Two researchers conducted a Western blot analysis to determine the expression level of a specific protein in cultured cells. They used the same membrane, the same primary and secondary antibodies, and the same imaging system. Researcher 'X' reported a protein band intensity corresponding to a relative expression level of 200 units, while researcher 'Y' reported 800 units. Which one of the following could most likely explain the discrepancy in researcher 'Y's result?
The membrane was not washed properly after the primary antibody incubation.
The membrane was exposed to the imaging system for a longer duration than necessary.
The standard curve used for quantification was incorrectly plotted.
The loading control bands were not properly visualized.