Anatomy the study of the structure of body parts. Physiology the study of the function of body parts. Chemical level: atoms smallest units of matter (ie, carbon, hydrogen, molecules made up of two or more types of atoms joined together by bonds (ie, h2o, c6h12o6. Cellular level: cells basic structural and functional units of an organism. Tissue level: tissue groups of cells, and the material surrounding the cells, with a specialized function. Organ level: organ group of two or more types of tissues with a specific function (ie, heart, stomach) System level: organ system related organs with a common function (ie, the cardiovascular system, the digestive system) Organism level: a living being that is made up of groups of organ systems. Homeostasis is the existence of a relatively stable internal environment, despite the changing external environment, maintained through the body"s regulatory processes. Homeostasis is a dynamic, steady state that is maintained through feedback loops.