Most tiny creatures belong to this category. Prokaryotes include bacteria and archaea. However, these two groups are very different, which is why they each represent a separate one of the three major domains (bacteria, archaea, eukaryotes). Prokaryotes have no cell nucleus, hardly any internal organelles and circular chromosomes. Archaea differ from bacteria in their cell membrane, cell wall, amino acids and genome structures. In genetic terms, they are even more similar to humans than to bacteria.
Explanation for children:
Bacteria belong to the prokaryotes. Bacteria do not have a cell nucleus, so they are not a peach, but rather an orange. They have DNA floating around inside the cell. The other representatives of the prokaryotes are called archaea. They are also like an orange without a nucleus. However, the other building blocks of archaea are very different to the building blocks of bacteria, which is why they each belong to a separate domain.