Bacteria Click on image for full size (22K jpeg) Image courtesy of JPL/NASA

Despite their small size, bacteria are the most abundant of any organism on Earth. And they're everywhere! Bacteria can be found in the air, soil, water, on you, and inside you. In fact, there are more bacterial cells inside your gut and on your skin than there are cells in your entire body - no matter how many times you try to wash them off!

The cells of all bacteria (and therefore, the cells of all Monerans) are classified as "prokaryotic", the simplest and most ancient of the cell types. Prokaryotes lack many of the structures found in the more complex, eukaryotic cells.

Bacteria often get a bad reputation because certain types are responsible for causing a variety of illnesses, including many types of food poisoning. However, most bacteria are completely harmless and many even perform beneficial functions, such as turning milk into yogurt or cheese and helping scientists produce drugs to fight disease. Bacteria were among the first life forms on Earth.