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B2.1.6—Channel proteins

Channel proteins provide selective hydrophilic pathways for facilitated diffusion of ions and polar molecules down concentration gradients without ATP; Selectivity comes from channel structure and the chemical nature of the transported particle.

Syllabus
First assessment 2025
Objective
B2.1.6
Level
HL

Exam analysis

Chance of appearing6%of analysed past papers
Latest appearanceMay 2023
Most common paperPaper1
Typical marks1

Common command terms

  • Identify
  • Explain
  • Describe
  • Outline

Scoring notes

Common mistake
Adding ATP to facilitated diffusion even when the movement is passive.

Recent exam appearances

May 2023Paper1 ["HL"] · TZ23[ 1 ]B2.1.6—Channel proteins
November 2021Paper1 ["HL"] · TZ01[ 1 ]B2.1.6—Channel proteins
November 2019Paper1 ["HL"] · TZ02[ 1 ]B2.1.6—Channel proteins
November 2016Paper1 ["HL"] · TZ020[ 1 ]B2.1.6—Channel proteins
May 2016Paper1 ["HL"] · TZ015[ 1 ]B2.1.6—Channel proteins
Practice this objective

Coverage 2013–2023 · Updated 15 Jul 2026

Concept essentials

  • Channel proteins form hydrophilic pathways through the membrane.
  • Facilitated diffusion moves substances down gradients without ATP.
  • Specific channels are needed for many ions and polar solutes.
  • The rate of facilitated diffusion can depend on the number of transport proteins.
ConceptIB Biology HL