Food Dye Electrophoresis

In this lesson, students will explore the process of agarose gel electrophoresis to figure out which food dye molecules give Skittles® candy their colors. Initially, students predict the direction of dye migration based on their understanding of how size and charge govern the movement of molecules. Students then extract food dye from Skittles®, load these samples into an agarose gel using a micropipette, and run a current through the gel to separate the dye molecules. They will be able to predict, observe, and compare the movement of their extracts with known food dyes. To conclude, students will make a claim about which food dye(s) is/are present in their Skittle® and support it using evidence from their gel and reasoning about the scientific principles behind electrophoresis. This lab is helpful to complete before other labs involving gel electrophoresis such as DNA Forensics and PCR related labs.

In the online version of the lesson, students make their predictions and then watch a video of dye being extracted from Skittles®. They use sample images from gel electrophoresis to inform their CER.

Learning Objectives

  • Perform agarose gel electrophoresis to separate food dye molecules based on charge and size
  • Predict the behavior of a molecule on an agarose gel based on its size and charge
  • Make a claim about which dyes are used to make Skittles and support it using evidence and reasoning

Prior Knowledge

  • Relationship between atoms and molecules
  • Difference between positively and negatively charged molecules
  • Using micropipettes to measure and transfer small volumes

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Disciplinary Core Ideas:

PS1.A Structure and Properties of Matter
“…interactions of matter at the bulk scale are determined by electrical forces within and between atoms.”

PS2.B Types of Interactions
“…Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter….”

Science and Engineering Practices:

Engaging in argument from evidence

Crosscutting Concepts:

Structure and Function”

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Burton HS
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Lincoln HS
San Francisco, CA

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Glenbrook South HS
Glenview, IL

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South San Francisco HS
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