Name:_____________________________Hr.:___
Osmosis Lab
Background Information:
To perform their functions, cells must maintain an
internal steady state in the midst of an ever-changing
environment. This constancy, or homeostasis, is maintained in
part by the regulation of the movement of materials into and out
of the cell. To achieve this control, a cell is surrounded by a
membrane that can distinguish between different substances, slowing down or stopping
the movement of some while allowing others to pass through freely. Because not all
substances penetrate the cell membrane equally well, the membrane is said to be
selectively permeable.
Osmosis is the diffusion of water through a selectively permeable membrane from a
region of higher water concentration to a region of lower water concentration. In this
study you will become familiar with osmosis and examine some of the factors that
influence this process.
Purpose:
 To observe the effects of water movement on cells.
 To observe what happens when a cell is placed in a hypotonic, hypertonic, and
isotonic solutions.
Materials: (per student group):
red onion epidermis, forceps, droppers, distilled water, 10% sodium chloride
(table salt) solution, paper towel, microscope, slide, and cover slip
Procedure:
1. Make a wet mount of the red onion epidermis and elodea using the water they
are submerged in.
2. Examine the onion cells under low power. When you have a clear view of several
cells, switch to high power. Make a labeled drawing, properly labeled in your data
table. This will give you a record of the original appearance of the cells.
3. Repeat #2 for the elodea cells.
3. Take a dropper and add several drops of salt solution to one side of your cover
slip while placing a small piece of paper towel along the opposite edge of the cover
slip for both slides. The paper should draw out the water and draw in the salt
solution. Do this several times, being careful not to disrupt the cells.
4. Observe the effects of the saline (salt) solution on the onion and elodea cells.
Make a properly labeled, careful drawing of the cells' appearance in your data
table for both slides.
5. Replace the sodium chloride solution with distilled water in the same way that
the salt solution was added. Make a properly labeled drawing of the cells'
appearance in your data table.
6. Answer the questions which follow your data.
Name:_____________________________Hr.:___
DATA:
Draw initial condition of elodea and onion, after adding 10% NaCl, and after
flushing with distilled H2O. Label cell wall, cell membrane, cytoplasm, chloroplasts
(if visible), nucleus and note color of specimen for each diagram. Fill entire box
with diagram. Repeat observations and diagrams after treatment with test
solutions.
Group of four onion cells (initial)
Description:
Group of four onion cells (10% NaCl)
Description:
Group of four onion cells (flushed with dH2O)
Description:
Group of four Elodea cells (initial)
Description:
Group of four Elodea cells (10% NaCl)
Description:
Group of four Elodea cells (flushed with dH2O)
Description:
Name:_____________________________Hr.:___
QUESTIONS:
1. Which type of water was hypotonic?
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2. On what evidence do you base this?
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3. Which type of water was hypertonic?
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4. On what evidence do you base this?
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5. Explain why your cells appeared the way they did after each treatment.
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APPLICATIONS:
1. Why do grocery store owners spray fresh fruits and vegetables with
water?
2. Roads are sometimes salted to melt ice. What does this do to plants
around the roadside and why?
3. If a bowl of fresh strawberries is sprinkled with sugar, a few minutes
later the berries will be covered with juice. Why?