Fall Colors
Why do tree leaves change color in autumn?
Author:
Title 4
Learning objectives :
This activity allows students to scientifically analyze leaf color changes in fall. It makes the link between visual observation of plant biology and spectral analysis of colors.
Concepts covered
Plant pigments; Colorimetry; Photoreceptors; Chlorophyll and carotenoids; Leaf life cycle; Pigment degradation
What students will do :
The student uses the FizziQ colorimeter to analyze the colorimetric composition of leaves from the same tree at different stages of autumn coloring. By measuring the proportions of red, green and blue in each leaf, the student observes the decrease in chlorophyll (green component) and the increase in carotenoids (yellow to red components) to understand the biochemical mechanism of color change.
What is required :
Smartphone with the FizziQ application; Leaves of the same tree at different stages of coloring (green yellow red brown); White support for placing the sheets; FizziQ experience notebook
Scientific background :
The FizziQ colorimeter uses the smartphone camera equipped with a Bayer filter to break down the light reflected by an object into its red, green and blue (RGB) components. This technology allows quantitative analysis of leaf color changes. In summer, leaves appear green because they contain a high concentration of chlorophyll, a pigment that primarily absorbs red and blue wavelengths and reflects green. With the arrival of autumn, the reduction in day length and the drop in temperatures trigger biochemical processes: the tree stops producing chlorophyll and begins to degrade it to recover nutrients before the leaves fall. As chlorophyll disappears (visible in the decrease in the green component), carotenoids and anthocyanins, present all year round but masked by chlorophyll, become visible (increase in the red and yellow components). Carotenoids (yellow-orange) are accessory pigments that participate in photosynthesis, while anthocyanins (red-purple) are synthesized in the fall and play a protective role against UV rays. The variation in the proportions of these pigments explains the diversity of autumn colors.