Materials Needed

• A variety of leaves (especially green and some already colored, if available)
• Rubbing alcohol (isopropyl alcohol)
• Small, clear jars or glasses (2-3)
• Coffee filters (or strips of paper towel)
• Small dish or shallow pan (to hold hot water for the experiment)
• Pencil or stick (to hang the coffee filter strips)
• Measuring spoon
• Mortar and pestle (or plastic bag and spoon for crushing leaves)
• Source of heat (hot plate, low stove setting, or just very hot tap water, supervised)
• Timer or clock
• Plain white paper or notebook
• Colored pencils or markers

Introduction: The Mystery of the Changing Colors

Hook: Is It Magic or Science?

Imagine standing in a forest in late September. All summer, the trees were vibrant green. Suddenly, they transform into fiery reds, oranges, and golds. The change seems almost magical, but it's one of the best examples of plant chemistry in action.

Question for Heidi/Learners: If leaves are green all summer, where do those bright reds and yellows hide until fall?

Learning Objectives (What We Will Learn Today)

By the end of this lesson, you will be able to:

1. Identify the three main chemical pigments (chlorophyll, carotenoids, and anthocyanins) responsible for leaf color.
2. Explain how environmental factors (light, temperature, and water) act as the "switch" for color change.
3. Conduct and Analyze a scientific experiment (chromatography) to physically separate the different pigments hidden inside a leaf.

Lesson Body: The Chemical Color Factory

I Do: The Pigment Players (Direct Instruction & Modeling)

Think of a leaf as a small, sophisticated factory. The main product is food (sugar), and the workers are colored chemicals called pigments. We have three main players:

1. Chlorophyll (The Star Player)

• Color: Green.
• Role: This is the most important pigment because it captures sunlight and uses that energy to make food (photosynthesis). It's so dominant that it covers up all the other colors during the growing season.
• The Fall Trigger: As days get shorter and temperatures drop, the tree decides it’s time to stop food production for the winter. The chlorophyll breaks down, and the green color disappears.

2. Carotenoids (The Hidden Helpers)

• Color: Yellow and Orange.
• Role: These pigments are actually present in the leaf all summer long, helping chlorophyll capture light and protecting the leaf from damage.
• The Fall Reveal: When the chlorophyll breaks down, the carotenoids—which are much more stable—are revealed, giving us those bright golds and oranges. (Think carrots, corn, bananas—all rich in carotenoids!)

3. Anthocyanins (The Latecomers)

• Color: Red and Purple.
• Role: Unlike the others, this pigment is *newly produced* in the fall, specifically when there is lots of bright sunshine and cool (but not freezing) nights. Scientists believe it acts like a sunscreen, helping the tree recover vital nutrients before the leaf falls off.

We Do: Pigment Separation Experiment (Chromatography)

We are going to use a process called paper chromatography to prove that green leaves contain hidden yellow pigments!

Success Criteria for Chromatography:

• The colors must separate clearly on the filter paper.
• The process must be conducted safely with adult supervision (especially the use of alcohol/heat).

Step-by-Step Instructions:

1. Prepare the Leaf Paste: Place several pieces of green leaf tissue into the jar or plastic bag. Add a small amount of rubbing alcohol (just enough to cover the leaves, about 1-2 teaspoons). Crush the leaves thoroughly using the mortar/pestle or the back of a spoon until the alcohol becomes dark green.
2. Prepare the Paper: Cut a strip of coffee filter paper (or paper towel) about half an inch wide and long enough to reach into the alcohol without touching the bottom of the jar. Draw a faint pencil line about half an inch from the bottom.
3. Add the Pigment: Dip the very bottom of the filter paper into the green alcohol repeatedly, letting it dry briefly between dips, until a dark green line forms just above the pencil line.
4. Set Up the Separation: Place the filter paper into the jar so that only the very tip is resting in the alcohol. Use a pencil or stick across the top of the jar to hold the paper strip in place.
5. The Heat Bath (Critical Step - Adult Supervision Required): Place the bottom of the jar into a shallow pan of very warm (not boiling) water. The heat helps the alcohol rise quickly up the paper strip.
6. Observe: Watch for the next 15–30 minutes. As the alcohol (the solvent) travels up the paper, it will carry the different pigments with it. Because the pigments are different sizes and weights, they will travel at different speeds, separating into distinct color bands.

Formative Check: While the chromatography is running, draw and label a diagram showing the three pigments and their colors. Discuss where the green band (Chlorophyll) is relative to the yellow band (Carotenoids).

You Do: Predict the Peak (Independent Application)

The amount and brightness of the red color (anthocyanins) depend heavily on the weather. Use the following scenario to apply what you learned.

Scenario: The Best Fall Ever?

A specific week in October had the following weather pattern:

• Daytime Temperatures: Warm (around 65°F / 18°C)
• Nighttime Temperatures: Chilly (around 35°F / 2°C)
• Sunlight: Very sunny and clear for 5 days straight.
• Rain: Low rainfall.

Task: Based on the role of Anthocyanins, predict the color quality of the maple trees during this week. Explain your reasoning in 3-4 sentences, focusing on why temperature and light are ideal.

Differentiation and Extension

• Scaffolding (For learners needing more structure): Provide a template sentence starter: "The colors will be very vibrant and mostly red because the warm days allow for [photosynthesis process] and the cold nights trap [chemical compound] in the leaves, which encourages the production of [pigment]."
• Extension (For advanced learners): Research the difference between a tree that drops its leaves (deciduous) and one that doesn't (evergreen). Why don't pine needles change color and fall off seasonally?

Conclusion: Recap and Final Reflection

Recap: Review the Chemical Cast

Let's quickly review our star players:

• Which pigment gives the leaf its green color? (Chlorophyll)
• Which pigment is always hidden, waiting to be revealed? (Carotenoids - Yellow/Orange)
• Which pigment is newly produced in the fall based on sunshine and cold? (Anthocyanins - Red/Purple)

Summative Assessment: The Postcard Scientist

Task: Create a "Scientific Postcard" explaining the fall color change to a younger friend or family member. The postcard must include:

1. A drawing showing the chromatography results (the separate color bands).
2. A simple explanation of why the green disappeared (Chlorophyll breakdown).
3. A mention of what causes the red colors (Anthocyanins + light/cold).

Success Criteria for the Postcard:

The postcard successfully demonstrates understanding if the three main pigments are correctly linked to their roles in the color change process.