A Microbiology Student in a Research Lab Repeated an Experiment

Multiple Choice

A microbiology student in a research lab repeated an experiment described by others using the identical bacterial isolate, the same growth medium, and the same growth conditions. However, the student was unable to achieve the same O.D. at 600 nm. What is the LEAST likely cause for this discrepancy in measured turbidity?

A) One experiment used 16 mm wide test tubes while the other used 18 mm wide test tubes.
B) One experiment subtracted the yellow color of the growth medium away from the final turbidity reported whereas the other used colorless water.
C) One experiment vigorously dispersed the bacterial pellicle with vortexing while the other did not.
D) The two experiments were carried out at vastly different elevations and did not consider the influence of pressure.