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A4.1.11 (HL)—Abrupt speciation in plants

Abrupt plant speciation can occur when polyploidy instantly creates chromosome-set differences that reproductively isolate a fertile new lineage from parents.

Syllabus
First assessment 2025
Objective
A4.1.11
Level
HL

Exam analysis

Chance of appearing9%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks1–5

Common command terms

  • Explain
  • Describe
  • Discuss

Scoring notes

Common mistake
Confusing polyploidy with aneuploidy involving one extra chromosome rather than whole chromosome sets.

Recent exam appearances

May 2025Paper2 ["HL"] · TZ38(c)[ 4 ]A4.1.11 (HL)—Abrupt speciation in plants
November 2024Paper1 ["HL"] · TZ035[ 1 ]A4.1.11 (HL)—Abrupt speciation in plants
November 2023Paper2 ["HL"] · TZ28(b)[ 5 ]A4.1.11 (HL)—Abrupt speciation in plants
November 2023Paper2 ["HL"] · TZ18(b)[ 5 ]A4.1.11 (HL)—Abrupt speciation in plants
November 2022Paper2 ["HL"] · TZ08(b)[ 5 ]A4.1.11 (HL)—Abrupt speciation in plants
Practice this objective

Coverage 2014–2025 · Updated 15 Jul 2026

Concept essentials

  • Polyploid organisms have more than two complete sets of chromosomes.
  • Unreduced gametes or chromosome doubling can generate polyploid cells.
  • Diploid-tetraploid crosses often produce sterile triploids, isolating the tetraploid lineage.
  • Chromosome doubling in hybrids can restore fertility and create a new plant species.
ConceptIB Biology HL