B3.3.2 (HL)—Sliding filament model
Sliding filament contraction occurs when calcium exposes actin binding sites and ATP-powered myosin heads pull actin inward to shorten sarcomeres.
- Syllabus
- First assessment 2025
- Objective
- B3.3.2
- Level
- HL
Exam analysis
Chance of appearing26%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–3
Common command terms
- Explain
- Draw
- Identify
- Describe
- Analyse
- State
- Outline
- Label
- Deduce
Scoring notes
- Common mistake
- Saying actin or myosin filaments shorten instead of sliding past each other.
Recent exam appearances
November 2025Paper2 ["HL"] · TZ13(b)[ 3 ]B3.3.2 (HL)—Sliding filament model
May 2025Paper1A ["HL"] · TZ225[ 1 ]B3.3.2 (HL)—Sliding filament model
November 2024Paper2 ["HL"] · TZ07(c)[ 7 ]B3.3.2 (HL)—Sliding filament model
May 2024Paper1 ["HL"] · TZ137[ 1 ]B3.3.2 (HL)—Sliding filament model
May 2024Paper3 ["HL"] · TZ23(b)(ii)[ 2 ]B3.3.2 (HL)—Sliding filament model
Practice this objective
Coverage 2012–2025 · Updated 15 Jul 2026
Concept essentials
- Sarcomeres are repeating contractile units between Z lines.
- Calcium binds to troponin and causes tropomyosin to expose actin binding sites.
- Myosin heads form cross-bridges with actin and pull actin inward.
- ATP binding detaches myosin heads, while ATP hydrolysis re-cocks them.
- Contraction shortens sarcomeres and light bands, not the actin or myosin filaments.