IB Biology HL B3.3.2 Hl Sliding Filament Model Questions
Explore how actin and myosin slide between Z lines, calcium exposes binding sites and ATP powers repeated cross-bridge cycles in IB Biology HL B3.3.2.
Syllabus
First assessment 2025
Course
Biology HL
Level
HL
Exam points
Identify sarcomeres between Z lines, thin actin and thick myosin filaments, and interpret band or micrograph changes as filaments slide and the sarcomere shortens.
Explain that calcium released from the sarcoplasmic reticulum binds troponin, moves tropomyosin and exposes myosin-binding sites on actin.
Explain the ATP cross-bridge cycle: myosin attachment, power stroke, ATP-driven detachment and ATP hydrolysis/reset, repeated to shorten sarcomeres.
The diagram shows a section through part of the leg of an insect and antagonistic muscles X and Y. The tibia moves in the direction shown by the arrow when the muscle is flexing.
Explain the role of calcium ions in muscle contraction.
Calcium released from sarcoplasmic reticulum. Calcium binds to troponin. Causes tropomyosin to move. Uncovers binding sites. Myosin heads bind to the actin forming cross bridges.