Question 18M.2.HL.TZ1.8c

a. muscle fibre contains many myofibrils 

b. made up of sarcomeres/labelled diagram showing one or more sarcomeres 

c. nerve impulse/signal from (motor) neuron causes release of calcium (ions)/Ca²⁺ 

d. calcium (ions)/Ca²⁺ released from sarcoplasmic reticulum 

e. calcium (ions)/Ca²⁺ link to troponin 

f. tropomyosin moves to expose actin binding sites 

g. ATP hydrolysis/ATP to ADP and phosphate/release of phosphate from ATP 

h. ATP binds to myosin heads and causes them to cock/change angle/release/gain energy 

i. myosin heads bind/form cross-bridges to actin 

j. myosin heads push on actin and then detach from actin 

k. actin moved towards centre of sarcomere/sliding of filaments 

l. sarcomere becomes shorter (resulting in muscle contraction)

Accept any mark point if clearly made on an annotated diagram.