Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object, co-developed between FDA and NSTA, is the first of four Science Objects in the Science of Food Safety SciPack. It explores self-replicating life forms, which are all composed of cells. Living cells contain similar types of complex molecules that support the basic activities of life. These molecules interact in a soup, composed of about 2/3 water, surrounded by a membrane that controls what can enter and leave the cell. Cells have particular structures for cell functions, protection, and in some cases the ability to move. A single living cell represents the smallest individual unit of life. Single-celled organisms vary in the complexity of their structure and the amount of genetic material they contain, and populate all environments on Earth in astounding numbers and types. Those with less genetic material and simpler structures are more numerous. Bacteria are one type of single-celled organism that have an interdependent relationship with humans.