Draw a labelled diagram to show the structure of a sarcomere.

Describe how skeletal muscle contracts.

Award [1] for each structure clearly drawn and correctly labeled.
Z lines;
thin actin filaments shown attached to Z lines;
thick myosin filaments with heads;
light and dark bands;
Award [2 max] for poorly drawn/inaccurate diagram

action potential arrives at the neuromuscular junction/depolarizes muscle cells;
release of calcium ions from the sarcoplasmic reticulum;
(calcium binding to troponin exposes actin) to form cross-bridges;
heads push actin filament towards centre of sarcomere (so sarcomere becomes shorter);
use of ATP to break cross-bridges/re-set myosin heads;

The diagram of a sarcomere was very poorly drawn 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 answered. 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. Very few could accurately describe the sequence of events in skeletal muscle contraction.