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Egg_Osmosis_Lab_and_student_worksheet

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									Egg Osmosis Lab                              Team__________________Per____

Purpose: The purpose of this lab is to demonstrate what happens when an animal cell is
exposed to varying osmotic conditions

Questions:
        What happens when a cell is subjected to a solution where the water concentration
is higher than that inside a cell (hypotonic solution)?
         What happens when a cell is subjected to a solution where the water
concentration is lower than that inside a cell (hypertonic solution)?
        What happens when a cell is subjected to a solution where the water concentration
is equal to that inside a cell (isotonic solution)?

The cell is like a salty sea that is mostly water. The cell membrane in an animal cell is
both a protective barrier and a filter to keep unwanted materials out and bring needed
materials inside. Water can move freely through the cell membrane with osmosis. So
can small molecules such as sodium and calcium ions. Large molecules like
polysaccharides and proteins need assistance in moving through the cell membrane. In
this experiment, you will be looking at the movement of water.

Your teacher has soaked the eggs in vinegar. This dissolves the hard shell and leaves a
soft outer covering that acts like the cell membrane of a cell.


Materials:
      Egg
      Plastic cup
      Water
      Vinegar
      Corn syrup

Procedure:
Day 1
   1. Mark the cup with a sharpie with your period number, group initials, and the first
      soaking solution (water, vinegar, or corn syrup).
   2. One group member should take one egg from the soaking container. Each egg
      should be rinsed under the tap and gently patted dry.
   3. Weigh the egg and place the egg in the container. (The egg’s weight must be
      identified with the solution in order for the experiment to work).
   4. Record weight in the table in the data section.
   5. Gently pour a solution into the container so that the egg is covered to about ¾.
      Record the weight in your lab book.
   6. Put on a tray designated by your teacher.
Day 2
   1. One group member should take the egg gently out of each container, rinse gently
      under tap water, pat dry, and weigh.
   2. Record weight in the table in your lab book.
   3. Dispose of water down the drain.
   4. Then exchange the liquid for the vinegar.



Day 3
   1. One group member should take the egg gently out of each container, rinse gently
      under tap water, pat dry, and weigh.
   2. Record weight in the table in your lab book.
   3. Dispose of vinegar down the drain.
   4. Then exchange the liquid for the corn syrup.



Day 4
   1. One group member should take the egg gently out of each container, rinse gently
      under tap water, pat dry, and weigh.
   2. Record weight in the table in your lab book.
   3. DO NOT put corn syrup down the drain.
   4. Dispose of eggs, used cups and corn syrup in the garbage can
                                Student worksheet
Pre-Lab Definitions:

   1. Diffusion –


   2. Osmosis –


   3. Hypotonic solution-


   4. Hypertonic solution –


   5. Isotonic solution –


Pre-Lab Predictions:

    What will happen to the weight of the egg in corn syrup? Why?


     What will happen to the weight of the egg in the water? Why?


        What will happen to the weight of the egg in the vinegar? Why?



                   Weight start    Weight end          Difference in     % Change in
Soaking              (grams)        (grams)            Weight            Weight*
Solution                                               (end-start)

Water


Vinegar


Corn Syrup

* Calculate % Change in Weight = Difference in Weight x 100%
                                 Weight start
Note that % Change in Weight can be negative or positive
.

Analysis Questions:

    1. Create a bar graph of the percentage of weight change for EACH material

    2. How did the results compare to your pre-lab predictions?

    3. In a controlled experiment, you should only change one variable and you hold
       others constant. List three variables you held constant during this experiment.

    4.   Which of the solutions was hypertonic? What is your evidence?

    5. Which of the solutions was hypotonic? What is your evidence?

    6. A student’s experiment showed that her egg gained mass overnight with the
       vinegar and distilled water. She had about a +1% change for vinegar and a +10%
       change for distilled water. She had hypothesized that the egg’s mass would not
       change significantly with vinegar. She concluded that her hypothesis about
       vinegar was not supported (because it did change in mass). Her teacher told her
       that the data indicated that her hypothesis was supported, especially with the 10%
       change for the distilled water. What did the teacher mean?

    7. What is the biggest source of error for the lab? (student’s writing down numbers
       wrong, calculating, or using the wrong scale do not count)

								
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