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B1.1.12—Phospholipid bilayers

Phospholipids are amphipathic molecules whose hydrophilic phosphate heads and hydrophobic fatty-acid tails self-arrange into stable membrane bilayers in water-rich environments.

Syllabus
First assessment 2025
Objective
B1.1.12
Level
SL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2022
Most common paperPaper2
Typical marks1–2

Common command terms

  • Outline
  • Annotate

Scoring notes

Common mistake
Reversing the hydrophilic phosphate head and hydrophobic fatty-acid tails.

Recent exam appearances

November 2022Paper2 ["SL"] · TZ02(a)[ 2 ]B1.1.12—Phospholipid bilayers
November 2012Paper2 ["SL"] · TZ01(d)[ 1 ]B1.1.12—Phospholipid bilayers
Practice this objective

Coverage 2012–2022 · Updated 15 Jul 2026

Concept essentials

  • Phospholipid heads are hydrophilic and phosphate-containing.
  • Fatty-acid tails are hydrophobic and avoid water.
  • In water, phospholipids self-arrange so tails are shielded from water.
  • Phospholipid bilayers form the basic barrier structure of cell membranes.
ConceptIB Biology SL