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C3.2.11—HIV transmission

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

Syllabus
First assessment 2025
Objective
C3.2.11
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2014
Most common paperPaper1
Typical marks1

Common command terms

  • Explain

Recent exam appearances

November 2014Paper1 ["HL"] · TZ024[ 1 ]C3.2.11—HIV transmission
Practice this objective

Coverage 2014–2014 · Updated 16 Jul 2026

HIV spreads through particular body-fluid routes

HIV spreads through particular body-fluid routes.

HIV transmission requires infected blood, semen, vaginal fluids or breast milk to reach susceptible tissue. It is not spread by casual contact, food sharing or intact skin.

source fluid; route of exposure; susceptible tissue; prevention barrier.

Sharing a contaminated needle can transfer infected blood directly into circulation, whereas a handshake cannot.

Transmission risk depends on exposure and viral load; a positive test does not identify the route by itself.

HIV transmission

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Explain.

Command terms

Explain

What earns marks

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

Representative question

Question 1

[Maximum number: 1]

How has the transmission of HIV been reduced?

A

Delaying the progression of HIV to AIDS

B

Single use of disposable needles

C

Treatment with antibiotics

D

Vaccination

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

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