Cell forms an
invagination
• Materials dissolve
in water to be
brought into cell
• Called “Cell
Drinking”
Example of Pinocytosis
pinocytic vesicles forming
mature transport vesicle
Transport across a capillary cell (blue).
Receptor-Mediated Endocytosis
Some integral proteins have receptors
on their surface to recognize & take in
hormones, cholesterol, etc.
Endocytosis – Phagocytosis
Used to engulf large particles such as
food, bacteria, etc. into vesicles
Called “Cell Eating”
Three Forms of Transport Across the Membrane