In Haiti in 2010…
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Haiti cholera death toll passes 900 (cnn.com)
Health workers alarmed over trend in Haiti’s
cholera outbreak (cnn.com)
Cholera deaths up in Haiti, with worst to come
(nytimes.com)
You are the doctor, and you must save a
cholera patient’s life. Here is what you
have to work with…what would you use?
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Antiviral medication
Antibacterial medication (antibiotics)
Salt
Aspirin
Sugar
Water
Pepsi
How did we do?
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Share how your group decided to treat the
patient.
What is cholera?
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Infection of the small
intestine which is caused by a
bacteria, Vibrio cholerae.
Symptoms include diarrhea
and vomiting, and may lead
to death due to dehydration.
The disease is transmitted
through contaminated food
and water.
So…what happened?
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Why did some groups save their patients while
other groups ended up killing their patient?
The answer lies in understanding osmosis &
diffusion.
Osmosis, Diffusion &
the Cell Membrane
Two quick demonstrations
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Ink
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What is going to happen if we let this beaker sit for
the rest of class? Why?
Perfume
If I spray some perfume in the room (don’t worry, I
won’t), what is going to happen?
 Who will be able to detect the scent first? Why?
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Ever been to a party where there are a
ton of people in one room? What do you
do?
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Most likely, you spread
out to another room
where it is less crowded.
If you were a molecule,
this would be diffusion.
Diffusion
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The movement of molecules from areas of high
concentration (where there are a lot) to areas of
low concentration (not so many).
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This explains why the perfume smell spreads
throughout the room & why the ink spreads
throughout the glass
Requires no energy
Increasing heat can speed up rate of diffusion
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Why does sugar dissolve faster in hot tea than in cold
tea?
Next question…
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How do you prevent a
“bad guy” from breaking
into your home at night?
Cell Membrane
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Just as your house has ways to protect against
unwanted visitors, the cell does too.
The cell membrane is made up of phospholipids
Roles:
Separate the cell from the environment
 Control what comes in the cell & what goes out of the
cell
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Cell Membrane
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The cell membrane is semi-permable
Means that certain molecules can pass through the
phospholipid bilayer (i.e. water) but certain things
cannot
 Size usually plays a factor but so may other qualities,
such as electrical charge
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i.e. I can keep burglars out of my home but I sometimes
have trouble keeping ants & insects out
Osmosis
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Many molecules are able to diffuse in and out of
cells.
Water is one such molecule.
The diffusion of water is so important to cells that
we have a special term for it.
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Diffusion of water across a semi-permeable membrane
osmosis.
During osmosis, WATER moves from an area of
high concentration (where there is more water) to
an area of low concentration (where there is less
water)
Osmosis Example
Ways of Describing Solutions
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Solute – component of solution in lesser amount
(i.e. in potato lab, it was the salt or sugar)
Solvent – component of solution in greater
amount (i.e. in potato lab, it was the water)
3 Ways of Comparing Solutions
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Hypotonic
Root word means “below”
 Describes a solution with a lower concentration of
solute than the solution across a selectively
permeable membrane
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3 Ways of Comparing Solutions
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Hypertonic
Root word is above (i.e. think about “hyperactive”
meaning “above active”)
 Describes a solution with a higher concentration of
solute molecules than the solution across a
selectively permeable membrane
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3 Ways of Comparing Solutions
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Isotonic
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Describes solutions with equal solute concentrations
on either side of a selectively permeable membrane
What does this mean to cells?
Skin
Intestine
Body
Skin
Salt
Intestine
Body
Salt
Salt
The cholera
bacteria
releases a
toxin that
causes cells to
secrete salt
into the
intestine.
Salt
Salt
Salt
Salt
Salt
So, there is a
greater amount of
salt inside the
intestine compared
to the outside of
the intestine. Using
what you know
about osmosis,
explain what
happens next.
Net Flow of Water
Osmosis
Salt
Salt
Salt
Salt
Salt
Salt
Net Flow of Water
Salt
Salt
Salt
Net Flow of Water
Salt
How would you treat the
patient using osmosis?
Cell Membrane Structure
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Made of two layers (lipid
bilayer)
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Gives cell membranes a
flexible structure that
forms a strong barrier
Contains protein and
carbohydrate molecules
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Helps materials cross the
membrane
Cell Membrane Structure
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Phospholipid
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Proteins embedded in bilayer
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Hydrophobic tail; Hydrophilic head
May act as channels
Carbohydrate chains
Cellular identification
 Like a flag
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Facilitated Diffusion
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Cell membrane has
certain channels
(proteins) that make it
easy for certain
molecules to cross the
membrane
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Will only occur if there is
a higher concentration on
one side of the membrane
Back to that party…
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What if you wanted to move from the empty
room to the crowded room?
It would require energy on your part to fight
your way through the crowd.
Active Transport
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Sometimes it is beneficial for cells to move
certain molecules “against the tide”
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From areas of low concentration to areas of high
concentration
This requires cells to use energy
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The cell has to use ATP (energy currency of the cell)
in order to make this happen
Active Transport
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Small molecules and ions are carried across membranes
by proteins
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Endocytosis
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Requires energy, cells use majority of their energy for
transport
Process of taking material into the cell by folding of cell
membrane
Exocytosis
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Membrane of vacuole fuses with cell membrane forcing
contents out of cell
Wrap-Up Question, 10/13
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Compare/contrast diffusion with active
transport.
Wrap-Up Question, 10/15
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What did you expect to happen with the eggs?
How did the actual results compare with your
prediction?