The document defines key vocabulary terms related to cell structures and organelles such as the cell membrane, chloroplasts, mitochondria, nucleus, and others. It then discusses the history of cell theory, from early microscope observations of plant and animal cells by Hooke, Schleiden's conclusion that plants are made of cells, Schwann's proposal that cellular basis applies to all life, and Virchow cementing that cells only come from pre-existing cells. The modern cell theory is that cells are the fundamental unit of life, all organisms are composed of cells, and all cells come from pre-existing cells.