This month, we have another outstanding plant biology experiment from Michael Wilkinson and his 4th Grade Science Classroom at Fieldston Lower School (ECFS). If you missed the SeedSpinner project, you can follow the links to his project page and lesson.
In this project, my students were curious about how plants might respond to different wavelengths (colors) of light. Having learned that we perceive objects as a particular color because those wavelengths are reflected back to our eyes, my students hypothesized that green light was not used by the plants because they appeared green. The chloroplasts in the leaves must be using other colors of light for photosynthesis.
Their hypothesis was formally stated as: Chlorophyll is not expressed under green light or in the dark.
After brainstorming procedures, they determined that the experiment would need the following trials:
Now the question was, how to limit the light exposure to those specific colors? Enter littleBits. Since my students have worked with littleBits before, it was natural for them to think of them and their potential to support this investigation. Working in small groups, students built and tested prototypes to achieve each of the lighting conditions above. Prototypes were shared and groups converged on the following circuits:
-For white light: USB power + wire + branch + 3x Bright LED
-For red light: USB power + wire + branch + 3x RGB LED
-For green light: USB power + wire + branch + 3x LED (shown below)
-For blue/violet light: USB power + wire + branch + 3x RGB LED
These circuits were mounted inside the top of an opaque box large enough to cover a small container of petri dish germination chambers. The same box was used for the dark trial with no LEDs. Brassica rapa seeds (FastPlants) were germinated in each of the 5 lighting condition and grown for 5 days. The chambers were then removed for observations, noting specifically the color of the cotyledons (seed leaves). Chromatography strips were used to separate each of the plant pigments for comparison. Plants have 4 major pigments: Chlorophyll A (dark blue-green), Chlorophyll B (light yellow-green), Xanthophyll (yellow-orange), Carotene (orange-brown) and Anthocyanin (red). If my students’ hypotheses were correct, the chlorophyll would be reduced or eliminated in the dark and green light conditions.
The littleBits circuits made this experiment accessible to my 4th graders, while allowing them to design a sophisticated and scientifically valid experiment. They were able to prove that red and blue light were the most important colors of light for photosynthesis.
As a result of these labs, we’re pleased to hear Michael’s observation on the ease of use of littleBits in his students’ experimental design process:
“The power of littleBits is in their flexibility. My students have really capitalized on this flexibility to construct various apparatus to support their scientific investigations. The design of the bits – compact, magnetic, and functional – make them an ideal “organic” material in the classroom. In other words, reaching for the material as it is needed, just as one would pencils, calculator, hand lenses, etc. These materials are part of accomplishing a larger goal, not the goal themselves. As my students engage in an engineering or design process, or they formulate a solution to test a hypothesis, they consider the Bits modules for any application that might require motion, light, sound, or sensors.”
Kudos to Michael and his class for creating and sharing such a great experiment – we look forward to seeing more of your work in the future!