Cells are the basic units of structure and function in living things.
All cells come from preexisting cells. The smallest cells are less than 1 micrometer in diameter. A micrometer is one millionth of a meter. On the other end of the cell spectrum, the yolks of birds' eggs are a single cell, and are quite visible to the naked eye, and some of the nerve cells in your body run between your toes and your spine. However, most cells are in the range of 5 - 50 micrometer in diameter.