This process creates an oxygen gradient, where there will be atmospheric concentrations of oxygen at the top of the tube and very little oxygen present at the bottom of the tube. Facultative anaerobes...This process creates an oxygen gradient, where there will be atmospheric concentrations of oxygen at the top of the tube and very little oxygen present at the bottom of the tube. Facultative anaerobes grow best in the presence of oxygen as evidenced by the thick layer of growth at the top of the tube, however, they can also grow (more slowly) in the absence of oxygen.
