Olivia Pearson
Colby College 2016
January 11, 2016
Teacher’s Guide: What’s in Your Food?
Description: This lesson plan shows the students which foods contain starch and shows
them how to detect the presence of starch. Demonstrations and activities are utilized to
display how indicators work and allow the students to understand different components of
their food.
Learning Goals:
Students will test:
1. Whether starch is present in potatoes and cooked pasta
2. Whether starch is present in a leaf performing photosynthesis
Students will observe:
1. How an indicator changes color when introduced to an acid or a base by making
green eggs with red cabbage juice
Students will understand:
1. Which foods contain starch
2. The function of starch within plants
3. How different indicators function and what they can tell us
Recommended Grades: 4th-8th
Estimated Time Required: ~50 minutes, including 5-10 mins prep time
Key Concepts and Definitions of Terms:
Acids and Bases – acids are compounds that can donate a hydrogen ion to another
compound and has a pH less than 7. Bases are compounds that can accept a
hydrogen ion from other compounds and has pH greater than 7.
Acid-Base Indicators – substances that change color with a different pH, usually a
weak acid or a weak base. Common indicators are red cabbage juice and iodine
dissolved in an aqueous solution of potassium iodide.
Photosynthesis – the process through which plants obtain their energy. Sunlight is
converted into molecules of sugar.
Starch – the molecule used by most plants to store food. They are found in the
chloroplasts of the leaves and are used up when the leaves are deprived of light.
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Olivia Pearson
Colby College 2016
January 11, 2016
Materials needed:
-2-3 potatoes
-2-3 scoopers (used to carve out pieces of potatoes)
-Vegetable oil
-4-5 potassium iodide solutions (one per each group of students)
-4-5 plastic petri dishes (one per each group of students)
-8-10 weighing boats or small plastic containers (on per each group of students)
-1 large pan that can be placed on a hot plate and can be filled with water
-1 hot plate
-Ethanol solution (can be substituted with Vodka)
-30 glass beads
-1 medium/large thin leaf, freshly plucked from a plant that has been in sunlight within the
past 12 hours (one per each group of students)
-4-5 pairs of tongs to handle the leaves
-1 egg
-1 1000mL beaker
-Stirring rod
-8-10 mL of red cabbage juice
-1 paper plate
Estimated Cost: ~$30
Safety Information:
-Safety goggles should be worn at all times
-The teacher should handle the boiled ethanol and water
General Outline of Procedures
Green Eggs Demonstration – How to make Green Eggs (Ham not included)
1. Explain to the students the concept of an indicator and how it can be used to test
certain foods to see if they are acidic or basic.
2. Line the 1000 mL beaker with vegetable oil and place on top of the hot plate.
Crack the egg and add only the whites to the beaker. Save the yolk. Add 8-10 mL of
red cabbage juice to the egg whites and stir until the egg whites have solidified.
3. Pour the scrambled egg onto a plate and add the egg yolk to the center.
4. Post-lab Question: Ask the students what the change in color to the egg whites
tells us about the egg whites (that egg whites are basic).
What Happens: The red cabbage juice reacts with the basic egg whites to
produce a bluish-greenish color.
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Olivia Pearson
Colby College 2016
January 11, 2016
Detecting Starch in Potatoes and cooked pasta – Is there starch present?
1. Have the students, in groups of 4 or 5, scoop out little bits of potato into a
weighing boat.
2. Add 2-3 drops of iodine to the pieces of potato. Observe any color changes that
take place.
3. Ask the students if the test detected starch in the potatoes (a dark black color
indicates starch is present, a red color indicates there is no starch)
4. Ask the students which other foods they think contain starch
5. Distribute a few pieces of cooked pasta per group in fresh weighing boats.
6. Add 2-3 drops of iodine to the pieces of potato. Observe any color changes that
take place.
7. Ask the students if the test detected starch in the cooked pasta.
What Happens: The iodine forms a complex with starch that produces a
dark purple-black color in both the potatoes and cooked pasta.
Detecting Starch in leaves
1. Fill the pan with water and set it on top of the hot plate.
2. Fill a 250mL beaker with 50-100 mL of ethanol depending on how large the leaf
is/how many leaves are being used.
3. Add the 30 glass beads to the beaker of ethanol and place beaker in the pan of
water (glass beads help weigh down the beaker).
4. Turn on the hot plate and allow the ethanol to come to a boil in the water pan.
(note: this should be done by a teacher).
5. Dip the leaf in the hot water for ~1 min. After drying the leaf off, dip it in the
boiling ethanol for 2 minutes or until the leaf starts to turn white.
6. Dip the leaf in cold or room temperature water and allow it to dry.
7. Split the leaf into 4-5 sections, one for each lab group. Place each part of the leaf
into a weighing boat and distribute them to the groups.
8. Have the students add 2-3 drops of iodide to the leaf and wait two minutes.
Observe any color changes in the leaf.
9. Ask the students if they found that starch was present in the leaf.
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Olivia Pearson
Colby College 2016
January 11, 2016
10. Post-lab question: which leaf would have more starch – a leaf measured at the
beginning of the day or a leaf measured at the end of the day?
What happens: The hot water kills the leaf and the ethanol breaks down the
chlorophyll in the leaf and removes the green pigment. The iodine forms a
complex with starch that produces a dark purple-black color.
Special Notes:
-It takes a decent amount of time for the water and ethanol to heat up – while they are
heating, the potato and pasta activities can be performed.
-The leaf used should be thin and plucked within the last 12 hours. It should also come from
a plant that has access to sunlight throughout the day. If possible, this experiment should be
done towards the end of the day, as the leaf will have the greatest amount of starch present.
-To make the red cabbage juice:
http://www.carolina.com/teacher-resources/Interactive/red-cabbage-guice-homemade-phindicator/tr10851.tr
References:
"Acids and Bases Are Everywhere." Chem4Kids.com: Reactions: Acids and Bases. Web. 11 Jan.
2016. <http://www.chem4kids.com/files/react_acidbase.html>.
"Acid-Base Indicators." Web. 11 Jan. 2016.
<http://chemistry.elmhurst.edu/vchembook/186indicator.html>.
"Photosynthesis: Testing for Starch." Web. 11 Jan. 2016.
<http://www.hometrainingtools.com/a/starch-test>.
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Olivia Pearson
Colby College 2016
January 11, 2016
Student Worksheet (k-4th Grade)
1. Where do plants get their energy?
2. How do our bodies use starch?
3. Draw what happens to the potato and the leaf when iodine is added.
4. Draw two other foods that contain starch (on the back).
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Olivia Pearson
Colby College 2016
January 11, 2016
Student Worksheet (5th-8th Grade)
1. How do plants make starch?
2. Would a plant have more starch at the beginning or at the end of the
day?
3. Name two differences between plant cells and animal cells.
4. How does the iodine change color when it touches the potato and the
leaf? Why?
5. Name 3 other foods that contain starch
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