Draw a labelled diagram of a sarcomere.

Explain the role of calcium ions in muscle contraction.

Award [1] for each structure clearly drawn and correctly labelled.
Z lines;
actin filaments;
myosin filaments with heads;
light bands and dark bands;

Ca²⁺ ions released when a nerve impulse arrives at the muscle;
Ca²⁺ ions are released from the sarcoplasmic reticulum;
binding sites for myosin heads are exposed;
this allows cross-bridges between myosin and actin to form;

The diagram of a sarcomere was very poorly done on the whole, with many bearing little resemblance to what was required. Those who did attempt a diagram often managed to gain a mark for showing Z lines, but little else. Quite a large number of candidates left this part of the option blank.

This was also not well done. It is a challenging topic, and proved to be a good discriminator for the more able candidates. It is obviously an area which students find difficult to understand.