Thursday, September 20, 2012

Tree and Leaf Unit

Sebby said I shouldn't call this unit "Trees and Leaves" because leaves are already part of trees. He's right, but I'm calling it that anyway. And if this unit sounds like a gratuitous excuse to get outside at this time of year and see the Fall Leaves, it is. I love taking advantage of the season to learn about things we'd be wondering about anyway!

We discovered lots of interesting things during this unit. I remembered from my own school days that the autumn-colored pigments were in the leaves all along, just masked by the chlorophyll, but I learned for the first time that only the yellows and oranges (carotene and xanthophyll) are actually present all year. Red leaves appear when glucose is left in the leaves (from photosynthesis) rather than all used up when the weather turns colder. When the glucose is exposed to sunlight, another pigment (anthocyanin) is made, giving the leaf its red color.

We also learned that the largest living organism is a grove of aspen trees in Utah! Its name is "Pando," which means "I spread," which freaks me out just a little, but I'm okay.

The kids really liked this online quiz about things that come from trees.

This website has some interesting tree/leaf information. Every year I try to remember what kind of weather makes for the brightest leaves, but I always forget. So I was quite happy that this site told me:
A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions – lots of sugar and light – spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year.  
The amount of moisture in the soil also affects autumn colors. Like the weather, soil moisture varies greatly from year to year. The countless combinations of these two highly variable factors assure that no two autumns can be exactly alike. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.
We enjoyed extracting the chlorophyll from leaves (see here)

And I had the kids memorize this poem, which is one of my favorites:

Gathering Leaves
by Robert Frost

Spades take up leaves
No better than spoons,
And bags full of leaves
Are light as balloons.

I make a great noise
Of rustling all day
Like rabbit and deer
Running away.

But the mountains I raise
Elude my embrace,
Flowing over my arms
And into my face.

I may load and unload
Again and again
Till I fill the whole shed,
And what have I then?

Next to nothing for weight,
And since they grew duller
From contact with earth,
Next to nothing for color.

Next to nothing for use.
But a crop is a crop,
And who's to say where
The harvest shall stop?

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