Question

Maria has a sore throat. Her father takes her to the doctor and she is given an antibiotic. After ten days, Maria is still sick. Use the model seen here and describe what has happened to Maria in terms of natural selection.
Responses
A The medicine causes some bacteria to become resistant to antibiotics. They survive and reproduce.The medicine causes some bacteria to become resistant to antibiotics. They survive and reproduce.
B Some of the bacteria are resistant to the antibiotic. They survive and reproduce, keeping Maria sick.Some of the bacteria are resistant to the antibiotic. They survive and reproduce, keeping Maria sick.
C After being subjected to the antibiotics, some bacteria change and they can survive the medicine. Maria remains sick.After being subjected to the antibiotics, some bacteria change and they can survive the medicine. Maria remains sick.
D In a population of bacteria, variation exists. The bacteria that have increased resistance to medicine outcompete the non-resistant bacteria for food.

Answer 1

B.

Some bacteria in Maria already carried genes that made them resistant. The antibiotic killed the susceptible bacteria, but the resistant ones survived and reproduced, so the bacterial population became dominated by resistant strains and the infection persisted. (Resistance arises by mutation or horizontal gene transfer, then is favored by the antibiotic as a selective pressure.)