| Date | May 2013 | Marks available | 4 | Reference code | 13M.3.SL.TZ1.6 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
Draw a labelled diagram to show the structure of a sarcomere.
Explain the roles of actin and myosin in muscle contraction.
Markscheme
Award [1] for each structure clearly drawn and correctly labelled.
a. Z lines;
b. thin actin filaments shown attached to Z lines;
c. thick myosin filaments with heads;
d. light and dark bands;
a. calcium/Ca2+ frees myosin binding sites on actin/thin filament;
b. ATP (linked to myosin head) hydrolysed to ADP + P(i);
c. myosin head cocked/assumes high energy configuration;
d. myosin head binds to actin / forms a cross-bridge;
e. actin filament slides towards center of sarcomere / dark band;
f. combined sliding of actin filaments shortens muscle fiber / muscle;
g. ATP binds to myosin head and breaks cross-bridge;
Accept answers with properly annotated diagrams.
Examiners report
A relatively small number of candidates answered this option, but those who did generally achieved well.
The diagram of the structure of a sarcomere was well answered on the whole.
A relatively small number of candidates answered this option, but those who did generally achieved well.
Most candidates had difficulty explaining the roles of actin and myosin in muscle contraction.
