Q BankQuestion BankDocsDocuments

C3.2.13—Antibiotics

Antibiotics explains how a specific barrier, pathogen interaction, immune mechanism, treatment response or population process contributes to protection against infectious disease.

Syllabus
First assessment 2025
Objective
C3.2.13
Level
SL

Exam analysis

Chance of appearing8%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper1
Typical marks1–2

Common command terms

  • Explain
  • Outline
  • Identify
  • Distinguish
  • Suggest

Scoring notes

Common mistake
Explaining antibiotic action as antibody stimulation instead of inhibition of bacterial processes.

Recent exam appearances

May 2024Paper1 ["SL"] · TZ124[ 1 ]C3.2.13—Antibiotics
November 2023Paper1 ["SL"] · TZ126[ 1 ]C3.2.13—Antibiotics
May 2019Paper1 ["SL"] · TZ227[ 1 ]C3.2.13—Antibiotics
November 2018Paper1 ["SL"] · TZ026[ 1 ]C3.2.13—Antibiotics
November 2017Paper2 ["SL"] · TZ02(b)[ 2 ]C3.2.13—Antibiotics
Practice this objective

Coverage 2010–2024 · Updated 16 Jul 2026

Antibiotics target bacterial processes

Antibiotics target bacterial processes.

Antibiotics inhibit bacterial structures or pathways such as cell-wall synthesis or ribosomes. They work only when the illness is caused by susceptible bacteria.

identify bacterial target; drug action; selective toxicity; treatment limit.

A cell-wall antibiotic can kill dividing bacteria while leaving human cells without bacterial walls largely unaffected.

Antibiotics do not cure viral infections and should not be judged by whether a fever has another cause.

Antibiotics exam focus

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain / Outline / Identify.

Command terms

Explain / Outline / Identify / Distinguish / Suggest

What earns marks

Mark schemes repeatedly reward named details, correct sequence and clear distinctions between similar processes.

Watch for

Explaining antibiotic action as antibody stimulation instead of inhibition of bacterial processes.

Representative question

Question 1

[Maximum number: 3]

(i) Estimate the diameter of the zone of inhibition of chloramphenicol.
(ii) Distinguish between the action of tetracycline and penicillin on B. subtilis.
(iii) Suggest a reason for the result with disc X .

Defence Against Disease

  • Skin, mucus, cilia, lysozyme and clotting form primary barriers against pathogens.
  • Innate immunity is rapid and broad: phagocytes recognize, engulf and digest pathogens. Adaptive immunity is antigen-specific and forms memory.
  • Helper T-cells coordinate responses; activated B-cells undergo clonal selection, producing antibody-secreting plasma cells and memory cells. A second exposure therefore triggers a faster, stronger response.
  • HIV infects CD4 helper T-cells; their loss weakens immune coordination and can lead to AIDS.
  • Antibiotics target bacterial processes, not viruses. Antibiotic exposure selects resistant variants, which can spread by reproduction or plasmid transfer.
  • Vaccination creates active artificial immunity; high population immunity can indirectly protect susceptible people.
  • Evaluate disease and vaccine claims using reliable sources, trends, controlled comparisons, incidence and efficacy—not raw totals alone.

Concept essentials

  • Antibiotics has to be linked to the exact pathogen, cell, molecule or population process involved.
  • The biological effect of antibiotics depends on the sequence from trigger to protective outcome.
  • Clear distinctions within antibiotics prevent confusion with neighbouring immune responses.
  • Evidence for antibiotics is strongest when mechanism and consequence are explained together.
ConceptIB Biology SL