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Oct. 13, 2010

The Color of Flowers

by Science Friday Education

Click to enlarge images
Flowers are found around the world in a variety of environments, and in all kinds of sizes, shapes and colors. Flowers are collected for many different reasons. Scientists collect flowers to find cures for diseases or to study insect behavior.
 
Gardeners and florists collect flowers because of their beautiful array of flower colors for a bed or display, or to symbolize emotion. Artists and photographers, like Robert Creamer, collect flowers as inspiration or as subjects for their art. But where do all these beautiful colors come from?
 
In this activity, students will perform an experiment to find out where flower colors come from. Students will extract petal juice, use acid and base indicators, and observe chemical reactions to investigate how the amount of acid or base influences the color of a petal.
 
Grade Level: 6th – 8th grade
Subject Matter: Life Science
National Standards: NS.5-8.1, NS.5-8.3
Robert Creamer, a photographer based in Maryland, uses a high-resolution scanner as his camera. Creamer's subjects are largely botanical, plucked from his own greenhouse. He arranges flowers over the scanner, sometimes suspending them with wires, even burning them during the scan. Creamer’s work has been featured at the Smithsonian Institution Museum of Natural History in Washington, DC.
 
Activity Materials
Red, blue and purple flowers with large petals, one of each color for each student. Red roses and purple or blue irises are ideal.
Ziploc bags, one for each student
Hammers, one for each pair of students
Water
Clear plastic cups, four for each student
Teaspoons, one for each student
Empty white Styrofoam egg cartons, one for each student
Droppers, one for each pair of students
Bottle of vinegar
Baking soda
 
Vocabulary
pH scale: a scale used to measure the acidity or basicity of a solution.
Acid: a chemical compound that usually tastes sour and measures less than 7 on the pH scale.
Base: a chemical compound that usually tastes bitter and measures between 8 and 14 on the pH scale.
Hydrogen: a colorless gas.
Molecule: the smallest unit of a substance that can exist independently.
 
What To Do
Prep: Make the baking soda solution in advance of class by mixing two cups of water with one teaspoon of baking soda. Place solution in small plastic cups, one cup of solution for each student.

1. Begin the lesson by having the students watch the Science Friday video, “Beauty Scans.” Have students track the different colors of the flowers in the video, and have them name the flower colors that they have observed themselves. Discuss with students why they think flowers come in so many colors, and where the colors come from.

2. Tell students they will perform an experiment to find out where flower colors come from. They will begin by extracting petal juice for each of the colored flowers. Can they think of a method of extracting petal juice from the flowers?

3. Hand out a red flower to students, and instruct them to remove five petals from the flower, tear the petals into small pieces, and place them in a Ziploc bag. Squeeze the air out of the bag and seal it.

4. Have students lay the bag of petals on a flat surface and carefully use the hammer to smash the petals in the bag without ripping the bag. Students should keep hammering until all the petals are smashed into a pulp.

5. Have students open the bag, add five teaspoons of water, and then close the bag. Instruct students to use their fingers and thumbs to rub and squish the petals until the water turns the color of the petals.

6. Have students pour the petal juice into a clear plastic cup, and squeeze the petal pulp until all the juice comes out of the pulp. Then discard the pulp.

7. Have students repeat steps 3-6 for the blue and purple flowers, so that they make three separate samples of the petal juice for each of the three flowers.

8. Hand out an empty white Styrofoam egg carton to each student.

9. Have students use a dropper to place one teaspoon of the red petal juice into one well of the egg carton. Then tell students that they should add a few drops of vinegar to the red petal juice. What do they think will happen?

10. Have students add the drops of vinegar until they observe a color change. Students can compare the color to the original color in the petal juice cup. What new color was made? What flowers exist with this color? Why do they think this color change took place?

11. Have students repeat steps 9-10 for the blue and purple petal juice. Can they predict what colors the petal juice will change into?

12. Hand out a small cup of baking soda solution to each student. Tell students that they will perform the same experiment, using a mixture of baking soda and water. What do they predict will happen to each petal juice color? What do they know about baking soda?

13. Have students repeat steps 9-10, adding the baking soda solution instead of vinegar to each of the two other petal juice colors. What new colors are produced? Why do they think that the petal juice changed colors when the solution was added?

What’s Happening?
Colored molecules known as pigments give flower petals their colors. Each color molecule of a pigment has a specific molecular structure. Any change in the molecular structure of the color molecule can cause a big change in the color.
In this activity, the petals are crushed to extract the color molecules. The petal juice made from a red rose is dark red. When vinegar is added, the dark red petal juice color turns pink or orange because the vinegar is acidic. This causes a chemical reaction because acid adds a hydrogen atom to the color molecule, changing the molecular structure of the molecule and turning it to pink or orange.
 
When the baking soda solution is added to the petal juice, it turns purple/blue or green/yellow -- depending on the amount of baking soda in the solution. This happens because baking soda is a base, and also causes a chemical reaction. In bases, the hydrogen atom falls off the color molecules, which makes them purple/blue. Flowers that have acid in their petals are shades of red, while flowers that have base in their petals are purple/blue. The varying amounts of acid or base in a flower petal can create a variety of colors.
 
Topics for Science Class Discussion
• How does the color of a flower assist with its reproduction?
• Why would some flowers change color throughout their lifecycle?
• Why do leaves change color in autumn?
 
Extended Activities and Links
Have students experiment by adding different types of acidic solutions (lemon juice, orange juice, etc.) to their petal juice, or by varying the amount of baking soda in the baking soda solution. Students can maintain a chart demonstrating the colors resulting from each type of solution added.
 
Have students research the various ways that flower pigments have been extracted and used throughout history. Students can create their own work of art using flowers pigments, and demonstrate their technique to the class. Link science and history by assigning students to read Mauve: How One Man Invented a Color that Changed the World
http://www.amazon.com/Mauve-Invented-Color-Changed-World/dp/0393323137
 
Conduct an experiment to analyze if the pigments in all red flowers are the same:
http://www.sciencebuddies.org/science-fair-projects/project_ideas/PlantBio_p035.shtml
 
Observe time-lapse movies of flowers blooming:
http://plantsinmotion.bio.indiana.edu/plantmotion/flowers/flower.html
 

 

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