Question

In an experiment in a laboratory, a population of bacteria in a petri dish is exposed to an antibiotic. The antibiotic kills most of the population. However, a few bacteria survive and soon repopulate the petri dish with antibiotic-resistant bacteria. According to modern evolutionary theory, the correct explanation for this experiment is:

• A. Some of the bacteria tried and successfully adapted to the new conditions in the petri dish.
• B. Some members of the bacteria population developed a resistance to the antibiotic immediately after exposure.
• C. Some members of the bacteria population already had a resistance to the antibiotic so they were not killed.
• D. Some of the bacteria quickly evolve into a new species that resist the antibiotic.
• E. Some of the bacteria protected themselves from the antibiotic long enough to develop a resistance.

Answer 1

The correct option is C Some members of the bacteria population already had a resistance to the antibiotic so they were not killed.

The bacterial population was a mix of antibiotic-resistant and susceptible members. Exposure to antibiotics leads to the killing of susceptible members while those carrying antibiotic resistance survived and reproduced to make the whole colony again. The evolution of antibiotic resistance and speciation are slow and gradual processes.

Thus, the correct answer is option C.