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A3.1.12 (HL)—Difficulties with biological species concept

The biological species concept fits bacteria poorly because they reproduce asexually and can exchange genes across species boundaries through horizontal transfer.

Syllabus
First assessment 2025
Objective
A3.1.12
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1

Common command terms

  • Outline

Recent exam appearances

November 2025Paper2 ["HL"] · TZ37(c)[ 1 ]A3.1.12 (HL)—Difficulties with biological species concept
Practice this objective

Coverage 2025–2025 · Updated 15 Jul 2026

Concept essentials

  • Bacteria usually reproduce asexually by binary fission.
  • The biological species concept relies on sexual interbreeding and fertile offspring.
  • Horizontal gene transfer can move genes between different bacterial lineages.
  • Bacterial species boundaries often require genetic and ecological evidence rather than breeding tests.
ConceptIB Biology HL