The purpose of this experiment was to determine how the population size of nitrifying bacteria would affect ammonia concentrations. I hypothesized that if the population size of the nitrifying bacteria was increased, then the ammonia levels would decrease. Using the data I collected, I discovered that a lower ammonia level was caused by a higher nitrifying bacteria population, supporting my hypothesis. Through my research, I discovered that nitrifying bacteria are obligate chemolithotrophs, which means that the bacteria use inorganic compounds for energy. Some, such as Nitrosococcus oceani, oxidize ammonia and convert it to nitrite to support their energy needs. Others, such as Nitrobacter winogradskyi, oxidize nitrite to nitrate, where the