Osmosis: Why Do Our Fingers Prune When Immersed in Water?

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Updated on Jun 17, 2013

Grade Level: 7th - 10th; Type: Life Science

In this study we will be examining the movement of water. Using a model of a cell we will demonstrate how our fingers prune when in water.


  • How does water move with respect to concentration?
  • From this experiment determine why our fingers prune during prolonged exposure to water.

When you take a bath or go swimming for a prolonged period of time your fingers start to prune.

  • Dialysis tubing - available at medical supply stores or laboratory suppliers online.
  • String or dental floss
  • Sodium Chloride (NaCl)
  • Beakers - 2x 2000mL, 5x 500mL, 1x 250mL
  • Erlenmeyer Flask (50mL)
  • Graduated cylinder
  • Scale (with a range of 0.1g to 1000g)
  • Sharpies - 3 colors

  1. Make your salt solutions:
    1. 1% NaCl = 20 grams NaCl + 2000mL H2O
    2. 10% NaCl = 10 grams NaCl + 100mL H2O
    3. 50% NaCl = 500grams NaCl + 1000mL H2O
  2. Soak the dialysis tubing in a 500mL beaker of H2O for at least 10 minutes.
  3. Prepare the cells:
    1. Cut the dialysis tubing into four 3-4" sections. Place the tubing back into the water.
    2. Tie one end of the dialysis tubing closed with string or dental floss. Do this for all four.
    3. Take 1 tube section and fill it with 5mL of the 1% NaCl solution. You may need to use a funnel or pipette. Mark the ends of the tube with a Sharpie. Use the three colors for the three NaCl solutions.
    4. Close the other end with the string/dental floss.
    5. Repeat steps 3-4: Fill two tubes with 10% NaCl.
    6. Repeat steps 3-4: Fill 1 tube with 50% NaCl.
    7. Weigh each of the tubes/cells. Record on the chart ****
  4. Label a 500mL beaker with 50% NaCl and fill it with 400mL of the 50% NaCl solution.
  5. Label three 500mL beakers with 1% NaCl and fill them with 400mL of the 1% NaCl solution.
  6. Place one 10% NaCl cell into the 400mL of 50% NaCl solution
  7. Place the 1%, 10%, and 50% NaCl cells into each of the three 400mL 1% NaCl solutions.
  8. Wait 20 minutes.
  9. Remove the cells, one by one, and weigh. Record the weights on the chart.
Cell Concentration
Initial Weight
Solution Concentration
Final Weight
Weight Difference
1% NaCl
1% NaCl
10% NaCl
1% NaCl
10% NaCl
50% NaCl
50% NaCl
1% NaCl
  1. Which cells lost water? Which cells gained water? Explain your results.
  2. How do your results explain why our fingers prune?

Terms/Concepts: Osmosis; Hypotonic; Hypertonic; Isotonic; Permeable; Active transport; Facilitated diffusion


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