osmosis challenge lab

							Name ______________________________________                               Period _______


                                             OSMOSIS CHALLENGE

You will now be given the opportunity to apply the principles you learned in the previous exercises.

Question: What is the actual molarity of a potato cell?

Guidelines:
You have the following materials to use:
       potatoes
       beakers
       sucrose solutions at the following concentrations:
        0.2, 0.4, 0.6, 0.8 and 1.0M.
       scale
       aluminum foil
       a graph for your final results (in % change in mass)

In order for the class to have similar data to compare use the following:
         4 potato cylinders per solution, cut using the cork borer.
         All 5 sucrose solutions
         Limit the amount of solution to 100ml per beaker (so I don’t have to make so much).

Pre – Lab
        (This will be your ‘entry ticket’ to the lab).

With your partners (3 per group), design an experiment that will demonstrate the actual molarity (concentration of
sucrose) in a potato cell.

Your experiment must include:
       1. A detailed procedure that can be followed without any explanation on your part.
               (Neatly written to be put in your lab notebook unchanged).
       2. Identification of the manipulated, responding and controlled variables.
       3. A control group.
       4. A data table.


Post lab
 Data Section
        1. Completed data table.
        2. Completed graph.

 Analysis Section (presented in a logical order of your choice)
      1. Explanation of the data in the table. (Cite at least 3 data points).
      2. Explanation of the graph. (Cite at least 3 data points).
      3. Possible sources of error /inaccuracy. (Necessary only if there is data that you are uncomfortable with
           or seems inaccurate).

 Conclusion Section:
      1. Answer to the question: “What it the actual molarity of a potato cell?”
      2. Describe how you could improve on your lab.
      3. Other areas of investigation or questions to be answered from this lab.

 Summary questions
                                                 Summary Questions

1. Based on your observations in the lab:

    a. The mass of cells in a hypotonic solution will _____________________ (increase/decrease/stay constant)

       because _____________________________________________________________.

    b. The mass of cells in a hypertonic solution will _____________________ (increase/decrease/stay constant)

       because _____________________________________________________________.

    c. The mass of cells in a isotonic solution will _____________________ (increase/decrease/stay constant)

       because _____________________________________________________________.

Salt movement into and out of cells is similar to that of sucrose. Knowing that, answer the following questions:

2. In the winter, icy roads are often salted to remove the ice and make them less slippery. Grasses and other
   plants often die near the side of these roads. What causes this to happen?

   _________________________________________________________________________________________

   _________________________________________________________________________________________

   _________________________________________________________________________________________

3. When a person is given fluid intravenously (an I.V.) in the hospital, the fluid is typically a saline (salt) solution
   isotonic to human body tissues. Explain why this is necessary.

   _________________________________________________________________________________________

   _________________________________________________________________________________________

   _________________________________________________________________________________________

4. What if the unthinkable happened at the hospital! A patient was given an I.V. bag with distilled water in it rather
   than saline solution. Describe what would happen to their red blood cells and explain why this would occur.

  _________________________________________________________________________________________

  _________________________________________________________________________________________

  _________________________________________________________________________________________

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5. Many freshwater one-celled organisms, like Paramecium, have contractile vacuoles. These structures collect and
   pump out excess water that accumulates in the cell. Explain why these organisms needs such a structure.
   _________________________________________________________________________________________

  _________________________________________________________________________________________

  _________________________________________________________________________________________

  _________________________________________________________________________________________
6. Explain why contractile vacuoles would be of little value to one-celled organisms living in salt water.

  _________________________________________________________________________________________

  _________________________________________________________________________________________

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7. Popcorn sold at movie theaters is very salty, causing people to become thirsty and to buy soft drinks. Explain
   why salty popcorn causes this thirst.

  _________________________________________________________________________________________

  _________________________________________________________________________________________

  _________________________________________________________________________________________

  _________________________________________________________________________________________

8. Explain why soft-bodied invertebrates, like slugs, die when you pour salt on them.
   _________________________________________________________________________________________

  _________________________________________________________________________________________

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9. In each case, label the diagrams as to whether the red blood cells are in a hypertonic, isotonic, or hypotonic
   solution.