1. Why Leaves Change Colors K. Wardman kwardman@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) The leaf pigments (more about that later) Length of night Length of night Weather Weather

4. Pigments are natural substances that are produced within the leaf’s cells. These pigments are what give the leaves their color. The three pigments that are found in leaves are: Chlorophyll (green) Chlorophyll (green) Carotene (yellow, orange, and brown) Carotene (yellow, orange, and brown) Anthocyanins (red) Anthocyanins (red) The Colors in Leaves

5. 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. (Color of Leaves cont.)

6. 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. Length of Night

7. 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 Temperature Moisture Moisture Weather’s Influence

8. (Weather’s 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.

9. 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

10. 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 Environmental Education for Kids Environmental Education for Kids Environmental Education for Kids http://www.dnr.state.wi.us/org/caer/ce/eek/veg/trees/tree struecolor.htm#from Science Made Simple www.sciencemadesimple.com Science Made Simple www.sciencemadesimple.com Science Made Simple Science Made Simple