DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ1.c

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Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ1.c
Level SL Paper 2 Time zone TZ1
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 7]
22M.2.SL.TZ1.c

Explain the development of antibiotic resistance in terms of natural selection.

[7]

Markscheme
  1. antibiotics can (generally) kill/destroy bacteria;
  2. some bacteria show variation/antibiotic resistance;
  3. variation/resistance is due to a random mutation;
  4. resistant bacteria are not killed/destroyed by the antibiotic
    OR
    bacteria without the mutation die;
  5. (resistant) bacteria have a selective advantage / unequal success;
  6. the bacteria with this variation/resistance reproduces/multiplies;
  7. mutation/gene is passed on to the offspring / the offspring will be resistant to the antibiotic;
  8. resistant bacteria become more common;
  9. bacteria have evolved to be resistant to the antibiotic;

Award [6 max] if pathogen is used instead of bacteria throughout the answer with no mention of bacteria.

Examiners report

This natural selection question had better responses than in previous years. There seems to be a widespread misconception that bacteria can mutate after exposure to an antibiotic rather than surviving because of a genetic variation. Some confusion was demonstrated concerning the use of antibiotics: some candidates did not understand that antibiotics are used against bacteria (not viruses). There was lots of confusion in the use of different but similar words — antibiotics / antibody / antigen

Syllabus sections