The changing leaves of autumn are really awesome to look at, but they're also a really striking
The changing leaves of autumn are really awesome to look at, but they're also a really striking

example of nature taking extreme measures to protect itself.
example of nature taking extreme measures to protect itself.

You’re probably familiar with photosynthesis — it's the process plants use to turn carbon
You’re probably familiar with photosynthesis — it's the process plants use to turn carbon

dioxide, water, and light energy into sugars and oxygen.
dioxide, water, and light energy into sugars and oxygen.

And you probably also know that photosynthesis depends on a pigment -- a colored compound
And you probably also know that photosynthesis depends on a pigment -- a colored compound

called chlorophyll -- but you may not realize that plants contain lots of other pigments,
called chlorophyll -- but you may not realize that plants contain lots of other pigments,

as well.
as well.

Some of the most important are the carotenoids -- yellow, orange, and brown pigments that
Some of the most important are the carotenoids -- yellow, orange, and brown pigments that

give color to things like corn, carrots, pumpkins, and sweet potatoes -- and anthocyanins, which
give color to things like corn, carrots, pumpkins, and sweet potatoes -- and anthocyanins, which

give red and purple color to cherries, berries, pomegranates, and red apples, to name a few.
give red and purple color to cherries, berries, pomegranates, and red apples, to name a few.

All of these pigments play an important role in the plant’s functions, but there’s
All of these pigments play an important role in the plant’s functions, but there’s

usually far more chlorophyll in a plant than anything else, because photosynthesis is a
usually far more chlorophyll in a plant than anything else, because photosynthesis is a

plant’s number one job.
plant’s number one job.

However, many trees are less active in the winter because they grow at northern and southern
However, many trees are less active in the winter because they grow at northern and southern

latitudes that get less sunlight during those months.
latitudes that get less sunlight during those months.

These trees are called deciduous, from the Latin word that means “to fall off”.
These trees are called deciduous, from the Latin word that means “to fall off”.

Since deciduous trees don’t do much photosynthesis in the winter, it doesn’t really make sense
Since deciduous trees don’t do much photosynthesis in the winter, it doesn’t really make sense

to spend a bunch of energy maintaining big green leaves.
to spend a bunch of energy maintaining big green leaves.

So when the days get shorter and the temperature gets cooler, they send less of their limited
So when the days get shorter and the temperature gets cooler, they send less of their limited

resources to the leaves, and start using what water and nutrients they have to keep the
resources to the leaves, and start using what water and nutrients they have to keep the

rest of the tree alive.
rest of the tree alive.

The chlorophyll in the leaves breaks down, and the green color gradually goes away.
The chlorophyll in the leaves breaks down, and the green color gradually goes away.

And when that happens, the other pigments -- which were there all the time -- are better
And when that happens, the other pigments -- which were there all the time -- are better

able to show off their colors, before the leaves die entirely and fall off the tree.
able to show off their colors, before the leaves die entirely and fall off the tree.

So, the leaves aren’t really changing pigments -- they’re just losing their strong green
So, the leaves aren’t really changing pigments -- they’re just losing their strong green

pigment to reveal the other colors in the tissue.
pigment to reveal the other colors in the tissue.

After the tree stops the supply of food and water to the leaves, all that’s left is
After the tree stops the supply of food and water to the leaves, all that’s left is

for the tree to cut them off.
for the tree to cut them off.

The tree forms a special layer of weakly-bound cells near the base of the leaf’s stalk.
The tree forms a special layer of weakly-bound cells near the base of the leaf’s stalk.

Then another layer of cells at the very bottom of the stalk expands to push the leaf away.
Then another layer of cells at the very bottom of the stalk expands to push the leaf away.

Eventually the leaf can be knocked off easily, even by light wind.
Eventually the leaf can be knocked off easily, even by light wind.

And then it’s your job to rake them up.
And then it’s your job to rake them up.

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