# What is the size of 1 bacteria

## Worksheet 1c: - How small / big are viruses?

Viruses: 15 to 400 nm (nanometers)
Bacteria: 0.3 to 1 µm (micrometers)
Human: 1.5 to 2 m (meters)

 Small number prefixes: 10 -3                   10 -6                   10 -9                   10 -12                  10 -15 Milli- (m) micro- (µ) nano- (n) pico- (p) femto- (f)

400 nm = 0.4 µm
The largest viruses are as big as the smallest bacteria.

Most bacteria can be made visible with a light microscope. The resolution of the light microscope is not sufficient for viruses and very small bacteria. You need an electron microscope.

Resolving power of the human eye: 0.02 mm or 20 µm

I.e. if two lines are 0.02 mm apart, then we can just recognize them as two lines; when they are closer together we see them as a line.

Look at a ruler or graph paper. The smallest division is millimeters, one millimeter is 1000 µm or 50 by 20 µm. So imagine if a millimeter were again divided into 50 graduation lines. Our eyes are so good that they could still tell two lines apart.