The basic unit of life is the cell. In 1838, scientists Theodor Schwann and Matthias Schleiden came up with the original version of the cell theory, which concluded that the basic unit of living things is the cell.
Robert Hooke first saw these units in his microscope study of slices of cork and named them "cells." Anton van Leeuwenhoek used his microscope to see cells in a drop of water. With the advent of technology, including better microscopes and specimens, the cell theory took form.
The original cell theory had some flaws that were worked out later by Rudolph Virchow. The modern cell theory presents several observations about the cell. Cells make up all organisms, they are the structural and functional units of living things, and cells can come only from other existing cells and do not generate spontaneously.