Answer:
When bacteria are exposed to an antibiotic, such as penicillin, they often mutate.
Step-by-step explanation:
This means that part of their DNA changes, giving the antibiotic resistance to the bacteria.
In this way, the bacteria can generate a copy of their DNA and transmit it to their offspring, giving their resistance.
On other occasions, a resistant bacterium dies from causes unrelated to the antibiotic, leaving its DNA free.
If other bacteria manage to capture that DNA, it will also acquire antibiotic resistance.