Cells are defined as the smallest structural and functional units of life, capable of carrying out all basic activities necessary for survival. Each cell works like a tiny factory, producing energy, synthesizing proteins, and maintaining life's essential processes. Cell theory, developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells , that cells are the fundamental unit of structure and function in all organisms, and that all cells come from pre-existing cells . All cells can be sorted into one of two groups: eukaryotes and prokaryotes. A eukaryote has a nucleus and membrane-bound organelles, while a prokaryote does not. Plants and animals are made of numerous eukaryotic cells , while many microbes, such as bacteria, consist of single cells . Introduction to the cell | Cells | High school biology | Khan Academy Fundraiser Khan Academy 9.11M subscribers
