Diffusion and Osmosis
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Transcript Diffusion and Osmosis
Solutions
Water
is considered the solvent.
The substance(s) dissolved in water is /
are the solute(s).
Together, solvent + solute solution.
Concentration is the number of solutes
in each volume of solvent
Osmosis
The
diffusion of water across
a semipermeable membrane
is called osmosis.
In a solution, there are water
molecules and dissolved
particles (the solute).
The more dissolved particles
there are, the lower the
concentration of water
molecules.
ANIMATION
Comparing Solutions
A solution
may be desribed as isotonic,
hypertonic or hypotonic relative to
another solution
These are comparisons; they require a
point of reference (ie, my hair is shorter…
…than it was last year).
The comparison in biology is usually to the
inside of a cell.
Isotonic
A solution is isotonic to a
cell if it has the same
concentration of dissolved
particles as the cell.
This means the water
concentration is also the
same.
Water molecules move into
and out of the cell at an
equal rate in an isotonic
solution.
The cell size remains the
same.
Hypertonic
A hypertonic solution has
a higher concentration of
dissolved particles than a
cell.
This means the water
concentration is lower than
that of the cell.
Thus, water flows out of
the cell – so, the cell will
shrivel and eventually die.
ANIMATION
Hypotonic
A hypotonic solution has a
lower concentration of
dissolved particles than a
cell.
Therefore the water
concentration is higher
than that of the cell.
Thus, water diffuses into
the cell – causing the cell
to expand and potentially
burst.
Impact on Cells
In an isotonic solution (center), water enters / exits
red blood cells at equal rates.
In a hypertonic solution (like salt water – right),
water rushes out and the cell shrivels.
In a hypotonic solution (like distilled water – left),
water rushes in and the cell swells / bursts (lysis).
Video clips:
RBC in isotonic solution
RBC in hypertonic solution
RBC in hypotonic solution
Adaptations - Plants
Plant
cells use the cell wall to prevent bursting.
At center, the plant cell is in an isotonic solution. Water
moves in / out at equal rates (no NET movement)
At left, the plant
cell is in a
hypotonic
solution.
At right, the
plant cell is in
a hypertonic
solution.
Water rushes
in, filling the
vacuole.
Water rushes
out of the
cell, draining
the vacuole.
This cell is
turgid / has
high turgor
pressure.
Video: Elodea in isotonic / hyper / hypo
This is called
plasmolysis.
Adaptations - Protists
Paramecia live in
freshwater
This makes paramecia
hypertonic to their
surroundings
Water is constantly
rushing into the
paramecium
So the paramecium uses
a contractile vacuole to
pump the water back out
(and prevent bursting)
Video: The contractile vacuole in action