Osmosis in Potatoes

Potato Osmosis

Introduction:

A shipwrecked sailor is stranded on a small desert island with no fresh water to drink. They know they could last without food for up to a month, but if they didn't have water to drink they will be dead within a week. Hoping to postpone the inevitable, their thirst drives them to drink the salty seawater. They are 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:

The concentration of solute in a solution will affect the movement of water across potato cell membranes.

Materials:

potato, corer, 3 plastic cups, marker, salt, sugar, distilled water, paper, pencil, electronic balance, metric ruler, small ziplock plastic bag, foil or plastic wrap

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 3 vertical holes.

3. Remove the potato cylinders from the cork borer & measure their length in centimeters.

4. Cut the 3 potato cylinders to the same length (about 4 -5 centimeters long).

5. Record the length & turgidity(firmness and flexibility) of the potato cylinders in your data table (day 1).

6. Place the 3 potato cylinders in a small ziplock bag to prevent them from dehydrating before they're used.

7. Take 3 plastic cups and label them with the solution that will be placed in each one --- sugar, salt, distilled water.

8. Prepare a saturated solution of salt by mixing as much salt as you can with water.

9. Repeat this step by making a saturated sugar solution.

10. Now fill each cup 2/3's full of the correct solution ---- sugar water, salt water, or distilled water.

11. Mass each of the potato cylinders & record this mass in grams on your data table.

12. Place one of your potato cylinders into each cup and cover the top of the cup with foil or plastic.

13. Leave the potato cylinders in the solution for 48 hours.

Day 2

1. Carefully remove the potato cylinder from the distilled water solution & pat it dry on a paper towel.

2. Measure the length of the potato cylinder & record this length & the appearance of the cylinder on your data table. (day 2)

3. Measure & record the mass of this cylinder.

4. Repeat steps 13-15 for the potato cylinders in the salt solution & the sugar solution.

5. Clean up your equipment & area and return materials to their proper place.

Data:

Results of Osmosis in Potato Cells

Solution Initial length

cm

(day1) Final length

cm

(day2) Change in length

cm Initial Mass