The cell is the smallest unit of living matter that can exist by itself. Some plants and animals consist of only a single cell. Others are composed of billions of cells.
Cells exist in a variety of shapes and sizes. They may, for example, be cube- shaped or flat. Scientists who study cells have determined that a single cell may be as large as a tennis ball, or so small that thousands would fit on the period at the end of a sentence on your paper. The yolk of a hen's egg is actually a large cell. By contrast, bacteria- each one of which is a tiny cell- are among the smallest cells. Regardless of its shape or size, every cell contains the 'machinery' to maintain life. …
