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Observing Different Microbes

Author(s): Barbara Tharp, MS, and Nancy Moreno, PhD

Let's Talk About Bacteria

In this activity, students will observe the bacteria in yogurt (Lactobacillus* and others), which are rod-shaped. Other types of bacteria can be spherical or spiral-shaped. Bacteria are examples of prokaryotes, which are almost always microscopic and single-celled (unicellular).

Typically, prokaryotes are surrounded by a cell wall and lack internal compartmentalization. In the Five Kingdom system of classification, all prokaryotes are assigned to the Kingdom Monera. More recent classifications, however, separate the prokaryotes into two different Domains: Domain Bacteria and Domain Archaea. A third Domain, Eukarya, consists of all Eukaryotic organisms, such as plants, animals, fungi and protists. Learn more about recent classification of prokaryotes at

Most bacterial cells are 1-5µm in diameter, but there are exceptions. (Thiomargarita namibiensis, for example, is 750µm in diameter and is visible to the naked eye.) Because most bacteria are so small, their internal structures are not visible through most classroom microscopes. Instead, students will see rod shapes, such as those above, distributed throughout the yogurt on the slides they prepare.

*Lactobacilli are found in the intestines of humans and generally are beneficial. They convert lactose and other sugars to lactic acid. Some species produce vitamin K and anti-microbial substances.

Funded by the following grant(s)

Science Education Partnership Award, NIH

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605