A2.3 Viruses [HL only]

Viruses are structurally diverse, acellular parasites whose host-dependent replication cycles, multiple evolutionary origins, and rapid genetic change shape infection and immune escape.

What you’ll learn

6 learning objectives

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

Exam analysis

An aggregate view of how the complete A2.3 Viruses [HL only] appears across past papers.

Chance of appearing7%of analysed past papers

Latest appearanceNovember 2025

Most common paperPaper2

Most tested objectives

A2.3.1 (HL)—Common structural features8 questions
A2.3.2 (HL)—Diversity of virus structure5 questions
A2.3.6 (HL)—Rapid evolution in viruses3 questions

Common question formats

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

Exam question appearances

November 2025Paper2 ["HL"] · TZ17(b)[ 7 ]A2.3.2 (HL)—Diversity of virus structure

November 2025Paper2 ["HL"] · TZ32(b)[ 2 ]A2.3.6 (HL)—Rapid evolution in viruses

November 2025Paper1A ["HL"] · TZ313[ 1 ]A2.3.1 (HL)—Common structural features

November 2025Paper1A ["HL"] · TZ112[ 1 ]A2.3.1 (HL)—Common structural features

November 2025Paper1B ["HL"] · TZ31(d)[ 3 ]A2.3.3 (HL)—Lytic cycle

Practice this topic

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

Coverage 2010–2025 · Updated 15 Jul 2026