MYP Biology sample question: Natural selection and antibiotic resistance

Some bacteria have become resistant to antibiotics that once killed them.

1. (a)Explain how antibiotic-resistant bacteria become more common in a population.[4]
   Show the mark scheme for (a)

   • • There is variation: a mutation makes some bacteria resistant (1)
   • • The antibiotic kills the non-resistant bacteria (1)
   • • Resistant bacteria survive and reproduce, passing on the resistance allele (1)
   • • The proportion of resistant bacteria increases over generations (1)

Use the four steps of natural selection in order: variation, selection pressure, survival and reproduction, inheritance.