Cell Theory is a fundamental concept in biology that explains the properties and functions of cells. It states that all living organisms are made up of one or more cells, which are the basic units of life. This means that whether it's a tiny bacterium or a large tree, cells are the building blocks that make up all living things. Additionally, Cell Theory asserts that all cells arise from pre-existing cells through the process of cell division. This idea, proposed by scientists like Theodor Schwann and Matthias Schleiden in the 19th century, emphasizes that life is continuous and that new cells are created from existing ones, ensuring the growth and repair of organisms.