What fundamental idea is associated with Theodor Schwann?

Theodor Schwann is primarily recognized for his role in the development of the cell theory, which fundamentally states that all living organisms are composed of cells. Specifically, Schwann contributed to this theory by asserting that animals, like plants, are made up of cells. This idea extended the concept of cellular organization by highlighting that animals share this fundamental structural unit with plants, reinforcing the notion that cells are the basic building blocks of all living things. Schwann's work laid the groundwork for understanding the similarities in the biological makeup of different forms of life, solidifying the concept of the cell as the basic unit of structure in both plants and animals.