Dichotomous Keys c. Each is a single cell. Cells are the basic unit of structure and function in living things, the smallest things that can perform all of the functions of life. A neuron is also a single cell, and may stretch up to two feet in length. An ostrich egg, which may weigh up to two pounds, is actually a single cell.
Bacteria are extremely small, single-celled organisms.
Aside from the occasional ostrich egg or nerve cell, most cells are very small and can't be seen without magnification. As a result, our knowledge of cells has grown as technology has allowed us to see them. The art of glassmaking in the 1600s led to the creation of the first simple microscope lenses, making it possible to see cells up close and personal for the first time. Robert Hooke, an English scientist, first described cells in 1665. When he looked at a very thin slice of cork through his microscope, Hooke noticed that the cork was porous and comprised of many tiny square boxes that reminded him of the small rooms in a monastery.