Why Leaves Change Colors

1
Why Leaves Change Colors

• K. Wardman
• kwardman_at_nmu.edu

2
A Quick Review of Photosynthesis

• The green packages in the leaves (chlorophyll)
  catch the sunlight and, using it for energy, they
  change water from the ground and carbon dioxide
  (a gas in the air) into sugars (glucose). They
  then use these sugars as food and energy to grow.

3
Three Important Factors

• There are three factors that help a leaf to
  change its color. They are
• The leaf pigments (more about that later)
• Length of night
• Weather

4
The Colors in Leaves

• Pigments are natural substances that are produced
  within the leafs cells. These pigments are what
  give the leaves their color. The three pigments
  that are found in leaves are
• Chlorophyll (green)
• Carotene (yellow, orange, and brown)
• Anthocyanins (red)

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(Color of Leaves cont.)

• Chlorophyll, carotene and anthocyanins are all
  found in leaves during the growing season. But
  since chlorophyll is so important to the process
  of photosynthesis, there is a lot of it in the
  leaves during those spring and summer months.
• Since there is so much, it covers up the carotene
  and anthocyanins so that none of the yellow,
  brown, orange or red colors can be seen.

6
Length of Night

• As autumn gets closer, the days become shorter
  and the nights become longer. The longer the
  nights, the less sunlight there is. The tree
  responds to these autumn months by producing less
  and less chlorophyll until it stops producing it
  at all.
• When that happens, the carotene and anthocyanins
  that are already in the leaves can finally show
  through. That is when all the yellows, browns,
  oranges and reds that were in the trees leaves
  all along can be seen.

7
Weathers Influence

• The amount and brightness of the colors in the
  trees are related to the weather conditions that
  take place before and during the time the amount
  of chlorophyll in the leaves is becoming less.
  The two main influences to the color are
• Temperature
• Moisture

8
(Weathers Influence cont.)

• A lot of sunny days with cool (but not freezing)
  nights will bring out the brightest colors,
  especially if the soil has been moist and not too
  dry during the day. During the sunny days,
  photosynthesis produces a lot of sugars and the
  cool nights stop the sugars from leaving the
  leaves but not freezing. These days produce many
  anthocyanin pigments which bring out the bright
  red, purples and crimson colors.

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Review

• Here is a link to a worksheet on the information
  you just learned about. There is a link to the
  answers on the webpage.
• Worksheet
• C\CS 255\P12\worksheetleaves.pdf

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A List of Resources

• Here are some resources if you want to learn more
  of the details that cause leaves to change
  colors. I suggest you check them out to get most
  out of this lesson!
• Environmental Education for Kids
• http//www.dnr.state.wi.us/org/caer/ce/eek/veg/tre
  es/treestruecolor.htmfrom
• Science Made Simple www.sciencemadesimple.com