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Diffusion & Osmosis
Diffusion & Osmosis
Cell exist in a constantly changing
environment.
Homeostasis: Biological balance, or
stability that a cell maintains with its
environment.
MOLECULES TEND TO MOVE
INTO THOSE AREAS THAT ARE
LESS CONCENTRATED!
Diffusion
 Process by
which
molecules
spread from an
area of greater
concentration
to an area of
lesser
concentration.
Diffusion Continued….
Concentration
Gradient –
Difference in
concentration of a
substance across
space.
Equilibrium
When the concentration of the
molecules of a substance is the same
throughout the space.
Diffusion Across Membranes
 Permeable:
Membranes that
allow substances
to pass through
them.
 Not all molecules
pass through the
membrane
Size
Type
Molecular
Structure of
membrane
Osmosis
The process by
which water
molecules diffuse
through a
membrane from
an area of greater
concentration to
an area of lesser
concentration.
Direction of Osmosis
Hypertonic – Greater solute
concentration
Hypotonic – Lesser solute
concentration
Isotonic – Equal solute concentration
Direction of Osmosis
Condition
Environment
solution is:
Cell Solution
is:
Water will
move:
If solute
concentration in env.
is less than the cell
hypotonic hypertonic
If solute
concentration in env.
is more than in cell
Out of the
hypertonic hypotonic
cell
If solute
concentration in env.
is equal to the cell
isotonic
isotonic
Into the
cell
Water will
not move
Passive & Active Transport
Passive Transport
Greater concentration to lesser concentration.
No use of energy
Example: facilitated diffusion, simple diffusion
Active Transport
Lesser concentration to greater concentration
Use of energy (against concentration gradient)
Example: Sodium-Potassium pump; Endo- &
Exocytosis
Passive Transport vs. Active Transport
Carrier Molecules
Proteins that function in transport.
Each is specialized to allow the movement
of only one type of molecule across a
membrane.
Carriers used in
gated channels &
facilitated diffusion
Passive Transport
Simple Diffusion
Movement through lipid bi-layer
Gated Channel
Protein controlled passage that permits cell to
be as permeable as needed.
Facilitated Diffusion
Carrier molecules transport solute molecules
through a membrane without expending energy.
Endocytosis & Exocytosis
Endocytosis: process by which cells
engulf substances that are too large to
pass through the membrane.
Pinocytosis: Solute or fluids into the cell.
Phagocytosis: Large food particles or whole
microorganisms into the cell.
Exocytosis: passage of large molecules
out of the cell.
The Role of Osmosis
Plasmolysis: Condition in which water
leaves the cell, and cell wilts.
Cytolysis: Condition in which a cell takes
in so much water that they burst.