DISSECTING AC ELL AND EXAMINING ITS COMPONENTS

							                                                    CLASS COPY DO NOT WRITE ON THIS PAPER

                    DISSECTING A CELL AND EXAMINING ITS COMPONENTS
 BACKGROUND: A few cells, like the egg cells (many centimeters) of birds, are
large enough to study macroscopically; without a microscope. Most cells are
too small to see with the naked eye. Most organelles (mitochondria, Golgi
bodies) are even too tiny to be visualized with a light microscope. Molecules
are too small to be seen even with standard electron microscopes and have
only recently been “seen” with a new scanning, tunneling microscope.
         When molecules are studied, they are often visualized indirectly.
 Through the use of indicators, specific molecules can be detected. Indicators
 are chemicals that change color when another molecule is present. For example, phenol red is an
 indicator of the molecule carbon dioxide (CO2). When CO2 is added to phenol red it changes from a red
 to a yellow color. The color change is actually due to a drop in the pH.
         Some other indicators that are useful in a laboratory include; Benedict’s solution, Lugol’s
 Iodine and Biuret reagent. These indicate the presence of glucose, starch, and protein molecules.
         Since cells are composed of a variety of molecules, a first step in understanding an organism
 and its components is to analyze its molecular composition. The basic composition of a cell can be
 determined through dissection and testing with indicators.

PURPOSE:
            To examine the molecular composition of an egg cell.
            What are positive indicator tests for proteins, carbohydrates, and fats?
            What components can be shown to be present?

MATERIALS:
              1 Egg                                                      Starch Solution
              250 mL beaker (glass)                                      Gelatin Solution
              (3) 100 mL beakers                                         Oil
              Water                                                      9 Culture Tubes
              Biuret Reagent (10% NaOH, 5% CuS04)                        Transfer Pipets (5)
              Benedict’s solution                                        Paper towels
              Lugol’s (Iodine) solution                                  Plastic Spoon
              Sudan III solution                                         Plastic Knife
              Glucose solution

    PROCEDURES: PART 1
       1. Start a hot water bath, by placing 100 mL of Distilled water in a GLASS 250 ml
          beaker and putting it on you hot plate.
       2. Turn the hot plate on to the 8 setting.
       3. Place your thermometer in to verify that it is 100.C, this will be used later
       4. Now, Obtain a decalcified egg from the teacher lab station
       5. Describe the appearance of the egg. ____________________
       6. How does it look and feel different from a normal egg?
          _______________________________________________________________
          _______________________________________________________________
       7. To expose the cell components, gently slice open the egg’s membrane with the
          plastic knife and let the cytoplasm (the egg white) drip through the slots of the
          spoon into a beaker.
              a. Try to get all the cytoplasm into the beaker without piercing the yolk
                  (nucleus).
       8. Dump the egg yolk into another beaker and set aside the plasma membrane.

         Following the steps below, you will test 4 items for the presence of the
      macromolecules. These are called standards and they will give you an idea of
      what a positive test should look like if the molecule being tested for is present.
                                              ___
*** WE WILL COMPLETE THIS PART AS A CLASS! ***

PROCEDURES: PART 2:                 STANDARD SOLUTIONS

DATA TABLE 1: RESULTS OF STANDARD MOLECULE TESTING USING DIFFERENT INDICATORS
Standard Indicator Used    Description of Positive Results Description of Negative Results
glucose   Benedict’s
starch    Iodine
protein   Biuret Reagent
fat       Brown Paper

*** YOU WILL COMPLETE THIS PART WITH YOUR LAB GROUP! ***

PROCEDURES: PART 3: TEST OF CELLULAR COMPONENTS
1. Test each of the cell components for the presence of all 4 biological molecules. To do this,
   just substitute the cellular component to be tested for the sugar, starch, protein, or fat in the tests
   below.

2. To test the membrane you will need to tear the membrane into small pieces, two or three pieces per
   test is enough.

3. For test results use the following system, based on a comparison with the standard tests:

             A. To test for glucose - Mix 2mL of each cell part (separately) with 2 mL of Benedict's
                solution. Heat for 2 min. Record all color changes and the time to change.

         This is the only test that gets heated, once you are done with this test turn off the hotplate

          B. To test for starch - Mix 2mL of each cell part (separately) with 2 drops of iodine. Record
             color change.
          C. To test for protein - Mix one dropper full of 10% sodium hydroxide (NaOH) and ½ a
             dropper of 5% copper sulfate (CuSO4) this mixture is called Biuret Reagent;
              Now add 2mL of each cell part (separately). Mix well. Record color change after 30 sec.
4. Record data on the 2nd chart.
DATA TABLE 2: THE RELATIVE AMOUNT OF MACROMOLECULES FOUND IN CELLS
Cell Component                      Benedict’s          Iodine     Biuret Reagent             Sudan III
Cytoplasm (Egg White)
Nucleus (Yolk)
Plasma Membrane (Shell)

KEY: very strong / positive test (+++)    strong / positive test (++)   weak / positive test (+)   Negative (-)


ANALYSIS QUESTIONS: (ANSWER ON A SEPARATE PIECE OF PAPER)
1. Recreate all data tables to turn in with Analysis Questions.
2. Why do you think we choose a Chicken Egg to represent our “CELL” for this lab?
3. Can most organelles be seen with a light microscope?
        a. What kind of microscope can be used to study organelles?
4. What was the purpose of creating the “STANDARDS”?
5. What is an indicator?
6. Why do we use indicators?
7. What is the indicator Phenol Red used for?
8. If I wanted to test for the presence of Starch what type of indicator would I use _____________________
9. What if I wanted to test for sugar _____________________
10. Why does paper turn black when you drop Iodine on it?
11. What chemicals do we use to test for protein? __________________
        a. What does the positive reaction look like?
        b. What does the standard look like?
12. Research Question: Why does the vinegar dissolve the shell but not the membrane?