All living things are made of cells. Cells are the basic units of life.
Cells come only from other cells.
These organisms were able to survive and reproduce in a very limited environment because of their simplicity. Over time, some of these protocells came together and shared their specialization in a symbiotic relationship. These colonies of protocells eventually became the cells we know today. Their small size means these bacteria contain only 100 million to 120 million atoms. While this may seem like a large number, keep in mind that the human body has over 5 Billion cells.