In BIO 5, we'll ignore the Domain Archaea. Recently, evidence that the archaea are also present in oceans has been discovered. However, our contact with members of the Domain Archaea is much less likely than contact with members of the Domain Bacteria. Like all prokaryotic cells, bacteria cells are very small. We will barely be able to see bacteria with our microscopes in lab.
Prokaryotes are the smallest organisms but they have all of the characteristics of life.
The first image of bacteria above has both round and rod-shaped bacteria. The second image shows spiral-shaped bacteria. While the images included here are easily visible, they were photographed using a research microscope. Our microscopes are less powerful, and it will be more difficult to tell the shapes. An example of a bacterium that is round is Streptococcus .