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B2.1.11 (HL)—Fatty acid composition and fluidity

Fatty acid saturation changes membrane fluidity because unsaturated tails kink and reduce packing while saturated tails pack more tightly; Temperature responses depend on how tightly the fatty acid tails can pack.

Syllabus
First assessment 2025
Objective
B2.1.11
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1

Common command terms

  • Identify
  • Outline

Scoring notes

Common mistake
Reversing the effects of saturated and unsaturated fatty acids on membrane fluidity.

Recent exam appearances

November 2025Paper1A ["HL"] · TZ315[ 1 ]B2.1.11 (HL)—Fatty acid composition and fluidity
May 2025Paper2 ["HL"] · TZ23(e)[ 1 ]B2.1.11 (HL)—Fatty acid composition and fluidity
May 2022Paper1 ["HL"] · TZ23[ 1 ]B2.1.11 (HL)—Fatty acid composition and fluidity
Practice this objective

Coverage 2022–2025 · Updated 15 Jul 2026

Concept essentials

  • Unsaturated fatty acid tails increase membrane fluidity by reducing tight packing.
  • Saturated fatty acid tails reduce fluidity because they pack more closely.
  • Membranes can adjust lipid composition to maintain workable fluidity at different temperatures.
ConceptIB Biology HL