Botany - Cell - The Unit of Life Question with Solution | TestHub

Schleiden and Schwann proposed a cell theory. He said that cells are the basic unit of life and all plants and animals are composed of the cells. In 1855, Rudolf Virchow added the third principle to cell theory. He states that Omnis e cellula e cellula means that all living cells come from pre-existing cells. Virchow's theory not applied to the virus because viruses are obligate parasites which means they cannot complete its life cycle without a host. They do not have cellular machinery whereas in others it is present.