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Autumn Leaf Science
Have you ever wondered why green leaves turn those beautiful shades of red, orange and yellow?
Being in the northeast, many of us at hBAR love this time of year! Though it may not be a typical fall with football tailgating, packed apple cider mills, or homecomings, mother nature still amazes us with gorgeous hues of red, gold, and orange as the leaves change color.
But why does this happen? Well, with the shorter and cooler fall days arriving, there is not enough sunlight and water for efficient photosynthesis to occur.
Photosynthesis occurs in the leaves’ green chlorophyll. When it's not being used, the chlorophyll begins to disappear, revealing the less dominant yellow and orange pigments from carotene in the leaves.
Yes, carotene and the yellow to orange color is always present in leaves - it's just masked by the intense green color of the chlorophyll during the spring and summer.
In appreciation of the colors of fall, and the science behind them, here are two fun activities you can do at home, or in the classroom -
1. Leaf Rubbings
This is a simple, yet favorite activity for all ages. All you need is a leaf (or several), paper and crayons (with their paper removed). Simply place the paper over the leaf (or leaves) and rub the long edge of a crayon across the paper. Not only will you see the outline of the leaf blade but also the petiole, midrib and veins.
Want to add some science?! Collect the leaves while out on a nature walk and observe the difference in leaf sizes, colors and shapes. You can identify the different tree species that various leaves come from, as well as the parts of the leaves and how they differ between species. You can even label the parts of each leaf, or identify the species, right on your leaf rubbing.
2. Autumn Leaf Chromatography
In a nutshell, chromatography is a technique to separate different parts of a mixture.
There are 3 important parts to every chromatography activity: the mixture, mobile phase, and stationary phase.
The mixture needs to be in a liquid called the mobile phase. This mobile phase carries the mixture through a solid material called the stationary phase. The various parts of the mixture will separate as they travel through the stationary phase, because they move at different rates due to their differences in size.
You will need:
- Several leaves of various colors (green, yellow, orange, red, purple etc)
- 70% Isopropyl Alcohol or Rubbing Alcohol (for the mobile phase)
- Several glass containers (glass beakers, jars, cups etc)
- Filter paper, or coffee filters cut into 1-2” wide strips (stationary phase)
- Safety goggles
- Collect and sort leaves by color.
- Tear up the leaves into small pieces, and place them in a glass beaker or jar (1 color per container).
- Pour the rubbing alcohol to cover the torn leaves.
- Let sit for 1-2 hours to allow the pigments (mixture) to come out of the leaves and into the alcohol (mobile phase).
- Place 1 piece of filter paper (stationary phase) into each container, and allow the mobile phase (alcohol + pigments) to move about ¾ of the way up the filter paper.
- Remove the filter paper from each container and allow them to dry.
- Observe all the different pigments that were present in each color of leaves!