Name ___________________________________________ Date ______________ Period _____________
Identifying Biomolecules Virtual Lab
Scientists use a combination of biology and chemistry for their understanding of life and life processes.
Carbohydrates make up a large group of chemical compounds found in cells. Carbohydrates are an energy
source or are used in making cell structures.
Pre-Lab Questions:
1. What three elements are found in all carbohydrates?
2. What is the ratio for all carbohydrate formulas?
3. What are examples of monosaccharides?
4. What are examples of disaccharides?
5. What are examples of polysaccharides?
6. What four elements are found in proteins?
7. What are the monomers for proteins called?
8. Lipids do not have a set structure but do contain two components that help to identify them called?
**You will learn how to test for these organic molecules by completing a virtual lab at
http://faculty.kirkwood.edu/apeterk/learningobjects/biologylabs.htm.
Complete each of the tests for carbohydrates, proteins and fats.
Step 1: Testing for Carbohydrates
Monosaccharides are single sugars that react with an indicator called Benedict's solution. The reaction
changes the color of the reagent to green, red or orange depending on how much sugar is present.
Polysaccharides are complex sugars that react with an indicator such as Iodine. The reaction changes the color
of iodine to a dark blue/black color in the presence of starches.
Step 2: Testing for Proteins
Proteins react with Biuret reagent. The reaction turns the color of biuret from a light blue to violet.
Step 3: Testing for Fats
Fats are a type of lipid. There are two methods of testing for fats. One method is to rub a fat sample on brown
paper to observe if the paper becomes translucent. Another method is to use an indicator such as Sudan IV
which is a dye that will dissolve in fats. It will not dissolve in carbohydrates or proteins. Sudan IV will change
the color of a fat to red.
Create a chart of all tested food sources:
Name ___________________________________________ Date ______________ Period _____________
Food
Sample
Sugar
Starch
Protein
Lipids
Benedict’s Color
after Heating
Iodine Color
after Addition
Biuret Color
after Addition
Sudan III color
after addition
Foods that contain
the biomolecule
Conclusions:
1. What was the purpose of testing distilled water with each indicator in a lab activity with indicator
solutions?
2. Both glucose and starch are considered carbohydrates. Why are two separate test procedures and
indicators necessary?
3. If the test for a starch indicated it did not contain glucose (simple sugar), does that mean the food
source does not contain carbohydrate? Explain.
4. If you needed a quick source of energy, which type of food source would be your best choice? Explain.
5. Explain why it is an advantage for us to eat foods that contain more than one type of molecule.