Name_______________________________________ Period____
Macromolecules Lab
Introduction:
Most matter in your body that is not water is made up of organic compounds.
Organic compounds contain carbon atoms. There are four principle classes of
organic compounds made or used by living things: carbohydrates, lipids, proteins,
and nucleic acids . Without these compounds, cells could not function.
Carbohydrates are made of carbon, hydrogen and oxygen and are key sources of
energy. They include glucose, fructose, galactose, sucrose, ribose, deoxyribose,
cellulose and chitin. The monomers for carbohydrates are monosaccharides. Lipids
include fats (a source of stored energy), phospholipids (key components of the cell
membrane), steroids and waxes. Proteins are large molecules made up of chains of
amino acids. Proteins are important molecules in living things because they are
responsible for the proper functioning of all cells and the structure of some cells.
Proteins include: muscle tissue, skin, bone, hair, enzymes and antibodies.
Purpose:
This lab activity provides an opportunity for the development of skills involved in
chemically testing for the presence of the carbohydrates, lipids and proteins found
in food samples. You will learn how to test for the presence of proteins using the
Biuret test, to test for the presence of monosaccharides using the Benedict’s test,
to test for the presence of starches (polysaccharides) using Lugol’s iodine solution
and to detect the presence of lipids using Sudan III. Using the skills that you
develop, you should be able to determine which organic compounds are present in
the unknown solutions provided in this lab.
Materials:
Lugol’s iodine in dropper bottle
Benedict’s solution in dropper bottle
Biuret Reagent in dropper bottle
Sudan III in dropper bottle
Unknown Solution A
Unknown Solution B
Unknown Solution C
Unknown Solution D
Plastic cups
Test tubes
Pipettes
Hot Plate
Test tube holder (beaker)
Safety Alert
1. Do not touch, taste, or smell any substances.
2. Point test tubes away from all people when heating samples.
3. Handle hot test tubes with test tube clamp.
Background Information On Solution Testing:
Part I: Testing for Lipids
Sudan III can be used to detect the presence of lipids. In the presence of a
lipid-rich solution and water, Sudan III will diffuse through the solution
producing an orange-pink color ring at the top. DO NOT mix or shake the
solution. Record observations for the lipid test in Data Table 1.
*Add 3 drops of Sudan III to the test tube
Part II: Testing for Proteins
Biuret reagent can be used to test for the presence of protein. Biuret reagent
will change color from light blue to violet in the presence of protein. Record
observations for the protein test in Data Table 1.
* Add 6 drops of Biuret’s reagent
Part III: Testing for a Polysaccharide called Starch
Lugol’s Iodine solution can be used to test for the presence of the
polysaccharide called starch. In the presence of starch, the Lugol’s Iodine
solution will change color from amber to dark blue/black. Record observations
for the starch test in Data Table 1.
* Add 1 drop of Lugol’s iodine solution
Part IV: Testing for Monosaccharides
Benedict’s solution can be used to detect the presence of monosaccharides. In
the presence of a monosaccharide like glucose, Benedict’s solution will change
color from blue to orange when heated. Record observations for the glucose
test in Data Table 1.
* Add 1 dropperful of Benedict’s solution. Place the tube in a beaker of boiling
water and boil for 5 minutes. (Use test tube clamps to hold hot test tubes.)
Procedure: Each group will be assigned 1 Solution to test
Solution A:
1. Place 2 dropperfuls of the unknown solution A in each of your test tubes and
cups. Complete Testing for Parts I - IV. Note any change in color!
2. Rinse out your test tube and determine whether or not the unknown Solution
A you've been assigned contains any Macromolecules. Record your findings in
Data Table 2.
Solution B:
1. Place 2 dropperfuls of the unknown solution B into each of your test tubes
and cups. Complete Testing for Parts I - IV. Note any change in color!
2. Rinse out your test tube and determine whether or not the unknown B
solution you’ve been assigned contains any Macromolecules. Record your
findings in Data Table 2.
Solution C:
1. Place 2 dropperfuls of the unknown solution C in each of your test tubes and
cups. Complete Testing for Parts I - IV. Note any change in color!
2. Rinse out your test tube and determine whether or not the unknown C
solution you’ve been assigned contains any Macromolecules. Record your
findings in Data Table 2.
Solution D:
1. Place 2 dropperfuls of the unknown solution D in each of your test tubes and
cups. Complete Testing for Parts I - IV. Note any change in color!
2. Rinse out your test tube and determine whether or not the unknown D
solution you’ve been assigned contains any Macromolecules. Record your
findings in Data Table 2.
Data and Observations:
Data Table 1: Positive Test
Observations
Test Performed
Sudan III
Biuret's Test
Lugol's Test
Benedict's Test
Data Table
2: Results
Test
Performed
1. Sudan III
2. Biuret
Test
3. Lugol’s
Iodine Test
4. Benedict’s
Test
Which
Organic
Compound
is it ?
Positive Result
Put “+” If
Color Change
Sol A
Sol B
Put “-“
If No Color
Change
Sol C
Sol D
Conclusion Questions:
1. What are the monomers for each of these macromolecules?
a. Carbohydrates _____________________
b. Lipids ____________________________
c. Proteins __________________________
2. Circle any of the following compounds that would be classified as
carbohydrates.
a. Amino acids
e. fructose
b. Triglycerides
f. hemoglobin
c. Glucose
g. chitin
d. cellulose
h. starch
3. If you were given an unknown food sample and asked to identify its contents,
which chemical identification test would you use to determine the presence of:
a. Lipids _______________________________
b. Proteins______________________________
c. Glucose_______________________________
d. Starch________________________________
4. Was the data collected in this experiment qualitative or quantitative? Explain?
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
5. Predict the primary macromolecule that should be present in the following
food substance and indicate which test you would apply in order to detect
the presence of that macromolecule. You may need to consult additional
resources.
Food Substance
a. Potato
b. Cracker
c. Gelatin
d. Honey
Predicted Macromolecule
Test to be used