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Chemistry and Color

Chemistry and Color. The Chemistry of Autumn Color. Angela Knapp, Kelley Jones, Michelle Blankenship, and Alyssa Pell. What is responsible for the green color of leaves?. Chlorophyll Chemical formula C 55 H 70 MgN 4 O 6 Large molecule Attached to chloroplasts, the site of photosynthesis

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Chemistry and Color

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  1. Chemistry and Color The Chemistry of Autumn Color Angela Knapp, Kelley Jones, Michelle Blankenship, and Alyssa Pell

  2. What is responsible for the green color of leaves? • Chlorophyll • Chemical formula C55H70MgN4O6 • Large molecule • Attached to chloroplasts, the site of photosynthesis • Absorbs red and blue light from sunlight that falls on leaves, normally the light that is reflected is diminished in red and blue and therefore appears green • Two types: chlorophyll a and chlorophyll b

  3. Some Other Pigments That Color Leaves: • Chlorophyll • Carotene (C40H36) • Anthocyanins

  4. Additional Pigments In Leaves • Xanthopyll- yellows and oranges • Tannins- browns • Each different pigment has the ability to absorb different wavelengths of light • The visible spectrum of light is from 380-750nm • Any substances that absorb light are called pigments

  5. Colors The Various Main Pigments Absorb: Thus, here are the colors that they reflect: GREENYELLOWRED

  6. The color produced by these pigments is sensitive to the pH of the cell sap. If the sap is acidic, the resulting color is bright red. If the sap is less acidic, the resulting color is purplish red. Formed by a reaction between sugars and certain proteins in the cell sap This reaction requires a high sugar concentration and light Also apparent in the bright red skin of apples and in the purplish red skin of grapes The Effect of pH on Anthocyanins:

  7. Interactions of light with matter in a chloroplast:

  8. Photosynthesis • An endothermic reaction (the products store more free energy than reactants) • Energy of the sunlight that is absorbed by the chlorophyll is converted into chemical energy that is then stored in carbohydrates • carbon dioxide + water  oxygen + carbohydrates • xCO2+yH2O+light energyxO2+Cx(H20)y • Pigments absorb the light that powers the reaction in photosynthesis

  9. Okay…enough about pigments! Why do the leaves actually change? • Both a change in the environment (the arrival of cooler temperature, and shorter days with less hours of sunlight) and the genetic codes in trees also play a role. • Shorter days and cooler temperatures slow down the production of chlorophyll…and the chlorophyll that remains breaks down. All of the pigments that were masked by the chlorophyll begin to appear. • Also, anthocyanins increase when the amount of sugar in leaves increases. Cool nights increase the sugar content of leaves as the plant starts to store energy for the winter.

  10. Formula of Chlorophyll:(a large molecule)

  11. Chlorophyll Molecules chlorophyll a and chlorophyll b differ slightly in their structures

  12. Websites • http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html • http://www.accuweather.com/iwxpage/paws/fallfaq.htm • http://www.brainpop.com/science/ecology/autumnleaves/ • http://photoscience.la.asu.edu/photosyn/education/colorchange.html • http://www.chem.ox.ac.uk/mom/autumn/autumn.html

  13. Experiment • We can separate the pigments from leaves… this is partially due to the fact that pigment molecules are so large! • Think of tea, or the juice that is left over in the bottom of a bowl of cooked spinach or greens.

  14. Two easy ways to see the pigments in leaves of any color! • Grind leaves up and place the grinds in alcohol for about 20 minutes OR • Grind leaves up and add water, then boil

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