MadSci Network: Biochemistry |
Methylene blue exists in a form that can be chemically reduced (it can gain electrons). Its color is due to the way that its atoms are bonded to each other. The chemical bonds absorb some wavelengths of visible light leaving a blue color. When electrons are added to methylene blue, the nature of the chemical bonds are altered and they no longer absorb visible light, and there is no color.
When the microorganisms in a solution that contains methylene blue consume all the available oxygen (in other words, have reduced all the oxygen) the microorganisms essentially start to chemically reduce other molecules. So the methylene blue gains electrons, altering it’s chemical bonding, and changing its color.
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