By Laura Nelson
Do you know why leaves change colors in the fall? The answer has to do with chemical compounds in leaves known as pigments. You may have heard of the green pigment chlorophyll. At the Nokomis Market on July 27, visitors explored how other pigments are present in leaves all the time but are invisible until autumn. Seasonal changes, including shorter daylight hours, cause plants to break down chlorophyll which is quite “expensive” in the amount of energy needed to produce it. Visitors explored the importance of chlorophyll in photosynthesis by recreating the photosynthetic cycle on a felt board. When photosynthesis slows in the fall and a plant breaks down chlorophyll into its components, it will recycle these component nutrients. Other pigments that were once hidden become visible because of the breakdown of chlorophyll. The pigments xanthophyll (yellows and browns), carotenoids (orange), and anthocyanins (reds and purples) are the vibrant colors we see showing through in autumn.
To explore the idea hidden pigments, market goers performed chromatography, the process of separating a substance into its components. Visitors separated colors by marking a dot on a piece of chromatography paper, dipping it in water, and observing the water soak up the paper through capillary action. The results showed that secondary colors like green separated into primary colors like blue and yellow. You can perform your own chromatography with markers at home using coffee filters.
Separating leaf pigments takes up to an hour, so market goers prepared their own take-home leaf chromatography kits. Market Scientists provided leaf samples from a common houseplant called Zebrina with bright purple and green leaves. Visitors tore the leaves into small sections, put them in a plastic vial, and covered the leaf bits with a small amount of isopropyl alcohol. Equipped with their own leaf samples, chromatography paper, and instructions, market goers left with science kits to explore leaf pigments. Curious about the results? Take a look at the chromatography paper below. Can you pick out the two primary pigments anthocyanin and chlorophyll?
Visitors separated colors with a prism, but instead of pigments, they saw different wavelengths in the visible light spectrum. Our youngest visitors also enjoyed observing leaf trichomes, or hairs, under a microscope. Thank you to Nokomis Market for welcoming the Market Scientists and for all the visitors who explored leaf colors with us!