Plain yogurt with active cultures
Compound student microscope, like one of THESE.
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