Macromolecules

In this experiment you will test four different solutions using four different indicator solutions to determine which macromolecules are present in each. In this activity, the experimental hypothesis might be that the addition of an indicator dye to each test solution will result in a color change if the test solution contains the macromolecule of interest. The null hypothesis might be that the addition of an indicator dye will not result in a color change in any of the test solutions.

Before beginning the test, place 16 clean test tubes in a tube rack in four rows of four tubes and label each row A through D and each column one through four. Label each test tube with its corresponding position in the test tube rack. For example, the second tube in the first row should be labeled A2.After this, stir solution A thoroughly and use a pipette to add four milliliters of solution A to each tube in Row A.Next, stir solution B until it is well mixed and use a new pipette to add four milliliters of solution B to each tube in Row B.After stirring solution C thoroughly, add four milliliters of solution C to each tube in Row C.Then add four milliliters of soybean derived vegetable oil to each tube in Row D.When all of the tubes have been filled with their respective test solutions, add 200 milliliters of water to a 400 milliliter beaker on a hotplate and set the hotplate to high.

To perform the Benedict's Test, add two milliliters of Benedict's reagent to test tubes A1, B1, C1, and D1 while the water is warming. Observe the initial color of the tubes. When the water begins to boil, transfer each test tube to the beaker and heat the tubes in the boiling water bath for three to five minutes.

Then, record the final color of each of the tubes in the appropriate cells of the table and turn off the hotplate. To perform an Iodine-Potassium-Iodide Test, first observe the color of the solutions in the test tubes in column two. Then, add one milliliter of iodine potassium iodide reagent to tubes A2 to D2 and record the final color change in each of the tubes.

For the Sudan IV Test, observe and record the color of the solutions in the test tubes in column three. Then, add two to three drops of Sudan IV reagent to test tubes A3 through D3 and record the color change, if any, in each tube. For the Biuret Test, observe the color of the solutions in the test tubes in column four.

Then, add one milliliter of Biuret reagent to test tubes A4 through D4 and record the final color in each of the tubes. Using the results from the indicator tests, each of the four original solutions can be identified as a sugar, starch, lipid, or protein. Reference the Concepts video to help you determine which tubes contain which macromolecules.

First, look at the results from the Benedict's Test. Can you determine which of the test solutions contain sugar based on these results? Next, look at the results from the Iodine-Potassium-Iodide Test.

Did any of the test solutions contain starch? Now review the results from the Sudan IV Test. Using these observations, can you determine if any of the test solutions contain lipids?

Finally, look at the results from the Biuret Test. Did any of the test solutions contain proteins? How can you tell?