Biology II
Ms. Chen
Name: Date:
Purpose:
To learn how to identify several major types of organic molecules found in living systems.
All known life is made out of a small group of chemical compounds called organic molecules.
Common organic molecules include proteins, carbohydrate, lipids, and nucleic acids. Since our bodies are made up of organic molecules, we need each of these molecules as nutrients in our food. In this lab, you will conduct tests for lipids, proteins, glucose and starch. Each of these classes of molecules has specific properties that can be identified by simple chemical tests.
In this lab you will be learning how to identify:
• monosaccharides/glucose using the Benedict’s test
• polysaccharides/starch using iodine
• lipids using Sudan IV solution
• proteins using Biuret’s solution
Answer the questions below to familiarize yourself with this lab.
Directions: Answer these questions before starting the Organic Molecules Lab
1.
What are the four types of organic molecules? Explain why each molecule is important to living organisms.
2.
What do all organic molecules have in common? Name 2 similarities.

Biology II
Ms. Chen
3.
Draw a representation of protein, lipid, carbohydrate, and nucleic acid.
4. What organic molecules you expect to find for each food item below. Some items may contain more than one. a. Sugar- b. Molasses- c. Cornstarch- d. Oil- e. Mayonnaise - f. Peanut butter- g. Flour- h. Salt (NaCl)-
4. What is the purpose of this lab?
5. Read through the directions for the lab to answer these questions. What will using Benedict’s solution, Iodine, Biuret’s solution and Sudan IV solution show you in this lab? Be specific. How will you know if a food sample has protein, lipids, or carbohydrates?
Show your answers to your instructor before you start the lab.

Biology II
Ms. Chen
Directions: Visit the Benedict’s solution, Iodine, Biuret’s solution and Sudan IV solution stations and carefully follow the testing instructions.
E XERCISE 1: T ESTING FOR C ARBOHYDRATES
Benedict’s Solution Test for Monosaccharides
The basic structural unit of carbohydrates is the monosaccharide (or single sugar).
Figure 1. Glucose
Monosaccharide molecules (single sugars found in carbohydrates) react with Benedict’s reagent to form a colored change.
Color
Blue
Green
Amount of monosaccharides (single sugars)
None
Yellow
Orange
Dark Orange/Brown
Small
Medium
Large
Mostly
1.
Set up three test tubes. Use a marker to label the tubes with your initials and label as shown on the next page. Figure 2.
2.
Tube 1: Add sugar to the 1 st line
Tube 2: Add molasses to the 1 st line
Tube 3: Add salt to the 1 st line
3.
Add 50 drops of water to each tube.
4.
Add 10 drops of Benedict’s solution (blue liquid) to each test tube and swirl.
5.
Record the original color of each tube’s contents in Table 1 in the appropriate column.
6.
Heat the test tubes in boiling water for 3 minutes. Record the color of each tube at the end of three minutes in Table 1.
7.
Clean up.

Biology II
Ms. Chen
#1
Sugar
Your
Initial
#2
Molasses
Your
Initial
#3
Salt
Your
Initial
Figure 2. Test tube set up.
Table 1. Benedict’s Solution Monosaccharide Indicator Results
Tube # and Contents Benedict’s Test
Original color before boiling Final color after boiling
1. Sugar
2. Molasses
3. Salt
Iodine Test for Polysaccharides (Starch)

Biology II
Ms. Chen
Polysaccharide molecules (carbohydrates/starch) may contain structures that react with iodine and produce a color change. Iodine changes from a brownish or yellowish color to blue-black when starch is present, but there is no color change in the presence of monosaccharides or disaccharides
Iodine Test Indicator Key
Iodine Test Indicator Color
Yellowish-brown
Dark blue
Blue-black
Amount of polysaccharides (starch)
None
Medium
Mostly
Careful! IODINE STAINS!
1.
Set up 3 cups and fill each with a small amount (1/4 teaspoon) of cornstarch, flour, and salt separately.
2.
Add 20 drops of water to each cup.
3.
Add 1 or 2 drops of iodine to each dish and mix with a toothpick.
4.
Record all color changes in Table 2.
5.
Clean up your area.
Table 2. Iodine Polysaccharide Indicator Results
Food Sample
Cornstarch
Flour
Salt
Polysaccharide Indicator Color
EXERCISE 2- TESTING FOR LIPIDS

Biology II
Ms. Chen
Sudan IV Solution Test for Lipids
Lipid molecules (fats) may contain structures that react with Sudan IV and produce a color change. Sudan IV is a soluble dye used to detect the presence of lipids.
Figure 2. Triglyceride, an example of a lipid
Sudan IV Solution Test Color Key
Appearance
Floating Red Droplets/Red Layer
Presence of fat
Present
No floating red droplets Absent
1.
Set up 3 cups and add a small amount oil, salt, and mayonnaise separately.
2.
Add 10 drops of water to each cup.
3.
Add 10 drops of Sudan IV solution to each cup.
4.
Record all color changes in Table 3.
5. Clean up your area.
Table 3. Sudan IV Lipid Indicator Results
Food Sample
Oil
Salt
Mayonnaise
Lipid Indicator Color

Biology II
Ms. Chen
EXERCISE #3- TESTING FOR PROTEINS
Biuret’s Solution Test for Protein
Protein molecules are made of a chain of amino acids. Biuret’s solution reacts with bonds between amino acids of protein. Biuret’s solution is light blue, but in the presence of proteins turns it violet.
Color
Light Blue
Violet
Black
Biuret’s Solution Test Color Key
Amount of protein
None
Medium
Mostly
Figure 3. Leucine, an amino acid
1.
Set up 3 cups and fill each with a small amount of peanut butter, cream cheese, and salt separately.
2.
Add 30 drops of water to each cup.
3.
Add 10 drops of Biuret’s solution into each cup and mix with a toothpick.
4.
Wait 2 minutes and record your findings in Table 4.
5.
Clean up your area.
Table 4. Biuret’s Solution Protein Indicator Results
Food Sample
Peanut Butter
Cream Cheese
Salt
Protein Indicator Color

Biology II
Ms. Chen
EXERCISE 4- Extra Credit Food Sample
Pick up to 5 extra food samples and test with iodine, Sudan IV solution, and Biruet’s solution
Record your findings in Table 5.
Food Sample Results
Iodine Indicator Sudan IV Indicator Biruet’s Indicator Food Sample
CLEAN UP YOUR AREA and continue to the next page.

Biology II
Ms. Chen
Analysis
Directions: Go back to your data tables and look at the indicator key table at the beginning of each section. Indicate how much of each organic molecule is found in the food samples.
Sample
Salt
Sugar
Monosaccharide Polysaccharide
-----------------
Lipid
-----------------
Protein
----------------
Molasses ----------------- ----------------- -----------------
Oil
Peanut butter
Cream cheese
-----------------
-----------------
-----------------
-----------------
-----------------
-----------------
-----------------
--------------
--------------
-----------------
-----------------
----------------- Flour
Cornstarch
Mayonnaise
Extra Credit 1
-----------------
-------------- --------------
----------------- -----------------
--------------
Extra Credit 2
Extra Credit 3
Extra Credit 4
Extra Credit 5
--------------
--------------
--------------
--------------
--------------

Biology II
Ms. Chen
Conclusions
Answer the following questions with your class notes and the information in this lab.
1. In general, where do we find organic molecules?
2. What is the difference between a monosaccharide and a polysaccharide?
3. If you mixed bread with iodine, what color change would you expect according to the iodine chart in his lab? Why? Remember to use the indicator key.
4. If you mixed bread with Biuret’s solution, what color would you expect? Why?
5. From this lab, what do we know about salt? Why do you think salt was tested at each station?

Biology II
Ms. Chen
6. The leaves of many plants are coated with a waxy substance that causes them to shed water.
Would you expect this substance to “react” with Sudan IV? Explain.
7. A sample of food product X has a positive test for both Benedict’s and iodine’s reagents. For what group of nutrients would this food be a good source? Why is this specific group of nutrients needed by living organisms?
8. Predict what the chart would look like if you tested blood, hair strand, and water.
Write “+” if you predict that molecule is present and “-“ for absent.
Sample Monosaccharide Polysaccharide Lipid Protein
Blood
Hair strand
Water
(adapted from: http://www.mysciencebox.org/book/export/html/453 ,  AP  biology  the  Wheeler
School )