Botany · Ch 5 — Cell: The Unit of Life
Cell Theory
5.2
Cell Theory
The cell theory is the central generalisation of biology that describes what every living body is made of and where every cell comes from. It was not the work of a single person but was built up and refined by several scientists over the mid-nineteenth century.
How the theory took shape
- Matthias Schleiden (1838), a German botanist, studied a great many plants and concluded that all plants are built from different kinds of cells, and that these cells make up the tissues of the plant.
- Theodore Schwann (1839), a German zoologist, examined many types of animal cells at about the same time. He noticed that cells are bounded by a thin outer layer — the structure we now call the plasma membrane. From his work on plant tissues he also recognised that a cell wall is a special feature belonging to plant cells. On this basis Schwann put forward the idea that the bodies of both animals and plants are made up of cells and the products of cells.
- Working together, Schleiden and Schwann formulated the cell theory. However, their version had a gap: it did not explain how new cells actually come into being.
- Rudolf Virchow (1855) filled this gap. He was the first to explain that cells divide, and that every new cell arises from a pre-existing cell — captured in the phrase Omnis cellula-e cellula. By adding this, Virchow modified the earlier hypothesis and gave the cell theory its final form.