| Date | May 2012 | Marks available | 1 | Reference code | 12M.1.HL.TZ1.39 |
| Level | Higher level | Paper | Paper 1 | Time zone | Time zone 1 |
| Command term | Outline | Question number | 39 | Adapted from | N/A |
Question
What is the role of calcium ions during muscle contraction?
A. To block the myosin binding site on actin when the muscle is not contracting
B. To move the molecules blocking the myosin binding site on actin
C. To form cross-bridges between the actin and myosin filaments
D. To provide the energy for resetting the myosin heads
Markscheme
B
Examiners report
In question 39, substantial numbers of candidates thought that calcium ions form cross bridges between actin and myosin filaments during muscle contraction. The expected answer was that they move the molecules blocking the myosin bonding sites on actin. Teachers need to be aware that some You Tube clips on this topic are misleading and of course all material taken from the internet should be treated with circumspection.
