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Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, Deanne Erdmann, MS, Sonia Rahmati Clayton, PhD, and James Denk, MA.

Observing Different Microbes

Microbes are organisms too small to be seen with the naked eye. There are enormous variations in the kinds and sizes of microbes. This activity allows students to observe representatives of three different groups of microbes—bacteria, fungi and protists—first hand. 

First, students will observe bacterial cells in yogurt, which will be visible only as tiny rods. (Rod-shaped bacteria are called bacilli.) Yogurt is created when milk is fermented by Lactobacillus and other kinds of bacteria. It has a slightly sour taste, is acidic, and stays fresh longer than milk. A yogurt recipe is in­cluded as an extension to this activity.

Students also will observe yeast, which are single-celled fungi. This group also includes organisms like mushrooms and molds. Fungi are not able to trap energy through photosynthesis and must feed on other organisms. Many fungi are important decomposers within ecosystems. Yeasts have numerous applications in food production, such as leavening in bread and fermentation for alcoholic beverages. Some kinds of yeast also cause diseases, such as diaper rash or thrush (a painful infection of the mouth and throat). 

Finally, students will observe a paramecium. “Slipper-shaped” paramecia are among the largest microorganisms in the protozoan group, which are considered to be protists. Most of the 40,000 species of protozoa are found in aquatic environments or in moist soil. A few are parasites. Protozoa do not have rigid cell walls (such as those in the onion skin cells). Paramecia take in particles of food through an “oral groove” located on one side of the organism, and they use tiny hairs, called cilia, to propel themselves through water. 

Funded by the following grant(s)

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605