The document defines key cellular biology terms including cell theory, differentiation, emergent property, growth, homeostasis, magnification, metabolism, paramecium, response, scale bar, Stargardt's disease, stem cell, surface area to volume ratio, system, and tissue. Cell theory states that all organisms are composed of cells, cells are the smallest independent unit of life, and all cells come from pre-existing cells. Differentiation is the alteration of a cell's morphology and physiology through gene expression changes. An emergent property is a characteristic of a system that results from the interaction of its components and makes the whole greater than the sum of its parts.