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C3.2.12—HIV infection and AIDS

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

Syllabus
First assessment 2025
Objective
C3.2.12
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–4

Common command terms

  • Identify
  • Explain
  • Discuss

Scoring notes

Common mistake
Confusing plasma cells, memory cells and helper T-cells in the activation sequence.

Recent exam appearances

November 2025Paper2 ["HL"] · TZ18(c)[ 4 ]C3.2.12—HIV infection and AIDS
November 2019Paper1 ["HL"] · TZ022[ 1 ]C3.2.12—HIV infection and AIDS
May 2012Paper1 ["HL"] · TZ221[ 1 ]C3.2.12—HIV infection and AIDS
Practice this objective

Coverage 2012–2025 · Updated 16 Jul 2026

HIV can cause AIDS by reducing CD4 T cells

HIV can cause AIDS by reducing CD4 T cells.

HIV infects and progressively destroys CD4 helper T cells. As immune coordination falls, opportunistic infections and cancers become more likely; this clinical state is AIDS.

HIV entry/replication; CD4 decline; loss of coordination; opportunistic disease.

A person with low CD4 counts may develop an infection that a healthy immune system would normally control.

HIV infection and AIDS are not synonyms: treatment can delay or prevent progression to AIDS.

HIV infection and AIDS

Assessment in practice

1 marks
How it is assessed

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

Command terms

Identify / Explain / Discuss

What earns marks

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

Watch for

Confusing plasma cells, memory cells and helper T-cells in the activation sequence.

Representative question

Question 1

[Maximum number: 4]

Discuss the consequences of infection with HIV.

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