For microorganism to grow and form a population, they require both chemical and physical requirements. The chemical requirements required are gas such as oxygen and also mineral elements. The elements that are required are nitrogen and phosphorous. The physical elements required include the temperature of the environment. According to temperature organism are classified into three groups. Psychrophilic microorganisms are found in the cold temperatures, mesophilic are the ones which are found in the moderate temperatures and the thermophilic are found in areas with high temperatures.