Activity: What’s in Your Lunch?
Goals:
1. To use testing procedures for identifying lipids and starches.
2. To predict whether some familiar foods contain starches and/or lipids
Background Information: There are four important organic compounds: carbohydrates, lipids
(fats), proteins, and nucleic acids. They are found in most of the foods that we eat. All animals,
including humans, take these organic compounds into their bodies when they eat. Organic
compounds provide living things with a source of energy, the ingredients needed for growth,
development and to repair damage, and the instructions for all of life’s activities.
Certain types of foods have more of one kind of organic compound than others. For example,
some foods are mostly carbohydrates; others are mostly proteins, while others are mostly lipids.
In this lab, you are going to use tests for identifying lipids and a type of carbohydrate known as
starch.
Materials: A small cup of cornstarch, small cup of vegetable oil, samples of familiar foods such
as bread, apple, rice, potato chip, milk, cheese, iodine solution, brown paper square divided into
several smaller squares, styrofoam or plastic plates divided into sections with a pen, plastic
droppers, plastic stirrers, data collection sheet, testing chart models
Procedure:
1. What I Know: Recall what you already know about carbohydrates and lipids (fats). You
may have heard these terms on TV or in a health class. What do you know or think you
know about carbohydrates and lipids?
2. Prediction: Before doing the lab activity, record what you predict about the food items
on the data table. Predict which ones you think may be carbohydrates and which ones
may be lipids and complete the column labeled predictions on your data table.
Part 1. Setting up the tests for starches and lipids.
3. Obtain samples of both the cornstarch and vegetable oil, as well as the food items listed
in the materials section of this activity description sheet.
4. Set up your brown paper (fats/lipids) testing sheet and your starch testing plastic or
styrofoam plate as directed in the separate handouts.
5. Place a small amount cornstarch and vegetable oil on the appropriately labeled areas of
brown paper and styrofoam plate.
6. Place 4 drops of iodine solution on the cornstarch on the styrofoam plate. Note the color
of the cornstarch after the iodine has been added. Did the solution turn the brownish color
of iodine or did it turn a purple/black color. Record your results on the data collection
chart by placing a plus (+) sign on the chart if the food turned a purple black color when
iodine was added or a minus (-) sign on the chart if the food remained the brownish color
of iodine when added to the food. If the food turned a purplish black color it indicates the
food contains starch. If the food remains a brownish color the food does not contain
starch.
7. Go back to the brown paper with the cornstarch on it. Brush away the cornstarch. Is there
a grease stain (oily stain), which makes the paper translucent when held up to the light or
no stain? If the food item leaves behind a grease stain, place a plus (+) sign on your chart.
If the food item does not leave behind a grease stain, place a minus (-) sign on your chart.
A grease stain indicates that the food item contains lipids (fats). A minus sign indicates
that the food does not contain lipids (fats).
8. Perform the same two tests with the vegetable oil. Place a few drops of vegetable oil on
the appropriately labeled square of brown paper.
9. Place 4 drops of iodine solution into the cup of vegetable oil. Note the color of the
vegetable oil after the iodine has been added. Did the solution turn the brownish color of
iodine or did it turn a purple/black color? Record your results on the chart.
10. Go back to the brown paper with the vegetable on it. Is there an oily stain, which makes
the paper translucent when held up to the light or just dried cornstarch? Record your
results on the chart.
Part 2.
11. Continue to test for the presence of starch and lipids with a variety of familiar foods and
record your results on your chart.
12. The cornstarch/iodine results (the purple/black color change) will be your standard for a
positive test for starch. The vegetable oil results (an oily stain that makes the paper
translucent when held up to the light) will be your standard for a positive test for lipids.
13. When you finish recording your results of the tests, review them with your teammates.
14. What I Did: Write a summary of the procedure you used for this activity.
Summary Chart
Brown Paper Test
 Tests for lipids
 (+) Foods that contain lipids leave a grease stain on brown paper
 Lipid = grease stain
Iodine Test
 Tests for starch
 (+) Foods that contain starch will turn a purple/black color when iodine is
added
 Starch = purple/black color change
15. What I Observed: This will be the data table you complete.
Substance
1
Cornstarch
2
Vegetable Oil
3
Rice Cereal
4
Potato Chip
5
Apple
6
Butter
7
Bread
Prediction
(starch or
lipid)
Brown Paper
Test
(+ or -)
Iodine Test
Type of
Compound
(+ or -)
16. What I Learned: Write a summary of what you learned from completing this activity.
Be sure to relate your summary to the goals of the lesson and your observations.
17. What I Wonder: Pose a why or how question you still may have about the topic of this
activity.
18. Questions: Answer the following questions in complete sentences. Be sure to restate the
question in your answer.
a. What would it mean if a food sample shows a positive result for both?
tests?
b. What would it mean if a food sample does not show a positive result for
either test?
c. Did any of the test results surprise you? Explain.