TYPES OF OSMOTIC SOLUTIONS
A) Hypotonic Solutions (hypo - low solute)
A hypotonic solution contains a lower solute concentration than the solution in the cell.
Therefore the solution must also have a high solvent (water) concentration as compared to
the cell.
solute
100% H2O
0% solute
80% H2O
Outside the Cell
20% solute
Inside the Cell
H2O
Therefore the direction of osmosis is into the cell because
[H2O]outside is greater than the [H2O] inside.
The pressure produced by the movement of water into the cell is call osmotic pressure.
Effects on Animal Cells
As the animal cell gains water by osmosis,
the cell membrane is being stretched and if
swelling continues the cell will undergo
cytolysis (lyse) and cause the cell to burst.
Therefore animal cells need to remove excess
water.
Effects on Plant Cells
As the plant cell gains water by osmosis.
Water will enter and fill the central vacuole,
which will push on the cytoplasm and the cell
wall. This internal pressure is called turgor
pressure. The increase pressure causes the
cell to swell. The cell wall prevents the cell
from rupturing. In this condition the cell is
said to be turgid. This is an ideal state for
plants.
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B) Hypertonic Solutions (hyper - high solute)
A hypertonic solution contains a high solute concentration than the solution in the cell.
Therefore the solution must also have a low solvent (water) concentration as compared to the
cell.
solute
90% H2O
10% solute
99% H2O
Outside the Cell
1% solute
Inside the Cell
H2O
Therefore the direction of osmosis is out of the cell because
[H2O]outside is less than the [H2O] inside.
Effects on Animal Cells
An animal cell will lose water by osmosis.
The cell will shrivel or crenate.
A cell can conserve water by pumping out salt
(solute).
i.e. Bony fish in sea water
Effects on Plant Cells
As the plant cell loses water by osmosis, the
central vacuole will shrink causing the turgor
pressure to drop. The cell membrane will
come away from the cell wall causing the cell
to be less rigid.
This condition is called plasmolysis.
If the cell reaches this state it will be lethal
and the cell may not recover.
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C) Isotonic Solutions
An isotonic solution contains an equal solute concentration as the one found inside the cell.
solute
75% H2O
25% solute
75% H2O
Outside the Cell
25% solute
Inside the Cell
H2O
Therefore rate of osmosis into the cell is equal to the rate of osmosis out of the cell because
[H2O]outside is equal to [H2O] inside.
Therefore the net movement of molecules is zero.
Effects on Animal Cells
The volume of the animal cell remains
unchanged since there is a dynamic
equilibrium across the cell membrane.
Effects on Plant Cells
Since there is no net movement of water
across the membrane of the cell, the size of
the cell remains the same. The cell membrane
is just touching the cell wall.
The plant cell has become flaccid (limp) and
therefore the plant cell will lose some of its
structural support do to low turgor pressure.
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