Question

you expose the bacterium staphylococcus aureus to low levels of the antibiotic methicillin. the surviving bacteria are then exposed to higher concentrations of methicillin and the process repeated until a strain of methicillin - resistant s. aureus (mrsa) is remaining. to test your hypothesis, you perform an experiment by spreading the original strain of s. aureus and the mrsa strain onto agar plates containing methicillin, and only the mrsa survives. what are the independent variables in this experiment?

• the strain of s. aureus
• the dose of methicillin
• survival in the presence of methicillin
• the agar plates
• the time of bacterial growth

Explanation:

The independent variable is the factor intentionally changed in an experiment to test its effect. Here, the experiment compares the original S. aureus strain and the MRSA strain, so this is the manipulated variable. Survival is the dependent variable, while methicillin dose, agar plates, and growth time are controlled (kept constant) factors.

Answer:

the strain of S. aureus