Class Copy

ThinkQuest Osmosis Activity

Source: ThinkQuest Webcytology. Accessed 4/25/06. Modified by B.Rick.

Objective

To determine the biological changes that occur to potato cores over a period of time in different solutions and to relate these changes to the phenomenon of osmosis.

Background

By placing pieces of a potato into solutions with different concentrations of solute, water may flow into or out of the potato. Knowing whether or not water flowed into or out of the potato will give you an idea of approximately what percentage of a potato is water.

Materials

(3) potato cores, (3) beakers, distilled water, 10% by mass water/sucrose solution, 20% by mass water/sucrose solution, a graduated cylinder, a knife, a dissecting needle, a ruler, a balance, and plastic wrap

Procedure

  1. Using the knife, carefully cut each potato core into a cylinder of about three to five centimeters in length. Make sure that all of the potato cores are the same length and note this length for later use. Also measure and record the diameter of each potato core.
  2. Using the balance, measure and record the mass of each potato core.
  3. Use water displacement to measure and record the potato core volume. Attach each potato core, one at a time, to the end of the dissecting needle and hold it so that the potato core is completely submerged in the water.
  4. Place one potato core in the beaker with distilled water and label this beaker "100". Place the second core in the beaker of 10% sucrose solution and label the beaker "10%". Place the third core in the beaker with 20% sucrose solution and label this beaker "20%".
  5. Cover the top of each beaker with a piece of plastic wrap. Fold the plastic wrap down along the sides of the beaker so that it cannot fall off easily.
  6. Allow the beakers to sit for a day.
  7. Remove the cores from each beaker using the dissecting needle. Measure and record the length, diameter, mass, and volume of each potato core as you did earlier.
  8. Record the percentage change for each measurement. Be sure to show all calculations! Use this formula:

    [(ending measurement - starting measurement) / starting measurement]* 100

Observations

In your journal create this data table.

 
100% water
10% sucrose solution
20% sucrose solution
  Day 1 Day 2 Change Day 1 Day 2 Change Day 1 Day 2 Change
Length                  
Diameter                  
Mass                  
Volume                  

Note: Record any qualitative changes (in color, texture, etc.) you noticed in the potato cores.

 

Definitions of terms

Questions

  1. In this experiment, why was it important that the potato cores were the same length?
  2. Why was it important to cover each beaker with a piece of plastic wrap?
  3. Into which of the potato cores did water flow? From which of the potato cores did water flow? How can you tell?
  4. Which solutions (if any) were hypertonic, isotonic, or hypotonic? Explain how you know.
  5. Use the Lab report format to write a conclusion
  6. Identify any possible sources of error which may have affected the results of this experiment.