Biology 10A
Name:______________________
Lab #3: Detecting Organic Compounds
25 points, due 9/19(A) & 9/23(B)
Lab:
Detecting Organic Compounds
Introduction: We will use reactions to test for and become familiar with the biomolecules
necessary for life processes such as growth, development, reproduction, maintenance and
repair. In this investigation you will use specific chemical tests to verify the presence of sugar
(monosaccharide carbohydrate), starch (polysaccharide carbohydrate), proteins and lipids in
known solutions.
Then you are to use these tests to determine the presence of protein, lipids, sugar or starch in
unknown food samples. You will be performing a qualitative test, one in which you observe the
presence of a substance and not the quantity of that substance.
WARNING!!!!
PLEASE MAKE SURE YOU USE A CLEAN TEST TUBE FOR EACH TEST!!! You must clean
the test tubes between tests. When heating a sample, be sure to turn the test tube
away from yours or anyone else’s face.
Procedure:
Part A: Starch Test
Presence of starch can be detected by adding Gram’s iodine to a food sample. Caution:
If spillage occurs, rinse with water.
Place 3-5 drops of Gram’s Iodine to a test tube containing 1 dropper full of starch suspension.
A color change from red-brown to blue-black indicates the presence of starch. The concentration
of starch is indicated by the intensity of the blue-black color. A darker color indicates a lot of
starch. Record your results in the attached data table, using (-) if starch is not present
and (+) if it is.
Part B: Sugar Test:
Presence of a simple sugar, called a monosaccharide, can be detected by adding Benedict’s
solution to the sample and heating it. Place 6 drops of Benedict’s solution into a test tube
containing a dropper full of sugar solution. Heat the material gently by placing it in the boiling
water bath. Upon heating, the material will change to a green (+), yellow (+), orange
(+++), or brick red (++++). More +’s means a higher quantity of sugars present. Record
your results in the attached data table. Make sure to use (-) if sugar is NOT present,
and the proper number of (+’s) if it is.
Part C: Protein Test
Presence of protein can be detected by adding biuret reagent to a food sample and heating it.
CAUTION: BIURET REAGENT IS CORROSIVE AND WILL BURN SKIN. PLEASE BE CAREFUL WHEN
ADDING THE REAGENT TO THE TEST TUBE.
Place a dropper full of biuret reagent in a test tube containing a small amount of uncooked egg
white. Heat the material gently until it boils. Allow the tube to cool. The presence of protein is
indicated by a change from blue to a darker brownish color. Record your results in the
attached data table, using (-) if protein is not present and (+) if it is.
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Biology 10A
Name:______________________
Lab #3: Detecting Organic Compounds
25 points, due 9/19(A) & 9/23(B)
Part D: Lipid Test
(Brown Paper Bag Test)
One way to test for the presence of fats is to rub the sample on brown paper. Place a small drop
of cooking oil on a small piece of brown paper. Rub the oil over an area of approximately 5 cm,
and allow it to sit for 15 minutes. A translucent spot on the paper indicates the presence of fat.
Hold the paper towards a light to see the spot. Record your results in the attached data
table, using (-) if fat is not present and (+) if it is.
Part E: Testing Unknowns
Begin by visually examining each of the 5 unknowns. Based on appearance, hypothesize as to
which organic compound(s) you think each unknown will contain. You may choose more than
one organic compound for any or all of the unknown food samples. Once your Hypothesis it
complete, test each softened food sample for the presence of starch, sugar, lipid, and protein.
Perform each of the tests learned in Parts A-D of this lab on EACH unknown sample. Some
samples might contain more than one biomelecule, in which case they will show up positive for
more than one test.
- Blue (no sugar)
+ Green
Sugar Test Results:
++ Yellow
++++ Brick Red (the most sugar)
+++ Orange
Starch, Fat and Protein Results:
- Specific molecule absent
+ Specific molecule present
Material
Letter
A
B
C
D
E
Starch
Hypothesis
Sugar
Protein
Lipid
Table 1: Hypothesis of organic compound content for each of the unknown food samples.
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Biology 10A
Name:______________________
Lab #3: Detecting Organic Compounds
25 points, due 9/19(A) & 9/23(B)
Record all results in the following Data table:
Organic Molecule Test Results
Material to
be tested
Cooking Oil
Starch
Test
Sugar
Test
Protein
Test
Fat
Test
Observations (color change, etc)
Egg White
Glucose
Starch
Solution
A
B
C
D
E
Table 1: Actual test results of organic compound content for each of the unknown food samples.
Conclusion Questions:
1. Name any foods tested that have more than one compound present.
2. In the test for sugar, why do some tubes show a green color while others show a
brick red?
3. What factors might have hindered the four different tests? How could these
factors be corrected?
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Biology 10A
Name:______________________
Lab #3: Detecting Organic Compounds
25 points, due 9/19(A) & 9/23(B)
4. What is the difference between a qualitative and a quantitative experiment?
5. What is the purpose of testing standards first for this type of experiment?
Significance Task:
Design a way to express your data graphically.
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