Let's Get Small - According to the Reference Chart, an E. coli bacterium is 2 micrometers long. Assuming that it's 1.25 micrometers wide, could you determine how many E. coli could fit on the tip of one of your hairs?

The tip of your hair is about 0.1 millimeters (mm), or 100 micrometers (µm), wide. If you assume that the tip is roughly circular, and the area of a circle is pi times radius squared (3.14 X 50µm^2), then the area of the tip is about 7,850 µm. We're assuming a 2 µm long E. coli cell is 1.25 µm wide, so its area is length times width, or 2 µm x 1.25 µm, which equals 2.5 µm squared. Divide 7,850 µm by 2.5 µm and you find out that roughly 3,140 E. coli could fit on the tip of your hair.

 

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