Monday, September 13, 2010

Fall Science Part 2 - Leaf Chromatography - Predicting the Changing Fall Colors - Or Why Leaves Change Color In The Fall.

Most of the science experiments we do come from tried and true science experiment books for children. Usually, we are given a hypothesis, and then a set of experiments to prove the hypothesis. If the experiments don't prove it, then we know we did something wrong, because the books give us hypothesis that are correct, and can be proven.

I thought for a change it might be interesting to use an experiment to make a prediction, or answer a question - one that we will have to wait to see the results of, and that won't necessarily be correct. One like...


"What color will the leaves on the tree behind our fence change to this fall?" And, "Can we use chromatography to predict it?"

Just in case you've forgotten, chromatography is when you dissolve pigment into a liquid, and then let it rise up a piece of filter paper. Pigments that are more solvent than others, will rise higher on the paper, allowing you to separate out the colors of something, like an M&M's candy coating, or the pigments present in a leaf.

Strangely enough, we have a tree right behind our house, on the green space, that we cannot identify (mainly because we haven't tried), and also cannot remember what color it changed to the last few falls.

There are other trees on the green space as well, some like the aspen and maple, that we can not only identify, but that whose leaves have already started changing color, too.

So, I sent the children out to gather up green and yellow aspen leaves, and green and at least partially red maple leaves (we don't have any completely red, yet), and one green leaf off of our mystery tree.


We tore the leaves into tiny bits, each type into its own jar, making note of which jar was which in a notebook.


We poured enough rubbing alcohol into the jars, to cover the leaves, and left them to sit for about 90 minutes...


...at which time we could see the color from the leaves in the alcohol. Then, we added a strip of coffee filter into each, and left them to sit for about 4 hours, until we could see clear lines of color on the strips, and it appeared they had stopped rising.


At this point it's important to know what causes leaves to change color in autumn. So, I'll give you my best simplified answer based on this article, from Science Daily, this child friendly write-up, from Science Made Simple (where we found the chromatography idea), and this kind of complicated, collegiate paper, from Purdue, that I linked over a year ago when we were doing some plant chromatography.

Okay, so here goes:

Plant, and tree leaves contain three main pigments.

1. Chlorophyll - which is green, and necessary for photosynthesis.

2. Carotenoids - which is yellow, and is drowned out by the green color of chlorophyll.

3. Anthocyanin - which is orange, or red depending on how much sun it gets in the fall.

As the days get colder, and shorter trees stop producing chlorophyll (the Science Daily article above explains why, too). With the green gone the other colors shine through.

With that said, we took our strips of coffee filter, and compared our pigment samples. The filter from the yellow aspen leaves had only a band of yellow. The filter from the green aspen leaves had a band of green, with a thin strip of yellow above it.


The turning maple leaf had a high strip of red, a thin strip of yellow, and a low strip of green. While the unturned maple leaf had the green and yellow, with a high very thin line of brown.

This is very similar to what we saw in the mystery leaf as well, except that the mystery leaf produced a wider band of yellow.

So, based on our understanding of what is going on, we predicted that the leaves on the mystery tree will not turn yellow, but rather orange, or possibly even a reddish/brownish hue, given enough sunlight.

I'll be sure to let you know how it turns out.  (Click here to follow along with the next step in this science mystery).

It's great to be a homeschooler.

12 comments:

Phyllis said...

We are planning to do this experiment this year, but I never thought to do it in this way! What a wonderfully clever way of doing it. You have explained it quite well, too.

Raising a Happy Child said...

This is awesome activity! I predict that the leaves of this mystery tree will dry directly into brown. Let us know how it turns out!

Debbie said...

I will be curious to see how this turns out.

Christy said...

I am very impressed. Great experiment. Great explanations too.

Wonder Mom said...

I will be on waiting on pins and "pine needles" to see how the leaves turn out...(hee! hee!)

Lady Chadwick said...

oooh, that looks way cool. I really want to do this!

Brenda @ Tie That Binds Us said...

We live in Florida and don't have a whole lot of trees that change colors, but if we did we'd definitely do this experiment. Keep us informed on how your hypothesis' turned out!

GoodyGirlGoth said...

It is okay, i guess, but i looked it up and it says you have to leave it in a pan filled with 1 to 2 inches of hot water. Is this true?

An Almost Unschooling Mom said...

GoodyGirlGoth - I'm not sure what you mean - but you can see how it worked for us without heat.

Bella Mendez said...

I live in Florida, the leaves do not usually change colors due to the constant heat but I am wondering if it will still work or if there will he some kind of reaction.

Robert Wainblat said...

The experiment is even cooler with spinach which has so many different colours in it!

Crystal said...

Writing this down to try this Fall... Thanks for the post!