Humans use antibiotics to treat bacterial infections. The increased use of antibiotics has led to an increase in the number of strains of bacteria that are resistant to antibiotics. The evolution of antibiotic resistance in bacteria has resulted from natural selection. Outline how bacteria become resistant to antibiotics.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

1. any seven from:
2. [1] (random) mutation ;
3. [1] directional selection ;
4. [1] antibiotic acts as selection pressure / AW ;
5. [1] bacteria with, mutation / gene / allele, (that codes for antibiotic resistance), have selective advantage ;
6. [1] (so) survive / reproduce ;
7. [1] ref. binary fission / asexual reproduction / vertical transmission ;
8. [1] ref. transduction / transformation / conjugation / horizontal transmission ; I sexual reproduction
9. [1] (resistance) allele frequency increases / gives rise to a population of resistant bacteria ;
10. [1] fast (evolution) due to short generation time ;
11. [1] increased chance of resistance if people do not finish full course of antibiotics / overuse of antibiotics ;
12. [1] AVP; e.g. some antibiotics may act as mutagens e.g. enzymes that break down the antibiotic