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Learn9700Paper 2 · AS Level Structured QuestionsInfectious diseasesInfectious diseases and antibiotics
Infectious diseases · Subtopic 1 of 1

Infectious Diseases and Antibiotics

Cholera (bacterium Vibrio cholerae): contaminated water; toxin causes severe diarrhoea; controlled by clean water, sanitation, oral rehydration. Malaria (Plasmodium, a protoctist): spread by female Anopheles mosquitoes; controlled by nets, insecticides, drugs, draining water. Tuberculosis (Mycobacterium tuberculosis): airborne droplets; BCG vaccine, long antibiotic courses, contact tracing. Measles (virus): droplets; MMR vaccine. HIV/AIDS (retrovirus): body fluids; destroys T-helper cells; antiretroviral drugs, condoms, screening. Antibiotics target features of bacteria absent in human cells; penicillin inhibits enzymes building peptidoglycan cross-links, so cells burst by osmosis. Antibiotics don't affect viruses. Resistance arises by random mutation and spreads by natural selection and plasmid transfer, worsened by overuse and unfinished courses.

Cambridge 9700 Paper 1Cambridge 9700 Paper 2Edexcel YBI11 WBI14≈ 45 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe the cause and transmission of five infectious diseases.
  • Explain how control measures work.
  • Explain how penicillin acts and why antibiotics don't affect viruses.
  • Explain the development of antibiotic resistance.
Pause and think

Why does taking antibiotics for a cold not help, and can even cause harm?

Section 2 of 14

Core idea

Start hereGerms that travel

Cholera travels in water, malaria in mosquitoes, TB in coughs. Knowing the route tells you how to stop it.

The big idea

Control measures break the transmission route. Antibiotics target bacterial features we lack; resistance evolves by natural selection.

How antibiotic resistance spreads

Selection, not adaptation.

Worked exampleDisease incidence

30 new TB cases a year in a town of 40 000. Incidence per 100 000?

Goal
Rate.
Strategy
Scale up.
  1. 3040 000=7.5×10−4\frac{30}{40\,000}=7.5\times10^{-4}
    Cases per person.
  2. 7.5×10−4×100 000=757.5\times10^{-4}\times100\,000=75
    Per 100 000.
Answer75 per 100 000 per year.
✓ CheckBigger than 30 because population < 100 000 ✓.

Summary

  • Know pathogen, route, control.
  • Penicillin weakens walls.
  • Resistance by selection.
Key words
Pathogen
Organism that causes disease.
Vector
Organism that carries a pathogen between hosts.
HistoryFleming's mould. In 1928 Alexander Fleming noticed a mould killing bacteria on a culture plate; Florey and Chain turned penicillin into a drug in the 1940s.
Fun factThe deadliest animal. Mosquitoes, by transmitting malaria and other diseases, kill more humans each year than any other animal.
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