SBI4U
Name: ________________________
Laboratory Activity: Testing for Macromolecules
Biology 12 (Nelson 2012) - Pages 58-59
Purpose: To determine the presence of certain nutrients (single sugars, starches, proteins, lipids) using
laboratory tests
PART A: Carbohydrate (Monosaccharide) Test
Benedict’s reagent is an indicator for monosaccharides and some disaccharides, such as maltose. It changes
colour according to the sugar concentration. See Table 1 (page 58).
Materials:
-hot plate
-10-ml graduated cylinder
-test tube holder
-400-ml beaker
-5 labelled test tubes
-medicine dropper
-thermometer
-Benedict’s reagent
-distilled water; baking soda, glucose, starch, and unknown solutions
Procedure:
1. Heat 300 ml of tap water in a 400-ml beaker on a hot plate until it reaches about 80ºC.
2. Using the graduated cylinder, measure 3 ml each of distilled water; baking soda, glucose, starch, and
unknown solutions. Pour each solution into a separate, appropriately labelled test tube. Clean and rinse the
graduated cylinder after pouring each solution. Add 1 ml (15-20 drops) of Benedict’s reagent to each of the
test tubes using the medicine dropper.
3. Using a test tube holder, place each of the test tubes in the hot water bath. Observe for 6 minutes. Record
any colour changes in a table, and the approximate sugar concentration according to Table 1.
Starch Test
Lugol’s solution contains iodine and is an indicator for starch. Iodine turns blue-black in the presence of starch.
Materials:
-6 medicine droppers
-Lugol’s solution
-depression spot plate
-distilled water; baking soda, glucose, starch, and unknown solutions
Procedure:
1. Using a medicine dropper, place a drop of distilled water on a depression spot plate and add a drop of
Lugol’s solution. Record the colour of the solution.
2. Repeat this procedure, using drops of baking soda, glucose, starch, and unknown solutions. Record the
colour of each solution in a table and note which solutions indicate a positive test.
PART B: Lipid Test
Sudan IV solution is an indicator of lipids. Lipids turn from a pink to a red colour.
Materials:
-10-ml graduated cylinder
-Sudan IV indicator
-5 labelled test tubes
-5 stoppers
-distilled water, vegetable oil, skim milk; baking soda and unknown solutions
Procedure:
1. Using a 10-ml graduated cylinder, measure 3 ml each of distilled water, vegetable oil, skim milk, baking
soda and unknown solutions and pour into separate labelled test tubes. Make sure to rinse the graduated
cylinder with water after measuring each sample.
2. Add 6 drops of Sudan IV indicator to each test tube. Place a rubber stopper on each test tube and shake them
vigorously for 2 minutes. Record the colour of the mixtures in a chart and whether or not lipids are present.
Translucence Lipid Test
Lipids can be detected using unglazed brown paper. Because lipids allow the transmission of light through the
brown paper, the test is often called the translucence test.
Materials:
-unglazed brown paper
-distilled water, vegetable oil, skim milk; baking soda and unknown solutions
Procedure:
1. Using a pencil or pen, divide the paper into 5 different sections and label each section with one of the
following: water, vegetable oil, skim milk, baking soda, or unknown.
2. Place one drop of each substance in the respective section on the paper. When the water has evaporated,
hold the paper to the light and observe. Record whether or not the paper appears translucent in each section
and record if lipids are present in each.
PART C: Protein Test
Proteins can be detected by means of the Biuret reagent. Biuret reagent reacts with the peptide bonds that join
amino acids together, producing colour changes from blue to purple. See Table 2 (page 59).
Materials:
-10-ml graduated cylinder
-5 labelled test tubes
-water, gelatin, albumin, skim milk, unknown solution
-Biuret’s reagent
Procedure:
1. Using a 10-ml graduated cylinder, measure and pour 2 ml of water, gelatin, albumin, skim milk, and the
unknown solution into separate labelled test tubes.
2. Add 2 ml of Biuret’s reagent to each of the test tubes, then tap the test tubes with your fingers to mix the
contents. Record any colour changes in a chart, and record whether there is no protein or the relative number
of peptide bonds present (+, ++, or +++), as indicated on page 59.
--------------------------------------------------------------------------------------------------------------------------------------Analyze and Evaluate:
(Questions (a)-(e), Page 59)
Apply and Extend:
(Questions (f)-(h), Page 59)