Biology Name:
Period:
Identifying Macromolecules
This is a class set, do not write on!
Date:
Purpose:
Can you test for the presence of macromolecules in various foods?
Background:
The most common macromolecules (organic compounds) found in living organisms are lipids,
carbohydrates, proteins, and nucleic acids. Common foods, which often consist of plant
materials or substances derived from animals, are also combinations of these macromolecules.
Some of these compounds can be detected by taste, while others cannot. Therefore, scientists
use certain tests to identify the presence of macromolecules.
Introduction:
You’re a scientist at the Food and Drug Administration’s Center for the Nutrient Analysis in
Atlanta, Georgia. You analyze food based on the label declaration. Tests are performed for
proteins, lipids, and carbohydrates. Recently, there has been fear of an attck by a new species
of undead (similar to a zombie). Scientists believe that the only way to combat this attack is by
feeding them a substance with high levels of complex carbohydrates and proteins, since these
macromolecules appear to kill the new species cells. Scientists have also found that the undead
seem to thrive and grow rapidly when fed simple sugars. Your team is taking a break from the
regular task of food label analysis in order to determine which of two substances – yogurt A or
yogurt B – will be the best food to fight off the invasion, based on the tests you will be
performing today. It is up to you and your team to save Earth!
Materials:
Test tube rack
Test tubes – 12
Hot plate
Test tube clamps
Beaker with water
Benedict’s solution
Biuret’s reagent
Lugol’s Iodine
Brown paper bag
Tape for labels
Test tube holder
Pencil
Distilled water
Yogurt A
Yogurt B
Apple juice
Gelatin solution
Potato solution
Vegetable oil
Pipettes - 7
Procedure:
Lipid test:
1. Obtain a piece of brown paper bag.
2. Take the brown paper bag to the front of the room to collect samples.
a. Using a pipette, place 1 drop of vegetable oil on the brown paper bag.
b. Using a different pipette, place 1 drop of water onto the brown paper bag in a
different location.
3. Wait 10 seconds, then wipe oil and water off of paper bag using a paper bag. Be sure to
not wipe oil over water so as to not contaminate.
4. Look at paper bag and describe the change in appearance of paper. A positive result will
appear translucent (or “see through”). A negative result will appear not translucent.
5. Record appearance in data table I for oil and water and indicate + for positive for lipids
and – for negative for lipids.
6. Test yogurt A and B for lipids:
a. Take the brown paper bag to the front of the room to collect the samples.
b. Using a pipette, drop 1 drop of yogurt A onto brown paper bag.
c. Using a different pipette, place 1 drop of yogurt B onto brown paper bag.
d. Wait 10 seconds, wipe both with paper towel to remove yogurt.
Biology Name:
Period:
Date:
e. Record appearance in Data table II and indicate + or – for lipids.
7. Throw away the used brown paper bag.
Protein test:
1. Obtain 4 test tubes.
2. Label each with tape: distilled water, gelatin solution, yogurt A and yogurt B.
3. Take test tubes to front of room to collect samples.
a. Use a pipette to transfer 1 mL (1 pipette = 1mL) of distilled water into the
distilled water labeled test tube.
b. Use a different pipette to transfer 1 mL of gelatin solution into the gelatin
solution labeled test tube.
c. Using a pipette, place 1 mL of yogurt A into the labeled test tube.
d. Using a different pipette, place 1 mL of yogurt B into the labeled test tube.
4. Add 5 drops Biuret’s reagent to both the distilled water and the gelatin solution. Make
sure that the end of the dropper does not come into contact with the sample solutions.
5. **Buiret’s reagent is a strong base so if it comes in contact with your skin, wash off
immediately. Make sure the cap is securely tightened when not in use.
6. Buiret’s reagent is an indicator that will change color in the presence of proteins. It will
change from blue to violet in the presence of proteins (positive result). It will remain
blue if no proteins are present (negative result).
7. Observe the distilled water and the gelatin solution. Notice the color of the Biuret’s
reagent.
8. Record your observations in Data table I. Record the color observed and whether the
result is + or - .
9. Test yogurt A and B for proteins:
a. Add 5 drops Biuret’s reagent to each yogurt sample.
b. Observe the color of the Biuret’s reagent for color. Compare observations to the
colors of the distilled water and the gelatin results.
c. Record appearance in Data table II and indicate + or – for proteins.
Simple Carbohydrate Test:
1. Obtain 4 test tubes.
2. Label each with tape: distilled water, Apple juice, yogurt A and yogurt B.
a. Use a pipette to transfer 1 mL (1 pipette = 1mL) of distilled water into the
distilled water labeled test tube.
b. Use a different pipette to transfer 1 mL of apple juice into the labeled test tube.
c. Using a pipette, place 1 mL of yogurt A into the labeled test tube.
d. Using a different pipette, place 1 mL of yogurt B into the labeled test tube.
3. To the distilled water and apple juice, add 10 drops Benedict’s solution to each. Make
sure that the end of the dropper does not come into contact with the sample solutions.
Make sure the cap is securely tightened when not in use.
4. Gently shake both test tubes.
5. Place both labeled test tubes into the hot water bath for 3-5 minutes. Use the test tube
holders to remove the test tubes from the water bath. **Use caution, water is very hot.
Place the test tubes back into the test tube rack.
6. Observe the solutions. Record the color observed in Data table I and whether the result
is positive (+) or negative (- ).
a. Benedict’s solution is an indicator that will change color in the presence of simple
sugars. It will appear rusty-brown if there is a large amount of simple sugars (+ ),
Biology Name:
Period:
Date:
orange if there is a moderate amount of simple sugars (+), and green or yellow if
there is a small amount of simple sugars (+). A blue color indicates there are no
simple sugars present (- ).
7. Test yogurt A and B for simple sugars:
a. Add 10 drops Benedict’s solution to each yogurt sample.
b. Place in hot water bath for 3-5 minutes. Return to test tube rack
c. Observe the color and compare observations to the colors of the distilled water
and the apple juice results.
d. Record appearance in Data table II and indicate + or – for simple sugars.
Complex Carbohydrates test:
1. Obtain 4 test tubes.
2. Label each with tape: distilled water, gelatin solution, yogurt A and yogurt B.
3. Take test tubes to front of room to collect samples.
a. Using a pipette, place 1 mL of yogurt A into the labeled test tube.
b. Using a different pipette, place 1 mL of yogurt B into the labeled test tube.
c. Use a pipette to transfer 1 mL (1 pipette = 1mL) of distilled water into the labeled
test tube.
d. Use a different pipette to transfer 1 mL of potato solution into the labeled test
tube.
4. Add 2 drops iodine to both the distilled water and potato solution test tubes. Make sure
that the end of the dropper does not come into contact with the sample solutions.
5. **Iodine will stain. Make sure the cap is securely tightened when not in use.
6. Lugol’s Iodine will cause complex carbohydrates to turn dark blue or black (+).
Substances without complex carbohydrates will be colored reddish-brown by the iodine,
but they will not react (-).
7. Observe the distilled water and the potato solution. Notice the color of the contents.
8. Record your observations in Data table I. Record the color observed and whether the
result is positive (+) or negative (- ).
9. Test yogurt A and B for complex carbohydrates:
a. Add two drops of Iodine to each yogurt sample.
b. Observe the color of the yogurt and iodine. Compare observations to the colors
of the distilled water and the potato solution results.
c. Record appearance in Data table II and indicate + or – for carbohydrates.
Clean up:
After recording your observations in Data table I, Clean up your station.
1. Remove labels from all test tubes
2. Empty contents of test tubes into trash can
3. Wash all used test tubes with bottlebrush in bucket of soapy water.
4. Rinse test tubes in bucket of clean water
5. Drain and place test tubes upside down in test tube rack. Place a paper towel
under test tube rack to absorb excess water.
6. Make sure all caps are securely fastened on Biuret’s reagent, Benedict’s solution,
and iodine.
Biology Name:
Period:
Date:
To be filled out by each group member. Staple all group member’s labs together to turn in.
Date Table I: Testing macromolecules
Macromolecule
Lipids
Protein
Simple
Carbohydrate
Complex
Carbohydrate
Substance
tested
Observationd/Color
Positive (+)or
negative (-)
result
Distilled water
Vegetable oil
Distilled water
Gelatin solution
Distilled water
Apple juice
Distilled water
Potato solution
Data Table II: Testing Yogurt for presence of macromolecules
Food Sample
Yogurt A
Yogurt B
Macromolecule
tested
Observations/Color
Positive (+) or
negative (-)
result
Lipids
Proteins
Simple
Carbohydrate
Complex
Carbohydrate
Lipids
Proteins
Simple
Carbohydrate
Complex
Carbohydrate
Analysis and Conclusions: Answer the following questions. Be thorough in your responses.
Use lab data when applicable.
1. What was the purpose of using distilled water as one of your test substances?
2. What macromolecule did you not test for in today’s lab?
3. Which macromolecules were present in yogurt A?
Biology Name:
Period:
Date:
4. Which macromolecules were present in yogurt B?
5. You are getting prepared to take a “Man vs. Wild” hike. Using your data and your
understanding of nutrition, which of the yogurt samples would provide the best fuel for
your body to endure this long adventure? Explain.
6. Do the sugars in the apple juice need to be broken down by your digestive system before
they can be used as an energy source for your body? Explain.
7. People with diabetes are instructed to avoid foods that are rich in carbohydrates. How
could your observations in this investigation help you decide whether a food should be
served to a person with diabetes?
8. What conclusion could you make if a positive test for any of the macromolecules
occurred in the test tube containing only distilled water?
9. A very thin slice is removed from a peanut and is placed on a brown paper bag. Then a
drop of Biuret’s reagent is added to the peanut slice. When you examine the peanut on
the paper, you notice the paper is slightly see through and there is some violet colored
liquid on the peanut. What conclusion could you draw from your examination?
10. You must save the world! Using your data and the information provided by the
scientists (in the introduction), which yogurt is the best defense against the undead?
Why?
11. Using the brown paper bag test, what indicates the presence of a lipid?
12. Using iodine, what indicates the presence of a complex carbohydrate?
13. Using Benedict’s solution, what indicates the presence of a simple carbohydrate?
14. Using Buiret’s reagent, what indicates the presence of a protein?
15. Describe at least two errors your group may have made while completing this lab.
Explain how these errors may have impacted your results.
16. What could your group have done differently that would have made this lab run more
smoothly? Explain.