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. some of the original strain of s. aureus bacteria surviving in the presence of methicillin is an example of which of the following?
options: mutation, homeostasis, sexual reproduction, natural selection

Explanation:

• Mutation is a genetic change, but the question refers to survival of existing bacteria, not the origin of resistance.
• Homeostasis is maintaining internal balance, unrelated to antibiotic survival.
• Sexual reproduction does not occur in S. aureus, which reproduces asexually.
• Natural selection describes the survival of individuals with traits (here, antibiotic resistance) that allow them to survive an environmental pressure (methicillin), which matches the scenario.

Answer:

natural selection