This document discusses various ways of categorizing micro-organisms based on their nutritional requirements and metabolic processes. It describes categories such as chemotrophs and phototrophs based on energy sources, and organotrophs and lithotrophs based on reducing power sources. It also discusses categories like heterotrophs and autotrophs based on carbon sources. Further, it summarizes the key stages of aerobic respiration, anaerobic respiration, and the cell respiration process. It provides details on diagnostic tests like the oxidase test and catalase test used to identify microbes.