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 is the first of four Science Objects in the Cell Structure and Function SciPack. It explores the difference between living and non-living things as it looks at the many different types of cells. All self-replicating life forms are composed of cells,-from single-celled bacteria to elephants, with their trillions of cells. Although a few giant cells, such as hens' eggs, can be seen with the naked eye, most cells are microscopic. Multi-celled organisms are composed of many tiny microscopic cells, as opposed to fewer larger cells. Surface area to volume ratio makes efficient food absorption and waste removal possible in cells.