There are many types of bacteria found in the mouths of animals that form plaque. Within plaque, the outer layers have high levels of oxygen, as well as strong enamel that can be dissolved when in contact with high levels of acidity. Streptococcus mutans is a certain bacteria that thrive in the inner layers of the plaque causing cavities. There are other types of bacteria such as Streptococcus sanguinis that is also in the mouth. Due to the high levels of acidity, when against each other the S. sanguinis can not compete with S. mutans because S. sanguinis has low levels of tolerance with acidic levels and does not allow the bacteria to thrive. S. mutans has a tolerance in pH levels of 4 or less. S. mutans must have a biochemical pathway of fermentation. Fermentation is a process where glucose is broken down by bacteria without oxygen. Fermentation continues to a chain reaction of other processes and acid creations. Since S. mutans thrives in an environments that have low levels of oxygen and high levels of acid it is capable of using this process. Fermentation then creates anaerobic respiration. Anaerobic respiration is a process that transforms glucose into lactic acid. Lactic acid them contributes into a process called glycolysis. Glycolysis is the conversion of glucose into pyruvate acid and the way bacteria revives its energy. Pyruvate acid is what continues to lower the low pH levels in the inner plaque. Therefore benefiting the bacteria S. mutans and allowing to get into deeper layers of the plaque.When using toothpaste with alkaline, the S. mutans bacteria will likely decrease while, S. sanguinis bacteria will increase. Alkaline will cause an increase the levels of pH in the mouth. S. mutans can only thrive in areas with high acid levels. S. sanguinis thrives in area with denser, more neutral levels of pH. This leads my prediction that if alkaline increases pH in the environment then S. sanguinis will survive and the loss of acidity will lead to the unfitness of the bacteria S. mutans. The change in population size of bacteria is also a form of natural selection. The once thriving S. mutans lost its power when a change in its environment caused it to lose the acidity that allowed it to thrive. With the change of acidic levels the bacteria S. sanguinis, that can thrive in dense pH levels, gained the advantage because of the pH change and became the one able to survive. In conclusion, the bacteria S. mutans is able to survive in the mouth because of the biochemical pathway of fermentation. When using Alkaline toothpaste the population of the bacteria S. Mutans will decrease because of the increase of pH levels and loss of acidity. While the population of the bacteria of S. sanguinis will increase because it thrives in high levels of pH. The population decrease of S. mutans bacteria and increase in S. sanguinis bacteria is a form of natural selection.