Cells are the fundamental units of life — every organism on Earth is built from one or more cells, and every cell arises from a pre-existing cell. In this lesson we explore the structural and functional distinctions between prokaryotic and eukaryotic cells.
Hooke’s 1665 observation of “cellulae” in cork marked the first use of the term, but it was Schleiden, Schwann, and Virchow in the 19th century who established the cell theory: (1) all living things are made of cells, (2) the cell is the basic unit of structure and function, and (3) all cells come from existing cells.
Pay close attention to the difference between the plasma membrane that bounds every cell and the cell wall found in plants, fungi, and most bacteria.