C3.2 Defence against disease

Defence against disease combines physical barriers, clotting, phagocytes, lymphocyte specificity, vaccination, antibiotics and evolutionary responses to pathogens across human populations.

What you’ll learn

18 learning objectives

Choose one objective for a focused lesson, or study the complete topic.

Exam analysis

An aggregate view of how the complete C3.2 Defence against disease appears across past papers.

Chance of appearing50%of analysed past papers

Latest appearanceNovember 2025

Most common paperPaper1

Most tested objectives

C3.2.3—Blood clotting13 questions
C3.2.16—Vaccines and immunization13 questions
C3.2.8—B-lymphocyte activation9 questions

Common question formats

Structured response
Definition or recall
Data analysis
Evaluation
Process explanation
Diagram interpretation
Extended response
Calculation

Exam question appearances

November 2025Paper2 ["HL"] · TZ18(c)[ 4 ]C3.2.12—HIV infection and AIDS

November 2025Paper1A ["HL"] · TZ326[ 1 ]C3.2.8—B-lymphocyte activation

November 2025Paper2 ["HL"] · TZ32(a)[ 2 ]C3.2.2—Skin and mucous membranes

May 2025Paper2 ["HL"] · TZ25(b)[ 2 ]C3.2.10—Immunity from memory cells

May 2025Paper2 ["HL"] · TZ25(a)[ 1 ]C3.2.4—Innate vs. adaptive immune system

Practice this topic

8 original exam-style questions based on the patterns above.

Coverage 2012–2025 · Updated 16 Jul 2026