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A4.2.1—Biodiversity definition

Biodiversity describes variety within and between ecosystems, species, and genes, with species richness, evenness, and Simpson index enabling quantitative comparison.

Syllabus
First assessment 2025
Objective
A4.2.1
Level
HL

Exam analysis

Chance of appearing5%of analysed past papers
Latest appearanceMay 2023
Most common paperPaper3
Typical marks1–2

Common command terms

  • State
  • Discuss
  • Calculate
  • Analyse
  • Compare
  • Evaluate
  • Distinguish
  • Suggest

Scoring notes

Common mistake
Equating richness with overall biodiversity when evenness also affects diversity.

Recent exam appearances

May 2023Paper3 ["HL"] · TZ117(c)[ 1 ]A4.2.1—Biodiversity definition
November 2019Paper3 ["HL"] · TZ016(c)[ 1 ]A4.2.1—Biodiversity definition
May 2017Paper3 ["HL"] · TZ115(c)[ 2 ]A4.2.1—Biodiversity definition
May 2015Paper3 ["HL"] · TZ211(a)(ii)[ 2 ]A4.2.1—Biodiversity definition
May 2015Paper3 ["HL"] · TZ211(a)(i)[ 2 ]A4.2.1—Biodiversity definition
Practice this objective

Coverage 2012–2023 · Updated 15 Jul 2026

Concept essentials

  • Biodiversity includes ecosystem diversity, species diversity and genetic diversity.
  • Species richness is the number of different species present in a community.
  • Species evenness describes how similar the population sizes of different species are.
  • Simpson reciprocal index allows quantitative comparison of biodiversity between communities or over time.
ConceptIB Biology HL