Cell theory is the foundational framework of modern biology, consisting of three tenets established sequentially over roughly two centuries of microscopic observation: that the cell is the basic unit of structure in living things, that all living organisms are composed of cells, and that all cells arise from preexisting cells. The first two tenets were reached inductively by generalizing across independent domains — bacteria, plants, and animals — observing that organisms of widely differing form share the same underlying microscopic unit, while the third required the displacement of the competing theory of abiogenesis (spontaneous generation of life from non-living matter), achieved by direct observation of cell division and by controlled experiment demonstrating that apparent spontaneous growth was attributable to airborne contamination rather than to generation from non-life. The concept belongs to cell biology and microbiology, and it also serves as a case study in the parent discipline's epistemology: how a general theory is built by cross-domain generalization and how a rival hypothesis is eliminated by an experiment that isolates the single variable in dispute.
Cell theory is the foundational framework of modern biology, consisting of three tenets established sequentially over roughly two centuries of microscopic observation: that the cell is the basic unit…