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Diffusion and Osmosis
Warm Up
DEFINE DIFFUSION
Outline
• Learn the concepts of:
– Diffusion, osmosis, semipermeable membrane,
isotonic, hypertonic, &
hypotonic
• Plant/animal cells
exposure to water
– Hypertonic Env.
– Hypotonic Env.
– Isotonic Env.
Diffusion
• Solute molecules moving from
an area of high concentration
to an area of low
concentration
(water)
– Random motion drives
diffusion
– Movement is based on kinetic
energy (speed), charge, and
mass of molecules
– Equilibrium is reached when
there is an even distribution
of solute molecules
1
2
3
4
Osmosis
• Movement of water through a
semi-permeable membrane
– Semi-permeable: permeable to
solvents (WATER), but not to
large molecules
– High [water] to low [water]
• Dissolved molecules (i.e. glucose,
starch) are called solutes
• REMEMBER:
Water = solvent
Glucose, Starch = solutes
Effect of Water on Cells
• Hypertonic Environment
– High [solute], low [water]
• Hypotonic Environment
– High [water], low [solute]
Hypertonic
Hypotonic
Isotonic
• Isotonic Environment
– [water] = [solute]
Osmosis in Living Cells
Cellulose in
cell wall
Osmosis in Red Blood Cells
Isotonic
Crenation
Hypertonic
Hypotonic
Effect of Water on RBC
Diffusion and Osmosis
Warm Up
DEFINE OSMOSIS
INTRO
• Organisms are constantly responding to
their environment.
• Homeostasis = ability of an organism to
maintain a constant internal condition
despite external environmental changes.
INTRO
– Cell Membrane is selectively
permeable to different substances
– Some substances use energy to
transport across a membrane, while
others don’t need energy to move
across cell.
Passive Transport
• Movement across the cell membrane
that does NOT REQUIRE ENERGY from
the cell.
• Concentration Gradient = A difference
in the concentration of a substance
across a space
Passive Transport
• Equilibrium = A condition in which the
concentration of a substance is equal
throughout a space.
• Diffusion = The movement of a
substance from an area of high
concentration to an area of low
concentration caused by the random
motion of particles of the substance.
Passive Transport
• If diffusion is allowed to continue,
equilibrium results!
• The non-polar interior of the cell
membrane’s lipid bilayer repels ions and
polar molecules and prevents substances
from diffusing across the cell membrane.
• Small or non-polar molecules can diffuse
across the cell membrane down their
concentration gradient.
Water Diffuses Into & Out of Cells
By Osmosis
• Osmosis = The diffusion of water
through a selectively permeable
membrane.
• Involves the movement of water down
its concentration gradient.
• Type of passive transport!
Water Diffuses Into & Out of Cells
By Osmosis
• The direction of the water movement
across the cell membrane depends on
the concentration of free water
molecules in the cytoplasm and in the
fluid outside of the cell.
3 Possibilities for Direction of Water
Movement
1. H2O MOVES OUT – cell shrinks!
HYPERTONIC SOLUTION
2. H2O MOVES IN – cell swells!
HYPOTONIC SOLUTION
3. NO H2O MOVEMENT – cell remains same
size
ISOTONIC SOLUTION
3 Possibilities for Direction of Water
Movement
If swelling is left unchecked, cell could
BURST!
How do cells deal with this?
• Plant cells – rigid cell walls and contractile
vacuoles
• Animal cells – remove dissolved particles
from cytoplasm
– Increases free H2O molecules inside of cell
• Example: Common remedy for a sore throat
is to gargle with salt water. WHY?
Proteins Help Some Substances
Cross the Cell Membrane
• Transport Proteins – CHANNELS –
provide polar passageways through
which substances can move across the
cell membrane.
• Selective! – only specific substances are
allowed to pass! (sugars, amino acids)
Facilitated Diffusion
• Carrier Proteins = Transport protein
that carries a specific substance across
a cell membrane.
• Facilated Diffusion = When carrier
proteins are used to transport specific
substances (amino acids/sugars) DOWN
their concentration gradient.
Facilitative Diffusion
• http://highered.mcgrawhill.com/olc/dl/120068/bio02.swf
Diffusion and Osmosis
Day 3 Notes
Warm Up
What is the
difference between
active and passive
transport?
4:2 Active Transport
• Some substances are transported
against the concentration
gradient.
Active Transport
• Active transport = Transport of a
substance across a cell membrane
against its concentration gradient.
• Requires the cell to use energy –
supplied by ATP
Vesicles Move Substances Across
Membranes
• Endocytosis = The movement of a
substance into a cell by a vecisle
• Exocytosis = The movement of a
substance by a vesicle to the outside of
the cell
• Endocytosis
• Exocytosis