Question

In the late 1980s and early 1990s, the percentage of Icelandic children whose bacterial infections were caused by bacteria resistant to penicillin rose at an alarming rate. After public health officials initiated a campaign to reduce the use of penicillin, resistance dropped off. (See the accompanying figure.) This observation is consistent with the hypothesis that ________.

1) bacteria generate mutations so that they can evolve in order to become better adapted to their environment

2) the use of antibiotics generates mutations in bacteria that affects their resistance

3) antibiotics really have no effect on bacterial resistance; such fluctuations are natural and occur whether we use antibiotics or not

4) bacterial populations evolve in response to the selection pressure imposed by antibiotics

Answer 1

The use of penicillin created a selection pressure that favored penicillin-resistant bacteria, leading to their prevalence. Reducing penicillin use decreased this pressure, allowing non-resistant bacteria to thrive again, supporting the hypothesis that bacterial populations evolve in response to antibiotics.

Step-by-step explanation:

The observation that the percentage of Icelandic children with bacterial infections caused by penicillin-resistant bacteria decreased after reducing penicillin use supports the hypothesis that bacterial populations evolve in response to the selection pressure imposed by antibiotics. This is because the imprudent and excessive use of antibiotics leads to natural selection of resistant bacteria. When antibiotics kill most of the infecting bacteria, only the resistant forms survive and then reproduce, which increases the proportion of these resistant bacteria. It’s also significant to note that such resistant genes are already present in the gene pool of the bacteria before antibiotics are applied and don't arise as a response to antibiotics. Consequently, the campaign to reduce the use of penicillin eases the selection pressure, allowing non-resistant strains to increase in prevalence once more.