Each organism requires a specific environment to survive. Similarly to bacteria, different types of bacteria are able to survive and reproduce in different types of environments. Some factors that influence the growth of bacteria include temperature, the presence of certain gases, and the pH of the medium in which they are found. In this experiment, the variable changed was temperature. Temperature is a significant factor influencing the growth of bacteria. Each bacterial culture has its minimum, maximum and optimal temperatures. Bacteria thrive at their optimal temperature and are only able to survive between the minimum and maximum temperatures. If the temperature is significantly higher than the maximum temperature, the bacteria will be destroyed and this process is irreversible. Furthermore, since bacterial growth is influenced by many other factors such as the pH of the medium and the age of the bacteria, these factors must be kept constant throughout the experiment to ensure the accuracy of the results. Different types of bacteria have different temperature ranges that they are able to survive. They are generally divided into three types: psychrophilic, mesophilic and thermophilic. Psychrophilic bacteria are able to survive in low temperatures ranging from approximately -10 to 20°C while thermophilic bacteria are able to thrive in high temperatures ranging from 40 to 75°C. These two types of bacteria are also known as extremophiles due to their ability to survive in extreme conditions. Mesophilic bacteria are bacteria that thrive at temperatures between 10 and 45°C and usually have an optimal growth temperature of approximately 37°C (M. Furlong, n.d.). The thermal death point (TDP) is the temperature at which a culture of organism is killed in short... middle of paper... death points. The duration of the experiment should be increased since the thermal death times of B. subtilis at 60, 70 and 80°C were not able to be defined within 110 minutes. The duration can be increased to 180 minutes in order to better investigate its thermal death times. If after 180 minutes of exposure the presence of bacterial growth was still observed, it can be assumed that B. subtilis is able to survive well at that temperature. To confirm this hypothesis it is possible to carry out an exposure time of one day. The presence of abnormal bacterial growth can be checked under a microscope. If the organism analyzed is not the bacterium used in the experiment, it means that the growth of the bacterial culture examined is absent. Using this method it is possible to exclude contamination by foreign substances in the surrounding air and obtain more accurate results.