Natural Selection Drives Bacterial Antibiotic Resistance

Steps:

• Identify key events: Resistance arises from random mutations; antibiotics kill susceptible bacteria, allowing resistant ones to survive and reproduce.
• Evaluate statement 1: True—resistant bacteria proliferate due to survival advantage, increasing allele frequency.
• Evaluate statement 2: True—bacteria reproduce asexually, passing resistance alleles to offspring via binary fission.
• Evaluate statement 3: True—selection pressure from penicillin ensures resistant cells survive while others die.
• Evaluate statement 4: False—mutations occur randomly, not caused by penicillin; antibiotic presence selects for pre-existing mutants.

Why A is correct:

• Matches Darwin's natural selection: Variation (mutations), differential survival (3), reproduction (2), and population change (1) explain resistance evolution.

Why the others are wrong:

• B includes false 4, ignoring random mutation principle.
• C omits survival (3) and inheritance (2), incomplete mechanism.
• D excludes population increase (1), missing full evolutionary outcome.

Final answer: A