Name ______Date ______

Mrs. Geithner-Marron (Bio 200) Period ______

Compounds in Living Organisms

The compounds your body need for energy and growth are carbohydrates, proteins, fats, vitamins and other nutrients. These compounds are present in the plants and animals you use for food. In this investigation, you will observe tests for specific compounds and then you will use those tests to determine which compounds are found in ordinary food.

Materials: (per team of 2-3)

·  safety goggles

·  lab aprons

·  4 test tubes

·  Test tube rack (or beaker)

·  test tube clamp

·  Benedict’s solution in dropping bottle

·  Biuret solution in dropping bottle

·  Lugol’s iodine in dropping bottle

·  Isopropyl alcohol

·  Brown wrapping paper (paper lunch/grocery bag)

·  Foods (types will vary)

Procedure:

Part A: Test Demonstration

Reagents are chemical solutions that scientists use to detect the presence of certain compound. A change in color indicates that there has been a chemical change.

1.  Observe the reagent tests your teacher performs. In Table 1, describe the results of each test.

Part B: Compounds in Foods

1.  Predict the substances that you expect to find in the sample food your teacher assigns to you.

2.  Then test your sample as your teacher demonstrated (and as described in steps 2- 7) and record the results of each test in Table 2, using a + (plus sign) if the substance is present and a – (minus sign) if it is not present.

*****NOTE: Use only SMALL pieces of food that won’t get stuck in your test tube!!!*****

a.  Protein test:

  1. Place a small piece of the assigned food in a test tube.
  2. Add 10 drops of Biuret solution. (You may have to look on the piece of food itself to see if there was any color change.)
  3. Record the results the protein column in Table 2, using a + (plus sign) if the substance is present and a – (minus sign) if it is not present.

b.  Glucose test:

  1. Place a small piece of the assigned food in a test tube.
  2. Add 10 drops of Benedict’s solution.
  3. Place the test tube in a beaker of boiling water (at the front of the room) and heat for five minutes. Use a test tube clamp/tongs to retrieve your test tube. *****Remember, hot glass looks the same as cold glass!!! Do NOT touch the glass with your bare hands so you do not burn yourself.*****
  4. Record the results the glucose column in Table 2, using a + (plus sign) if the substance is present and a – (minus sign) if it is not present. (You may have to look on the piece of food itself to see if there was any color change.)

c.  Starch test:

  1. Place a small piece of the assigned food in a test tube.
  2. Add 5 drops of Lugol’s iodine solution. (You may have to look on the piece of food itself to see if there was any color change.)
  3. Record the results the starch column in Table 2, using a + (plus sign) if the substance is present and a – (minus sign) if it is not present.

d.  Lipid/Fat test:

  1. Rub the assigned food on a piece of brown wrapping paper (lunch/grocery bag).
  2. Hold the paper up to the light.
  3. NOTE: When food contains only a small amount of fat, the fat may not be detected. If this happens:
  4. Place the assigned food along with 10mL of a fat solvent such as isopropyl alcohol (99%) in a test tube.
  5. Allow the food to dissolve in the solvent for about five minutes.
  6. Then, pour the solvent on brown paper.
  7. Check the paper in about ten minutes; the spot should be dry.
  8. Record the results the lipid/fat column in Table 2, using a + (plus sign) if the substance is present and a – (minus sign) if it is not present.

Data:

Table 1: (Positive) Reagent Tests of Known Food Substances

Food Substance / Reagent Test / Results
Gelatin / Biuret solution
(protein test)
Glucose / Benedict’s solution
(glucose test)
Starch / Lugol’s iodine solution
(starch test)
Butter or vegetable oil / brown paper
(lipid/fat test)

Table 2: Analysis of Compounds in Common Food (+ positive, - negative)

Substance / Protein / Glucose / Starch / Lipid (fat)
Prediction
Test results
Prediction
Test results
Prediction
Test Results
Prediction
Test results

Analysis:

1.  How did your predictions compare with the test results?

2.  On the basis of your test, which food(s) could be used as a source of:

protein? ______glucose?______

starch?______lipids/fat?______