Name: ________________________________________
Date: _________________
Period: ______
Organic Molecules Pre-Lab Questions
Directions: Read through the background information and procedure to answer the following questions before
we begin our experiment.
1.) What does it mean for a molecule to be called “organic?”
2.) What are the four types of organic molecules found in living systems?
3.) If starch is present in the food sample, what color will Lugol’s iodine solution turn it?
4.) If protein is present in the food sample, what color will Biuret reagent turn it?
5.) How will you know if fat is present in your food sample?
6.) Why must we rinse each beaker before beginning the test for proteins?
7.) How many drops of each food sample are we using in the test for fat?
8.) What must you be careful of when crushing the potato chip?
9.) Record your hypotheses in the chart below. Place a “+” if you think the food sample will test positive for
the identified organic molecule and a “-“ if you think it will test negative.
Table 1: Lugol’s Test for Starch
Food Sample
1. Water
2. Milk
3. Bread
4. Table Sugar
5. Potato
6. Chicken Broth
Prediction
(+/-)
Table 2: Biuret’s Test for Protein
Food Sample
1. Water
2. Milk
3. Bread
4. Table Sugar
5. Potato
6. Chicken Broth
Prediction
(+/-)
Table 3: Test for Fat
Food Sample
1. Water
2. Fruit Punch
3. Vegetable Oil
4. Potato Chip
Prediction
(+/-)
Organic Molecules Pre-Lab Reading
Background:
Organic molecules are molecules that contain carbon. Living systems are made up of organic molecules. The 4
main classes of organic molecules are carbohydrates, lipids, proteins, and nucleic acids. In this lab we will test
various substances for the presence of complex carbohydrates (starch), proteins, and lipids.
Carbohydrates: Carbohydrates can be divided into three groups, monosaccharides, disaccharides, and
polysaccharides. Mono and disaccharides are simple sugars. Polysaccharides are complex carbohydrates such
as starch. We will be testing various food samples for the presence of starch. Lugol’s iodine solution will turn a
dark purple/black color in the presence of starch molecules.
Proteins: Proteins are large polymers made up of many amino acid monomers. Proteins are the workers of life.
They perform various tasks inside living things. Proteins also make up muscle tissue, hair, and fingernails. We
will be testing for the presence of proteins in various substances using Biuret reagent. Biuret reagent turns from
a blue color to a violet/purple when in the presence of proteins.
Lipids: Lipids are made up of building blocks called glycerol and fatty acids. Lipids typically feel greasy to the
touch. One category of lipids includes both saturated and unsaturated fats. We will test for the presence of fat
food samples using a simple paper towel test. If fat is present in the food sample, it will leave behind a
translucent (see through) spot on the paper towel.
Organic Molecules Lab Procedure
Test 1: Starch Test
Procedures:
1. Place a very small amount of each substance listed into each of your beakers.
2.
3.
4.
5.
6.
7.
Water
Milk
Bread
Table Sugar
Potato
Chicken Broth
Record the original color in Table 1.
Add 2 drops of Lugol’s solution on top of each sample (Lugol’s solution is liquid iodine).
Mix contents by gently swirling if necessary.
Record the final color in Table 1.
Record the results in Table 1 (+ or – for starch).
RINSE EACH BEAKER THOROUGHLY!
Test 2: Protein Test
Procedures:
1. Place a very small amount of each substance listed into each of your beakers.
2.
3.
4.
5.
6.
7.
Water
Milk
Bread
Table Sugar
Potato
Chicken Broth
Record the original color in Table 2.
Add 5-10 drops of Biuret solution on top of each sample.
Mix contents by gently swirling if necessary.
Record the final color in Table 2.
Record the results in Table 2 (+ or – for protein).
RINSE EACH BEAKER THOROUGHLY!
Test 3: Fat Test
Procedures:
1. Place a very small amount of each substance listed onto your paper towel.
- 1 drop of Water
- 1 drop of Fruit Punch
- 1 drop of Vegetable Oil
- Potato Chip
2. Label each spot according to where sample it is.
3. With your paper towel flat against the table, use your finger to crush the potato chip and gently grind it
into the paper towel. BE CAREFUL NOT TO RIP YOUR PAPER TOWEL!
4. Brush the potato chip pieces off of the paper towel.
5. Hold the paper towel up to the light and observe each spot for transparency. Record transparency in
Table 3.
6. Record the results in Table 3 (+ or – for fat).
7. Throw away your paper towel and return your lab tray containing all of the supplies.
Name: ________________________________________
Date: _________________
Period: ______
Organic Molecule Lab
Results:
Table 1: Lugol’s Test for Starch
Food Sample
Original Color
1. Water
2. Milk
3. Bread
4. Table Sugar
5. Potato
6. Chicken Broth
Table 2: Biuret’s Test for Protein
Food Sample
Original Color
1. Water
2. Milk
3. Bread
4. Table Sugar
5. Potato
6. Chicken Broth
Table 3: Paper Towel Test for Fats
Food Sample
Transparent
(yes/no)
1. Water
2. Fruit Punch
3. Vegetable Oil
4. Potato Chip
Final Color
Results (+/-)
Final Color
Results (+/-)
Results (+/-)
Conclusion: Answer the following questions in complete sentences.
1. What was the manipulated (independent) variable in this experiment?
2. What was the responding (dependent) variable in this experiment?
3. In the space provided below, summarize your results from each test in a short paragraph.
4. Explain why we included water in each of the tests.
5. Table sugar is definitely a carbohydrate. How can you explain the results you got when you tested it for
starch?
6. Based on what you have learned and your background knowledge, complete the table below by
identifying what types of food generally contain starches, protein, and fats?
Starch:
Protein:
Fat: