Now explain the importance of oxygen as relates to the atp tally.

Aerobic respiration produces 38 ATP from a six-carbon glucose molecule while anaerobic produces 2 ATP. Respiration that occurs in the mitochondria, to form ATP, is a redox reaction. Oxygen is the electron acceptor in the oxidative phosphorylation process. ATP synthase catalyzes this reaction.

Both anaerobic and aerobic breakdown of glucose molecules produces pyruvate and the generation of 2 ATPs in glycolysis process. However, in the presence of oxygen in aerobic respiration, the pyruvate is converted to Acetyl-CoA and enters the Krebs cycle and the oxidative phosphorylation process where a net of 36 ATP are produced. However, in anaerobic respiration, the pyruvate is converted to lactate and no further respiration occurs.  

Antibiotics

Explanation:

The selective agent in this question would be the antibiotics. As the body grows resistant via the antibiotics, the bacteria itself has as well.