“Why do leaves change color?”
It’s the chlorophyll that gives leaves their green color. As temperatures drop and the days become shorter, trees stop making food and the amount of chlorophyll inside of leaves decreases.
With less chlorophyll, the other colors in leaves (orange and yellow) become visible. These colors were in the leaves all summer, but the green color of the chlorophyll covered them up.
When the chlorophyll leaves, the leaves show their other colors.
Red, purple, and brown colors are the result of other chemical reactions that occur inside leaves when the temperature drops—leftover food (glucose) in leaves causes red and purple colors, and waste products in leaves cause a brown color. Leaves will become a more vibrant red when the autumn weather is sunny, cool, and dry.
LESSON PLAN: Hidden Colors Experiment
Conduct a simple experiment to reveal the “hidden” colors of green leaves. Although this activity is simple enough for elementary students, even my middle school kids had liked seeing the results from this experiment. This is a good lesson for introducing (or reviewing) the concept of photosynthesis.
Common Core ELA and Next Generation Science Standards
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- Green leaves from several different trees (Trees with a dramatic color change, like maples, work best.)
- Beaker or drinking glass, one per group
- Dish or container to hold hot water, large enough to hold 1 beaker or glass
- Isopropyl (rubbing) alcohol
- Plastic wrap
- Chromatography or filter paper (you can use coffee filters), 1 strip per group
- Pencil, 1 per group
- Have students collect a variety of green leaves. Keep leaves from different types of trees separate and follow the steps below for each set of leaves, so you can compare results.
- Divide students into small groups. Have them tear the leaves from one type of tree into several pieces and place them in a beaker or glass. Mash the leaves as much as possible.
- Have students cut a strip of filter paper about a half inch wide and tape it to a pencil.
- (Adult should do this step when working with young children.) Add just enough rubbing alcohol to cover the leaves in the beaker. Cover the beaker with plastic wrap to keep the alcohol from evaporating.
- Put the beaker in a dish of hot tap water for about 30 minutes, until the alcohol turns green as the pigments from the leaves are absorbed into it.
- Suspend the pencil across the beaker and let the strip just barely touch the alcohol and pigment mixture. Wait 60-90 minutes. Have students observe the colors they see on the paper. (The “green” color breaks up into several different colors as the different pigments begin to separate. You’ll see different shades of green, yellow, and perhaps other colors as well, depending on the type of leaves.)
- Explain/review photosynthesis and the role that cholophyll plays in making appear green when making food.
“Why do leaves fall off of trees?”
I found the best (and easiest to understand) explanation in Highlights Magazine.
- Read aloud the book Leaf Man, written by Lois Elhert. Focus on illustrations and the way leaves created the whimsical characters.
- Take students outside to collect an assortment of leaves and other natural objects for their own collages.
- Back inside, have students create leaf collages of animals and people. Both young children and older students enjoy using this imaginative activity.
Have students write acrostic poems to accompany their leaf collages.
Common Core Standards (ELA K-3)
- Reading: Literature: Craft and Structure: 1.4. 2.4, 3.4, 4.4, 5.4
Next Generation Science Standards (DCI K-3)
- LS1-A: Structure and Function
- LS1-B: Growth and Development of Organisms
- LS1-C: Organization for Matter and Energy Flow in Organisms
- LS1-D: Information Processing