Lesson 5. Introduction to Osmosis
Estimated Time: 1 period
Objective: to define osmosis in terms of diffusion principles and concentration through a
comparison to diffusion
EQ: How are osmosis and diffusion similar? How are they different?
Bridge: Answer the following questions
1. The diagram below represents a laboratory setup used by a student during an
investigation of diffusion.
Which statement best explains why the liquid in tube A will rise over a period of time?
(1) The starch concentrations are equal on both sides of the membrane.
(2) The water will pass from a region of lower starch concentration to one of higher starch
concentration.
(3) Water and starch volumes are the same in both tubes A and B.
(4) The fluids in both tubes A and B will change from a higher temperature to a lower
temperature.
2. A laboratory setup for a demonstration is represented in the diagram below.
Describe how an indicator can be used to determine if starch diffuses through the membrane into
the beaker. In your answer, be sure to include:
• the procedure used [1]
• how to interpret the results [1]
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Mini Lesson: Go over the questions from the bridge.
Ask the students what, other than the iodine (starch indicator) and the glucose, moved through
our selectively permeable membrane and what evidence supported that this happened (repeat of
the closing from yesterday).
Tell the students that when water moves across a concentration gradient from high to low
concentration, we give this process a special name: osmosis. The movement of water molecules
is dependent on the solute concentration of the surrounding environment.
Expectations for the Work Period: You will be reading the background information for part two
of the Diffusion through a Membrane lab today. Complete the reading and graphic organizer
independently.
Then using the information in the reading and working with a partner, create a set of 3 before
and after diagrams that illustrates the concept of osmosis and its effect on a cell.
Work Period: graphic organizer and diagrams
Summary: Answer the EQ
Closing: Answer the following questions:
An investigation was set up to study the movement of water through a membrane. The results are
shown in the diagram below.
Based on these results, which statement correctly predicts what will happen to red blood cells
when they are placed in a beaker containing a water solution in which the salt concentration is
much higher than the salt concentration in the red blood cells?
(1) The red blood cells will absorb water and increase in size.
(2) The red blood cells will lose water and decrease in size.
(3) The red blood cells will first absorb water, then lose water and maintain their normal size.
(4) The red blood cells will first lose water, then absorb water, and finally double in size.
If vegetables become wilted, they can often be made crisp again by soaking them in water.
However, they may lose a few nutrients during this process. Using the concept of diffusion and
concentration, state why some nutrients would leave the plant cell. [1]
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SPED and ELL Modifications:
1. Allow creative responses for longer responses – draw, type, etc..
2. Prerecord the independent practice article.
3. Highlight the key terms in the article \
Apps and Internet Activities:
A word search: http://www.proprofs.com/games/word-search/diffusion-and-osmosis
A crossword puzzle: http://biologycorner.com/worksheets/diffusion_osmosis_crossword.html
Answers:
http://www.biologycorner.com/worksheets/diffusion_osmosis_crossword_key.html
Independent Practice: Read article and describe why the woman died. In your explanation, be
sure to use the terms:
Diffusion
concentration
osmosis
Either hypotonic, isotonic, or hypertonic (extra credit if you use all three)
solute
Name __________________________________________________
School
Living Environment
Date __________________________
Reading: Diffusion of Water Across a Membrane (Osmosis)
Osmosis is a special type of diffusion. Specifically, it is the diffusion of water across a
membrane. Osmosis is a very important process because it enables cells to maintain the proper
water balance. Generally water will diffuse across a membrane, resulting in equal concentrations
of water on both sides.
If the cytoplasm of a cell is 95% water, the remaining 5% is dissolved materials (solute).
If the liquid that surrounds the cell has the same concentration of water as the cytoplasm, no net
diffusion occurs in either direction. In other words, equal numbers of water molecules move into
and out of the cell, but there is no net change in size of the cell. This is what we refer to as an
isotonic solution, where iso- means equal.
If the liquid outside the cell has a higher concentration of water (less solute) than the
cytoplasm, water will diffuse into the cell trying to reach equilibrium. The solution outside of
the cell would be considered hypotonic to the solution inside the cell, where hypo- means less
(less solute in the solution than in the cell). This will cause the cell to swell up, and in the case
of animal cells, the cell will lyse, or explode. Plant cells have a separate cell structure that keeps
their cells from exploding. This structure is called a cell wall.
If the liquid outside the cell has a lower concentration of water (more solute) than the
cytoplasm, water will diffuse out of the cell trying to reach equilibrium. The solution outside of
the cell would be considered hypertonic to the solution inside the cell, where hyper- means more
(more solute in the solution than in the cell). This will cause the cell to shrink up, leaving very
little space in the cell for any chemical reactions to take place or room for the organelles to
properly do their jobs.
You may wish to view this video: http://www.youtube.com/watch?v=_slUL3kMZlU to help
you with understanding of isotonic, hypertonic, and hypotonic.
If the solution on the outside is the same
concentration on the inside, what will happen?
Definition:
If the solution on the
outside is more
concentrated than the
solution inside, what
will happen?
Main Idea:
If the solution on the
outside is less
concentrated than the
solution on the inside,
what will happen?
In the diagram below, the o represents water and the x represents the solute. Show what will happen
to the concentrations on each side of the model cell (osmosis) based on the reading above and your
knowledge of osmosis.
x o
x
x
o o o x
x o o o o
x ox
x
o
o
ox
ox
Diagrams:
Based on the description of each model and the information in the reading, draw what the cell
would look like in the final state after sitting for 15 minutes.
Diagram 1. 5% salt solution both inside and outside the artificial cell
Initial State
Final State
Diagram 2. 20% salt solution outside the artificial cell, 5% salt solution inside the cell
Initial State
Final State
Diagram 3. 5% salt solution outside, 20% salt solution inside the cell
Initial State
Final State
Dictionary Help for Diffusion Through a Membrane: Osmosis Reading
Word
cytoplasm
Definition
The gooey liquidy inside of
the cell that is made mostly of
water. It is the place where
many of the chemical
reactions in a cell takes place.
It also helps to keep
organelles (cell parts) in place
in the cell, and helps protect
the organelles by cushioning
movements (like shocks on a
car)
lyse (lysis)
The process of a cell bursting
when it can no longer hold the
molecules trying to move into
a cell (like blowing up a
balloon until it pops in your
mouth because it cannot hold
any more air)
cell wall
Organelle found in plant cells,
some bacteria, some fungi,
and some protists. It serves to
give the cells support,
structure, and protection from
the environment and is found
just outside of the cell
membrane.
Picture
Article for independent practice:
Woman dies after waterdrinking contest
Water intoxication eyed in ‘Hold Your Wee for a Wii’ contest death
SACRAMENTO, Calif. — A woman who competed in a radio station’s contest to see
how much water she could drink without going to the bathroom died of water
intoxication, the coroner’s office said Saturday.
Jennifer Strange, 28, was found dead Friday in her suburban Rancho Cordova home
hours after taking part in the “Hold Your Wee for a Wii” contest in which KDND 107.9
promised a Nintendo Wii video game system for the winner.
“She said to one of our supervisors that she was on her way home and her head was
hurting her real bad,” said Laura Rios, one of Strange’s co-workers at Radiological
Associates of Sacramento. “She was crying and that was the last that anyone had
heard from her.”
It was not immediately know how much water Strange consumed.
A preliminary investigation found evidence “consistent with a water intoxication death,”
said assistant Coroner Ed Smith.
John Geary, vice president and marketing manager for Entercom Sacramento, the
station’s owner, said station personnel were stunned when they heard of Strange’s
death.
“We are awaiting information that will help explain how this tragic event occurred,” he
said.
Initially, contestants were handed eight-ounce bottles of water to drink every 15
minutes.
“They were small little half-pint bottles, so we thought it was going to be easy,” said
fellow contestant James Ybarra of Woodland. “They told us if you don’t feel like you can
do this, don’t put your health at risk.”
Ybarra said he quit after drinking five bottles. “My bladder couldn’t handle it anymore,”
he added.
After he quit, he said, the remaining contestants, including Strange, were given even
bigger bottles to drink.
“I was talking to her and she was a nice lady,” Ybarra said. “She was telling me about
her family and her three kids and how she was doing it for kids.”
© 2012 The Associated Press.