WEBVTT - Why Do Leaves Change Color in the Fall?

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<v Speaker 1>Welcome to brainstuft, a production of iHeart Radio, Hey, brain Stuff,

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<v Speaker 1>Flour and vog obam here enthusiastic snowball fights in winter

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<v Speaker 1>or blazy summer days at the beach. Notwithstanding, autumn might

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<v Speaker 1>be the most beloved season of the mall. Every year,

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<v Speaker 1>people in temperate climates watch in awe as the trees

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<v Speaker 1>begin their magical transformation from green powerhouses to veritable Morgese

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<v Speaker 1>boards of brilliant yellows, fiery oranges, and vibrant reds. It's

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<v Speaker 1>even a tourist attraction. The northeastern United States, for example,

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<v Speaker 1>hosts millions of leaf peepers from all over the world

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<v Speaker 1>who come to observe nature's fine art gallery. Myths about

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<v Speaker 1>why this occurs stretch back through time, from the hot

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<v Speaker 1>and O'shannee to the Algonquin to the Wye Dot. A

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<v Speaker 1>few Native American people's legends feature a wayward bear, sometimes

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<v Speaker 1>represented by ursa Major or the Big Dipper, which returns

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<v Speaker 1>to the sky every autumn. The legends say that the

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<v Speaker 1>bear was injured in a hunt or a fight, and

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<v Speaker 1>that's blood tends the leaves red each year. Much more recently,

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<v Speaker 1>researchers have sussed out the science behind these transformations, involving

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<v Speaker 1>photosynthesis and pigments. For a large part of the year,

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<v Speaker 1>leaves are a tree's workhorses, constantly converting carbon dioxide, water,

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<v Speaker 1>and sunlight into energy in the process called photosynthesis. The

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<v Speaker 1>key to this process is the pigment chlorophyll, which is

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<v Speaker 1>what gives leaves their green color for much of the year.

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<v Speaker 1>But while chlorophyll is the star of the show, it

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<v Speaker 1>has some help in the form of other pigments like

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<v Speaker 1>caroteene and xanthophill. Xanto is Greek for yellow, and Caroteene

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<v Speaker 1>is named for carrots because it's what gives them and

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<v Speaker 1>other things their orange color. These two pigments are always

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<v Speaker 1>present in leaves and help absorb sunlight, which they transfer

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<v Speaker 1>to chlorophyll for photosynthesis to occur. As summer nears its

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<v Speaker 1>end and days get shorter, the decreased amount of sunlight

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<v Speaker 1>incites trees to prepare for a sort of hibernation. The

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<v Speaker 1>leaves won't be able to continue photosynthesizing during winter due

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<v Speaker 1>to the dry air and lack of light, so the

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<v Speaker 1>tree does two things. First, it forms a separation layer

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<v Speaker 1>made of cork like cells at the base of each leaf,

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<v Speaker 1>to seal it off from the tree the second it

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<v Speaker 1>stops producing chlorophyll, since it won't need this pigment until

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<v Speaker 1>the days start to Lengthen once again in the spring,

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<v Speaker 1>with chlorophyll out of the picture, the yellow and orange

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<v Speaker 1>pigments get a chance to shine. The red hues which

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<v Speaker 1>come from pigments called anthocyanins, are slightly more complicated. Whereas

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<v Speaker 1>all trees contain chlorophyll, carotene, and xanthophill, and not all

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<v Speaker 1>of them produce anthocyanins, even the ones that do have

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<v Speaker 1>anti synons only produce it under certain conditions. Remember that

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<v Speaker 1>layer of cork like cells at the base of the leaf.

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<v Speaker 1>Its purpose is to protect the tree during the colder winter,

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<v Speaker 1>conserving energy and preventing the tree from drying out. And

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<v Speaker 1>when the separation layer is complete, the leaves fall off

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<v Speaker 1>of the tree. But before the leaves fall off and

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<v Speaker 1>the tree closes up shop, it wants to pull in

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<v Speaker 1>as much sugar and nutrients as possible from its leaves,

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<v Speaker 1>which is where the antisyonin comes into play. Although scientists

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<v Speaker 1>offer several different possible reasons for why some trees produce anthocyanins,

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<v Speaker 1>the prevailing theory is that these pigments protect the leaves

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<v Speaker 1>from excess sunlight and enable the trees to recover any

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<v Speaker 1>last remaining nutrients. The reason you'll see more vibrant reds

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<v Speaker 1>during some years is that stressors like an overabundance of

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<v Speaker 1>sunlight and dry weather increase the sugar concentration in tree sap,

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<v Speaker 1>triggering the tree to release more anthocyanins in a lastic

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<v Speaker 1>effort to gather up enough energy to get through the winter.

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<v Speaker 1>In addition, near freezing weather, low nutrient levels, and other

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<v Speaker 1>plant stressors seem to trigger increased levels of antisynins. So

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<v Speaker 1>if it's been especially rainy and overcast, you won't see

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<v Speaker 1>much red foliage. Without bright sunlight, the trees don't need

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<v Speaker 1>the added protection that the red pigments provide, so they

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<v Speaker 1>don't bother producing them. If autumn just isn't the same

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<v Speaker 1>for you without that splash of red, hopefully the weather

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<v Speaker 1>will collaborate. Today's episode is based on the article why

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<v Speaker 1>do Leaves change color in the Fall? On how stuff

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<v Speaker 1>works dot Com written by Jennifer Horton. Brain Stuff is

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<v Speaker 1>production of I Heart Radio and partnership with how stuff

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<v Speaker 1>works dot Com, and it's produced by Tyler Klang. For

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<v Speaker 1>more podcasts from My heart Radio, visit the heart Radio app,

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