One of the things we’re trying to figure out is how big (or small) microorganisms really are. You’ve probably heard of molecules before; these are groups of two or more atoms stuck together. So, how do they compare?

Let’s look at two common examples: a DNA molecule and an E. coli bacteria (made up of one cell).

Growing a Culture Excerpt

Microorganisms are microscopic—they are so small that we cannot see just one or two of them with the naked eye. But, when there are millions or trillions, we can actually see them without a microscope. One way that scientists can observe microorganisms is by letting them multiply (reproduce) until the populations are big enough to see with the naked eye. This is called growing a culture.

Example: you might not think that there are any microorganisms on this bread on Day 1. But 7 days later, the microorganisms have multiplied so many times that you can actually see them!