Springtime Science: Exploring the Pigments in Red Flowers
In the springtime it can be easy to spot flowers in a dazzling array of colors at flower gardens and in plant nurseries. And with Mother’s Day just around the corner, stunning flower bouquets are even more readily available in stores. Have you ever wondered what pigments make a flower appear a certain color to us? For example, what pigments make a rose be a deep, rich shade of red? Do different flowers use the same pigments? In this activity you’ll get to use paper chromatography to investigate if the pigments from one type of red flower are different from those in another type of red flower.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
The pigments in a flower are involved in attracting the attention of possible pollinators, such as honeybees, butterflies, and hummingbirds. There are two major classes of flower pigments: carotenoids and flavonoids. Carotenoids include carotene pigments (which produce yellow, orange, and red colors) and flavonoids include anthocyanin pigments (which produce red, purple, magenta, and blue colors). Usually, the color of the flower depends on the color of the pigments in the flower, but this can be affected by other factors. For example, blue cornflowers have the same pigments as red roses, but the pigments in the cornflower petals are bound to other pigments and metal ions, making cornflowers look blue.
In this activity you’ll use paper chromatography to investigate the pigments in flowers. Chromatography is a technique that is used to separate out the components of a complex mixture, or solution. In paper chromatography, a solution is dabbed onto the bottom of a paper strip, and the strip is then placed in a liquid. The liquid moves up the paper and, depending on how soluble they are in the liquid, the pigments are carried up the paper with the moving liquid. Ideally the components move at different speeds so they can be separated.
Extra: Try this activity with flowers that are even more different in color. Do other colored flowers have pigments similar to the ones in the red flowers?
Extra: Some plants grow very colorful leaves, such as coleus plants, bromeliads, and purple clovers. You could try this activity again but this time investigate colorful leaves on plants instead of flowers. What pigments make the leaves so colorful? Are these the same as the pigments in similarly colored flowers?
Extra: A more accurate way to identify flower pigments using paper chromatography is by determining their retention factor (Rf factor). The Rf value is the ratio between how far the pigment travels and the distance the liquid travels from a common starting point (the pencil line you drew on the strips). If other conditions are kept the same, the Rf value for a certain pigment should be consistent. You can do this activity again but this time measure these distances and calculate the Rf value for the pigments. Based on the Rf values, do the pigments look like they’re the same in different types of red flowers?
Observations and Results
Did you find that most (or all) of the red flowers used the same pigments? Did the pigments create a reddish-purplish band on the paper towel strips?
Carotene pigments (which are carotenoids) produce yellow, orange, and red colors while anthocyanin pigments (which are flavonoids) produce red, purple, magenta, and blue colors. Most red flowers use anthocyanin pigments to produce their red coloring (although some use carotenoids). On the paper strips, the anthocyanin pigments may have appeared as a purplish-reddish band. If different red flowers made similarly colored bands around the same height on the paper towel strip as each other, then they likely have the same pigment. However, if the bands are different colors and/or at different heights, then they’re probably different pigments. Carotene pigments are more commonly found in vegetables, and, in fact, they are what make carrots look orange. Yellow and orange flowers can have carotenoids or flavonoids, and blue flowers often have anthocyanin pigments that are modified. Some flowers even have chlorophyll that gives them green coloring.
In paper chromatography, the pigments move up the paper with the liquid and are separated based on the solubility of the pigments. So, if a pigment is very soluble in the diluted isopropyl rubbing alcohol, it should be easily carried up the paper strip, while a less soluble pigment will generally travel a shorter distance. Because different pigments often have different solubilities, they can be separated from each other on the paper strip.
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Teisha Rowland, PhD, Science Buddies
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