Transcript Goal #1

Photosynthesis uses pigments to capture light
Pigments = light-absorbing molecules
a. Found in chloroplasts
b. Chlorophyll a & b, carotene,
Why Do Leaves Change Color in the Fall?
ScienceDaily (Oct. 16, 2007)
When chlorophyll disintegrates rapidly, carotene shines through as the yellow in
maple, aspen and birch leaves. Many of the colors we see in fall are always
present, but normally they’re hidden from view, says UW-Madison Arboretum
native plant gardener Susan Carpenter.
The leaves of trees and other plants contain three main pigments: carotene,
anthocyanin, and the photosynthetic pigment, chlorophyll, which captures the sun’s
energy to make food for plants. As the most abundant pigment, chlorophyll is
what gives leaves their green hue in spring and summer.
Another chemical in leaves, auxin, controls a special band of cells at the base of
each leaf stem, called the abscission layer. During the growing season, auxin
prevents this layer from fully developing and blocking the tiny, internal tubes that
connect each leaf to the rest of the tree’s circulatory system.
In fall, however, cooler and shorter days trigger an end to auxin production,
allowing the abscission layer to grow and cut off the circulation of water, nutrients
and sugar to the leaves. When this happens, chlorophyll disintegrates rapidly,
letting carotene shine through as the yellow in maple, aspen and birch leaves.
Anthocyanin, meanwhile, provides the oranges and reds of maples, sumacs and
oaks. When there’s less sun, anthocyanin isn’t as chemically active and leaves are
Visible Spectrum
1. The colors we see are called the
visible spectrum (ROYGBIV)
2. The color you see of an object is the
reflection of that color
a. all other colors are absorbed
b. i.e. a red shirt reflects red and absorbs OYGBV
4. “black” is a reflection of all colors of the
visible spectrum