Name
Date
Investigating Carbohydrates: Testing for Starches in Food
Plants produce glucose to use as an energy source. If a plant makes more glucose than it needs, the
extra molecules are stored in the form of starch. Starch is a carbohydrate made up of long chains of
glucose molecules.
Many kinds of animals, including humans, consume the starches in plants. Some of the most popular
starch plant products are potatoes, corn, and grains. Grains include wheat and rice. These starches
are used to produce a wide variety of foods. In the animal diet, starches serve as quick sources of
energy.
In this lab, you will test several kinds of food for the presence of starch. Iodine, a reddish-brown
liquid, turns blue or black on starch.
Materials
safety goggles
lab coat or apron
10 or more small samples of
food (such as cheese, bread,
raw potato, cooked pasta,
luncheon meat, mayonnaise,
lettuce, tomato, apple, onion, radish,
cucumber, milk)
pipette
small bottle of iodine
paper towel
Procedure
Food Sample
1. Put on safety goggles and a lab coat or
apron. Safety Alert: Iodine can permanently
stain clothing.
1.
2. Select 10 food samples and place them on a
paper towel.
3.
2.
4.
3. In the left column of the data table at right,
list the foods you have selected.
5.
6.
4. Put a drop of iodine on the first sample. If
the iodine on the food sample turns blue or
black, write “Yes” in the table beside that
sample. If the iodine remains the same color,
write “No.”
7.
8.
9.
10.
5. Follow the same procedure for each food
sample.
© Pearson Education 2010
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Turns Iodine
Blue/Black
Name
Date
Investigating Carbohydrates: Testing for Starches in Food, continued
Cleanup/Disposal
Follow your teacher’s instructions for cleanup and disposal of materials.
Analysis
1. Of the foods that tested positive for starch, how many of them were of animal origin?
For example, how many were items such as meat, milk, or cheese? ___________
How many were of plant origin, such as bread, potato, or onion? ___________
2. Circle the three foods that are your personal favorites of the ones tested.
Are they carbohydrates? ___________
Conclusions
1. The black substance produced by the combination of iodine with starch is a new substance that
did not exist before. Knowing this, is the production of the black substance a chemical or physical
change? Why?
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________________________________________________________________________________
2. Before an important event, an athlete might eat a lot of carbohydrates to stock up on energy
reserves. Suggest a meal that is rich in carbohydrates.
________________________________________________________________________________
________________________________________________________________________________
3. Which group of people do you think needs more carbohydrates in their diets: people who work at
a computer all day or people who load packages on trucks? Explain your answer.
________________________________________________________________________________
________________________________________________________________________________
Explore Further
Starch and cellulose are both made of long chains of glucose molecules. Find out how the
chemical structures of the two macromolecules differ. Explain how the chemical structures are
different.
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© Pearson Education 2010
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