Since we are familiar with the structure of prokaryotic cells, we can discuss the activities that enable these microbes to thrive. The life-support processes of even the most structurally simple organism involve a large number of complex biochemical reactions. Most, although not all, of the biochemical processes of bacteria also occur in eukaryotic microbes and in the cells of multicellular organisms, including humans. However, the reactions that are unique to bacteria are fascinating because they allow microorganisms to do things we cannot do.

For example, some bacteria can live on cellulose, whereas others can live on petroleum. Through their metabolism, bacteria recycle elements after other organisms have used them. Still other bacteria can live on diets of inorganic substances such as carbon dioxide, iron, sulfur, hydrogen gas, and ammonia. Microbial metabolism allows some microorganisms to grow in or on the human body as shown in dental plaque.

Physiology is the study of the processes which go no in living organisms. While on the other hand the term Metabolism to refer to the sum of all chemical reactions within the cells of a living organism. Because chemical reactions and the processes involve building up (Anabolism) while breaking down of nutrients within a cell is termed (Catabolism).

Metabolism can be viewed as an energy-balancing act and this balanced flow of chemicals and energy maintains the life of a cell. These chemical reactions provide energy and create substances that sustain life. So Pathways can be categorized into two general types— catabolic and anabolic.