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Biology 12: Osmosis and Diffusion
DIFFUSION: the movement of any substance, EXCEPT WATER, from a region of
high concentration to low concentration. They flow WITH ( OR "ALONG" or
"DOWN" ) a concentration gradient.
This is very valuable… many processes in the body: absorbing O2, getting rid of CO2,
absorbing nutrients, getting rid of waste, etc
EQUiLIBRIUM is reached when the solute and solvent particles are evenly and equally distributed.
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OSMOSIS is the tendency for water to DIFFUSE a differentially permeable
membrane… again from HIGH to LOW concentration.
All cells are surrounded by a membrane. The membrane is SELECTIVELY (or
differentially) PERMEABLE because it can SELECT which types of molecules can
pass through. In the example below, LARGE molecules cannot pass through, but
small molecules can. As a result, the LARGE molecules are unevenly distributed, and
the small molecules are evenly distributed.
In which direction would these water molecules go ?
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The movement of water across the membrane results in OSMOTIC PRESSURE.
Now, consider the example of an animal cell below. It has a selectively permeable
membrane. It has salt (squares) and water (circular) molecules in side.
IF we place this animal cell in PURE WATER, what will happen? Why?
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So, what will happen to a fish if it swims in FRESH water?
OSMOTIC PRESSURE is
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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TONICITY:
Solutions (when co pared to their environment) can be 1 of three things:
ISOTONIC, HYPOTONIC or HYPERTONIC.
ISOTONIC means that the water concentration and solute concentration is equal. ISO means equal.
If a solution is HYPOTONIC it has LESS solute (and therefore more water) than its environment.
If a solution is HYPERTONIC it has MORE solute (and therefore less water) than its environment.
In Animal Cells ( with no cell wall):
LYSIS
CRENATION
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In Plant Cells (with a cell wall)
Normal
= flaccid
water enters and exits at
the same rate
Plasmolysis
More water has exited
than entered
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Turgid
More water has entered
than has exited
Answer these questions in full sentences on separate paper. See pp. 71-73 in Mader 10th.
1.
Explain the difference between OSMOSIS and DIFFUSION.
2.
Explain the terms hypertonic, isotonic and hypotonic.
3.
If a salmon migrates into a river from the sea, is the river isotonic, hypotonic or hypertonic to
the fish ? Is the fish isotonic, hypotonic or hypertonic to the river?
4.
Here is a plant cell that is a bit dehydrated. What will
happen to it when we..
a. place it in fresh water?
b. Place it in a hypotonic solution?
c. place it in a hypertonic solution?
5.
Here is an animal cell. What will happen to it when we…
a. Place it in an isotonic solution?
b. Place it in a hypotonic solution?
c. place it in a hypertonic solution?
6.
What is a selectively permeable membrane?
7.
Molecules will always flow from ____________ concentration to ______________
concentration. If those are water molecules flowing from _________ to _________ , we call
the process osmosis. If the particles are anything BUT water, we call the process
____________ .
8.
The point at which water molecules enter and leave a cell at the same rate is called _____
9.
What is meant by the terms turgor pressure, crenation and plasmolysis?
10a.
Why is turgor pressure not used in reference to animal cells?
b.
Why is crenation not used in reference to plant cells?
11.
not?
If a cell is placed in an ISOTONIC solution, is water moving across the cell membrane, or
Explain.
12.
Which of the following conditions describe a hypotonic solution that a cell is placed in?
a) a higher solute concentration outside the cell
b) a lower solute concentration outside the cell
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c) a equal solute concentration both inside and outside the cell
d) none of the above
13.
The movement of molecules from a region of low concentration to a region of high
concentration is
a) endocytosis
b) osmosis
c) diffusion
d) active transport
14.
The red blood cell which is about 80% water will do the following when placed in distilled
water
a) shrink
b) swell
c) stay the same
d) plasmolyze
15.
A plant cell placed in a salt solution will undergo
a) plasmolysis
b) diffusion
c) turgor
d) deplasmolysis
16.
A ________________________ barrier allows only certain particles to pass through.
17a.
A marathon runner collapses after running on a hot day. Although the runner consumed
adequate water along the route, blood testing showed that many of his red blood cells had
burst. Why was this the case? (hint: on hot days, well-trained runners drink fluids that contain
sugar and salt and thus avoid this problem).
b.
The challenge with making a sports drink is that you need to drink salty water without making
it taste too salty. The scientists who figured this out created the first sports drink called
Gatorade. At which U.S. university was th is first created and used, and why do you think it
was that school, rather than, for example, the University of Washington?
18.
When gardeners bring in fresh vegetables from the garden, they sometimes soak them in
saltwater before rinsing them and soaking them in freshwater. Why would they do this?
19.
In what type of solution (hypotonic, isotonic or hypertonic) will a red blood cell undergo
crenation?
20.
In what type of solution (hypotonic, isotonic or hypertonic) will a red blood cell undergo
lysis?
21.
In what type of solution (hypotonic, isotonic or hypertonic) will a red blood cell undergo
plasmolysis?
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22.
The diagram below shows a bag made with dialysis tubing... dialysis tubing is permeable to
water and NaCl, but not large molecules like maltose. The bag is attached to a rubber stopper,
and open at the top , where a glass tube
protrudes from the opening.
Once the dialysis bag ( containing a
solution of 6% maltose and 4% NaCl) is
placed into the water ( containing 4%
NaCl)
a.
Will the water level go up the tube, or will
water be sucked out of the bag ?
b.
What will happen to the [ ] of water in the
bag? Why?
c.
What will happen to the [ ] of maltose in
the bag? Why?
d.
What will happen to the [ ] of NaCl in the
bag? Why?
23.
Shown below is a beaker divided in half by a semi-permeable membrane. The membrane is
NOT permeable to salt. On one side is a solution of pure water, on the other is a 30% salt
solution. Why will the level on the salt-solution side go up?
QuickT ime™ and a
TI FF (Uncompressed) decompressor
are needed to see this picture.
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