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Osmosis
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What is osmosis?
Osmosis is the diffusion of water molecules from a low
concentration solution to a high 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
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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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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 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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Glossary
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Anagrams
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Which process?
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Multiple-choice quiz
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