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Photosynthesis: Fall's Most Valuable Lesson

Autumn is here! Fall's colors provide the perfect motivation for teaching about photosynthesis across the grades.
Included: We've raked up a pile of activities for you to "leaf" through!

It's fall! That means shorter days and cooler nights. And, in many parts of the United States, it means that trees will soon shed their leaves after a final colorful salute to summer.

Trees that drop their leaves each fall are called deciduous trees. You might ask your students why they think dentists refer to baby teeth as "deciduous teeth"? See if your students can figure out the connection!

And here's another question for your students: Did you know that a tree's leaves are orange and yellow -- even in summer? Most leaves include the pigments of all three colors. It's just that the pigment chlorophyll (the pigment that makes the leaves green) is a much stronger pigment than the others. It covers the yellow (xanthophyll) and orange (carotene) pigments that are natural to a tree's leaves. But, come fall, a tree's leaves produce less chlorophyll. Now the other colors can show through. And that they do -- in brilliant explosions of color!

Another pigment (anthocyanin), which produces reds and purples, isn't present all year long in most green leaves. It only shows up as the nights get cooler.

Fall is a great time of year for teaching about the process that gives life to trees. This process is called photosynthesis, which translated means "putting together with light." As winter nears, less sunlight and less water -- elements essential to the process of photosynthesis -- will be available to trees. That means less food for deciduous trees! Soon the tree's photosynthesis (food-making) "factory" will shut down and the tree will rest until spring when water and light again awaken the process.

PHOTOSYNTHESIS ON THE WEB!

On the Web, you'll find a wide variety of sites for teaching about the arrival of fall's colors. The Internet is full of valuable resources for you and your students. Some sites are scientific in their orientation -- and others are just full of pretty pictures.

If it's pretty pictures you're looking for, check out New England Foliage. Here you'll find all kinds of clickable pictures. (Just click on the picture to see a larger, full-screen version of the image.) Check out the fall colors all across the United States at the Fall Foliage on the Web site. See colorful images from the eastern U.S. as well as from California, Michigan, Wisconsin, and more.

If it's a simple explanation of why some trees' leaves turn color each fall, check out Why Leaves Change Color from the College of Environmental Science and Forestry of the State University of New York. For a more detailed explanation (including an "I Can Read" version written just for young students), and for a handful of hands-on science activities that teach about fall's colors, see Simply Science's Why Do Leaves Change Color in the Fall? One really cool experiment at this site involves the use of rubbing alcohol, so it might be appropriate only for older students. Also, check out the Fun Fact question (What do autumn leaves and ripening bananas have in common?), which will help teachers of all grades to teach an important leaf-color concept.

Looking for simple explanations and activities? Newton's Apple, the PBS science series for kids, offers Photosynthesis. The site includes a discussion of the process, vocabulary, resources, and activities.

Also check out The Miracle of Fall, a page of foliage cam links from the University of Illinois Extension.

And, for more advanced information about synthesis there are a ton of sites. Check out the ASU Photosynthesis Center. From Arizona State University, the site includes links to many other sites.

WE RAKED UP A PILE OF ACTIVITIES! JUMP IN!

Read aloud. Top Secret by John Reynolds Gardiner (author of Stone Fox) is a great read-aloud book for the elementary/middle school grades. Written at about a fourth grade level, the book tells the story of a boy who decides to solve the mystery of photosynthesis for a school science project. Students learn all about photosynthesis from the book.

Science/study skills. Collect a variety of leaves and challenge students to use a tree guide from the library to identify the kind of tree from which each leaf comes. To protect the leaves, you might laminate them. You might even join a listserv and post a message asking teachers in other regions to join in a leaf exchange. You're bound to meet up with a teacher willing to share native leaves.

Preserving leaves. Collect samples of colorful leaves and place the leaves between sheets of wax paper. Set the iron to a hot setting. Cover the layers of wax paper with a couple sheets of newspaper and iron them.

Hands-on science. Students can observe the effects of light on the color of leaves. When leaves on a tree are still green, invite each student to cover part of a leaf with aluminum foil. (Choose a tree that you know will turn bright colors.) Use masking tape to tape the foil to the leaf. Students can sign their name on the masking tape. Wait until the leaves on the tree change color. Then remove the foil and see the colors that were in the leaf all summer!

Graphing. Let students work in teams to take a census of the trees in your school yard, an area of a nearby park, or another defined area. Students can use the survey data to create bar graphs that show the numbers of trees of different species.

Spelling. Invite students to unscramble some fall-related words. Spelling counts! Choose appropriate words for your grade level. Possible words: llaf, veales, pinkump, rogane, Sbermpete, tamuun, tempgin, phlorlochyl, lowley (fall, leaves, pumpkin, orange, September, autumn, pigment, chlorophyll, yellow)

Art. Leaf rubbing is a fun art project. Students first place a leaf flat on the table. Then place a sheet of tracing paper over the leaf. Use a soft pencil or a crayon and gently rub over the tracing paper until the outline of the leaf shows through. Add additional leaves and use different colors for a nice effect.

 

RELATED RESOURCES

  • How and Why the Leaves Fall: A Story Sketch by Bert Horwood and Bob Henderson, Pathways: The Ontario Journal of Outdoor Education, July-August 1995. A short story compares an old man's tale of why the woodland animals prepare for winter and why the leaves change colors with a teacher's science-based explanations. Commentary distinguishes inquiry of wonder (why) and inquiry of power (how), and suggests ways to record the story for oral retelling and adapt it for use with young, older, and university audiences.

     

  • Hands-On Whole Science: A Leaf Sampler by Lynne Kepler, Instructor, October 1991. Two activities to help elementary students learn about autumn. The activities use autumn leaves to teach that each type of tree has its own distinctive type of leaf. One activity involves tracing, drawing, and writing about leaves; the other involves making a quilt using leaf designs.

     

  • Fall for Science, Learning, October 1992. Presents a collection of inexpensive autumn science activities for elementary students. A full moon activity encourages observational and critical thinking skills. A pumpkin activity teaches physics. A spider activity teaches biology and alleviates unnecessary fears. A student page has children create a bookmark that shows faces in the full moon.

 

Article by Gary Hopkins
Education World® Editor-in-Chief
Copyright © 2010 Education World

 

Last updated 10/13/2011
 

 

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