The document explains how to use a scale bar to calculate the actual size of microorganisms. It provides instructions to measure the length of a protist called Oxytricha trifallax using a ruler, as well as the length of the scale bar. The measurement of the protist is then multiplied by the number on the scale bar to determine the actual size in micrometers, taking into account the conversion between micrometers and millimeters.

1. Calculating the size of an organism using a
scale bar
How do you know the size of a microorganism? You will notice that many
pictures of microorganisms have a scale bar. A scale bar is a very useful tool
that allows us to calculate the actual size of objects. Follow the instructions
below to figure out the length of this Oxytricha trifallax protist.
INSTRUCTIONS:
a) Measure the length of Oxytricha trifallax using your ruler. (Express your answer in
mm.)
b) Measure the lengthof the scale bar withyour ruler.(Expressyouranswerinmm.)
c) To findthe actual size of the organisms,take youranswerandmultiplyitbythe
numberonthe scale bar.The unitsonthe scale bar are inμm and so youranswermust
be in μm. Howbig isOxytrichatrifallax?
d) How manyμm are there ina mm?
e) Howmany Oxytrichatrifallaxcouldlie endtoendin1 mm?