How Flowers Get Their Colors

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The main reason people grow flowers is for their colors and the feelings these colors evoke for weddings, funerals, holidays, gifts, birthdays, anniversaries, and dates.
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“Ask a Science Teacher” by Larry Scheckel answers over 200 common questions about science.

Ask a Science Teacher(The Experiment, 2011) by Larry Scheckel is sure to resolve the everyday mysteries you’ve always wondered about. You’ll learn how planes really fly, why the Earth is round, how microwaves heat food, and much more — before you know it, all your friends will be asking you! This section answers how flowers get their colors.

The pigment anthocyanin gives color to most flowers and fruits. Anthocyanins are water-soluble pigments in a class of chemicals called flavonoids. A pigment is an organic compound that gives a characteristic color to plant or animal tissue. For example, chlorophyll gives the green color to plant leaves and stems. Hemoglobin gives blood its red color.

Flavonoids, compounds found in many vegetables and fruits, have antioxidant properties. Some flavonoids protect blood vessel walls, some alleviate allergies, and some defend against cancer and viruses. Others have anti-inflammatory properties.

The flower colors of blue, purple, pink, and red come from anthocyanins. Plants produce other pigments, too, like carotene, which makes the orange of carrot roots and the red of tomatoes; chlorophyll, which gives leaves their green color; and xanthophyll, which makes foods like egg yolks and corn yellow.

A common experiment uses the anthocyanins in red cabbage as a pH indicator, because anthocyanins change color depending on their pH. A strip of paper treated with red cabbage juice will turn red if placed in an acidic (low-pH) solution and green/yellow if placed in a basic (high-pH) solution. The strip will remain purple if placed in a neutral-pH solution.

Colors are instrumental in a flowering plant’s reproduction. Flowers reproduce by having male organs called stamens, loaded with pollen, and female organs named stigmas. The function of the stigma is to receive pollen from another plant of the same species. But plants can’t move, so they rely on insects and birds to move their pollen for them. The bright flower petals attract insects and birds to the nectar or edible pollen produced by the plants. Yellow flowers are an advertisement for bees, and red attracts birds.

Some flowers change color during the growing season. For example, forget-me-nots change from pink to blue. Larkspur, or delphiniums, change color, too. Color shifts send a signal to insects that a flower has aged and is past pollination.

Certain flowers close up at night. The morning glories that had to be pulled out of the cornfields on my farm closed up at night and opened during the day. These flowers react to changes in light and temperature. Heat makes the inner surface of the flower grow faster, and the flower opens. When the temperature goes down in the evening, the outer surfaces grow faster than the inner and the flower closes up. Flowers that respond to light have cells that contain a pigment called phytochrome.

These photoreceptor cells increase and decrease in size based on the amount of incident light.

The main reason people grow flowers is for their colors and the feelings these colors evoke for weddings, funerals, holidays, gifts, birthdays, anniversaries, and dates. We think of lilies for Easter, poinsettias for Christmas, roses for Mother’s Day. The red of the rose generally stands for love, pink for gentility, happiness, grace, and thankfulness. Daffodil or chrysanthemum yellow signifies joy and friendship. White is for purity, innocence, silence, and heaven. Coral- or peach-colored flowers are common for a first date. Purple flowers demonstrate royalty and ceremony. There are claims that the blue of hydrangeas and irises calms worries and represents peace and serenity. However, the science behind these claims is dubious.

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Excerpted from Ask a Science Teacher: 250 Answers to Questions You’ve Always Had About How Everyday Stuff Really Works © Larry Scheckel, 2011, 2013. Reprinted by permission of the publisher, The Experiment. Available wherever books are sold.