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

What Do You Know About Microbes?

Microbiologists study organisms consisting of a single cell or a cluster of a few similar cells. Known as microbes or microorganisms, these organisms usually cannot be observed with the naked eye. The term “microbe” was coined by Charles Sedillot, a French scientist. It means any living thing that must be magnified to be visible.

Microbes are the most prevalent organisms on our planet, both in mass and number. They comprise a diverse group and include bacteria, microscopic algae, yeast cells, and even protozoa. Most biologists also consider viruses to be microbes, even though according to many definitions, viruses are not true “living” organisms.

Microbes produce most of the Earth’s oxygen and are essential parts of all ecosystems. Although some microbes cause illness, others play a role in digestion, disease resistance and other vital human functions. Microbes also are involved in the production of common foods, including sandwich bread and yogurt. This activity allows students to share their knowledge about microbes.


1. Explain to students that they will be learning about the most numerous organisms on Earth—microbes. However, before starting the unit, they will complete a pre-assessment activity. The pre-assessment questions will require students to reflect upon what they already know about microbes. At the end of the unit, students will answer the same questions on the post-assessment.

2. Distribute copies of the “What About Microbes?” page. Have students complete the questions on their own. Tell students to answer each question using their existing knowledge and experiences.

3. Collect the student sheets. Ask, Does anyone think he or she knew all the answers? Does anyone have questions or observations? Record questions on chart paper to revisit at the end of the unit. Do not discuss answers to the pre-assessment questions. Students will have an opportunity to review their answers as part of the last activity of this guide. 

4. Give each student a paper clip. Tell students that the mass (weight) of the clip is approximately one gram (gm). If time allows, have students estimate the mass (weight) of different objects in grams. Have students use a balance or scale to compare their estimates to actual measurements. 

5. Next, have the materials manager of each group pick up a water bottle that you have treated with Glo Germ™ powder. Ask, What is the mass of the bottle and its contents, in grams? Each member of the group should hold the bottle and estimate (predict) the total mass of the bottle (weight of contents plus weight of the container), in grams. 

6. After everyone has held the bottle, ask students to write their estimates on sticky notes. Create a class bar graph by lining up the notes according to increasing weight in a row across the wall or chalkboard. Stack notes with about the same weights above or below each other in vertical columns. 

7. Tell students the bottle weighs about as much as the microbes in a person’s body—slightly more than 1,000 grams (gm), or 1 kilogram (kg). 

8. Review the graph and discuss students’ estimates. Ask, Was anyone close to the correct weight? Why was it difficult to estimate? At this time, you may want to discuss metric measures and standard equivalents.

9. Next, ask students to examine their hands, first with the naked eye and then with the hand lens. Ask, Can you see anything? 

10. Bring out the black light(s) and have students examine their hands again under the light. Ask, What do you see? Was it there before? Why couldn’t it be seen? Explain that the glowing material on their hands is a harmless powder that spreads by contact, just as many microbes spread. The powder, however, becomes visible under special lighting  conditions. Microbes cannot be observed in the same way. 

11. Ask, What do you know about microbes or microorganisms? Why do you think they are important? (Microbes are organisms too small to be seen without magnification. They are the most prevalent life forms on earth, both in mass and number. Most cannot be seen without a microscope, yet microbes influence every person’s life. Some students may be able to name a few examples, such as bacteria. Students may think all microbes are harmful, but this is not true.)

Ask, Why do you think you were taught always to wash your hands before eating and after using the restroom? OR Have you noticed signs in almost all public restrooms stating that all employees must wash their hands before returning to work? Why might this be? Allow students to discuss their ideas. 

12. Finally, have students discuss what they know about microbes or microorganisms, and ask each group to begin a concept map (see illustrations, PDF), that demonstrates its collective knowledge of microbes. Tell students that while they may not have much information now, they will be adding to their concept maps throughout the unit. Display the concept maps around the room.

Funded by the following grant(s)

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605