Abstract: A natural science concerned with the study of all living organisms. Living organisms, from the viewpoint of biology (biological science), share a number of unifying themes, including their origin from the same basic cellular structure and their molecular basis of inheritance. Still, they are diverse in many other aspects. Because of the diversity of life (see illustration), biological science can be split into many divisions that focus on the various aspects of living organisms. The primary divisions of study in biology consist of zoology (animals), botany (plants), and protistology (one-celled organisms), and are aimed at examining such topics as origins, structure, function, reproduction, growth, development, behavior, and evolution of the different organisms. In addition, biologists consider how living organisms interact with each other and the environment on both an individual basis and a group basis. Therefore, within these divisions are many subdivisions, including molecular and cellular biology, microbiology (the study of microbes, including bacteria and viruses), taxonomy (the classification of organisms into special groups), physiology (the study of function of the organism at any level), immunology (the investigation of the immune system), genetics (the study of inheritance), and ecology and evolution (the study of the interaction of an organism with its environment and how that interaction changes over time)