SBI 3C
Purpose:
Lab Activity #1: Testing for Macromolecules
To determine which type of macromolecule makes up certain food items.
Materials:
distilled water
iodine solution
hot plate
Samples: ______________
______________
6 test tubes
Biuret Reagent
300 mL beaker
______________
eye dropper
test tube holders
Benedict’s solution Sudan IV solution
10 mL graduated cylinder
______________ ______________
Summary of Tests:
Biuret Reagent
(copper sulphate &
potassium hydroxide)
Reacts with proteins,
turns purple or pink
Benedict’s Solution
Reacts with sugars, turns
green (less sugar) – yellow
– orange (more sugar) after
heated
Iodine Solution
Reacts with
starch, turns
brown to black
Sudan IV
Solution
Reacts with
lipids, turns
bright red
Procedure:
Part 1: Testing for Carbohydrates (Sugars)
1. Prepare a water bath by placing 250 mL of tap water into the large beaker and placing
the beaker on a hot plate. Bring the temperature to near a boil (simmer). Maintain the
water level by adding more water if necessary. While the water is heating, read
through the method and prepare materials.
2. Using masking tape, label one of the test tubes control and label the remaining 5 test
tubes to correspond with the 5 food samples you will test.
3. Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add
6 drops of Benedict’s to the test tube. Carefully mix the contest of the test tube by
gently swirling it in a circle. Place the test tube in the warm water bath for 3 minutes.
Record the colour of the solution in Table 1 – Control Results. You now know what
colour the solution will be if no sugars are present in a sample.
4. Place a small sample of each food in the appropriately labelled test tubes. Add 5
drops of Benedict’s to each sample. Swirl gently to mix.
5. Place the 2 of the samples in the warm water bath for 3 minutes. After 3 minutes use
the test tube clamp to place it in the test tube rack and heat remaining test tubes for 3
minutes. Place in rack, turn off heat and leave water bath on hot plate to cool.
6. Record your results in Table 1.2 – Sugar Data Table.
7. Pour out contents of test tubes and wash test tubes carefully.
Part 2: Testing for Carbohydrates (Starches)
1. Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add
5 drops of iodine to the test tube. Carefully mix the contents of the test tube.
2. Record the colour of the solution in Table 1 – Control Results. You now know what
colour the solution will be if no starches are present in a sample.
3. Using the same foods as tested in Part 1, add a small amount to the already labelled
test tube.
4. Add 5 drops of iodine to each test tube. Carefully mix contents.
5. Record results in Table 1.3 – Starch Test Data Table.
6. Pour out contents and wash test tubes.
Part 3: Testing for Proteins
1. Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add
5 drops of Biuret to the test tube. Carefully mix the contents.
2. Record the colour of the solution in Table 1 – Control Results. You now know what
colour the solution will be if no proteins are present in a sample.
3. Using the same foods as tested in Part 1, add a small amount to the already labelled
test tube.
4. Add 5 drops of iodine Biuret to each test tube. Carefully mix contents.
5. Record results in Table 1.4 – Protein Test Data Table.
6. Pour out contents and wash test tubes.
Part 4: Testing for Lipids
1. Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add
5 drops of Sultan IV to the test tube. Carefully mix the contents of the test tube.
2. Record the colour of the solution in Table 1 – Control Results. You now know what
colour the solution will be if no lipids are present in a sample.
3. Using the same foods as tested in Part 1, add a small amount to the already labelled
test tube.
4. Add 5 drops of Sultan IV to each test tube. Carefully mix contents.
5. Record results in Table 1.3 – Lipid Test Data Table.
6. Pour out contents, wash test tubes and place in drying rack.
Analysis Questions: Answer each of the following in complete sentences and paragraph
form (one paragraph for each).
1. Describe the stain that is used to test for the presence of mono/disaccharides?
What colour indicates a negative result for mono/disaccharides? What colour
indicates a positive result? Which of your samples tested positive for mono or
disaccharides?
2. Describe the stain that is used to test for the presence of polysaccharides? What
colour indicates a negative result? What colour indicates a positive result? Which of
your sample tested positive for polysaccharides?
3. Same as above for proteins.
4. Same as above for lipids.
Conclusion Questions:
1. Why do experimental procedures include control samples?
2. Assume you have tested an unknown sample with both Biuret Reagent and
Benedict’s solution and that both tests result in a blue colour. What have you
learned?
Lab Reports:
All Lab Reports must be typed. It should include:
1. Title, name, date, course, and teacher.
2. Purpose
3. Materials
4. Procedure: “refer to handout: Lab Activity #1: Testing for Macromolecules.”
5. All data tables.
6. Analysis questions.
7. Conclusion.
Lab Report is due: _________________________