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B2.1.5—Osmosis and aquaporins

Osmosis moves water passively across selectively permeable membranes, often through aquaporins, toward regions with higher solute concentration; Aquaporins make this water movement faster and more physiologically responsive.

Syllabus
First assessment 2025
Objective
B2.1.5
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1B
Typical marks1–2

Common command terms

  • Describe
  • Identify
  • Define
  • State
  • Explain
  • Distinguish

Scoring notes

Common mistake
Describing movement of solute instead of net movement of water.

Recent exam appearances

May 2025Paper1B ["HL"] · TZ32(b)(i)[ 2 ]B2.1.5—Osmosis and aquaporins
May 2025Paper1B ["HL"] · TZ32(a)[ 1 ]B2.1.5—Osmosis and aquaporins
May 2024Paper3 ["HL"] · TZ22(a)[ 1 ]B2.1.5—Osmosis and aquaporins
Practice this objective

Coverage 2024–2025 · Updated 15 Jul 2026

Concept essentials

  • Osmosis is passive net movement of water across a selectively permeable membrane.
  • Water moves toward higher solute concentration or lower water potential.
  • Aquaporins are protein channels that increase water movement across membranes.
  • Cell volume can change quickly when aquaporins increase water uptake.
ConceptIB Biology HL