Download Osmosis and animal cells

Osmosis
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What is osmosis?
Osmosis is the diffusion of water molecules from a low
sugar concentration solution to a high sugar concentration
solution across a partially-permeable membrane.
A partially-permeable membrane has holes in it that permit
water molecules through, but are too small to allow larger
molecules through. Osmosis can be demonstrated using
visking tubing filled with a solution and placed in a beaker
of pure water.
partiallypermeable
membrane
(visking tubing)
water
Glucose
(solute)
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Dilute vs. concentrated
During osmosis, water molecules diffuse from pure water or
dilute solution to more concentrated solutions.
 Dilute solutions have a high concentration of
water molecules.
 Concentrated solutions have a low concentration
of water molecules.
pure water
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dilute solution
concentrated
solution
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Predicting osmosis
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Osmosis in action
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 The concentration of solutes inside your body cells
needs to stay at the same level for them to work
properly.
 However, the concentration of the solutions outside
your cells may be very different to the concentration
inside them.
 This concentration gradient can cause water to move
into or out of the cells by osmosis
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• If the concentration of solutes in the solution outside the
cell is the same as the internal concentration the solution
is ISOTONIC to the cell
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• If the concentration of the solutes in the solution
outside the cell is higher than the internal
concentration the solution is HYPERTONIC to the cell
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• If the concentration of the solutes in the solution outside
the cell is lower than the internal concentration the solution
is HYPOTONIC to the cell
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In Plants
 If more water is lost by osmosis the vacuole
and cytoplasm shrink and eventually the cell
membrane pulls away from the cell wall.
 This is PLASMOLYSIS
 Plasmolysis cells die very quickly unless the
osmotic balance is restored.
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Osmosis and cells
Plant and animal cells are surrounded by a partiallypermeable plasma membrane. This allows water and other
small molecules to diffuse across.
Plant cells additionally have a strong cell wall surrounding
the membrane which offers support and protection.
plasma
membrane
cell wall
plant cell
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red blood cell
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OSMOSIS IN PLANTS
• Plants rely on osmosis to support their stems and
leaves
• When water moves into a cell by osmosis this
causes the vacuole to swell which presses against
the cytoplasm against the cell wall – this pressure
is called TURGOR PRESSURE
• This pressure makes the cell hard and rigid
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• If more water is lost by osmosis, the vacuole and
cytoplasm shrink, and eventually the cell membrane
pulls away from the cell wall.
• This is PLASMOLYSIS.
• Plasmolysed cells die quickly unless osmotic balance
is restored.
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Osmosis and plant cells
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Osmosis and plants
Root cells in plants absorb water
through osmosis.
Many fine root hairs increase the
surface area of a plant’s roots,
allowing them to draw in more
water from the surrounding soil.
The presence of water in plant cells
gives the plant structural support
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Osmosis and animal cells
Animal cells do not have a cell wall. This means they
respond differently to plant cells to the gain and loss
of water.
In dilute solutions, osmosis can
cause animals cells, such as red
blood cells, to swell up and burst.
This is called lysis.
In concentrated solutions, water
loss causes the cells to shrink.
When this happens to red blood
cells, it is called crenation.
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Osmosis and animal cells
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Osmosis and animal cells
In order to remain healthy, animal cells need to maintain
an isotonic water balance. This means that the water
concentration both inside and outside the cell is equal.
hypothalamus
The concentration of water
and salt in the blood is
controlled by the kidneys.
The kidneys are controlled
by the portion of the brain
called the hypothalamus.
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• PRACTICAL
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OSMOSIS and DIFFUSION
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Concentration gradient
Concentration Gradient - change in the concentration of a
substance from one area to another.
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PLANT CELLS
Hypotonic
Solution
Turgor Pressure builds
in the cell and causes
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to stop
Hypertonic
Solution
Plants will wilt when cells
lose water through osmos
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ELODEA CELLS
As viewed under the microscope
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Glossary
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Anagrams
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Which process?
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Multiple-choice quiz
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