Define cell theory.

Cell theory is a fundamental concept in biology that explains the basic properties and functions of cells in living organisms.

According to cell theory, all living organisms are made up of one or more cells, the cell is the basic unit of structure and function in living organisms, and all cells arise from pre-existing cells.

This theory was developed by scientists such as Schleiden, Schwann, and Virchow based on their observations and research.

Cell theory forms the foundation of modern biology, helping us understand how organisms grow, develop, and function at the cellular level.