What makes a cell? ‘The nature of cells’ considers the cell ℄ the smallest unit of life ℄ by looking at basic cell characteristics, membranes and cell walls, and the interior of the cell. The distinction between prokaryotic and eukaryotic cells is explained. The main characteristic of eukaryotic cells is their ability to alter their shape, components, and metabolism to fulfil a particular task — to differentiate — a facility which allows them to come together and form multicellular tissues, to combine those tissues into organs, and then form an entire organism such as a human being. Finally, in vitro studies, where plant or animal cells are grown in laboratories, are discussed.