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Comparing Sizes of Microorganisms

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

How Big Is That?

If your students have had limited experience with the metric system, now might be a good time to review it with them. The fundamental unit for measuring length in the metric system is the meter (m). Every other metric unit of length is defined as some part or multiple of a meter, using prefixes. For instance, the prefix “centi-” means 1/100. It originates from the Latin word centum (“hundred”). Thus, a centimeter is equal to 1/100 of a meter.

Other metric conversions

  • 1 nanometer (nm) = 0.000000001m (1/1,000,000,000m)
  • 1 micrometer (μm) = 0.000001m (1/1,000,000m)
  • 1 millimeter (mm) = 0.001m (1/1,000m)
  • 1 centimeter (cm) = 0.01m (1/10 0m)
  • 1 decameter (dam) = 10m
  • 1 kilometer (km) = 1,000m

Explain to your students that a micrometer is a metric unit of measurement too small to see with the naked eye. Have students look at their rulers and find the centimeter and millimeter markings. Ask, How many centimeters are in a meter? and How many millimeters are in a centimeter? Once they seem to have a good understanding of the different metric units, you may want to ask your students to attempt some conversions, such as How many micrometers are in a centimeter? and How many millimeters are in a kilometer?

Finally, ask your students to answer the question on the slide, "How many periods from your text strip could be lined up, end-to-end, within a meter?" (1m/500μm = 1,000,000μm/500μm = 2,000) 

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Funded by the following grant(s)

Science Education Partnership Award, NIH

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605