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Potato in Solutions Activity (dimensions and mass)

Questions:

  1. What are the effects on a potato core's mass and dimensions when placed in fresh water?
  2. What are the effects on a potato core's mass and dimensions when placed in salt water?

Background:

(Refer to your notes and textbook. This should include discussion of selective permeability, diffusion, hypertonic, hypotonic, isotonic, osmoregulation and osmosis.) (4 pts)

Hypotheses (predictions):

(Record your predictions on your paper. Note there are two questions so there will be two predictions). (4 pts)

Equipment:

(2) potato cores (2) test tubes (1) balance test tube rack
tape, marker & ruler fresh water table salt graduated cylinder

Procedure:

  1. Be sure to show all calculations! (6 pts)
  2. Make 25 ml of a 3% salt water solution. Show your calculations!
  3. Measure the dimensions and mass of the potato cores. Each core will be different.
  4. Place a potato core in each of the test tubes. Label the test tubes.
  5. Nearly fill the first test tube with fresh water.
  6. Nearly fill the second test tube with 3% salt solution.
  7. The next day, measure the dimensions and mass of the potato cores.

Data Section:

  1. Record the before and after length, diameter, and mass of each core. Calculate the volume.
    Fresh Water (6 pts) Before After % change
    Length (cm)      
    Diameter (cm)      
    Mass (g)      
    Volume (cm3)      
     
    Salt Water (6 pts) Before After % change
    Length (cm)      
    Diameter (cm)      
    Mass (g)      
    Volume (cm3)      
  2. Record the percentage change for each measurement. Use this formula:

    [(after measurement - before measurement) / before measurement]* 100

  3. Graph the solution concentration (x-axis) vs. percentage potato core mass change. (6 pts)

Analysis:

Answer these analysis questions in complete sentences.

  1. For each solution did the potato core grow, shrink or stay the same? (2 pts)
  2. Why would the potato core change size? (2 pts)
  3. Make a before sketch of a typical plant cell and two after sketches: one for the fresh water core and one for the salt water core. (6 pts)
  4. Describe the two solutions in terms of being hypotonic, hypertonic and isotonic solutions. (2 pts)
  5. Looking at your graph, estimate what salt concentration would be an isotonic solution for the potato core ? Hint: what would a 0% mass change mean? (4 pts)