Activity: Observing Bacteria in Yogurt (1)

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  • Plain yogurt with active cultures

  • Compound student microscope, like one of THESE.

  • Slides, coverslips

  • Distilled water

  • Dropper


  • Clean your slides and coverslips for dust and other particles.

  • Place a very small portion of plain yogurt onto the slide, and add one drop of water. Place the coverslip on top.

  • Under low power, find a section where the yogurt is pretty thin; this is where you will find the bacteria.

  • Switch to high power (400X for most microscopes) for a better view of the bacteria. If you have a microscope with an oil immersion lens, it will give you an even better view of these small organisms.

  • Make a sketch of your view under different magnifications.


  • How many different kinds of bacteria could you find?

  • What other foods have bacteria living in them?


High School Senior from Fairfax, VA

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