# Potato Osmosis - DOC by malj

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Potato Osmosis

Introduction:

A shipwrecked sailor is stranded on a small desert island with no fresh water to
drink. She knows she could last without food for up to a month, but if she didn't
have water to drink she would be dead within a week. Hoping to postpone the
inevitable, her thirst drove her to drink the salty seawater. She was dead in two
days. Why do you think drinking seawater killed the sailor faster than not drinking
any water at all? Today we explore the cause of the sailor's death. We'll prepare
solutions of salt water to represent the sea, and we'll cut up slices of potato to
represent the sailor. Potatoes are made of cells, as is the sailor!

Objective:

To determine how the concentration of solute in a solution affects the movement
of water across potato cell membranes.

Materials:

o   Potato
o   Corer
o   knife
o   6 beakers
o   marker
o   salt solutions (0.2M, 0.4M, 0.6M, 0.8M, 1.0M)
o   distilled water
o   paper
o   pencil
o   electronic balance
o   aluminum foil

Procedure:

Day 1

1. Use a knife to square off the ends of your potato. Your potato's cells will
act like the sailor's cells.
2. Stand your potato on end & use your cork borers to bore 6 vertical holes.

3. Remove the potato cylinders from the cork borer & cut them to the same
length (about 4 -5 centimeters long).
4. Record the turgidity (flexibility), mass, length and volume of each potato
5. Take 6 beakers and label them with the solution that will be placed in each
one --- distilled water, 0.2 M salt solution, 0.4M salt solution..etc
6. Fill each beaker 2/3's full of the correct solution
7. Place one of your potato cylinders into each cup and cover the top of the
cup with foil or plastic.
8. Leave the potato cylinders in the solution for 24 hours.

Day 2

1. Carefully remove the potato cylinder from the distilled water solution & pat
it dry on a paper towel.
2. Record the appearance of the cylinder on your data table. (day 2)
3. Measure the mass, length and volume of the potato cylinder & record
4. Repeat steps 1-3 for each potato cylinder
5. Clean up your equipment & area and return materials to their proper
place.

Data:

Prepare a data table which will allow you to record the initial and final mass,
length and volume of each of the potato cylinders. Include a column for
observations of the flexibility of the potato cylinders.

Determine the % change in mass and volume for each of the potato cylinders.
Record these values in a new data table

Graph the % change in mass of each of the potato sections. Plot the % change
on the y axis (vertical) and the salt concentration on the x axis (horizontal)

Graph the % change in volume of each of the potato sections. Plot the % change
on the y axis (vertical) and the salt concentration on the x axis (horizontal)

Questions:

1. Did any of the potato cylinders change in their turgidity (flexibility), and if
so, which ones changed? Explain why the flexibility of the potato slices
changed.
2. Explain the changes observed in %mass and %volume.
3. Define isotonic, hypotonic, & hypertonic solutions.
4. In which solutions was their a greater solute concentration outside of the
cells?
5. Which solution served as the control for this experiment & why?
6. Sketch the following showing the movement of water molecules (for b, c
and d indicate the concentrations of the salt solution)
a. the potato cylinder in distilled water
b. the potato in a hypertonic solution
c. the potato in a hypotonic solution
d. the potato in an isotonic solution
7. In what type of solution do plant cells do best & why?
8. Using the information you've discovered from this experiment, explain why
the sailor died that drank saltwater.

Conclusions

Address the objective of the experiment in a few sentences.

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