Question

Many bacteria are now resistant to penicillin, because ______.

Options

• previously resistant forms survived and reproduced better than non-resistant forms

• penicillin triggers the synthesis of resistant proteins

• penicillin causes gene mutations, some of which are beneficial

• environment inhibits competition among bacteria

Answer 1

Many bacteria are now resistant to penicillin, because previously resistant forms survived and reproduced better than non-resistant forms.

Explanation:

Many bacteria are resistant to penicillin because some individuals in the original bacterial population had mutations that conferred resistance. When penicillin is used, these resistant bacteria survive and reproduce, while non-resistant bacteria are killed off. Over time, the population becomes dominated by resistant forms. This is an example of natural selection in which the environment (the presence of penicillin) selects for resistant bacteria. The resistance arises due to pre-existing mutations, not because penicillin induces mutations.