Have you ever wondered why trees change color and drop their leaves every fall?
It’s not just for decoration — it’s part of a smart survival plan!
When we see bright reds, oranges, and yellows on trees in autumn, we’re watching science at work. In this essay, you’ll learn why leaves change color, why they fall, and how trees prepare for winter.
Let’s take a closer look at the amazing science of fall!
What Happens Inside a Leaf?
Every leaf on a tree is like a tiny solar panel, making food for the tree using photosynthesis (foh-toe-SIN-thuh-sis) — a big word that means “making food with light.”
➡️ Pronounce photosynthesis
Inside each leaf are green chemicals called chlorophyll (KLOR-uh-fil).
➡️ Pronounce chlorophyll
Chlorophyll absorbs sunlight and helps the tree make food from sunlight, water, and air.
During spring and summer, there’s plenty of sunshine — so leaves stay green because of all that chlorophyll working hard.
Why Do Leaves Change Color?
When fall arrives, the days get shorter and cooler. Trees notice the change in sunlight and temperature.
They begin to slow down photosynthesis, which means less chlorophyll is made.
As the green color fades, other pigments (colors) in the leaf begin to show:
- Carotenoids (KAIR-uh-ten-oydz) – make yellow and orange colors.
➡️ Pronounce carotenoids - Anthocyanins (an-tho-SY-uh-ninz) – make reds and purples.
➡️ Pronounce anthocyanins
So, when you see a forest glowing with yellow, red, and orange leaves, you’re really seeing the leaf’s hidden colors shining through!
Why Do Leaves Fall?
Now comes the next part of the tree’s plan — letting go of the leaves.
As winter gets closer, the ground freezes, and it becomes harder for trees to get water. Instead of keeping leaves that would lose water, the tree grows a thin layer of cells called an abscission (ab-SIH-zhun) layer.
➡️ Pronounce abscission
This layer acts like a tiny pair of scissors, gently cutting the leaf away.
Soon, the wind or gravity makes the leaf drop to the ground. This helps the tree save energy and stay healthy all winter long!
What Happens to the Fallen Leaves?
When leaves fall and pile up on the ground, they begin to decompose (dee-kom-POHZ) — or break down — into tiny pieces.
➡️ Pronounce decompose
This process returns nutrients to the soil, helping new plants grow in spring.
So, nothing goes to waste — it’s the circle of life in action!
More to Explore
Videos
Articles
- Why Do Leaves Change Color?https://www.nesdis.noaa.gov/about/k-12-education/understanding-our-planet/why-do-leaves-change-color
Hands-On Activity: “Leaf Color Detective!”
Goal
Discover what hidden colors are in a green leaf.
Materials
- Fresh green leaves
- Rubbing alcohol
- Jar or glass cup
- Coffee filter or paper towel strip
- Spoon
- Plastic wrap
- Rubber band
Steps
- Tear or crush the leaves and place them in the jar.
- Pour in enough rubbing alcohol to just cover the leaves.
- Use the spoon to mash the leaves a bit.
- Cover the jar with plastic wrap and a rubber band.
- Place the jar in a bowl of warm water for about 30 minutes.
- Hang a strip of coffee filter inside the jar so it dips into the liquid.
- Wait! After an hour or more, you’ll see bands of color move up the filter — green, yellow, or orange.
These are the pigments that were inside the leaves!
Activity Chart
Directions: On a sheet of paper, copy the chart.
| Leaf Type | Color Bands Seen | Which Pigments Do You Think They Are? | What Did You Notice About Different Leaves? |
|---|---|---|---|
Think About It
- Which colors appeared first on your filter strip?
- Why do you think some leaves had more yellow or red pigments?
- What does this tell you about how leaves change color?
Multiple-Choice Questions
- Why do leaves look green in summer?
A) They are painted by nature
B) They contain green chlorophyll that makes food for the tree
C) The air turns them green
D) Because it rains more in summer
- Why do trees stop making chlorophyll in fall?
A) The days are longer
B) The weather gets warmer
C) There is less sunlight and the trees prepare for winter
D) The tree runs out of water
- What makes leaves turn red and yellow?
A) The leaf’s hidden pigments like carotenoids and anthocyanins
B) The dirt on the leaves
C) The wind changing their color
D) Rainwater soaking into the leaves
- What helps leaves fall from trees?
A) A special layer called the abscission layer
B) Bugs biting the stems
C) The cold air freezing them off
D) Animals pulling them down
- Why do fallen leaves help trees?
A) They look pretty on the ground
B) They turn into soil that feeds the trees again
C) They protect tree roots from the wind
D) They make the forest smell nice
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